Field of the Invention
[0001] This invention relates to a continuous process for heating a plurality of articles
in a microwave heating system.
Background
[0002] Electromagnetic radiation, such as microwave radiation, is a known mechanism for
delivering energy to an object. The ability of electromagnetic radiation to penetrate
and heat an object in a rapid and effective manner has proven advantageous in many
chemical and industrial processes. Because of its ability to quickly and thoroughly
heat an article, microwave energy has been employed in heating processes wherein the
rapid achievement of a prescribed minimum temperature is desired, such as, for example,
pasteurization and/or sterilization processes. Further, because microwave energy is
generally non-invasive, microwave heating may be particularly useful for heating 'sensitive'
dielectric materials, such as food and pharmaceuticals. However, to date, the complexities
and nuances of safely and effectively applying microwave energy, especially on a commercial
scale, have severely limited its application in several types of industrial processes.
WO 2005/023013 A2 (UNIV WASHINGTON; TANG JUMING; LIU FANG; PATHAK SURYA KU) discloses an apparatus
for pasteurizing and/or sterilizing foodstuffs in accordance with the state of the
art.
[0003] Thus, a need exists for an efficient, consistent, and cost effective industrial-scale
microwave heating system suitable for use in a wide variety of processes and applications.
Summary
[0004] The present invention concerns a continuous process for heating a plurality of articles
in a microwave heating system according to claim 1. Dependent claims deal with particular
embodiments covered by the invention.
Brief Description of the Drawings
[0005]
FIG. 1a is process flow diagram depicting a microwave heating system for heating one
or more articles, particularly illustrating a system comprising a thermalization zone,
a microwave heating zone, an optional holding zone, a quench zone, and a pair of pressure
adjustment zones;
FIG. 1b is a schematic diagram of a microwave heating system 10, particularly each
of the zones of microwave heating system 10 outlined in the diagram provided in FIG.
1a;
FIG. 2a is a cross-sectional schematic end view of a process vessel, particularly
illustrating a conveyance system including a pair of convey lines arranged in a side-by-side
configuration;
FIG. 2b is a schematic top cut-away view of the process vessel shown in FIG. 2a, particularly
illustrating the laterally-spaced arrangement of the convey lines relative to the
convey axis extending through the vessel;
FIG. 2c is a cross-sectional schematic end view of another process, particularly illustrating
a conveyance system including a pair of convey lines arranged in a stacked configuration;
FIG. 2d is a schematic side cut-away view of the process vessel shown in FIG. 2c,
particularly illustrating the vertically-spaced arrangement of the convey lines relative
to convey axis extending through the vessel;
FIG. 3 is a perspective view of a carrier configured to secure and transport the articles
being heated through a liquid-filled process vessel;
FIG. 4a is a partial side cut-away view of a microwave heating system that includes
a pressure adjustment zone configured to transport one or more articles from the thermalization
zone to the microwave heating zone of the heating system using a carrier transfer
system;
FIG. 4b is a partial side cut-away view of a microwave heating system including a
pressure adjustment zone similar to the one depicted in FIG. 4a, but particularly
illustrating a carrier transfer system disposed nearly entirely within the pressure
adjustment zone;
FIG. 4c is a partial schematic view of the pressure adjustment zone similar to the
ones depicted in FIGS. 4a and 4b, but illustrating a carrier transfer system for moving
the articles from the thermalization zone to the microwave heating zone;
FIG. 4d is a partial schematic view of the pressure adjustment zone similar to the
ones depicted in FIGS. 4a and 4b, but illustrating another carrier transfer system
for moving the articles from the thermalization zone to the microwave heating zone;
FIG. 5a is a partial side cut-away view of a locking gate device, particularly showing
the gate assembly in an open position;
FIG. 5b is a partial side cut-away view of the locking gate device depicted in FIG.
5a, particularly showing the gate assembly in a closed position with the sealing plates
in a retracted position;
FIG. 5c is a partial side cut-away view of the locking gate device depicted in FIGS.
5a and 5b, particularly showing the gate assembly in a closed position with the sealing
plates in an extended position;
FIG. 5d is an enlarged partial view of the gate assembly shown in FIGS. 5a-c, particularly
illustrating, a bearing used to move the sealing plates of the gate assembly;
FIG. 6a is a schematic partial side cut-away view of a microwave heating zone, particularly
illustrating the heating vessel and the microwave distribution system;
FIG. 6b is a schematic top view of a microwave heating zone, particularly illustrating
one configuration of microwave launchers in a heating system employing a multi-line
convey system;
FIG. 6c is a schematic side view of the microwave heating zone illustrated in FIG.
6b, particularly showing the one set of microwave launchers configured to heat articles
passing along a convey line;
FIG. 7a is a partial side cut-away view of a microwave heating zone, particularly
illustrating a titled microwave launcher and showing what is meant by the term "launch
tilt angle" (β);
FIG. 7b is a partial side cut-away view particularly illustrating a microwave distribution
system comprising a plurality of tilted launchers;
FIG. 8a is a partial enlarged side cut-away view of a portion of a microwave heating
zone, particularly illustrating one embodiment of a microwave window located near
the discharge opening of at least one microwave launcher of the heating zone;
FIG. 8b is a partial enlarged side cut-away view of a portion of a microwave heating
zone, particularly illustrating another embodiment of a microwave window located near
the discharge opening of at least one microwave launcher of the heating zone;
FIG. 8c is a partial enlarged side cut-away view of a portion of a microwave heating
zone, particularly illustrating yet another embodiment of a microwave window located
near the discharge opening of at least one microwave launcher of the heating zone;
FIG. 9a is an isometric view of a microwave launcher;
FIG. 9b is a longitudinal side view of the microwave launcher depicted in FIG. 9a;
FIG. 9c is an end view of the microwave launcher depicted in FIGS. 9a and 9b, particularly
illustrating a launcher having a flared outlet;
FIG. 9d is an end view of the microwave launcher generally depicted in FIGS. 9a and
9b, particularly illustrating a launcher having an inlet and outlet of approximately
the same size;
FIG. 9e is an end view of the microwave launchers generally depicted in FIGS. 9a and
9b, particularly illustrating a launcher having a tapered outlet;
FIG. 10a is an isometric view of another microwave launcher, particularly illustrating
a launcher comprising a single microwave inlet and a plurality of microwave outlets;
FIG. 10b is a vertical cross-sectional view of the microwave launcher depicted in
FIG. 10a, particularly illustrating the multiple microwave outlets;
FIG. 10c is a vertical cross-sectional view of the microwave launcher depicted in
FIGS. 10a and 10b, particularly showing the pair of dividing septa used to create
individual microwave pathways between the inlet and multiple outlets of the microwave
launcher;
FIG. 11a is an isometric view of a microwave launcher, particularly showing an integrated
inductive iris disposed between the inlet and outlet of the launcher;
FIG. 11b is a horizontal cross-sectional view of the microwave launcher depicted in
FIG. 11a;
FIG. 11c is a horizontal cross-sectional view of another microwave launcher similar
to the launcher depicted in FIG. 11a, but including a pair of dividing septa in addition
to an inductive iris disposed between the inlet and outlet of the launcher;
FIG. 12a is a side cut-away view of a phase shifting device, particularly illustrating
a plunger-type tuning device that includes a single plunger;
FIG. 12b is a schematic side cut-away view of a phase shifting device, particularly
illustrating a plunger-type tuning device including a plurality of plungers driven
by a common rotatable shaft;
FIG. 13a is a side perspective view of a phase shifting, particularly illustrating
a rotatable phase shifting device;
FIG. 13b is a longitudinal cross-sectional view of the rotatable phase shifting device
depicted in FIG. 13a;
FIG. 13c is a lateral cross-sectional view of the rotatable section of the rotatable
phase shifting device depicted in FIGS. 13a and 13b, particularly showing the width
and spacing of the plates disposed within the housing;
FIG. 13d is an lateral cross-sectional view of the fixed section of the rotatable
phase shifting device depicted in FIGS. 13a and 13b, particularly illustrating the
dimensions of the fixed section;
FIG. 13e is a side cut-away view of a rotatable phase shifting device, particularly
illustrating a drive system that includes a rotating crank member;
FIG. 13f is a side cut-away view of a rotatable phase shifting device, particularly
illustrating a drive system that includes a set of compression springs;
FIG. 14a is a schematic partial side cut-away view of a microwave distribution system
utilizing two phase shifting devices for phase shifting and/or impedance tuning;
FIG. 14b is a schematic partial side cut-away view of a microwave heating vessel configured,
particularly illustrating a phase shifting device coupled to the vessel for use as
a frequency tuner;
FIG. 15a is a schematic partial side cut-away view of a portion of a microwave heating
system, particularly illustrating a thermalization zone including a plurality of fluid
jet agitators;
FIG. 15b is an end view of a thermalization zone similar to the one depicted in FIG.
15a, particularly illustrating one embodiment wherein the fluid jet agitator is circumferentially-positioned
within the thermalization zone;
FIG. 16 is a flowchart representing the major steps involved in a method of controlling
a microwave system;
FIG. 17 is a flowchart representing the major steps involved in a method for determining
the net power discharged from at least one microwave launcher using two or more pairs
of directional couplers; and
FIG. 18 is an isometric depiction of the location of thermocouples inserted into a
test package to determine the minimum temperature of the package for determining the
heating profile for an article.
Detailed Description
[0006] Microwave processes according to various embodiments of the present invention and
systems for heating a plurality of articles according to embodiments not covered by
the present invention are described below. Examples of suitable articles to be heated
in systems and processes can include, but are not limited to, foodstuffs, medical
fluids, and medical instruments. In one embodiment, microwave systems described herein
can be used for the pasteurization and/or sterilization of the articles being heated.
In general, pasteurization involves rapid heating of an article or articles to a minimum
temperature between 80°C and 100°C, while sterilization involves heating one or more
articles to a minimum temperature between 100°C to 140°C. However, pasteurization
and sterilization may take place simultaneously or nearly simultaneously and many
processes and systems can be configured to both pasteurize and sterilize one or more
articles. Various microwave systems and processes configured to heat one or more types
of articles will now be discussed in detail, with reference to the Figures.
[0007] Turning now to FIGS. 1a and 1b, a schematic representation of the major steps in
a microwave heating process is depicted in FIG. 1a, while FIG. 1b depicts a microwave
system 10 operable to heat a plurality of articles according to the process outlined
in FIG. 1a. As shown in FIGS. 1a and 1b, one or more articles can initially be introduced
into a thermalization zone 12, wherein the articles can be thermalized to a substantially
uniform temperature. Once thermalized, the articles can then be optionally passed
through a pressure adjustment zone 14a before being introduced into a microwave heating
zone 16. In microwave heating zone 16, the articles can be rapidly heated using microwave
energy discharged into at least a portion of the heating zone by one or more microwave
launchers, generally illustrated as launchers 18 in FIG. 1b. The heated articles can
then optionally be passed through a holding zone 20, wherein the articles can be maintained
at a constant temperature for a specified amount of time. Subsequently, the articles
can then be passed to a quench zone 22, wherein the temperature of the articles can
be quickly reduced to a suitable handling temperature. Thereafter, the cooled articles
can optionally be passed through a second pressure adjustment zone 14b before being
removed from system 10 and further utilized.
[0008] Microwave system 10 can be configured to heat many different types of articles. The
articles heated in microwave system 10 can comprise foodstuffs, such as, for example,
fruits, vegetables, meats, pastas, pre-made meals, and even beverages. The articles
heated in microwave system 10 can comprise packaged medical fluids or medical and/or
dental instruments. The articles processed within microwave heating system 10 can
be of any suitable size and shape. Each article can have a length (longest dimension)
of at least about 5.08 cm (2 inches) at least about 10.16 cm (4 inches), at least
about 15.24 cm (6 inches) and/or not more than about 45.72 cm (18 inches), not more
than about 30.48 cm (12 inches), or not more than about 25.4 cm (10 inches); a width
(second longest dimension) of at least about 2.54 cm (1 inch), at least about 5.08
cm (2 inches), at least about 10.16 cm (4 inches) and/or not more than about 30.48
cm (12 inches), not more than about 25.5 cm (10 inches), or not more than about 20.32
cm (8 inches); and/or a depth (shortest dimension) of at least about 1.27 cm (0.5
inches) at least 2.54 cm (1 inch), at least about 5.08 cm (2 inches) and/or not more
than about 20.32 cm (8 inches), not more than about 15.24 cm (6 inches), or not more
than about 10.16 cm (4 inches). The articles can comprise individual items or packages
having a generally rectangular or prism-like shape or can comprise a continuous web
of connected items or packages passed through microwave system 10. The items or packages
may be constructed of any material, including plastics, cellulosics, and other microwave-transparent
materials, and can be passed through microwave system 10 via one or more conveyance.
[0009] Each of the above-described thermalization, microwave heating, holding, and/or quench
zones 12, 16,20, and 22 can be defined within a single vessel, as generally depicted
in FIG. 1b, while, at least one of the above-described stages can be defined within
one or more separate vessels. At least one of the above-described steps can be carried
out in a vessel that is at least partially filled with a fluid medium in which the
articles being processed can be at least partially submerged. The fluid medium can
be a gas or a liquid having a dielectric constant greater than the dielectric constant
of air and can be a liquid medium having a dielectric constant similar to the dielectric
constant of the articles being processed. Water (or liquid media comprising water)
may be particularly suitable for systems used to heat edible and/or medical devices
or articles. Additives, such as, for example, oils, alcohols, glycols, and salts may
optionally be added to the liquid medium to alter or enhance its physical properties
(e.g., boiling point) during processing, if needed.
[0010] Microwave system 10 can include at least one conveyance system (not shown in FIGS.
1a and 1b) for transporting the articles through one or more of the processing zones
described above. Examples of suitable conveyance systems can include, but are not
limited to, plastic or rubber belt conveyors, chain conveyors, roller conveyors, flexible
or multiflexing conveyors, wire mesh conveyors, bucket conveyors, pneumatic conveyors,
screw conveyors, trough or vibrating conveyors, and combinations thereof. The conveyance
system can include any number of individual convey lines and can be arranged in any
suitable manner within the process vessels. The conveyance system utilized by microwave
system 10 can be configured in a generally fixed position within the vessel or at
least a portion of the system can be adjustable in a lateral or vertical direction.
[0011] Turning now to FIGS. 2a-2d, embodiments not covered by the invention of a process
vessel 120 that includes a conveyance system 110 disposed therein are provided. In
one embodiment generally depicted in FIGS. 2a and 2b, conveyance system 110 includes
a pair of laterally spaced, substantially parallel convey lines 112, 114 positioned
in a generally side-by-side configuration within vessel 120. As shown in the top,
cut-away view of vessel 120 in FIG. 2b, convey lines 112 and 114 may be laterally
spaced from each other and may be positioned on both sides of a convey axis 122, which
extends along the length of vessel 120 in the direction of conveyance of the articles
passing therethrough. Although shown in FIG. 2a as being at generally the same vertical
elevation within vessel 120, it should be understood that, in one embodiment, convey
lines 112, 114 may also be positioned at different vertical elevations. Additionally,
conveyance system 110 depicted in FIGS. 2a and 2b may also include multiple pairs
of laterally spaced convey lines (embodiment not shown), such that the pairs of laterally
spaced convey lines are vertically spaced from each other along the vertical dimension
of vessel 120.
[0012] Another embodiment of a conveyance system 110 that includes a pair of vertically-spaced,
substantially parallel convey lines 116, 118 positioned in a stacked arrangement within
the interior of vessel 120, is shown in FIGS. 2c and 2d. Convey lines 116 and 118
maybe configured above and below convey axis 122, which may generally extend along
the length of vessel 120, as shown in the cutaway side view of vessel 120 provided
in FIG. 2d. Additionally, in a similar manner as previously described, vessel 120
shown in FIGS. 2c and 2d may also include multiple pairs of convey lines, laterally
spaced from one another within the vessel. Further, each convey line of the pair may
or may not be offset from the other in a lateral direction. In a further embodiment
(not shown), vessel 120 may include a single convey line, positioned in the middle
one-third of the internal volume of vessel 120, or positioned at or near the centerline
of the vessel. Additional details of conveyance systems according to several embodiments
not covered by the present invention will be discussed in detail below.
[0013] When a conveyance system is used to transport articles through a liquid-filled process
vessel, one or more carriers or other securing mechanisms can be used to control the
position of the articles during passage through the liquid medium. One embodiment
of a suitable carrier 210 is illustrated in FIG. 3. As shown in FIG. 3, carrier 210
comprises a lower securing surface 212a and an upper securing surface 212b configured
to secure any suitable number of articles 216 therebetween. In one embodiment, upper
and/or lower surfaces 212b,a can have a meshed, grid, or grated structure, as generally
depicted in FIG. 3, while, in another embodiment, one or both surfaces 212a,b can
be a substantially continuous surface. Carrier 210 can be constructed of plastic,
fiberglass, or any other dielectric material and, in one embodiment, may be made of
one or more microwave-compatible and/or microwave-transparent materials. In some embodiments,
the material may be a lossy material. In some embodiments, carrier 210 can comprise
substantially no metal.
[0014] Lower and upper securing surfaces 212a, 212b may be attached to one another by a
securing device, shown as a fastener 219 in FIG. 3, and, as assembled, carrier 210
may be attached or secured to the conveyance system (not shown in FIG. 3) according
to any suitable attachment mechanism. In one embodiment, at least one side (or edge)
of carrier 210 can include one or more attachment mechanisms, such as, for example,
upper and lower hooks 218a, 218b shown in FIG. 3, for securing carrier 210 to a portion
(e.g., a bar, a rail, a belt, or a chain) of the conveyance system (not shown). Depending
on the thickness and/or weight of articles 216, carrier 210 may only include one of
hooks 218a, 218b for securing carrier 210 onto the conveyance system. The conveyance
system used to transport articles 216 may be configured to transport multiple carriers
along one or more conveyance lines and the carriers may be arranged in a side-by-side,
laterally-spaced configuration and/or in a vertically-spaced, stacked configuration
as described previously. When the conveyance system includes a plurality of convey
lines, each convey line may include a single carrier for holding a plurality of articles
216, or each convey line may hold multiple carriers stacked or laterally spaced from
each other.
[0015] Referring back to FIGS. 1a and 1b, the articles introduced into microwave system
10 are initially introduced into thermalization zone 12, wherein the articles are
thermalized to achieve a substantially uniform temperature. In one embodiment, at
least about 85 percent, at least about 90 percent, at least about 95 percent, at least
about 97 percent, or at least about 99 percent of all the articles withdrawn from
thermalization zone 12 have a temperature within about 5°C, within about 2°C, or within
1°C of one another. As used herein, the terms "thermalize" and "thermalization" generally
refer to a step of temperature equilibration or equalization. Depending on the initial
and desired temperature of the articles being thermalized, the temperature control
system of thermalization zone 12, illustrated in FIG. 1a as heat exchanger 13, can
be a heating and/or cooling system. In one embodiment, the thermalization step can
be carried out under ambient temperature and/or pressure, while, in another embodiment,
thermalization can be carried out in a pressurized and/or liquid-filled thermalization
vessel at a pressure of not more than about 68.9476 kpa (10 psig), not more than about
34.4738 kpa (5 psig), or not more than about 13.7895 kpa (2 psig). Articles undergoing
thermalization can have an average residence time in thermalization zone 12 of at
least about 30 seconds, at least about 1 minute, at least about 2 minutes, at least
about 4 minutes and/or not more than about 20 minutes, not more than about 15 minutes,
or not more than about 10 minutes. In one embodiment, the articles withdrawn from
thermalization zone 12 can have a temperature of at least about 20°C, at least about
25°C, at least about 30°C, at least about 35°C and/or not more than about 70°C, not
more than about 65°C, not more than about 60°C, or not more than about 55°C.
[0016] In one embodiment wherein thermalization zone 12 and microwave heating zone 16 are
operated at substantially different pressures, the articles removed from thermalization
zone 12 can first be passed through a pressure adjustment zone 14a before entering
microwave heating zone 16, as generally depicted in FIGS. 1a and 1b. Pressure adjustment
zone 14a can be any zone or system configured to transition the articles being heated
between an area of lower pressure and an area of higher pressure. In one embodiment,
pressure adjustment zone 14a can be configured to transition the articles between
two zones having a pressure difference of at least about 6.89476 kpa (1 psi), at least
about 34.4738 kpa (5 psi), at least about 68.9476 kpa (10 psi) and/or not more than
about 344.738kpa (50 psi), not more than about 310.264 kpa (45 psi), not more than
about 275.79 kpa (40 psi), or not more than about 241.317 (35 psi). In one embodiment,
microwave system 10 can include at least two pressure adjustment zones 14a,b to transition
the articles from an atmospheric pressure thermalization zone to a heating zone operated
at an elevated pressure before returning the articles back to atmospheric pressure,
as described in detail below.
[0017] One embodiment of a pressure adjustment zone 314a disposed between a thermalization
zone 312 and a microwave heating zone 316 of a microwave heating system 310 is illustrated
in FIG. 4a. Pressure adjustment zone 314a is configured to transition a plurality
of articles 350, which may be secured within at least one carrier, from lower-pressure
thermalization zone 312 to higher-pressure microwave heating zone 316. Although shown
in FIG. 4a as being a single carrier 352a, it should be understood that pressure adjustment
zone 314a may be configured to receive more than one carriers. In one embodiment,
the carriers may be received simultaneously, such that pressure adjustment zone 314a
contains multiple carriers at one time. In another embodiment, multiple carriers may
be lined up and ready, for example within thermalization zone 312, for being transitioned
through pressure adjustment zone 314a, details of which will now be discussed below.
[0018] In operation, one or more carriers 352a can be transitioned from thermalization zone
312 to microwave heating zone 316 by first opening an equilibration valve 330 and
allowing the pressure between thermalization zone 312 and pressure adjustment zone
314a to equalize. Next, a gate device 332 can be opened to allow carrier 352a to be
moved from a convey line 340a disposed within thermalization zone 312 onto a platform
334 within pressure adjustment zone 314a, as generally shown by the dashed-line carrier
352b in FIG. 4a.
[0019] Thereafter, gate device 332 and equilibrium valve 330 can be closed in sequence,
re-isolating pressure adjustment zone 314a from thermalization zone 312. Subsequently,
another equilibration valve 336 can be opened to allow the pressure between pressure
adjustment zone 314a and microwave heating zone 316 to equalize. Once equilibrium
is achieved, another gate device 338 can be opened to permit carrier 352b to be moved
onto another conveyance system 340b disposed within microwave heating zone 316, as
generally shown by dashed-line carrier 352c in FIG. 4a. Subsequently, gate device
338 and equalization valve 336 may be closed in sequence, re-isolating microwave heating
zone 316 from pressure adjustment zone 314a. The process may then be repeated to transport
additional carriers from thermalization zone 312 to microwave heating zone 316 as
needed.
[0020] According to one embodiment, each of microwave heating zone 316 and thermalization
zone 312 can be filled with a non-compressible fluid or liquid, such as, for example,
water or solutions including water. As used herein, the term "filled" denotes a configuration
where at least 50 percent of the specified volume is filled with the filling medium.
The "filling medium" can be a liquid, typically an incompressible liquid, and may
be or include, for example, water. In certain embodiments, "filled" volumes can be
at least about 75 percent, at least about 90 percent, at least about 95 percent, or
100 percent full of the filling medium. When thermalization zone 312 and/or microwave
heating zone 316 are filled with an incompressible fluid, gate devices 332, 338 and/or
pressure adjustment zone 314a may also include two or more one-way flaps or valves,
shown as valves or flaps 342, 344 in FIG. 4a, for preventing substantial fluid leakage
between thermalization zone 312 and microwave heating zone 316 when gate devices 332
and 338 are open and carrier 352 is passed therethrough.
[0021] The transportation of carrier 352 from thermalization zone 312 through pressure adjustment
zone 314a and into microwave heating zone 316 can be accomplished via one or more
automatic article transfer systems, several embodiments of which are illustrated in
FIGS. 4b-4d. In some embodiments, automatic transfer system 380 can include one or
more transfer devices, disposed within thermalization zone 312, pressure adjustment
zone 314a, and/or microwave heating zone 316 for moving carrier 352 into and/or out
of pressure adjustment zone 314a. In one embodiment shown in FIG. 4b, transfer system
380 includes two gear transfer devices 381, 382 configured to engage teeth 353 disposed
along the lower edge of carrier 352 and rotate, as indicated by the arrows 392a,b,
to pull carrier 352 into out of thermalization zone 312 and/or push carrier 352 into
microwave heating zone 316. As shown in FIG. 4b, first and second gear transfer devices
381, 382 remain substantially stationary (in terms of lateral motion) during the transportation
of carrier 352 and are nearly entirely, or entirely, disposed within pressure adjustment
zone 314a.
[0022] In contrast, some embodiments of automatic transfer system 380 can include one or
more transfer devices that are laterally shiftable (
i.e., movable in the direction of transport) during transport of carrier 352 into and/or
out of pressurize adjustment zone 314a. As depicted in one embodiment shown in FIG.
4c, a portion of the automatic transfer system 380 may be disposed in thermalization
zone 312 and/or microwave heating zone 316 and can be configured for extension into
and retraction out of pressure adjustment zone 314a. In the system 380 shown in FIG.
4c, the transfer devices include a pusher arm 381 configured to push carrier 352 into
pressure adjustment zone 314a and a puller arm 382 for pulling carrier 352 into microwave
heating zone 316. Neither pusher arm 381 nor puller arm 382 are disposed within pressure
adjustment zone 314a, but instead, each is configured to extend into and retract out
of pressure adjustment zone 314a, as generally shown by arrows 394a,b in FIG. 4c.
[0023] According to another embodiment depicted in FIG. 4d, automatic transport system 380
includes a platform 334 having a movable portion 384, which is configured to be extended
into and retracted out of thermalization 312 and/or microwave heating zone 316 to
thereby transport carrier 352 into and out of thermalization and microwave heating
zones 312, 316, as generally shown by arrows 396a and 396b. In contrast to the embodiment
shown in FIG. 4c, automatic transfer system 380 depicted in FIG. 4d is primarily disposed
within pressure adjustment zone 314a and is configured to extend out of and retract
back into pressure adjustment zone 314a.
[0024] Regardless of the specific configuration of the transfer devices utilized by automatic
article transfer system 380, the transfer system can be automated, or controlled,
by an automatic control system 390, as illustrated in FIGS. 4a and 4b. Although not
specifically depicted in the embodiments illustrated in FIGS. 4c and 4d, it should
be understood that such control systems 390 may also be employed in these embodiments.
Automatic control system 390 can be used to control the motion and/or timing of at
least one of first and second equilibration valves 330, 336, first and second gate
valves 332, 338, and first and second transfer devices 381, 382 of the automatic article
transfer system 380. In one embodiment, control system 390 can adjust the position,
speed, and/or timing of these devices or elements in order to ensure that the carriers
within the system move in an uninterrupted and consistent manner.
[0025] Turning now to FIGS. 5a-5d, one embodiment of a locking gate device 420, suitable
for use as gate device 332 and/or 338 in the portion of microwave system 310 depicted
in FIGS. 4a and 4b, is provided. Locking gate valve device 420 is illustrated in FIGS.
5a-d as generally comprising a pair of spaced apart fixed members 410, 412 that present
opposing sealing surfaces 414a,b and that define a gate-receiving space 416 therebetween.
The spaced apart fixed members 410, 412 can each define a flow-through opening 418a,b,
which are circumscribed by one of sealing surfaces 414a,b. Each of flow-through openings
418a,b are substantially aligned with one another such that the articles can pass
through the cumulative opening when gate valve device 420 is open.
[0026] Locking gate device 420 further comprises a gate assembly 422, which is configured
to be received within gate-receiving space 416 and is shiftable therein between a
closed position (as shown in FIGS. 5b and 5c), wherein gate assembly 422 substantially
blocks flow-through openings 418a,b, and an open position (as shown in FIG. 5a), wherein
gate assembly 422 does not substantially block flow-through openings 418a,b. In one
embodiment, gate assembly 422 comprises a pair of spaced apart sealing plates 424,
426 and a drive member 428 disposed between sealing plates 424, 426. When gate assembly
422 is configured in the closed position, drive member 428 is shiftable, relative
to sealing plates 424, 426, between a retracted position (as shown in FIG. 5b) and
an extended position (as shown in FIG. 5c). In one embodiment shown in FIGS. 5a-c,
gate assembly 422 comprises at least one pair of bearings 430 disposed within the
space defined between opposing sealing plates 424, 426, which is positioned in gate
receiving space 416 when gate assembly 422 is in a closed position, as particularly
shown in FIGS. 5b and 5c. When drive member 428 is shifted between a retracted position
as illustrated in FIG. 5b to an extended position as depicted in FIG. 5c, at least
one bearing of pair 430 can force at least one of sealing plates 424, 426 outwardly,
away from one another and into a sealed position, as shown in FIGS. 5c.
[0027] In one embodiment, one or more of the bearings of pair 430 can be secured, attached,
or at least partially housed within at least one of sealing plates 424, 426 and/or
drive member 428. According to one embodiment, at least one of the bearings 430 a
can be fixedly attached to drive member 428, as depicted in the enlarged partial view
of gate assembly 422 provided in FIG. 5d. As drive member 428 shifts downwardly into
gate receiving space 416, one of the bearings 430a from the pair can contact one of
sealing plates 424, 426 (shown as plate 426 in FIG. 5d) and can move along a ramp
(or slot) 427 therein. As the bearing travels through the slot 427 (or along the ramp
427), outward pressure is exerted on sealing plate 426, thereby moving it in a direction
as indicated by arrow 460. Although shown as including only a single pair of bearings
430, it should be understood that any number of bearings, positioned along the vertical
length of drive member 428 and/or sealing members 424, 426 can be used.
[0028] When in a sealed position, as shown in FIG. 5c, at least a portion of sealing plates
424, 426 engage or physically contact respective opposing sealing surface 414a,b,
to thereby form a substantially fluid tight seal. In one embodiment, each of sealing
plates 424, 426 comprises a resilient seal 423, 425 for engaging sealing surfaces
414a,b when sealing plates 424, 426 are in the sealed position. When drive member
428 is shifted from the extended position, as shown in FIG. 5c, back to the retracted
position, as shown in FIG. 5b, sealing plates 424, 426 retract towards one another
into the unsealed position, as shown in FIG. 5b. In the unsealed position, sealing
plates 424, 426 are disengaged from opposing sealing surfaces 414a,b, but may remain
disposed within gate receiving space 416. In one embodiment, sealing plates 424, 426
can be biased towards the unsealed position and can include at least one biasing device
429
(e.g., a spring or springs) for biasing sealing plates 424, 426 toward the unsealed position.
[0029] Referring again to FIGS. 1a and 1b, the articles exiting thermalization zone 12,
and optionally passed through pressure adjustment zone 14a, as described above, can
then be introduced into microwave heating zone 16. In microwave heating zone 16, the
articles can be rapidly heated with a heating source that uses microwave energy. As
used herein, the term "microwave energy" refers to electromagnetic energy having a
frequency between 300MHz and 30 GHz. In one embodiment, various configurations of
microwave heating zone 16 can utilize microwave energy having a frequency of about
915 MHz or a frequency of about 2.45 GHz, both of which have been generally designated
as industrial microwave frequencies. In addition to microwave energy, microwave heating
zone 16 may optionally utilize one or more other heat sources such as, for example,
conductive or convective heating or other conventional heating methods or devices.
However, at least about 85 percent, at least about 90 percent, at least about 95 percent,
or substantially all of the energy used to heat the articles within microwave heating
zone 16 can be microwave energy from a microwave source.
[0030] According to one embodiment, microwave heating zone 16 can be configured to increase
the temperature of the articles above a minimum threshold temperature. In one embodiment
wherein microwave system 10 is configured to sterilize a plurality of articles, the
minimum threshold temperature (and operating temperature of microwave heating zone
16) can be at least about 120°C, at least about 121°C, at least about 122°C and/or
not more than about 130°C, not more than about 128°C, or not more than about 126°C.
Microwave heating zone 16 can be operated at approximately ambient pressure, or it
can include one or more pressurized microwave chambers operated at a pressure of at
least about 34.4738 kpa (5 psig), at least about 68.9476 kpa (10 psig), at least about
34.4738 kpa (15 psig) and/or not more than about 551.581 kpa (80 psig), not more than
about 413.685 kpa (60 psig), or not more than about 275.79 kpa (40 psig). In one embodiment,
the pressurized microwave chamber can be a liquid-filled chamber having an operating
pressure such that the articles being heated can reach a temperature above the normal
boiling point of the liquid medium employed therein.
[0031] The articles passing through microwave heating zone 16 can be heated to the desired
temperature in a relatively short period of time, which, in some cases, may minimize
damage or degradation of the articles. In one embodiment, the articles passed through
microwave heating zone 16 can have an average residence time of at least about 5 seconds,
at least about 20 seconds, at least about 60 seconds and/or not more than about 10
minutes, not more than about 8 minutes, or not more than about 5 minutes. In the same
or other embodiments, microwave heating zone 16 can be configured to increase the
average temperature of the articles being heated by at least about 20°C, at least
about 30°C, at least about 40°C, at least about 50°C, at least about 75°C and/or not
more than about 150°C, not more than about 125°C, or not more than about 100°C, at
a heating rate of at least about 15°C per minute (°C/min), at least about 25 °C/min,
at least about 35°C/min and/or not more than about 75°C/min, not more than about 50°C/min,
or not more than about 40°C/min.
[0032] Turning now to FIG. 6a, one embodiment of a microwave heating zone 516 is illustrated
as generally comprising a microwave heating chamber 520, at least one microwave generator
512 for generating microwave energy and a microwave distribution system 514 for directing
at least a portion of the microwave energy from generator 512 to microwave chamber
520. Microwave distribution system 514 comprises a plurality of waveguide segments
518 and one or more microwave launchers, shown as launchers 522a-f in FIG. 6a, for
discharging microwave energy into the interior of microwave chamber 520. As shown
in FIG. 6a, microwave heating zone 516 can further comprise a conveyance system 540
for transporting articles 550 to be heated through microwave chamber 520. Each of
the components of microwave heating zone 516, according to various embodiments not
covered by the present invention, are now discussed in detail immediately below.
[0033] Microwave generator 512 can be any suitable device for generating microwave energy
of a desired wavelength (λ). Examples of suitable types of microwave generators can
include, but are not limited to, magnetrons, klystrons, traveling wave tubes, and
gyrotrons. Although illustrated in FIG. 6a as including a single generator 512, it
should be understood that microwave heating system 516 can include any number of generators
arranged in any suitable configuration. For example, in one embodiment, microwave
heating zone 516 can include at least 1, at least 2, at least 3 and/or not more than
5, not more than 4, or not more than 3 microwave generators, depending on the size
and arrangement of microwave distribution system 514. Specific embodiments of a microwave
heating zone including multiple generators will be discussed in detail below.
[0034] Microwave chamber 520 can be any chamber or vessel configured to receive a plurality
of articles. Microwave chamber 520 can be of any size and may have one of a variety
of different cross-sectional shapes. For example, in one embodiment, chamber 520 can
have a generally circular or elliptical cross-section, while, in other embodiments,
can have a generally square, rectangular, or polygonal cross-sectional shape. In one
embodiment, microwave chamber 520 can be a pressurized chamber and, in the same or
other embodiments, can be configured to be at least partially filled with a liquid
medium (a liquid-filled chamber). Microwave chamber 520 can also be configured to
receive at least a portion of the microwave energy discharged from one or more microwave
launchers 522 and, in one embodiment, can be configured to permit the creation of
a stable (or standing) wave pattern therein. In one embodiment, at least one dimension
of microwave chamber 520 can be at least about 0.30λ, at least about 0.40λ, or at
least about 0.50λ, wherein λ is the wavelength of the microwave energy discharged
therein.
[0035] Microwave distribution system 514 comprises a plurality of waveguides or waveguide
segments 518 for directing at least a portion of the microwave energy from generator
512 to microwave chamber 520. Waveguides 518 can be designed and constructed to propagate
microwave energy in a specific predominant mode, which may be the same as or different
than the mode of the microwave energy generated by generator 512. As used herein,
the term "mode" refers to a generally fixed cross-sectional field pattern of microwave
energy. In one embodiment not covered by the present invention, waveguides 518 can
be configured to propagate microwave energy in a TE
xy mode, wherein
x and
y are integers in the range of from 0 to 5. In another embodiment not covered by the
present invention, waveguides 518 can be configured to propagate microwave energy
in a TM
ab mode, wherein
a and
b are integers in the range of from 0 to 5. It should be understood that, as used herein,
the above-defined ranges of
a, b, x, and
y values as used to describe a mode of microwave propagation are applicable throughout
this description. In one embodiment, the predominant mode of microwave energy propagated
through waveguides 518 and/or discharged via launchers 522a-f can be selected from
the group consisting of TE
10, TM
01, and TE
11.
[0036] As shown in FIG. 6a, microwave distribution system 514 further comprises one or more
microwave launchers 522a-f, each defining at least one launch opening 524a-f for discharging
microwave energy into microwave chamber 520. Although illustrated in FIG. 6a as comprising
six microwave launchers 522a-f, it should be understood that microwave distribution
system 514 can include any suitable number of launchers arranged in any desirable
configuration. For example, microwave distribution system 514 can include at least
1, at least 2, at least 3, at least 4 and/or not more than 50, not more than 30, or
not more than 20 microwave launchers. Launchers 522a-f can be the same or different
types of launchers and, in one embodiment, at least one of launchers 522a-f can be
replaced with a reflective surface (not shown) for reflecting at least a portion of
the microwave energy discharged from the other launchers 522 into microwave heating
chamber 520.
[0037] When microwave distribution system 514 includes two or more launchers, at least some
of the launchers may be disposed on generally the same side of microwave chamber 520.
As used herein, the term "same-side launchers" refers to two or more launchers positioned
on generally the same side of a microwave chamber. Two or more of the same-side launchers
may also be axially spaced from one another. As used herein, the term "axially spaced"
denotes spacing in the direction of conveyance of the articles through the microwave
system (i.e., spacing in the direction of extension of the convey axis). Additionally,
one or more launchers 522 may also be laterally spaced from one or more other launchers
522 of the system. As used herein, the term "laterally spaced" shall denote spacing
in the direction perpendicular to the direction of conveyance of the articles through
the microwave system (i.e., spacing perpendicular to the direction of extension of
the convey axis). For example, in FIG. 6a, launchers 522a-c and 522d-f are disposed
on respective first and second sides 521a,b of microwave chamber 520 and launcher
522a is axially spaced from launcher 522b and 522c, just as launcher 522e is axially
spaced from launchers 522f and 522d.
[0038] Additionally, as shown in the embodiment depicted in FIG. 6a, microwave distribution
system 514 can comprise at least two (e.g., two or more) pairs of oppositely disposed
or opposed launchers. As used herein, the term "opposed launchers" refers to two or
more launchers positioned on generally opposite sides of a microwave chamber. In one
embodiment, the opposed launchers may be oppositely facing. As used herein with respect
to opposed microwave launchers, the term "oppositely facing" shall denote launchers
whose central launch axes are substantially aligned with one another. For simplicity,
central launch axis 523c of launcher 522c and central launch axis 523d of launcher
522d are the only central launch axes illustrated in FIG. 6a. However, it should be
understood that each of launchers 522a-f include a similar launch axes.
[0039] Opposed launchers may be generally aligned with one another, or may be staggered
from one or more other launchers disposed on the opposite side of microwave chamber
520. In one embodiment, a pair of opposed launchers may be a staggered pair of launchers,
such that the discharge openings 524 of the launchers 522 are not in substantial alignment
with one another. Launchers 522a and 522e constitute one exemplary pair of opposed
launchers arranged in a staggered configuration. Staggered opposed launchers may be
axially or laterally staggered from one another. As used herein with respect to opposed
microwave launchers, the term "axially staggered" shall denote launchers whose central
launch axes are axially spaced from one another. As used herein with respect to opposed
microwave launchers, the term "laterally staggered" shall denote launchers whose central
launch axes are laterally spaced from one another. In another embodiment, a pair of
opposed launchers may be directly opposite launchers, such that the discharge openings
of the launcher pair are substantially aligned. For example, launchers 522c and 522d
shown in FIG. 6a are configured as a pair of opposite launchers.
[0040] In some embodiments, microwave heating zone 516 can include two or more convey lines
operating simultaneously with one another. An exemplary multi-line conveyance system
540 is shown in FIGS. 6b and 6c. As shown in FIGS. 6b and 6c, conveyance system 540
can be configured to transport a plurality of articles 550 in a convey direction generally
represented by arrow 560 in FIG. 6b. In one embodiment, conveyance system 540 can
include at least two laterally spaced, substantially parallel convey lines, such as,
for example, first, second, and third convey lines 542a-c shown in FIG. 6b. Convey
lines 542a-c can, in one embodiment, comprise individual conveyance systems, while,
in another embodiment, each of convey lines 542a-c can be portions of an overall conveyance
system. Conveyance system 540 and/or convey lines 542a-c can be any suitable type
of conveyor or conveyance system, including those discussed in detail previously.
[0041] Microwave heating system 516 depicted in FIGS. 6b and 6c includes a plurality of
microwave launchers 522 that can be divided or organized into at least two groups
of two or more microwave launchers. Each of first, second, and third convey lines
542a-c can be configured to receive microwave energy from respective first, second,
and third groups of microwave launchers. In one embodiment, a "group" of launchers
can refer to two or more axially spaced launchers, generally position along the convey
direction (e.g., launcher group 522a-d, launcher group 522eh, and/or launcher group
522i-1 shown in FIG. 6b), while, in the another embodiment, a "group" of launchers
can include one or more pairs of opposed launchers positioned on different sides of
a microwave chamber (e.g., groups that include pair of launchers 522a and 522m, the
group that includes pair of launchers 522b and 522n, group that includes pair of launchers
522c and 522o, and group that includes pair of launchers 522d and 522p, as shown in
FIG. 6c). When the group of launchers comprises one or more pairs of opposed launchers,
the launchers can be arranged in a staggered configuration (not shown) or can be directly
opposite one another (e.g. oppositely facing), as illustrated in FIG. 6c. According
to one embodiment, at least one generator, shown as generator 512a in FIG. 6b, can
be configured to provide microwave energy to at least one group of microwave launchers.
[0042] As particularly shown in FIG. 6b, individual microwave launchers 522 of adjacent
convey lines 542 can be arranged in a staggered configuration relative to one another
in the convey direction. In one embodiment, one or more same-side microwave launchers
522a-1 may be axially staggered from one another. For example, in the embodiment shown
in FIG. 6b, launchers 522a-d associated with first convey line 542a are arranged in
a staggered configuration relative to each of respective launchers 522e-h associated
with second convey line 542b with respect to and/or along the convey direction 560.
As used herein with respect to same-side microwave launchers, the term "axially staggered"
shall denote launchers that are axially spaced from one another by distance greater
that ½ the maximum axial dimension of the launch openings of the launchers. As used
herein with respect to same-side microwave launchers, the term "laterally staggered"
shall denote launchers that are laterally spaced from one another by a distance greater
that ½ the maximum lateral dimension of the launch openings of the launchers.
[0043] Additionally, in the same or another embodiment, the microwave launchers associated
with the non-adjacent convey lines
(e.g., first and third convey lines 542a,c) can be arranged in a substantially aligned configuration
relative to one another, as illustrated by the arrangement of launchers 522a-d relative
to launchers 522i-1 shown in FIG. 6b. Alternatively, at least a portion of the launchers
522i-1 associated with third convey line 542c may be staggered with respect to launchers
522a-d of first convey line 542a and/or second convey line 542b (embodiment not shown).
Although generally depicted in FIG. 6b as including little to no space between launchers
of adjacent convey lines, it should be understood that, in one embodiment, that some
space may exist between launchers of adjacent lines (e.g., launchers 522a and 522e,
launchers 522b and 522f,
etc.). Further, individual launchers 522 can have any suitable design or configuration
and, in one embodiment, can include at least one feature from one or more embodiments
not covered by the present invention which will be described in detail herein.
[0044] Turning now to FIG. 7a, a partial view of one embodiment of a microwave heating zone
616 is shown. Microwave heating zone 616 includes at least one microwave launcher
622 that defines a launch opening 624 for discharging energy into a microwave chamber
620. As shown in FIG. 7a, microwave launcher 622 is configured to discharge microwave
energy along a central launch axis 660 toward a conveyance system 640 configured to
transport a plurality of articles 650 within microwave chamber 620 along a convey
axis 642. In one embodiment, central launch axis 660 can be tilted such that a launch
tilt angle, β, is defined between central launch axis 660 and a plane normal to convey
axis 642, illustrated as plane 662 in FIG. 7a. According to one embodiment, launch
tilt angle β can be at least about 2°, at least about 4°, at least about 5° and/or
not more than about 15°, not more than about 10°, or not more than about 8°.
[0045] Turning now to FIG. 7b, another embodiment of a microwave heating system 616 is shown
as including two or more launchers 622a-c, each configured to discharge energy into
microwave chamber 620 along respective tilted central launch axes 660a-c. In one embodiment
wherein microwave heating system 616 includes two or more tilted launchers, the central
launch axes of the launchers, especially the same-side launchers, can be substantially
parallel to one another, as generally illustrated by central launch axes 660a,b of
launchers 622a,b shown in FIG. 7b. As used herein, the term "substantially parallel"
means within 5° of being parallel. In the same or another embodiment, the central
launch axes of two or more launchers, especially opposed launchers, within microwave
heating zone 616 can be substantially parallel or substantially aligned, as illustrated
by launch axes 660a,c of microwave launchers 622a,c in FIG. 7b. When microwave heating
zone 616 comprises n tilted microwave launchers having central launch axes oriented
as described above, each launcher can define a respective launch tilt angle, β
n, within the ranges discussed previously. In one embodiment, each of the launch tilt
angles β
n of each launcher may be substantially the same, while, in another embodiment, at
least one of the launch tilt angles β
n can be substantially different than one or more other launch tilt angles.
[0046] Referring back to FIG. 6a, at least one of launch openings 524a-f of launchers 522a-f
of microwave system 516 can be at least partially covered by a substantially microwave-transparent
window 526a-f disposed between each launch opening 524a-f and microwave chamber 520.
Microwave-transparent windows 526a-f can be operable to prevent fluid flow between
microwave chamber 520 and microwave launchers 522a-f while still permitting a substantial
portion of the microwave energy from launchers 522a-f to pass therethrough. Windows
526a-f can be made of any suitable material, including, but not limited to one or
more thermoplastic or glass material such as glass-filled Teflon, polytetrafluoroethylene
(PTFE), poly(methyl methacrylate (PMMA), polyetherimide (PEI), aluminum oxide, glass,
and combinations thereof. In one embodiment, windows 526a-f can have an average thickness
of at least about 4 mm, at least about 6 mm, at least about 8 mm and/or not more than
about 20 mm, not more than about 16 mm, or not more than about 12 mm and can withstand
a pressure difference of at least 275.79 kpa (40 psi), at least about 344.738 kpa
(50 psi), at least about 517.107 kpa (75 psi) and/or not more than about 1378.95 kpa
(200 psi), not more than about 1034.21 kpa (150 psi), or not more than about 827.371
kpa (120 psi) without breaking, cracking, or otherwise failing.
[0047] Several embodiments of suitable configurations for microwave launcher windows are
generally depicted in FIGS. 8a-c. As shown in FIGS. 8a-c, each of microwave windows
726 define a chamber-side surface 725 that can optionally define at least a portion
of the sidewall 721 of microwave chamber 720. According to one embodiment shown in
FIG. 1, chamber-side surface 725 of window 726 can be configured such that at least
about 50 percent, at least about 65 percent, at least about 75 percent, at least about
85 percent, or at least about 95 percent of the total surface area of chamber-side
surface 725 is oriented at a tilt angle, α, from the horizontal. Tilt angle α can
be at least about 2°, at least about 4°, at least about 8°, at least about 10° and/or
not more than about 45°, not more than about 30°, or not more than about 15° from
the horizontal, illustrated as dashed line 762. In other embodiments, the tilt angle,
α, may also be defined between the axis of elongation 762 of microwave chamber 720
and/or an axis of convey (not shown in FIGS. 8a-c) when, for example, these axes are
parallel to the horizontal.
[0048] Chamber-side surface 725 of window 726 can be oriented from the horizontal regardless
of whether or not launcher 722 is oriented with a launch tilt angle as described above.
In one embodiment, window 726 can be substantially planar and sloped from the horizontal
(as shown in FIG. 8a), while, in the same or another embodiment, chamber-side surface
725 of window 726 can include one or more convexities (as shown in FIG. 8b) or concavities
(as shown in FIG. 8c). When chamber-side surface 725 is not substantially planar,
one or more (or
n) total tilt angles may be formed as described above. Depending on the exact configuration
of chamber-side surface 725, the multiple tilt angles formed thereby may be the same
as or different than other tilt angles formed by the same surface 725.
[0049] As discussed previously, the microwave launchers 522a-f depicted in FIG. 6a may be
of any suitable configuration. Several views of a microwave launcher 822 configured
according to one embodiment not covered by the present invention are provided in FIGS.
9a-f. Referring initially to FIG. 9a, microwave launcher 822 is illustrated as comprising
a set of opposing sidewalls 832a,b and a set of opposing end walls 834a,b, which collectively
define a substantially rectangular launch opening 838. When launch opening 838 comprises
a rectangular-shaped opening, it can have a width (W
1) and a depth (D
1) defined, at least in part, by the terminal edges of sidewalls 832a,b and 834a,b,
respectively. In one embodiment, sidewalls 832a,b can be broader than end walls 834a,b
such that the length of the lower terminal edge of side walls 832a,b, shown as W
1 in FIG. 9a, can be greater than the length of the lower terminal edge of end walls
834a,b, depicted in FIG. 9a with the identifier D
1. As shown in FIG. 9a, the elongated portion of side walls 832a,b and end walls 834a,b
can also collectively define a pathway 837 through which microwave energy can propagate
as it passes from the microwave inlet 836 to the at least one launch opening 838 defined
by launcher 822.
[0050] When used to discharge microwave energy into a microwave chamber, launch opening
838 can be can be elongated in the direction of extension of the microwave chamber
(not shown) or in the direction of convey of the articles therein. For example, in
one embodiment, side walls 832a,b and end walls 834a,b of launcher 822 can be configured
such that the maximum dimension of launch opening 838 (shown in FIG. 9a as W
1) can be aligned substantially parallel to the direction of extension of the microwave
chamber and/or to the direction of convey of articles passing therethrough. In this
embodiment, the terminal edges of side walls 832a,b can be oriented parallel to the
direction of extension (or the direction of convey), while the terminal edges of end
walls 834a,b may be aligned substantially perpendicular to the direction of extension
or convey within the microwave chamber (not shown in FIG. 9).
[0051] FIGS. 9b and 9c respectively provide views of a sidewall 832 and end wall 834 of
microwave launcher 822 illustrated in FIG. 9a. It should be understood that, while
only one of the side or end walls 832, 834 are shown in FIGS. 9b and 9c, the other
of the pair could have a similar configuration. In one embodiment, at least one of
side wall 832 and end wall 834 can be flared such that the inlet dimension (width
W
0 or depth D
0) is smaller than the outlet dimension (width W
1 or depth D
1), as respectively illustrated in FIGS. 9b and 9c. When flared, each of side and end
walls 832, 834 define respective width and depth flare angles, θ
w and θ
d, as shown in FIGS. 9b and 9c. In one embodiment, width and/or depth flare angles
θ
w and/or θ
d can be at least about 2°, at least about 5°, at least about 10°, or at least about
15° and/or not more than about 45°, not more than about 30°, or not more than about
15°. In one embodiment, the width and depth flare angles θ
w and θ
d can be the same, while, in another embodiment, the values for θ
w and θ
d may be different.
[0052] According to one embodiment, depth flare angle θ
d can be smaller than width flare angle θ
w. In certain embodiments, depth flare angle θ
d can be not more than about 0°, such that the inlet depth D
0 and the outlet dimension D
1 of microwave launcher 822 are substantially the same, as illustrated in the embodiment
depicted in FIG. 9d. In another embodiment, the depth flare angle θ
d may be less than 0°, such that D
1 is smaller than Do, as shown in FIG. 9e. When microwave launcher 822 comprises a
depth flare angle less than 0° and/or the depth D
1 of launch opening 838 is smaller than the depth D
0 of microwave inlet 836, microwave launcher 822 can be a tapered launcher having a
generally inverse profile. In one embodiment wherein microwave launcher 822 comprises
n launch openings, between 1 and
n of the openings can have a depth and/or width less than or equal to the depth and/or
width of the inlet of the launcher. Further embodiments of multi-opening launchers
will be discussed in detail below.
[0053] According to one embodiment not covered by the present invention, the depth D
1 of launch opening 838 can be no more than about 0.625λ, not more than about 0.5λ,
not more than about 0.4λ, not more than about 0.35λ, or not more than about 0.25λ,
wherein λ is the wavelength of the predominant mode of microwave energy discharged
from launch opening 838. Although not wishing to be bound by theory, it is believed
that minimizing the depth D
1 of launch opening 838, the microwave field created proximate launch opening 838 is
more stable and uniform than would be created by launchers having greater depths.
In one embodiment wherein microwave launcher 822 comprises n launch openings, the
depth of each launch opening, d
n, can be not more than about 0.625λ, not more than about 0.5λ, not more than about
0.4λ, not more than about 0.35λ, or not more than about 0.25λ. When microwave launcher
822 has multiple openings, each opening can have a depth that is the same or different
than one or more of the other launch openings of the same launcher.
[0054] Referring now to FIGS. 10a-c, another embodiment of a microwave launcher 922 suitable
for use in the microwave heating systems described herein is illustrated as comprising
a single microwave inlet 936 and two or more launch openings, shown as launch or discharge
openings 938a-c, for discharging microwave energy therefrom. Microwave launcher 922
illustrated in FIGS. 10a-c includes first, second, and third spaced apart launch openings
938a-c, which are laterally spaced from one another. Although described herein as
defining three launch openings, it should be understood that launcher 922 can include
any suitable number of launch openings including at least 2, at least 3, at least
4 and/or not more than 10, not more than 8, or not more than 6. The spacing between
each of first, second, and third launch openings 938a-c can be at least about 0.05
λ, at least about 0.075λ, or at least about 0.10 λ and/or not more than about 0.25
λ, not more than about 0.15 λ, or not more than about 0.1 λ, wherein λ is the wavelength
of the predominant mode of microwave energy discharged from launcher 922.
[0055] In one embodiment, each of first, second, and third launch openings are separated
by one or more dividing septum (or septa) 940a,b disposed within the interior of launcher
922, as shown in FIGS. 10a-c. Septa 940a,b typically have a thickness equal to the
desired spacing between the discharge openings 938a-c. When microwave launcher comprises
n septa, microwave launcher 922 defines (
n+1) separated launch openings and (
n+1) separate microwave pathways 937a-c defined between microwave inlet 836 and each
of launch openings 938a-c, as particularly shown in FIG. 10c. As shown in FIG. 10c,
each of microwave pathways 937a-c has a length, L
1-L
3, which extends from inlet 936 to a point perpendicular with respective launch opening
938a-c. Each of L
1-L
3 can be substantially the same, or at least one of L
1, L
2, and L
3 can be substantially different. According to one embodiment, particularly shown in
FIG. 10c, one or more pathways 937a-c can be longer than one or more other pathways
937a-c.
[0056] When one or more pathways 937a-c are of different lengths than one or more other
pathways, the dimensions (L
1, L
2, and/or L
3) of pathways 937a-c may be adjusted such that the phase velocity of the microwave
energy propagating therethrough accelerates at a more rapid pace within the longer
microwave pathways (e.g., L
1 and L
3 in FIG. 10c) than through the shorter pathways (e.g., L
2 in FIG. 10c). Although not wishing to be bound by theory, it is hypothesized that
such adjusting can be carried out to ensure uniform synchronization of individual
wave portions, thereby creating a uniform wave front as the microwave energy is discharged
into chamber 520. When microwave launcher 922 includes a single septum, only two microwave
pathways are created (embodiment not shown) and the length of each pathway is substantially
the same. Consequently, little or no control of the phase velocity of microwave energy
passing through the equal length pathways may be needed.
[0057] In the same or another embodiment, each of launch openings 938a-c can define a depth,
d
1-
3, as generally depicted in FIG. 10b. In one embodiment, each of depths d
1 through d
3 can be substantially the same, while, in another embodiment, at least one of the
depths d
1-d
3 can be different. As discussed previously, one or more of d
1-d
3 can be not more than about 0.625 λ, not more than about 0.5 λ, not more than about
0.4 λ, not more than about 0.35 λ, or not more than about 0.25 λ, wherein λ is the
wavelength of the predominant mode of microwave energy discharged from launch opening
938a-c. In addition, in one embodiment, at least one of d
1-d
3 can be less than or equal to the depth do of inlet 936 as discussed in detail previously.
As shown in FIG. 10b, the depths, d
1-
3, of each of launch openings 938a-c do not include the thickness of septa 940a,b,
when present.
[0058] Referring again to FIG. 6a, in one embodiment, the microwave distribution system
514 of microwave heating zone 516 can include at least one microwave distribution
manifold 525a,b for allocating or distributing microwave energy into chamber 520 via
a plurality of launchers 522a-c and 522d-f. In one embodiment, microwave distribution
manifold 525a,b can include at least three microwave allocation devices configured
to divide the microwave energy from generator 512 into two or more separate portions
prior to being discharged from at least some of microwave launchers 522a-f. As used
herein, the term "microwave allocation device" refers to any device or item operable
to divide microwave energy into two or more separate portions, according to a predetermined
ratio. As used herein, the term "predetermined power ratio" refers to the ratio of
the amount of power of each resultant separate portion exiting a specific microwave
allocation device. For example, a microwave allocation device configured to divide
the power passing therethrough at a 1:1 power ratio would be configured to divide
the power introduced therein into two substantially equal portions.
[0059] However, in one embodiment not covered by the present invention, at least one of
the microwave allocation devices, shown as inductive irises 570a-h and "T-shaped"
or two-way splitter 572 in FIG. 6a, of microwave distribution system 514 can be configured
to have a predetermined power ratio that is not 1:1. For example, one or more of the
microwave allocation devices 570a-h or 572 can be configured to divide the microwave
energy passing therethrough according to a predetermined power ratio of at least about
1:1.5, at least about 1:2, at least about 1:3 and/or not more than about 1:10, not
more than about 1:8, or not more than about 1:6.
[0060] Each of the allocation devices 570a2-h and/or 5 employed by microwave distribution
system 514 may be configured to discharge energy according to the same ratio, or one
or more of allocation devices 570a-h can be configured at a different power ratio.
Allocation devices 570a-h and 572 can be configured such that substantially the same
amount of power is discharged from each of launchers 522a-f, while, in another embodiment,
the allocation devices 570a-h and 572 can be collectively designed such that more
power is diverted to and discharged from one or more launchers 522a-f, with less power
being discharged through the remainder of the launchers 522a-f. The specific power
ratios utilized each of microwave allocation devices 570a-h and 572, as well as the
pattern or overall configuration of microwave energy allocation within the system,
can depend on a variety of factors including, for example, the type of articles being
heated, the desired operating conditions of the microwave heating zone 516, and other
similar factors.
[0061] In operation, an initial quantity of microwave power can be introduced into microwave
distribution system 514 and can be divided into two portions as it passes through
splitter 572. In one embodiment, the two portions of microwave energy exiting splitter
572 can be approximately of approximately the same power, while, in another embodiment,
one of the two portions may have more power than the other. As shown in FIG. 6a, each
portion may pass to a respective manifold 525a,b, optionally passing through a phase
shifting device 530 prior to entering manifold 525a,b. Described now with respect
to microwave distribution manifold 525a, it should be understood that analogous operation
is applicable to the lower manifold 525b shown in FIG. 6a.
[0062] The microwave power exiting splitter 572 and optionally phase shifting device 530
(embodiments of which will be discussed in detail below) may then pass through a microwave
allocation device, shown as iris 570a, whereupon the power can be divided into a first
launch microwave fraction and a first distribution microwave fraction. The first launch
microwave fraction can be directed toward launcher 522a and can be discharged via
outlet 524a The first distribution microwave fraction can be propagated down waveguide
518 toward the additional microwave launchers 522b,c. According to one embodiment,
the power ratio of the first launch microwave fraction to the first distribution microwave
fraction exiting iris 570a can be not more than about 1:1, not more than about 0.95:1,
not more than about 0.90:1, not more than 0,80:1, not more than about 0.70:1 or not
more than 0.60:1. In one embodiment, the power ratio of the first launch microwave
fraction to the first distribution microwave fraction is not 1:1.
[0063] As the first distribution microwave fraction propagates toward launchers 522b,c,
it can subsequently be divided into a second launch microwave fraction directed toward
launcher 522b to be discharged via launch outlet 524b, and a second distribution microwave
fraction that propagates down waveguide 518 toward launcher 522c. In one embodiment,
the ratio of second launch microwave fraction to second distribution microwave fraction
can be at least about 0.80:1, at least about 0.90:1, at least about 0.95:1 and/or
not more than about 1.2:1, not more than about 1.1:1, not more than about 1.05:1,
or can be approximately 1:1. Subsequently, the remainder of the microwave energy (e.g.,
the entirety of the second distribution microwave fraction) can then be directed to
the final microwave launcher 522c and discharged from launch outlet 524c.
[0064] According to another embodiment (not shown in FIG. 6a), microwave distribution system
514 can include a microwave distribution manifold 525a,b having more than three launchers.
For example, when microwave distribution manifold 525 includes n launchers, all but
the (
n-1)th step of dividing can be carried out such that the ratio of the launch microwave
fraction to the distribution microwave fraction is not 1:1. For each of the steps
except the (
n-1)th step, the power ratio can be not more than about 1:1, not more than about 0.95:1,
not more than about 0.90:1, not more than 0,80:1, not more than about 0.70:1 or not
more than 0.60:1, while the (n-1)th dividing step can be carried out such that the
ratio of the launch microwave fraction to second distribution microwave fraction can
be at least about 0.80:1, at least about 0.90:1, at least about 0.95:1 and/or not
more than about 1.2:1, not more than about 1.1:1, not more than about 1.05:1, or can
be approximately 1:1. The (
n-1)th distribution microwave fraction can then be sent, in its majority or entirety,
as an
nth launch microwave fraction to be discharged to the microwave chamber via the nth
microwave launcher.
[0065] In addition to one or more irises 570a-h positioned within microwave distribution
system 514, one or more of launchers 522 can also include at least one inductive iris
disposed within the launcher, as shown in one embodiment illustrated in FIGS. 11a
and 11b. Alternatively, one or more of irises 570b and/or 570d may be disposed within
launchers 522a and/or 522b, respectively, rather than be disposed within a waveguide
as shown in FIG. 6a.
[0066] One embodiment of a microwave launcher 1022 including an inductive iris disposed
therein is shown in FIG. 11a. Launcher 1022 may include at least one inductive iris
1070 located between its microwave inlet 1036 and one or more launch openings 1038,
as generally illustrated in FIGS. 11a and 11b. As shown in FIGS. 11a and 11b, iris
1070 may be defined by a pair of inductive iris panels 1072a,b disposed on opposite
sides of launcher 1022. Although illustrated as being coupled to narrower opposing
end walls 1034a,b of launcher 1022, it should be understood that first and second
iris panels 1072a,b could also be coupled to broader opposing side walls 1032a,b of
launcher 1022. As shown in FIGS. 11a and 11b, first and second iris panels 1072a,b
extend inwardly into the microwave pathway 1037 defined between microwave inlet 1036
and launch opening 1038 in a direction that is generally transverse to the direction
of microwave propagation through pathway 1037. In one embodiment, iris panels obstruct
at least about 25 percent, at least about 40 percent, or at least about 50 percent
and/or not more than about 75 percent, not more than about 60 percent, or not more
than about 55 percent of the total area of microwave pathway 1037 at the location
at which they are disposed. When microwave launcher 1022 comprises two or more launch
openings, as shown in FIG. 11c, first and second iris panels 1072a,b can be configured
to obstruct at least a portion of each of the launch openings 1038a-c of the launcher
1022.
[0067] As shown in FIG. 11a, first and second iris panels 1072a,b can be substantially coplanar
and can be oriented substantially normal to the central launch axis of microwave launcher
1022. In certain embodiments, the iris panels 1072a,b may be spaced from both the
microwave inlet 1036 and the launch opening 1038 of microwave launcher 1022. For example,
the iris panels 1072a,b can be spaced from microwave inlet 1036 of launcher 1022 by
at least about 10 percent, at least about 25 percent, or at least about 35 percent
of the minimum distance between microwave inlet 1036 and launch opening 1038 of launcher
1022. Further, iris panels 1072a,b can be spaced from launch opening 1038 of launcher
1022 by at least about 10 percent, 25 percent, or 35 percent of the maximum distance
(L) measured between microwave inlet 1036 and launch opening 1038 of launcher 1022.
[0068] Turning again to FIG. 6a, microwave distribution system 514 is illustrated as further
comprise one or more devices or for increasing the uniformity and/or strength of the
microwave field created within microwave heating chamber 520. For example, in one
embodiment, microwave distribution system 514 can include one or more devices designed
to modify and/or control the location and strength of the constructive interference
bands of the microwave field created within each of individual heating zones 580a-c,
which are respectively defined between pairs of launchers 522a and 522f, 522b and
522e, and 522c and 522d. In one embodiment, such a device can be a phase shifting
device, schematically represented in FIG. 6a as device 530, operable to cyclically
shift the phase of the microwave energy passing therethrough.
[0069] As the articles 550 move along conveyance system 540 within microwave chamber 520,
each article 550 can have an average residence time, within each individual heating
zone 580a-c, of at least about 2 seconds, at least about 10 seconds, at least about
15 seconds and/or not more than about 1 minute, not more than about 45 seconds, or
not more than about 30 seconds. In one embodiment, the average residence time for
articles 550 can be greater than the phase shifting rate (t) for which phase shifting
device 530 is configured. For example, the ratio of the average residence time of
the articles passing through one of individual heating zones 580a-c to the phase shifting
rate of device 530 can be at least about 2:1, at least about 3:1, at least about 4:1,
at least about 5:1 and/or not more than about 12:1, not more than about 10:1, or not
more than about 8:1.
[0070] Phase shifting device 530 can be any suitable device for rapidly and cyclically shifting
the phase of microwave energy passing through microwave distribution system 514. According
to one embodiment, phase shifting device 530 can be configured to shift the microwave
energy passing therethrough at a phase shifting rate (t) of at least about 1.5 cycles
per second, at least about 1.75 cycles per second, or at least about 2.0 cycles per
second and/or not more than about 10 cycles per second, not more than about 8 cycles
per second, and/or not more than about 6 cycles per second. As used herein, the term
"phase shifting rate" refers to the number of complete phase shift cycles completed
per second. A "complete phase shift cycle" refers to a phase shift from 0° to 180°
and back to 0°. Although shown as including a single phase shifting device 530, it
should be understood that any suitable number of phase shifting devices can be utilized
within microwave distribution system 514.
[0071] In one embodiment, phase shifting device 530 can comprise a plunger-type tuning device
operable to be moved in a generally linear (e.g., up-and-down motion) within a cylinder
to thereby cause the phase of the microwave energy passing therethrough to be cyclically
shifted. FIGS. 12a and 12b illustrate two embodiments of a plunger-type tuning device
1130a,b suitable for use in microwave distribution system 514. FIG. 12a depicts a
single-plunger phase shifting device 1130a that includes one plunger 1132 operable
to move within a single cylinder 1134 via an automatic driver 1136. FIG. 12b illustrates
another embodiment of a phase shifting device that comprises a multi-plunger phase
shifting device that includes a plurality of plungers 1132a-d disposed and operable
to moved within several corresponding cylinders 1134a-d. Plungers 1132a-d can be driven
by a single automatic driver 1136, which can be connected to each of plungers 1132a-d
via a rotatable cam shaft 1138. Either of plunger-type tuning devices 1130a,b can
be connected to a coupler, such as, for example, a short slot hybrid coupler (not
shown in FIGS. 12a and 12b) and can be employed in microwave distribution system 514
as a phase shifting device 530 as described above.
[0072] Another embodiment of a suitable phase shifting device is depicted in FIGS. 13a-e.
In contrast to the phase shifting or tuning devices illustrated in FIGS. 12a and 12b,
the phase shifting devices illustrated in FIGS. 13a-e are rotatable phase shifting
devices. For example, as shown in FIGS. 13a-c, one embodiment of a rotatable phase
shifting device 1230, also referred to as a variable phase short circuit, can comprise
a fixed section 1210 defining a first substantially rectangular opening 1212 and a
rotatable section 1240 positioned proximate said first opening 1212. As shown in FIG.
13a, a gap 1213 can be defined between rotatable section 1240 and fixed section 1210
and, in one embodiment, a microwave choke (not shown) can be at least partially disposed
within gap 1213 for preventing the leakage of microwave energy from fixed and rotatable
sections 1210 and 1240.
[0073] Rotatable section 1240 comprises a housing 1242 and a plurality of spaced apart,
substantially parallel plates 1244a-d received within housing 1242. As shown in FIG.
13a, housing 1242 comprises a first end 1243a and a second end 1243b and first end
1243a defines a second opening 1246 adjacent to first rectangular opening 1212 of
fixed section 1210. As indicated by arrows 1290, 1292 in FIG. 13a, rotatable section
1240 can be configured to be rotated relative to fixed section 1210 about an axis
of rotation 1211 extending through first and second openings 1212, 1246, as generally
shown in FIGS. 13a-c.
[0074] As particularly shown in FIGS. 13b and 13c, housing 1242 has a length (L
H), a width (W
H), and a depth (D
H). In one embodiment, at least one of L
H, W
H, and D
H are at least about 0.5 λ, at least about 0.65 λ, at least about 0.75 λ and/or not
more than about 1 λ, not more than about 0.9 λ, or not more than about 0.75 λ, wherein
λ is the wavelength of the microwave energy which variable phase short circuit 1230
is configured to pass between first and second openings 1212 and 1246. In one embodiment,
at least one of W
H and D
H are at least about 0.5 λ and both are not more than about λ. As generally shown in
FIGS. 13a-c, the cross-sectional shape of housing 1242 is substantially square, such
that the ratio of W
H:D
H is not more than about 1.5:1, not more than about 1.25:1, or not more than about
1.1:1.
[0075] Fixed section 1210 can be any suitable shape or size and may comprise a circular
or a rectangular waveguide. In one embodiment shown in FIG. 13d, first substantially
rectangular opening 1212 can have a width (W
R) and a depth (D
R) such that the ratio of W
R:D
R is at least about 1.1:1, at least about 1.25:1, or at least about 1.5:1. The width
of first openings 1212 of fixed section 1210 and the width of second opening 1246
of rotatable section 1240 are substantially the same, such that the ratio W
H:W
R is at least about 0.85:1, at least about 0.95:1, or at least about 0.98:1 and/or
not more than about 1.15:1, not more than about 1.05:1, or not more than about 1.01:1.
[0076] As generally shown in FIG. 13a, each of plates 1244a-d can be coupled to second end
1243b of housing 1242 and can extend generally toward first end 1243a of housing 1242
in a direction toward first and second openings 1212 and 1244. Each of plates 1244a-d
can have an extension distance or length, shown as L
e in FIG. 13b, of at least about 0.1λ, at least about 0.2λ, at least about 0.25λ and/or
not more than about 0.5λ, not more than about 0.35λ, or not more than about 0.30λ.
Additionally, as particularly shown in FIG. 13c, one or more of plates 1244a-d can
have a thickness, k, of at least about 0.01λ, at least about 0.05λ and/or not more
than about 0.10λ, or not more than about 0.075λ, wherein λ is the wavelength of the
microwave energy introduced into housing 1242 via first opening 1212. Adjacent plates
1244a-d can be spaced apart by a spacing distance,
j, which can be greater than, approximately the same as, or less than the thickness
of each plate. In one embodiment,
j can be at least about 0.01λ, at least about 0.05λ and/or not more than about 0.10λ,
or not more than about 0.075λ. Thus, in one embodiment, the ratio of the cumulative
surface area of the distal ends of plates 1244a-d, generally illustrated as the shaded
regions in FIG. 13c, to the total internal exposed surface area of second end 1243b
of housing 1242, generally illustrated as the unshaded regions in FIG. 13c, can be
at least about 0.85:1, at least about 0.95:1, or at least about 0.98:1 and/or not
more than about 1.15:1, not more than about 1.10:1, or not more than about 1.05:1.
[0077] Variable phase short circuit 1230 can be configured to rotate at a speed of at least
about 50 revolutions per minute (rpm), at least about 100 rpm, at least about 150
rpm and/or not more than about 1000 rpm, not more than about 900 rpm, or not more
than about 800 rpm about axis of rotation 1211, as illustrated in FIG. 13a. In one
embodiment, at least a portion of the movement of rotatable variable phase short circuit
1230 can be carried out via an actuator 1270 coupled to an automatic driver and/or
automatic control system (not shown). In another embodiment, at least a portion of
the movement can be carried out manually and may optionally include periods of non-rotation.
[0078] Additional embodiments of other rotatable phase shifting devices 1233 and 1235 suitable
for use in microwave distribution system 514 of FIG. 6a, are illustrated in FIGS.
13e and 13f, respectively. As shown in the embodiment depicted in FIG. 13e, rotating
phase shifting device 1233 can include a rotating crank member 1237 coupled via a
securing rod 1239 to a plunger 1241 disposed within a waveguide 1243. As crank member
1237 rotates as indicated by arrow 1261, rod 1239 facilitates a general up-and-down
movement of piston or plunger 1241 within waveguide 1243, as indicated by arrow 1263
in FIG. 13e. Another embodiment of a rotating phase shifting device 1235 is depicted
in FIG. 13f as including a cam 1245 coupled to a follower rod 1247, which can be integrated
with or coupled to a plunger 1241 disposed within waveguide 1243. As cam 1245 rotates,
follower rod 1247 moves plunger or piston 1241 in a general up-and-down motion within
cylinder 1243, as indicated generally by arrow 1263. Additionally, according to one
embodiment, rotating phase shifting device 1235 can further comprise one or more biasing
devices 1249
(e.g., one or more springs) for facilitating movement of plunger 1241 within waveguide 1243
in an upward direction.
[0079] In addition to being utilized as a rotatable phase shifting device, variable phase
short circuit 1230 (or, optionally, rotating phase shifting devices 1233, 1235) can
also be configured for use as a tuning device, such as, for example, as an impedance
tuner for tuning out or canceling unwanted reflections and/or as a frequency tuner
for matching the frequency of the generator to that of the cavity.
[0080] Turning now to FIG. 14a, one embodiment of a microwave distribution system 1314 utilizing
two variable phase short circuits 1330a,b as an impedance tuner for canceling or minimizing
reflected power is illustrated. As shown in FIG. 14a, each of variable phase short
circuits 1330a,b can be connected to adjacent outlets of a coupler 1340, which can
be a short slot hybrid coupler. In operation, each of variable phase short circuits
1330a,b can be individually adjusted to a desired position such that impedance tuner
tunes out energy reflected from microwave launcher 1322 back toward generator 1312.
According to one embodiment, one or both of variable phase short circuits 1330a,b
can be further adjusted as needed during the microwave process in order to accommodate
changes in the reflection coefficient of the articles being heated. In one embodiment,
the further adjustments can be at least partially carried out using an automatic control
system (not shown).
[0081] Variable phase short circuits as described herein can also be utilized as frequency
tuners for matching the frequency of the cavity to the frequency of the generator.
According to this embodiment, one or more variable phase short circuits, shown as
variable phase short circuit 1330c in FIG. 14b, can be directly coupled to individual
ports spaced along a resonant microwave chamber 1320. In this embodiment, variable
phase short circuit 1330c can be continuously or sporadically rotated and its position
can be manually or automatically adjusted depending on changes within microwave chamber
1320 and/or the articles being processed therein (not shown). As a result of this
adjustment of variable phase short circuit 1330c, the frequency of microwave energy
within the cavity can be more closely matched to the frequency of the generator (not
shown).
[0082] Referring again to the microwave heating system 510 shown in FIG. 6a, more thorough
and/or more efficient heating of articles 550 passed through microwave chamber 520
may be carried out by, for example, increasing the heat transfer coefficient between
the articles and the surrounding fluid medium. One embodiment of a microwave chamber
1420 configured to facilitate quicker and more efficient heating of articles 1450
through changes in the heat transfer coefficient within microwave heating chamber
1420 is illustrated in FIG. 15a. In one embodiment, the heat transfer coefficient
within microwave chamber 1420 can be increased, at least in part, by agitating the
gaseous or liquid medium within chamber 1420 using one or more agitation devices,
such as, for example, one or more fluid jet agitators 1430a-d configured to turbulently
discharge one or more fluid jets into the interior of microwave chamber 1420. In one
embodiment, the fluid jets discharged into microwave chamber 1420 can be a liquid
or a vapor jet and can have a Reynolds number of at least about 4500, at least about
8000, or at least about 10,000.
[0083] Structurally, fluid jet agitators 1430a-d can be any device configured to discharge
a plurality of jets toward articles 1450 at multiple locations within microwave chamber
1420. In one embodiment, fluid jet agitators 1430 can be axially spaced along the
central axis of elongation 1417 of microwave chamber 1420 such that at least a portion
of the jets are configured to discharge in a direction generally perpendicular to
central axis of elongation 1417. In another embodiment, particularly shown in FIG.
15b, one or more fluid jet agitators 1430a-d can be circumferentially positioned within
microwave chamber 1420 such that at least a portion of the jets are directed radially
inwardly toward the central axis of elongation 1417 of chamber 1420. Although shown
in FIG. 15b as being generally continuous along a portion of the circumference of
microwave chamber 1420, it should be understood that fluid jet agitator 1430a may
also include a plurality of distinct jets, radially spaced from one another along
at least a portion of the circumference of chamber 1420, each positioned to discharge
a fluid jet toward central axis of elongation 1417 of chamber 1420.
[0084] As shown in FIG. 15a, fluid jet agitators 1430a-d can be positioned along one or
more sides of microwave chamber 1420 and can be disposed between (alternately) with
one or more microwave launchers 1422. Use of one or more agitators 1430a-d can increase
the heat transfer coefficient between the fluid medium within microwave chamber 1420
and articles 1450 by at least about 1 percent, at least about 5 percent, at least
about 10 percent, or at least about 15 percent, as compared to the heat transfer coefficient
of a quiescent chamber,
ceteris paribus. In the same or another embodiment, one or more jets configured and/or operated in
a similar manner can be included within one or more other zones of microwave system
10 including thermalization and/or holding zones 12 and/or 20, illustrated previously
in FIGS. 1a and 1b.
[0085] Referring again to FIGS. 1a and 1b, after being withdrawn from microwave heating
zone 16, the heated articles can then optionally be routed to a temperature holding
zone 20, wherein the temperature of the articles can be maintained at or above a certain
minimum threshold temperature for a specified residence time. As a result of this
holding step, the articles removed from holding zone 20 can have a more consistent
heating profile and fewer cold spots. In one embodiment, the minimum threshold temperature
within holding zone 20 can be the same as the minimum temperature required within
microwave heating zone 16 and can be at least about 120°C, at least about 121°C, at
least about 122°C and/or not more than about 130°C, not more than about 128°C, or
not more than about 126°C. The average residence time of articles passing through
holding zone 20 can be at least about 1 minute, at least about 2 minutes, or at least
about 4 minutes and/or not more than about 20 minutes, not more than about 16 minutes,
or not more than about 10 minutes. Holding zone 20 can be operated at the same pressure
as microwave heating zone 16 and can, in one embodiment, be at least partially defined
within a pressurized and/or liquid-filled chamber or vessel.
[0086] After exiting holding zone 20, the heated articles of microwave system 10 can subsequently
be introduced into a quench zone 22, wherein the heated articles can be quickly cooled
via contact with one or more cooled fluids. In one embodiment, quench zone 22 can
be configured to cool the articles by at least about 30°C, at least about 40°C, at
least about 50°C and/or not more than about 100°C, not more than about 75°C, or not
more than about 50°C in a time period of at least about 1 minute, at least about 2
minutes, at least about 3 minutes and/or not more than about 10 minutes, not more
than about 8 minutes, or not more than about 6 minutes. Any suitable type of fluid
can be used as a cooling fluid in quench zone 22, including, for example, a liquid
medium such as those described previously with respect to microwave heating zone 16
and/or a gaseous medium.
[0087] According to one embodiment generally depicted in FIGS. 1a and 1b, microwave heating
system 10 may also include a second pressure adjustment zone 14b disposed downstream
of microwave heating zone 16 and/or holding zone 20, when present. Second pressure
adjustment zone 14b may be configured and operated in a manner similar to that previously
described with respect to first pressure adjustment zone 14a. When present, second
pressure adjustment zone 14b can be located downstream of quench zone 22, such that
a substantial portion or nearly all of quench zone 22 is operated at an elevated (super
atmospheric) pressure similar to the pressure under which microwave heating zone 16
and/or holding zone 20 are operated. In another embodiment, second pressure adjustment
zone 14b can be disposed within quench zone 22, such that a portion of quench zone
22 can be operated at a super-atmospheric pressure similar to the pressure of microwave
heating zone 16 and/or holding zone 20, while another portion of quench zone 22 can
be operated at approximately atmospheric pressure. When removed from quench zone 22,
the cooled articles can have a temperature of at least about 20°C, at least about
25°C, at least about 30°C and/or not more than about 70°C, not more than about 60°C,
or not more than about 50°C. Once removed from quench zone 22, the cooled, treated
articles can then be removed from microwave heating zone 10 for subsequent storage
or use.
[0088] In accordance with one embodiment not covered by the present invention, one or more
methods for controlling the operation of microwave heating system 10 are provided,
for example, to ensure a consistent and continuous exposure to microwave energy for
each article or package passing through microwave heating system 10. The major steps
of one embodiment of a method 1500 suitable for controlling the operation of microwave
system 10 are depicted by individual blocks 1510-1530 in FIG. 16.
[0089] As shown in FIG. 16, the first step of control method 1500 is to determine a value
for one or more microwave system parameters related to microwave heating zone 16,
as represented by block 1510. Examples of microwave system parameters can include,
but are not limited to, net power discharged, speed of conveyance system, and temperature
and/or flow rate of the water within the microwave heating chamber. Subsequently,
as shown by block 1520 in FIG. 16, the resulting determined value for the specific
parameter can then be compared to a corresponding target value for the same parameter
in order to determine a difference. Based on the difference, one or more actions can
be taken to adjust the operation of microwave system 10, as represented by block 1530
in FIG. 16. In one embodiment, the adjustment of microwave heating system 10 can be
undertaken when, for example, the magnitude of the difference is at least about 5
percent, at least about 10 percent, or at least about 20 percent of the value of the
target value and/or determined value for the specific microwave system parameter.
In one embodiment, at least a portion of the above-described method can be carried
out using an automatic control system.
[0090] In one embodiment, the basic steps of the above-described control method 1500 can
be utilized by microwave heating system 10 to ensure safety and/or regulatory compliance
of the articles (e.g., food and/or medical fluids or equipment) being heated therein.
According to this embodiment, the one or more microwave system parameters may be selected
from the group consisting of minimum net power discharged, maximum speed of conveyance
system, and minimum temperature and/or minimum flow rate of the water within the microwave
heating chamber. In one embodiment, the minimum temperature of the water in the microwave
chamber can be at least about 120°C, at least about 121°C, at least about 123°C and/or
not more than about 130°C, not more than about 128°C, or not more than about 126°C,
while the minimum flow rate can be at least 3.78541 l/min (1 gallon per minute, gpm),
at least about 18.9271 1/min (5 gpm), or at least about 94.6353 l/min (25 gpm). The
maximum speed of the conveyance system, in one embodiment, can be not more than about
16.4592 km/h (15 feet per second, fps), not more than about 13.1674 km/h (12 fps),
or not more than about 10.9728 km/h (10 fps) and the minimum net power discharged
can be at least about 50 kW, at least about 75 kW, or at least about 100 kW. When
control method 1500 is utilized to ensure product safety or compliance, the one or
more actions taken to adjust the operation of microwave heating system 10 can include,
but are not limited to, stopping the conveyance system, turning off one or more generators,
removing, isolating, and re-running or disposing of one or more articles exposed to
undesirable conditions, and combinations thereof.
[0091] In the same or another embodiment, the basic steps of control method 1500 can also
be utilized by microwave heating system 10 to ensure quality and consistency amongst
the articles (e.g., food and/or medical fluids or equipment) being heated. According
to this embodiment, the microwave parameters can include net power discharged, speed
of conveyance system, and temperature and/or flow rate of the water within the microwave
heating chamber. In one embodiment, the temperature of the water in the microwave
chamber can be at least about 121°C, at least about 122°C, at least about 123°C and/or
not more than about 130°C, not more than about 128°C, or not more than about 126°C,
while the flow rate can be at least about 68,1913 l/min (15 gallons per minute, gpm),
at least about 136.383 1/min (30 gpm), or at least about 227.304 l/min (50 gpm).The
speed of the conveyance system, in one embodiment, can be controlled to a speed of
at least about 5.4864 km/h (5 feet per second, fps), at least about 7.68096 km/h (7
fps), or at least about 10.9728 km/h (10 fps), while the net power discharged can
be at least about 75 kW, at least about 100 kW, or at least about 150 kW. When control
method 1500 is utilized to ensure product quality or consistency, the one or more
actions taken to adjust the operation of microwave heating system 10 can include,
but are not limited to, stopping the conveyance system, turning off one or more generators,
removing, isolating, and re-running or disposing of one or more articles exposed to
undesirable conditions, and combinations thereof.
[0092] In order to perform the comparison step 1520 of the method 1500 shown in FIG. 16,
one or more of the target values for at least one of the microwave system parameters
discussed above can be determined prior to heating the articles in microwave system
10. Determination of the magnitude of these target values may be accomplished by first
creating a prescribed heating profile for the specific type of article to be heated
using a small-scale microwave system. For example, in one embodiment, one or more
articles of a specific type (e.g., particular foodstuffs, medical devices, or medical
fluids) are first be loaded into a microwave chamber of a small-scale microwave heating
system. In one embodiment, the articles loaded into the small-scale heating chamber
can be of a single type such that the resultant prescribed heating determined can
be specifically applied to that type of article in a larger-scale heating system.
In one embodiment, the article can be a specific type and/or size of packaged food
(e.g., an 8-oz MRE package of meat) or can be a packaged medical fluid
(e.g., saline) or specific types and/or packages of medical or dental equipment.
[0093] Once loaded into the microwave chamber of the small-scale microwave heating system,
the article can be heated by introducing microwave energy into the chamber via one
or more microwave launchers. During this heating period, which can include multiple
heating runs, a prescribed heating profile can be determined for the article being
heated. As used herein, the term "prescribed heating profile" refers to a set oftarget
values of a variety ofparameters suggested or recommended for use when heating a specific
type of article. In addition to including a target values, prescribed heating profiles
can also be expressed, at least in part, as a function of time and/or position of
the article. In one embodiment, the prescribed heating profile can include at least
one target value for one or more microwave system parameters including, but not limited
to, net power discharged, sequential distribution of microwave power
(i.e., specifics regarding timing, location, and amount of microwave energy discharged),
temperature and/or flow rate of the fluid (e.g., water) in the microwave chamber,
and/or residence time of the article within the microwave chamber. In addition, the
prescribed heating profile can also include target or minimum values for one or more
parameters
(e.g., temperature, flow rate of fluid, pressure, and article residence time) related
to thermalization, holding, and/or quench zones 16, 20, 22 of microwave heating system
10.
[0094] Once a prescribed heating profile has been determined, a plurality of that type of
article can be loaded into a larger-scale microwave heating system and can then be
heated according to the prescribed profile determined with the small-scale microwave
system, optionally with the use of an automatic control system. In one embodiment,
the small-scale microwave heating system can be a batch or semi-batch system and/or
can comprise a liquid-filled microwave chamber having a total internal volume of less
than 2.83168 m
3 (100 cubic feet), less than 1.41584 m
3 (50 cubic feet), or less than 0.849505 m
3 (30 cubic feet). In the same or another embodiment, the large-scale microwave system
can be a continuous or semi-continuous process at least partially carried out in a
pressurized or liquid filled microwave chamber having a total internal volume of at
least about 2.83168 m
3 (100 cubic feet), at least about 7.079321 m
3 (250 cubic feet), or at least about 14.1584 m
3 (500 cubic feet). The above-described steps can subsequently be repeated as many
times as needed in order to create specific prescribed heating profiles for any number
of different articles. Subsequently, target values for one or more parameters described
above can be determined and used in the comparison step 1520 of method 1500 shown
in FIG. 16. Thereafter and based on the difference, one or more of the actions listed
above may be taken to ensure consistent heating of the final product.
[0095] One aspect of ensuring consistent heating is ensuring constant and measurable power
discharged into the heating zone. In one embodiment, a method for controlling the
net power discharged within microwave heating system 10 is provided. As used herein,
the term "net power discharged" refers to the difference between the forward and reflected
power within a waveguide or launcher. As used herein, the term "forward power" refers
to power propagating in an intended direction from the generator to a load, while
the term "reflected power" refers to power propagating in a non-intended direction,
usually from the load back into a waveguide or launcher and toward the generator.
[0096] The major steps of a method 1600 for determining the net power discharged from at
least one microwave launcher using two or more pairs of directional couplers are summarized
in the flow chart provided in FIG. 17. As represented by blocks 1610 and 1620, a first
and second value for net power discharged can be determined using two independent
pairs of directional couplers. Each pair of directional couplers can include one coupler
for measuring forward power and another for measuring reflected power and one or more
devices or systems for calculating the difference to thereby provide respective first
and second values for net power discharged. According to one embodiment, at least
one of the net power values can be used to adjust or control the output of the microwave
generator, while the other can be used as a backup or validation of the other.
[0097] Once values have been obtained from each pair of couplers, the first and second values
for net power can be compared to determine a difference, as illustrated by block 1630,
and, based on the difference, an action can be taken to adjust the operation of the
microwave heating system, as depicted by block 1640. In one embodiment, the action
can be taken when the difference exceeds a predetermined value, such as, for example,
a value that is at least about 1 percent, at least about 2 percent, or at least about
5 percent of the first and/or second net power values determined previously. In one
embodiment, action can be taken when the difference is at least about 1 percent, at
least about 2 percent, or at least about 3 percent of the lowest of first and second
net power values. In another embodiment, action may also be taken if one of first
or second net power values falls below a predetermined minimum and/or exceeds a predetermined
maximum. Depending, at least in part, on the articles being processed and the difference
determined, the action may include, but is not limited to, shutting down a generator
or conveyance system, increasing or decreasing generator output, and/or removing,
isolating, and disposing or rerunning one or more articles that were disposed within
the microwave heating chamber when the difference exceeded the predetermined value.
[0098] Microwave heating systems not covered by the present invention can be commercial-scale
heating systems capable of processing a large volume of articles in a relatively short
time. In contrast to conventional retorts and other small-scale systems that utilize
microwave energy to heat a plurality of articles, microwave heating systems as described
herein can be configured to achieve an overall production rate of at least about 15
packages per minute per convey line, at least about 20 packages per minute per convey
line, at least about 25 packages per minute per convey line, or at least about 30
packages per minute per convey line, which far exceeds rates achievable by other microwave
systems.
[0099] As used herein, the term "packages per minute" refers to the total number of whey
gel-filled 8-oz MRE (meals ready to eat) packages able to be processed by a given
microwave heating system, according to the following procedure: An 8-oz MRE package
filled with whey gel pudding commercially available from Ameriqual Group LLC (Evansville,
IN, USA) is connected to a plurality of temperature probes positioned in the pudding
at five equidistant locations spaced along each of the x-, y-, and z- axes, originating
from the geometrical center of the package, as shown in FIG. 18. The package is then
placed in a microwave heating system being evaluated and is heated until each of the
probes registers a temperature above a specified minimum temperature (e.g., 120°C
for sterilization systems). The time required to achieve such a temperature profile,
as well as physical and dimensional information about the heating system, can then
be used to calculate an overall production rate in packages per minute.