Field of the Invention
[0001] This invention is concerned with a method and apparatus for the sensing of refrigerant
temperatures in refrigerator systems and particularly with a method and apparatus
for the control of refrigerant loading in refrigerator evaporators.
Review of the Prior Art
[0002] The standard refrigeration compressor-operated system consists of a closed circuit
in which cool low-pressure refrigerant vapour from a suction line enters a compressor
which compresses it to a hot high pressure vapour, this hot vapour then flowing through
a discharge line to a condenser coil or coils where it is cooled below its condensing
temperature and becomes liquid. The liquid flows from the condenser through a return
line into a liquid receiver, and from the receiver through a liquid line to an indicator
and filter/drier, from whence it passes to a thermostatically controlled expansion
valve which maintains at an optimum value the flow of the liquid refrigerant into
an evaporator coil or coils, in which it evaporates with consequent temperature drop
and cooling of the coils and their environment; the resultant vapour passes through
the suction line back to the compressor to complete the circuit.
[0003] It is essential to control the expansion valve (usually called the TX valve) so as
to prevent any liquid refrigerant from reaching the compressor, which would damage
it, and this valve control usually consists of a remote temperature sensing fluid-containing
bulb connected by a metal capillary tube to a charged diaphragm capsule in the valve.
The capsule responds to changes in temperature of the sensing bulb to regulate the
flow through the valve. Equivalent electrical sensors have also been developed. The
sensor bulb or its equivalent normally is clamped tightly to the suction line at the
exit from an outlet manifold into which the evaporator coil or group of coils discharge
so as to sense the temperature of the vapour at this point. The temperature characteristic
of a vapourizing body of liquid is very standard in that its temperature will remain
relatively constant at about the respective vapourizing (saturation) temperature as
long as there is some liquid present to vapourize, and then will rise relatively rapidly
when all the liquid is gone. To ensure that no liquid escapes from the evaporator
the sensor is set for an operating temperature sufficiently higher than the saturation
temperature, and the difference between these two temperatures is known as the superheat.
As an example, a quite usual range of values for the saturation temperature of such
a system is about -7°C to about 4.5°C (20°F to 40°F), while a quite usual value for
the superheat is about 5.5°C (10°F), so that the range of control temperatures for
such systems will be -1°C to 10°C (30°F to 50°F).
[0004] In theory it should be possible to use a much lower superheat value, say 1°C (2°F),
but it is found in prior art practice that this has not been sufficient to ensure
the complete absence of liquid refrigerant from the evaporator manifold outlet and
the higher value is therefore almost universally used. As the superheat value varies
around the predetermined amount the TX valve opens and closes, and in theory should
be operable to maintain it quite accurately at that value, but in practice there is
a time lag between the sensing of the temperature by the sensor and the operation
of the TX valve, which also usually cannot respond fast enough, resulting in a fluctuating
superheat value necessitating the higher amount, thereby reducing the efficiency of
the system. There is therefore a continuing need for a temperature sensor for such
systems which can more accurately determine the temperature of the refrigerant vapour
in the suction line and thus improve the efficiency.
[0005] In commercial refrigerators, most evaporators consist of a large number, often as
many as fifty, separate "circuit coils" connected in parallel so as to obtain sufficient
cooling capacity without the individual coils being of too great length with consequent
high pressure drop. These circuit coils are arranged in sets, each set having its
own expansion valve and a common distributor interposed between the valve and the
coils of the set, the purpose of the distributor being to divide the flow as equally
as possible between individual small diameter feed pipes of equal length leading from
the distributor to the respective circuit coil pipe inlets. All of the circuit coil
pipe outlets are connected to a common outlet manifold or stand-pipe. Despite the
care that is taken to try to make the valve and distributor feed equal amounts of
liquid refrigerant to the circuit coils, and to make all of the circuit coils as equal
in length and flow characteristic as possible, it is in practice always found that
liquid refrigerant vapourizes in some of the coils at a different rate than in the
others, due to variables such as differences in the flow of air over the different
coils, and small differences in the pressure drop through each coil. The consequence
is that the circuit coil or coils which absorb the least amount of ambient heat allow
the liquid refrigerant to flow further along it or them before vapourizing, so that
it is this coil or coils that control the TX valve and close it down, starving the
remainder of the coils of liquid refrigerant and excessively superheating the refrigerant
vapour in the starved coils, and thereby reducing the cooling capacity of the system.
This reduction can be as much as from about 25 to 35% of the total capacity.
[0006] This unequal loading of the evaporator circuit coils can usually be observed by visual
inspection of the coils once the system has been in operation of a short time, when
the starved circuit coils are less frost coated toward the outlet end than the others.
This unequal loading is often mistakenly attributed to unequal distribution of the
refrigerant liquid among the coils.
[0007] There are disclosed in U.S. Patents Nos. 3,555,845 and 3,740,967, both issued to
Danfoss A/S of Denmark, a forced flow evaporator for compression type refrigerating
equipment in which part of the evaporator tube, or a tube immediately following the
evaporator tube, has its inner wall lined with gauze fabric to provide a capillary
system that will absorb any liquid refrigerant, the gauze fabric occupying less than
one-half of the cross-sectional area of the tubing, so that a substantial central
passage is left through which the vapour passes at high speed without mixing with
the liquid retained by the gauze fabric, which thereby effectively forms a relatively
stagnant layer on the wall of the tube.
[0008] U.S. Patent No. 4,229,949, issued to Stal Refrigeration AB of Sweden, discloses a
refrigerator system in which a flow disturbing element is located in the suction pipe
downstream of the evaporator, the element operating on the fluid in the pipe to give
the two phases found therein, namely liquid particles and superheated vapour, an increased
mutual relative speed to increase the the heat transfer rate between them and ensure
that the refrigerant exits exclusively in the vapour phase. This element consists
of a disc provided with openings and arranged perpendicularly to the flow direction
of the refrigerant, the disc creating turbulence that accelerates the temperature
equalisation.
Definition of the Invention
[0009] It is therefore a principal object of the present invention to provide a new method
and apparatus for the sensing of refrigerant temperatures in refrigerator systems,
and in particular a new method and apparatus by which the temperature of the refrigerant
exiting from an evaporator coil is sensed more efficiently by the temperature sensor
controlling the TX valve for more precise superheat control.
[0010] It is another principal object to provide a new method and apparatus from the control
of refrigerant loading in refrigerator evaporator coils.
[0011] In accordance with the present invention there is provided a method for the sensing
of the temperature of refrigerant exiting from a refrigeration system evaporator coil
outlet and for the control in accordance with the sensed temperature of a controllable
evaporator valve feeding liquid refrigerant to the evaporator coil inlet, the method
comprising:
feeding the refrigerant from the coil outlet to the interior of a turbulating and
mixing device having therein a refrigerant flow path and having at least part of a
wall thereof of heat conductive material for sensing the device interior temperature
through the wall part;
producing in the flow path turbulence and mixing of the refrigerant by turbulence
and mixing producing means that intercept the entire refrigerant flow and that changes
the direction of the entire refrigerant flow to ensure turbulence and mixing of all
liquid and vapour refrigerant phases present in the refrigerant flow and contact of
only mixed phases with the wall part; and
sensing the device interior temperature at the wall part by temperature sensing means
and controlling the evaporator valve in accordance with the sensed temperature.
[0012] Also in accordance with the invention there is provided apparatus for the sensing
of the temperature of refrigerant exiting from a refrigeration system evaporator coil
outlet and for the control in accordance with the sensed temperature of a controllable
evaporator valve feeding liquid refrigerant to the evaporator coil inlet the apparatus
comprising:
a turbulating and mixing device having an inlet and an outlet for refrigerant and
having therein a refrigerant flow path having at least part of a wall thereof of heat
conductive material for sensing the device interior temperature through the wall part;
turbulence and mixing producing means in the flow path intercepting the entire refrigerant
flow and creating turbulence and mixing of the refrigerant with changes in the direction
of the entire refrigerant flow to ensure turbulence and mixing of all liquid and vapour
refrigerant phases present and contact of only mixed phases with the wall part; and
the apparatus being adapted to have in heat conductive contact with the wall part
temperature sensing means for sensing the device interior temperature and for controlling
the evaporator valve in accordance with the sensed temperature.
[0013] Further in accordance with the invention there is provided a new method for the control
of refrigerant loading in a refrigerator evaporator coil comprising a plurality of
circuit coils connected in parallel with one another and all supplied with refrigerant
through a common thermostatically controlled refrigerant flow control valve and refrigerant
distributor, the valve being controlled to control the refrigerant flow by a superheat
temperature sensor detecting the average temperature of the refrigerant from all of
the circuit coils, characterized in that at or prior to the detection of the temperature
by the sensor the refrigerant flows from the circuit coils are mixed by a turbulating
and mixing device to provide vapourization of any liquid phase refrigerant present
by any superheated vapour phase refrigerant present average the temperatures of the
flows.
[0014] Further in accordance with the invention there is provided apparatus for use in a
refrigeration system comprising:
a refrigerant compressor;
a condenser coil receiving refrigerant from the compressor to cool it;
a common, thermostatically controlled refrigerant flow control valve receiving the
cooled refrigerant from the condenser coil;
an evaporator coil comprising a plurality of circuit coils connected in parallel with
one another so that all are supplied with refrigerant from the common control valve;
a common member having an inlet and an outlet receiving the refrigerant exiting from
all of the circuit coils; and
conduit means connecting the compressor, condenser coil, common control valve, evaporator
coil, common member inlet, common member outlet and the compressor in a closed loop
in the order stated;
a superheat temperature sensor detecting the temperature of the refrigerant at the
common member outlet and operatively connected to the control valve for control thereof;
the apparatus comprising the said turbulating and mixing device in the said loop at
the common member outlet and turbulating and mixing the refrigerant flows from the
circuit coils to average the temperatures of the flows, the temperature sensing means
sensing the device interior temperature.
Description of the Drawings
[0015] Methods and apparatus of the invention will now be described, by way of example with
reference to the accompanying schematic and diagrammatic drawings, wherein:
Figure 1 is a schematic diagram illustrating a typical refrigeration system and including
a device that is a first embodiment of the invention;
Figure 2 is a longitudinal cross-section to a larger scale of the device of Figure
1;
Figure 3 is a cross-section similar to Figure 2, illustrating a device that is a second
embodiment;
Figure 4 is a longitudinal cross-section through an apparatus comprising two devices
of Figure 2 in series;
Figure 5 is a longitudinal cross-section through a device thatis a fourth embodiment;
Figure 6 is a longitudinal cross-section through an apparatus comprising a device
of Figure 5 in series with a device of Figure 2;
Figure 7 is a longitudinal cross-section through a device that is a fifth embodiment;
Figure 8 is a longitudinal cross-section through an apparatus comprising a device
of Figure 7 in series with a device of Figure 2; and
Figure 9 is a longitudinal cross-section through a device that is a sixth embodiment.
[0016] The same or similar parts are given the same reference in all the figures of the
drawing, wherever that is possible.
Description of the Preferred Embodiments
[0017] Referring now to Figure 1, a typical refrigeration system to which the method and
apparatus of the invention can be applied comprises a refrigerant compressor 10 having
a suction inlet 12 and a high pressure outlet 14, the compressor feeding the hot compressed
refrigerant fluid via conduit 15 to a condenser coil 16 having an inlet 18 and an
outlet 20. Cooled refrigerant from the coil 16 passes via conduit 21 to a liquid accumulator
22, and thence via conduit 24 through a filter/drier 26, a liquid indicator 28 and
a common thermostatically controlled refrigerant flow control TX valve 30 into a distributor
32, from which it flows into two parallel-connected circuit coils 34a and 34b of an
evaporator coil. For convenience in illustration only two circuit coils are shown,
but in practice there can be as many as fifty in a single large evaporator coil, each
circuit coil being connected by a respective inlet pipe 36a and 36b to the common
distributor 32. Again in practice care is taken to make all of the circuit coils 34a,
34b, etc., and all of the pipes 36c, 36b, etc., of the same length and as equal as
possible, so that the refrigerant will be distributed as equally as possible among
them.
[0018] Each circuit coil has an inlet 38a, 38b respectively and an outlet 40a and 40b respectively,
the latter all being connected to a common header pipe 42 (sometimes also called a
stand-pipe or manifold), the single outlet 44 of which is connected to inlet 46 of
a turbulator and mixing device 48 of the invention. Asuperheat temperature sensing
bulb 50 by which the TX valve 30 is controlled is tightly clamped to the exterior
of the device 48 by a clamp 51 to be in good heat exchange with its interior and is
connected by a capillary tube 52 to the valve 30. The outlet 54 of the device 48 is
connected by conduit 56 to the pump inlet 12 to complete the system circuit. The usual
fans 58 and 60 are provided to circulate ambient air over the coils 16 and 34a, 34b
respectively. The numerous other circuit elements, controls and indicating devices
that such a system normally includes do not constitute part of this invention and
therefore do not need to be illustrated. The direction of flow of the refrigerent
is indicated by the broken arrows.
[0019] Referring now also to Figure 2, this particular device 48 is made of high conductivity
metal, such as copper or brass, and consists of a first inner cylindrical pipe 62,
one end of which is flanged and constitutes the inlet 46, and the other end 64 of
which is closed. A second outer cylindrical pipe 66 of larger diameter surrounds the
first inner pipe coaxial therewith and is sealed to the pipe at one end adjacent the
inlet 46, while the other end is flanged and constitutes the oulet 54. The interior
of the inner pipe is filled with a spirally wound coil 67 of stainless steel open
mesh material. The inner pipe has a plurality of holes 68 distributed uniformly along
its length and around its periphery, which holes direct the refrigerant vapour entering
the inlet 46, together with any liquid entrained therein, forcibly against the inner
wall of the outer pipe 66. The pipes and the bores therefore provide within the interior
of the device a direction-changing flow path between the unlet and the outlet, the
combination of the multitude of tortuous paths formed by the mesh coil 67, the abrupt
changes in direction of the fast-flowing fluid, the turbulence in the inner pipe 62
because of the impingement of the fluid against the closed end, and the turbulence
in the annular chamber 70 between the two pipes because of the said impingement against
the outer pipe inner wall, ensuring that the entire refrigerant flow in the flow path,
whether in the liquid or vapour phase, is all thoroughly mixed and rendered turbulent,
and particularly without any possibility of the relatively high velocity vapour phase
being able to flow through the device separately from the liquid phase. Moreover,
the vigorous impingement of the high velocity fluid against the outer pipe inner wall
ensures that any relatively stagnant barrier layer of refrigerant, or of the lubricating
oil that is always entrained therein, is thoroughly disrupted and removed from the
inner wall, so that it cannot prevent the efficient transfer of heat from the refrigerant
through the wall to the sensor bulb 50. The bulb is therefore sensing only the temperature
of a completely turbulent mixed and temperature averaged refrigerant flow as received
from the outlet of the headeer pipe 42, and in addition is much more sensitive to
changes in the refrigerant temperature and more accurately measures the device interior
temperature which corresponds to the averaged refrigerant temperature. This turbulating
and mixing function of the device 48 is effective in this manner whatever the evaporator
coil structure employed in the system.
[0020] When the device is used with a system as specifically described, namely with multiple
circuit coils, then in addition to turbulating and mixing the fluid flow in each evaporator
circuit coil it also performs a multiple mixing function, whereby the fluid flows
from all of the circuit coils are thoroughly mixed together, so that all of their
separate temperatures are averaged, and it is this average circuit coil temperature
that is detected by the bulb 50. Moreover, this very thorough turbulence and mixing
ensures that if one or more of the circuit coils is not evaporating all of its supply
of refrigerant, then the small quantities of liquid reaching the mixing device are
immediately atomized and consequently easily vapourized by heat from the superheated
vapour from the remaining coils. The supply of refrigerant to the strarved coil or
coils can therefore be increased until the superheated vapour they produce is not
able to vaporise the liquid refrigerant from the underloaded coil or coils.
[0021] The diameters of the pipes 62 and 66 are such that the flow capacities of the resultant
flow passages are about that of the remainder of the suction tube 56, while the number
and size of the apertures 68 are such that about the same flow capacity is achieved.
These flow capacities can vary between about 0.5 and 1.5 times the usual flow capacity
of the suction tube; it may be preferred to reduce the flow capacity of the apertures
68 somewhat below that of the suction tube in order to obtain sufficiently forceful
impingement of the fluid against the outer tube inner wall.
[0022] In one specific embodiment intended for use in a system of about 3-5 h.p. the outer
pipe 66 is about 20-25 cm (8-10 ins.) long and 4.0 cm. (1.6 ins.) outside diameter;
the inner pipe 62 is 2.75 cm (1.1. in.) outside diameter and is provided with 40 uniformly
spaced holes 68 of 0.47 cm (0.19 ins.) diameter. The mesh insert 67 consisted of a
piece of stainless steel fine wire mesh corrugated diagonally to its length measuring
10cm by 15cm (4ins by 6ins) wound into a spiral sufficiently tightly to permit its
insertion into the pipe, where it will expand to completely fill the space. It will
be understood that it is not possible to accurately illustrate such a tightly rolled
spiral in the drawings.
[0023] In another embodiment intended for a system of about 10-15 h.p. the outer pipe 66
is 5.25 cm (2.1 in.) outside diameter, the inner pipe 62 is 4.0 (1.6 in.) outside
diameter and the holes 68 are 0.6 cm (0.25 in.) diameter. It is found in practice
that the pressure drop through the devices of the invention is sufficiently low, usually
less than about 1 p.s.i., that it does not produce any appreciable loss of efficiency,
and any loss for this reason is amply compensated by the overall considerably improved
efficiencies that usually are obtained. The drop is sufficiently small that it is
difficult, if not impossible, to detect with the pressure gauges that are used in
standard refrigeration service practice.
[0024] Despite the lengthy period of time for which these problems have existed it does
not appear to have been understood how to provide turbulator means and/or mixing means
that will sufficiently improve the temperature detection and control of the TX valve,
and also in multiple coil systems to average the temperatures of the refrigerant flows
from the large number of individual circuit coils for the same purpose, and to the
best of my knowledge none of the arrangements proposed in U.S. Patent Nos. 3,555,845;
3,740,967 and 4,222,949 are in commercial use. Thus, the current literature in the
industry of which I am aware seems to assume that all that can be done is to make
the lengths of the circuit coils as equal as possible, to discharge all of the circuit
coils into a common header pipe, and to clamp the sensor bulb to the outside of the
outlet pipe from the header pipe, when the temperature will be measured as accurately
as possible and the flows will be mixed to the maximum obtainable extent.
[0025] I believe that this mistaken assumption may have resulted from a lack of adequate
appreciation of the flow conditions of the refrigerant fluid in the evaporator coils
and the outlet pipe or manifold. The refrigerant enters the coils as a low volume
liquid and is evaporated in the confined spaces thereof to a high volume vapour, with
the result that the exit speed of the vapour is relatively high, to the extent that
in the absence of the highly positive turbulating and/or mixing method and corresponding
apparatus of the invention, involving the entire fluid flow or flows, the flows in
the coils remain laminar and any liquid particles remain entrained without mixing,
while there is little or no opportunity for the flows from the different coils to
mix and average. Consequently there is little opportunity for any small quantities
of liquid refrigerant to be evaporated, before the temperature must be sensed by the
bulb 50. It is essential for the turbulating and mixing to be carried out across the
entire cross-section of the flow path, since any gaps will allow the corresponding
portion or portions of the high velocity fluid passing through them to remain laminar
with liquid particles entrained and defeat the purpose of the device. The situation
would not be made much better in the prior art apparatus by placing the sensor bulb
50 further along the suction pipe 56, since the flows will still remain relatively
laminar along the pipe, and any additional distance of the bulb from the evaporator
outlet and from the TX valve introduces additional difficulty because of the increased
time delay for operation of the valve.
[0026] As evidence of this current lack of appreciation of the problem there is and has
been considerable discussion of the best physical arrangement for the coils to ensure
that are equally loaded, and it has been considered important in prior refrigeration
systems to locate the sensor bulb 50 appropriately on the circumference of the suction
pipe in order to sense the superheat temperature as accurately as possible and operate
with minimum superheat. The manufacturers of TX valves in their installation manuals
stress the importance of proper location of the sensor bulb, but do not give a definitive
location for it. They advise that preferably the bulb should be fastened preferably
to a horizontal portion of the suction line, and clamped at different places around
its circumference at different places depending on the diameter, but the location
is finally chosen by the installer depending upon what appears to be suitable and/or
practicable for that installation, often with poor results. The theoretically ideal
location is at 6 o'clock on the circumference of a horizontal suction pipe, where
it should be able to sense most accurately any small quantity of liquid refrigerant
passing in the pipe, and would therefore permit the smallest amount of superheat.
In practice this has not been a satisfactory location because of the presence of lubricant
oil in the refrigerant, which flows along the bottom of the pipe and would thermally
insulate the sensor bulb from the refrigerant fluid. The usual location for the bulb
has therefore been at four or eight o'clock on the pipe circumference. It is found
that with the thorough turbulence and mixing provided that the location of the sensor
bulb around the circumference of the device is quite immaterial, and it can be placed
at the most convenient location from the point of view of installation as close to
the valve as possible and subsequent access for service. It will also be seen that
the sensor need not be located directly on the wall of the mixing device enclosure,
which is the preferred location, but should be located as close as possible to the
device outlet. In addition it is now found quite unnecessary to locate the sensor
bulb on a horizontal portion of the suction line, and the attitude of the device has
no effect upon its performance. It has also been found that the device is relatively
insensitive to being installed so that the inlet is the outlet, and vice versa, although
of course this is not recommended; a small decrease in efficiency of operation has
been noted when this has occured.
[0027] The effectiveness of a device of the invention can readily be seen by visual inspection
of the evaporator coil before and after its installation. Before installation it is
usually found that the frost deposition on the different circuit coils is non-uniform
with some of them completely frosted up to the outlet, while others are not frosted
for a substantial distance back from the outlet, showing that the latter are starved
of refrigerant and are working much below their maximum cooling capacity. Also the
evaporator common outlet member is only partially frosted. With the device installed
all of the circuit coils become more or less equally frosted, as well as the entire
length of the suction manifold, indicating that all of the circuit coils are now operating
at their full designed capacity. It is now found possible safely to reduce the amount
of superheat from the prior value of about 5.5°C (10°F) to as low as 2°C (4°F). In
some installations the resultant improvement in cooling capacity of the system can
reach as much as 25-35%, indicating that the system previously was operating at only
74-80% of the available capacity.
[0028] As a specific example, in an installation employing compressors totaling 200 H.P.
and eight forced air evaporator coils the system prior to the installation of the
devices of the invention took 3 hours, 10 minutes to cool the room temperature from
13°C (55°F) to -19°C (-2°F). With the devices installed the time taken was reduced
to 2 hours, 10 minutes, an improvement of 29% in efficiency or equivalent to increasing
the output of the compressors to about 258 H.P.
[0029] An important advantage that has been found to follow from use of the invention, demonstrating
its unexpected nature, is the flexibility that is obtained upon installation in not
having to closely match the size of the TX valve to the evaporator coil capacity without
the valve losing control of the refrigerant flow. The capacity of a TX valve is determined
both by the size of its flow aperture and the head pressure across the aperture, and
it has been important in prior art installations for this match to be as close as
possible. For example, one manufacturer provides 21 different sizes of valve to cover
the range 0.5-180 tons, those in the range 0.5 - 3 tons being rated in 0.5 ton increments,
with progressively increasing intervals up to the maximum. If the valve is too large
then with the high superheat values employed the valve hunts, overfeeding and underfeeding
the evaporator with resultant poor efficiency and danger of liquid reaching the compressor
because of the over-large flow capacity of the valve while open. On the other hand,
with the valve and coil sizes closely matched it becomes necessary to maintain the
head pressure above a minimum value, since otherwise the valve flow capacity becomes
too low. This penalizes the system in winter when the air cooled condensers are very
efficient and could operate with lower head pressure; instead it is necessary to maintain
it artifically high by various techniques that are available. This means that the
power required to compress the refrigerant must also be maintained at a corresponding
high uneconomical value.
[0030] This loss of control is easily observed in practice. For example, if the evaporator
fan stops for some reason, perhaps a broken fuse, or the flow of product being cooled
is interrupted, the load on the coil drops suddenly, faster than can be controlled
by the valve, and liquid floods the compressor, which then becomes covered with frost
when it should be frost-free. The liquid refrigerant washes out the lubricant, and
can cause valve breakage and damage. Again, if the automatic coil defrost system is
not operating satisfactorily and the coils become coated with ice the load on each
coil drops and control can be lost; this of course is easily detected by visual inspection
of the coils.
[0031] Upon installation of a device or devices of the invention it is found that this close
match of load capacities is no longer necessary and an oversize valve can be employed
successfully. In a specific example, in a system with a 1.5 ton evaporator the original
2 ton rated valve was replaced with an 8 ton rated valve; adequate control was maintained
with the superheat value fluctuating about 0.5°-1°C (1° - 2°F). Thus with a larger
orifice TX valve it is no longer necessary to keep the head pressure at an artificially
high value to maintain adequate refrigerant flow through the valve, and instead it
could be allowed to drop to a lower level and still maintain proper superheat control
with maximum evaporator capacity. This not only maximizes the efficiency of the system
but also provides the possibility of reducing the number of different sizes of valves
required for a full range of installation sizes.
[0032] As described above, the sensor bulb 50 preferably is installed on the device as close
as possible to the device outlet 54 where the maximum mixing has occured. In the embodiment
of Figure 3 the external tube 66 is provided with an integral elongated neck portion
66a constituting the outlet 54 to facilitate fastening of the bulb to the device.
In this embodiment the interior of the inner pipe 62 is completely filled with metallic
wool 86 as a mixing medium, in place of the rolled screen of the embodiment of Figure
1
[0033] Figure 4 shows another arrangement in which a second turbulating/mixing device 48b
of the invention, of essentially the same body structure as the first device 48, now
having the reference 48a, is connected in series with the first device, the sensor
bulb 50 being installed on the downstream device 48a. The second device provides additional
mixing with correspondingly improved performance of the TX valve, without too great
an increase in pressure drop along the suction line, by suitable choice of the flow
capacities of the respective internal passages and the bores 68. A mesh coil 67 (or
body 86 of metallic wool) can be installed in either or both of the devices and is
shown installed in device 48a.
[0034] Figure 5 shows an embodiment in which the refrigerant flow path is provided by conduits
forming two T-shaped junctions 74 and 76 connected by U-shaped connectors 78a and
78b; the connectors may be of smaller internal cross-section diameter to produce an
increase in flow velocity of the refrigerant. The junction 74 divides the refrigerant
flow from the common header 42 into two separate approximately equal sub-streams which
are rendered turbulent by their impact against the transverse wall of the T cross-bar,
the two streams moving separately at high velocity in the connectors 78a and 78b and
being re-combined with a "head-on" collision in the cross-bar of the junction 76 back
into a single stream. This collision of the two turbulent sub-streams produces even
more turbulent mixing thereof, so that effective mixing and turbulence takes place
before the refrigerant is delivered to the leg 77 of the second T-shaped junction
to which the bulb 50 is attached. Although in this embodiment the refrigerant flow
is divided into only two separate streams in other embodiments it may be divided into
more than two, all of which are simultaneously or sequentially recombined.
[0035] Figure 6 shows an arrangment in which the device 72 is followed by a device 48 so
as to obtain the combined effect of the two devices, the bulb 50 being in this case
attached to the downstream device 48.
[0036] Figure 7 shows a further embodiment wherein the device consists of a container 80
having an inlet 82 for unturbulated, unmixed refrigerant and an outlet 84 for turbulent
mixed refrigerant spaced from another along the length of the container, the inlet
and outlet both being disposed radially with respect to the longitudinal axis of the
container, so that abrupt changes in direction of the fluid flow path are produced.
The interior of the container is filled with a porous turbulating and mixing medium
86 through which all of the refrigerant must pass in moving from the inlet to the
outlet. The movement of the refrigerant fluid through the myriad of random interconnected
channels in the medium 86 ensures the necessary thorough turbulence and/or mixing
thereof. A suitable medium is for example metallic wools, foams or screens, or other
suitable metallic media, particularly of stainless steel or aluminum, packed sufficiently
densely to achieve the desired amount of turbulence and mixing without too great a
pressure drop. Other media such as open-celled porous plastic and ceramic foams can
also be used. Sensor bulb 50 is firmly clamped to the container exterior wall, which
is sufficiently heat conductive, as close as possible to the outlet 84. In an example
the container 80 was 10cm (4ins) in diameter and 25cm (10ins) long and was packed
with stainless steel wool. Advantageously the body of wool is surrounded by at least
a single layer of wire mesh to ensure that pieces of the wool cannot break off and
enter the system.
[0037] Figure 8 shows an arrangement in which the device 80 of Figure 7 is used as a pre-turbulator
and pre-mixer for a second downstream device 48, so as again to obtain the combined
effect of the two devices.
[0038] Figure 9 shows an embodiment in which the device comprises a straight length of pipe
66 the whole interior of which is filled with closely wound wire mesh 67, so that
again the entire refrigerant flow is intercepted, rendered sufficiently turbulent
and mixed to the necessary extent. Because in this embodiment there is no abrupt change
of direction in the flow path, except within the interstices of the wire mesh, the
device preferably is made much longer so as to provide a longer path than with the
previously described turbulating and mixing devices, the sensor bulb 50 being attached,
as with the other embodiments, as close as possible to the outlet end 54. As an example
of the additional length required a device fitted in a system with a compressor of
10 H.P. capacity employed a pipe 66 of 4.0 cm (1.6 in) outside diameter, enclosing
a tightly spirally rolled stainless steel mesh; the pipe was 45cm (18 in) long, as
compared with the length of 20-25cm (8-10 in) required for a device 48. However, it
may also be noted that in another specific example a device with a straight enclosure
between the inlet and the outlet consisted of a piece of pipe 25cm (10 in) long and
4cm (1.6 in) outside diameter. A piece of permanent aluminum filter material made
of woven aluminum strands, as used in air conditioning filters, measuring about 25cm
by 15cm (10 in by 6 in) and 6mm (0.25 ins) thick, was rolled tightly into a cylinder
and inserted endwise into the pipe. The device was employed with a coil of about 10
H.P. capacity with the sensor bulb fastened to the suction line immediately downstream
of the device. Despite its relatively short length it still resulted in an increase
of approximately 20% in the cooling capacity of the coil.
1. A method for the sensing of the temperature of refrigerant exiting from a refrigeration
system evaporator coil outlet (40a, 40b) and for the control in accordance with the
sensed temperature of a controllable evaporator valve (30) feeding liquid refrigerant
to the evaporator coil inlet, characterized by:
feeding the refrigerant from the coil outlet (40a, 40b) to the interior of a turbulating
and mixing device (48, 72 or 80) having therein a refrigerant flow path and having
at least part of a wall (66, 76, 80) thereof of heat conductive material for sensing
the device interior temperature through the wall part;
creating in the flow path turbulence and mixing of the refrigerant by turbulence and
mixing producing means (62, 68, 67, 86) that intercept the entire refrigerant flow
and that changes the direction of the entire refrigerant flow to ensure turbulence
and mixing of all liquid and vapour refrigerant phases present in the refrigerant
flow and contact of only mixed phases with the wall part; and
sensing the device interior temperature at the wall part by temperature sensing means
(50) and controlling the evaporator valve (30) in accordance with the sensed temperature.
2. A method as claimed in claim 1, characterized in that the turbulence and mixing
device (48) receives the refrigerant in a first passage (62) and delivers it to a
second passage (70) through a plurality of bores (68) producing an abrupt change in
direction of the flow with turbulence producing impingement of the flow through the
bores (68) against a first surface of the second passage, and that the temperature
sensing means (50) contact a second surface of the second passage (70) in heat exchange
contact with the first surface through the second passage wall (66).
3. A method as claimed in claim 2, characterized in that the refrigerant is introduced
into the first passage (62) at one end (46) thereof, and the other end (64) of the
first passage is closed for turbulence producing impingement of the refrigerant flow
against the closed end.
4. A method as claimed in claim 2 or 3, characterized in that the first passage (62)
has therein additional turbulating and mixing means (67) intercepting the refrigerant
flow in the passage.
5. A method as claimed in claim 4, characterized in that the additional turbulating
and mixing means (67) in the first passage is selected from metallic wool, metallic
foam, metallic screen, plastic foam or porous ceramic foam.
6. A method as claimed in claim 1, characterized in that the turbulating and mixing
device (72) comprises conduit means (74, 76, 78a, 78b) dividing the refrigerant flow
into two or more separate turbulent streams and subsequently re-combining the separate
streams with impingement against one another to create turbulence and mixing between
them, the temperature sensing means (50) being disposed at the point of recombination
of the two streams.
7. A method as claimed in claim 6, characterized in that the conduit means (74, 76,
78a, 78b)divide the refrigerant into said two or more separate turbulent streams with
turbulence producing impingement against a surface (76) transverse to the direction
of flow of the refrigerant into the device.
8. A method as claimed in claim 1, characterized in that the turbulating and mixing
device comprises within an enclosure (80) having its interior a body (86) of porous
turbulating and mixing medium intercepting the entire refrigerant flow and through
which all the refrigerant passes between the inlet and outlet.
9. A method as claimed in claim 8, characterized in that the said porous turbulating
and mixing medium (86) is selected from metallic wool, metallic foam, metallic screen,
plastic foam or porous ceramic foam.
10. A method as claimed in claim 8 or 9, characterized in that the flow direction
of the inlet (82) and the outlet (84) to the enclosure (80) are radial to the direction
of flow of refrigerant through the enclosure to cause corresponding abrupt changes
of direction thereof.
11. A method as claimed in any one of claims 1 to 10, characterized by two turbulating
and mixing devices (46, 76, 80) means connected in series with one another to increase
the turbulence and mixing of the refrigerant and improve temperature sensing.
12. A method as claimed in any one of claims 1 to 11, characterized by the control
of refrigerant loading in a refrigerator evaporator coil comprising a plurality of
circuit coils (34a, 34b) connected in parallel with one another and all supplied with
refrigerant through a common thermostatically controlled refrigerant flow control
valve (30) and refrigerant distributor (32), the valve being controlled to control
the refrigerant flow by a common superheat temperature sensor (50) sensing the interior
temperature of the respective turbulating and mixing device (48, 76, 80).
13. Apparatus for the sensing of the temperature of refrigerant exiting from a refrigeration
system evaporator coil outlet (40a, 40b) and for the control in accordance with the
sensed temperature of a controllable evaporator valve (30) feeding liquid refrigerant
to the evaporator coil inlet (38a, 38b) characterized in that it comprises:
a turbulating and mixing device (48, 76, or 80) having an inlet (44, 74, 82) and an
outlet (54, 76, 84) for refrigerant and providing therein a refrigerant flow path
having at least part of a wall thereof of heat conductive material for sensing the
device interior temperature through the wall part;
turbulence and mixing producing means (62, 68, 67, 86) in the flow intercepting the
entire refrigerant flow path and creating turbulence and mixing of the refrigerant
with changes in the direction of the entire refrigerant flow to ensure turbulence
and mixing of all liquid and vapour refrigerant phases present and contact of only
mixed phases with the wall part; and
the apparatus being adapted to have in heat conductive contact with the wall part
temperature sensing means for sensing the device interior temperature and for controlling
the evaporator valve (30) in accordance with the sensed temperature.
14. Apparatus as claimed in claim 13, characterized in that the turbulence and mixing
producing means comprises first and second (70) passages having a wall (62) in common
between them, the said common wall having therein a plurality of bores (68) through
which the refrigerant flows from the first passage to the second passage(70), the
bores (68) thereby producing an abrupt change in direction of the flow with impingement
of the flow against a first surface of the second passage to produce the said turbulence
and mixing of the flow in the second passage.
15. Apparatus as claimed in claim 14, characterized in that the first passage is provided
by a first tubular member (62), and the second passage is provided by a second tubular
member surrounding the first tubular member (66) to form an annular second passage
(70) between them, the said bores (68) being provided in the wall of the first tubular
member (62), and directing the refrigerant flow against the inner wall of the second
tubular member (66).
16. Apparatus as claimed in claim 15, characterized in that one open end of the first
tubular member (62) constitutes an inlet (46) to the first passage, and the other
end (64) of the member is closed for impingement of the refrigerant flow against the
closed end and resultant turbulence in the first passage.
17. Apparatus as claimed in any one of claims 14 to 16, characterized in that the
first passage (62) is filled with a body (67) of porous turbulatin and mixing medium
through which the refrigerant must pass from the inlet to the plurality of bores.
18. Apparatus as claimed in claim 17, characterized in that the said porous turbulating
and mixing medium (67) is selected from metallic wool, metallic foam, metallic screen,
plastic foam or porous ceramic foam.
19. Apparatus as claimed in claim 13, characterized in that the turbulating and mixing
device comprises first junction means (74) dividing the refrigerant flow into two
or more separate streams, second junction means (76) subsequently combining the said
separate streams with impingement of the streams against one another to create turbulence
and mixing between them, and conduit means (78a, 78b) connecting the first and second
junction means (74, 76) for flow of the separate streams between them, the temperature
sensing means (50) being disposed at the second junction (76).
20. Apparatus as claimed in claim 19, characterized in that the first junction means
(74) divide the refrigerant flow into two or more separate streams with turbulence
producing impingement of the streams against a surface of the junction means transverse
to the direction of flow of the refrigerant into the device.
21. Apparatus as claimed in claim 13, characterized in that the turbulating and mixing
device comprises an enclosure (80) having an inlet (82) and and outlet (84) and containing
within the enclosure (80) a body (86) of porous turbulating and mixing medium through
which the refrigerant must pass from the inlet (82) to the outlet (84).
22. Apparatus as claimed in claim 21, characterized in that the said porous turbulating
and mixing medium (86) is selected from metallic wool, metallic foam, metallic screen,
plastic foam or porous ceramic foam.
23. Apparatus as claimed in claim 21 or 22, characterized in that the flow direction
of the inlet (82) and the outlet (84) to the enclosure (80) are radial to the direction
of flow of refrigerant through the enclosure to cause corresponding abrupt changes
of direction thereof.
24. Apparatus as claimed in any one of claims 13 to 23, characterized by two turbulating
and mixing devices (48, 72, 80) connected in series with one another to increase the
turbulence and mixing of the refrigerant and improve temperature sensing.
25. Apparatus as claimed in any one of claims 13 to 24, characterized by its use in
a refrigeration system having an evaporator coil comprising a plurality of circuit
coils (34a, 34b) connected in parallel with one another so that all are supplied with
refrigerant for evaporation from a common control valve (30); a common turbulating
and mixing device (48, 76, or 80) common member receiving the refrigerant from all
of the circuit coils; and a common superheat temperature sensor (50) sensing the temperature
of the refrigerant in the common device and operatively connected to the control valve
(30) for control thereof.