[0001] The present invention relates to a method and an apparatus for heating a fluid, intended
in particular for household appliances.
[0002] As is known, regulations pertaining to the energy consumption of household appliances
are nowadays rather restrictive; household appliance manufacturers are thus compelled
to constantly and systematically look for new technical solutions leading to reduced
or anyway limited energy and water consumption.
[0003] For this reason, some washing machines and dishwashers include low-consumption wash
and/or rinse cycles, with recirculation of a part of the water in the tub.
[0004] Similar measures are taken,
mutatis mutandis, also for drying the load in clothes dryers and washing/drying machines, wherein
the management of the heated air is optimized by recovering a part thereof.
[0005] For this reason, some clothes dryers and washing/drying machines include recirculation
cycles for recirculating a part of the load drying air, thereby optimizing the management
of the heated air and recovering a part of the air circulating in the load chamber:
in this way, the energy used for heating the air is not wasted by discharging it into
the outside environment as soon as it has flowed through the chamber, as was the case
in the past.
[0006] Before proceeding any further with this description, it must be pointed out that
reference will be made hereafter, unless otherwise specified or apparent from the
context, mainly to clothes dryers; however, the following explanations should be understood
as applicable to washing/drying machines as well.
[0007] In this frame, the Applicant's attention has focused on reducing the energy consumption
for air heating in such household appliances.
[0008] As is known, in fact, fluids (air and water) are heated in clothes dryers and washing/drying
machines mainly by means of heat generated by electric resistors.
[0009] The latter may be of different types depending on the application, but they are usually
configured as bent bars, inside of which the actual electric resistor is arranged,
buried in refractory zirconium-based or silicon-based powders or the like.
[0010] This type of resistor has proven to be effective and reliable over time, although
it has a few drawbacks.
[0011] In fact, the thermal inertia and the time necessary to reach the required temperature
values are not always suited to the various needs: for example, as can be easily understood,
the drying cycles of a clothes dryer and the cooking cycles of an oven may require
different times and operating modes even when the respective resistors are substantially
similar from a structural viewpoint.
[0012] Furthermore, as far as consumption is concerned, the resistors known in the art do
not appear to be an optimal solution, also because they are rather rigid both from
a structural viewpoint, due to the above-mentioned configuration, and from a functional
viewpoint, since such a configuration does not allow them to be easily used in different
household appliances, so that they can be adapted to the particular requirements of
the latter.
[0013] As a matter of fact, it can be easily understood that the air heating conditions
in a clothes dryer are very different from those in a muffle of an oven, if only because
in the former case the air is heated outside the tub in dynamic conditions, whereas
in the latter case it is heated inside the muffle in static conditions.
[0014] The present invention aims at improving this state of the art; in other words, the
technical problem at the basis of the invention is to provide a new method for heating
the air in a clothes dryer or a washing/drying machine, with such operating features
that allow overcoming the above-mentioned limitations of the prior art.
[0015] The idea that solves this problem is to use electric resistors which are different
from traditional ones, and which consume less energy and/or are equally or more efficient
than the latter.
[0016] Within the scope of this general principle, the preferred solution found by the Applicant
is to use electric resistors based on non-metallic materials; among such materials,
composite fibers based on carbon, boron or the like are particularly suitable.
[0017] In this respect, it must be pointed out that the Applicant knows that these fibers
are used for civil heating applications and also for parts of machinery, such as,
for example, the defrosting systems for aircraft wings described in American patent
US 4,737,618.
[0018] However, the Applicant does not know of any application to household appliances,
in particular for heating fluids in household appliances in dynamic conditions.
[0019] According to the invention, it is possible to create heating systems that are functionally
flexible, so that they can be easily adapted to various household appliances in order
to reduce their energy consumption and improve their thermal efficiency.
[0020] The features of the invention are specifically set out in the claims appended to
this description; all such features will become more apparent in the light of the
following description of a few embodiments shown in the annexed drawings, wherein:
- Fig. 1 shows the drum of a clothes dryer including a heating system according to the
invention;
- Fig. 2 is a view, with a part removed for clarity, of a detail of the heating system
of Fig. 1;
- Fig. 3 is a sectional view along line III-III of Fig. 2;
- Fig. 4 is a view, with a part removed for clarity, of a variant of the detail of the
heating system of Fig. 2, without the electric resistor applied thereto;
- Fig. 5 is a view of the detail of Figure 4, with a resistor applied thereto;
- Fig. 6 is a sectional view along line VI-VI of Fig. 5.
[0021] With reference to the above-listed drawings, the figures show an application of the
heating of the invention to a clothes dryer; more in particular, Figure 1 illustrates
a tub or chamber 1 of a clothes dryer in a distinct condition, i.e. without the rest
of the structure of the clothes dryer, since the latter is unimportant for comprehending
the invention.
[0022] Prior to describing the examples of the invention, it is worth pointing out that
in this description reference will essentially be made to those elements which are
necessary or useful for understanding the invention, neglecting for brevity the other
parts of the household appliances to which the invention is applicable, for further
details of which reference should be made to the technical teachings known in the
art of clothes dryers and washing/drying machines.
[0023] To this end, reference should be made to the broad technical and patent literature
on this matter, as well as to the household appliances manufactured by the present
Applicant.
[0024] Furthermore, in the drawing the wash chamber 1 is shown with a part thereof removed,
in order to make the inside thereof, with the rotary drum 2, partially visible.
[0025] On the outside of the chamber 1 there is an air circulation circuit 10 that comprises
an intake channel 11 extending from the back wall 3 of the chamber 1 to the upper
region of the latter, and a delivery channel 12 that extends from the upper region
to the load opening 3 of the chamber 1.
[0026] Between the intake channel 11 and the delivery channel 12 there is a heating device
20, which is better visible in Figure 2, wherein a part has been removed for the sake
of clarity.
[0027] As can be seen, the heating device 20 comprises a body or outer shell 21 secured
to the chamber 1 by means of bolts (not shown in the drawings) engaging into matching
eyelets 22 arranged along the edges of the shell 21.
[0028] One end of the latter is configured with a lobe 23 that houses an impeller 25, driven
by an electric motor 26.
[0029] The impeller 25 takes in air from the chamber 1 through the associated duct 11, and
delivers it into a collector 28 consisting of the central portion of the shell 21
having a substantially regular cross-section, within which there is a heater 30.
[0030] The shell 21 has a heated air outlet mouth or end 29 that preferably has a divergent
shape, so as to increase the pressure of the air exiting the collector 28; the outlet
mouth 29 is connected to the delivery channel 12 that supplies the air into the drying
chamber 1.
[0031] As Figure 3 clearly shows, the heater 30 comprises a pair of support plates 32, 33
for respective heating resistors 34, 35.
[0032] The plates 32, 33 are substantially parallel to each other and extend along the outer
body 31, as clearly shown in the sectional view, thus defining an upper passage portion
36, a lower passage portion 37 and an intermediate passage portion 38 for the air
flow.
[0033] According to the invention, the plates 32, 33 are preferably of the radiating type;
to this end, they are made of an appropriate material, i.e. a material that can provide
maximum irradiation of thermal radiations (i.e. radiations comprised in the range
from infrared to ultraviolet, with wavelengths of 10
-1 to 10
2 µm) in the temperature range of 80 °C to 150°C.
[0034] Therefore, suitable materials for the support plates 32 are some metals (preferably
with treated surfaces), such as, for example, aluminium or alloys thereof, nickel,
and also non-metallic materials such as mica, ceramic materials, glassy materials,
or even synthetic materials.
[0035] Furthermore, according to a preferred embodiment, also the plates 32, 33 are coated
with or made of carbon; thus, they can absorb and emit radiations in the infrared
range for the above-specified temperatures; for special solutions, carbon can be deposited
onto a substrate in the form of nanometric particles (the so-called nanotubes).
[0036] The choice of the material for the plate will depend on several factors, such as
the dimensions and weight of the heating device 20 (also related to the air flow circulating
therein), its shape (the device may also have a cylindrical geometry), and the like.
[0037] On the plates 32, 33 respective carbon-fiber resistors 34, 35 are wound, consisting
of wires the diameter of which may vary, according to the application, between 1 and
6 mm
2; the diameter of the carbon wires will depend on the heat to be supplied, and hence
on the current required for obtaining it.
[0038] To this end, the heating carbon wires 34, 35 preferably have no sheath, for improved
thermal exchange.
[0039] Wires suitable for the present applications are commercially available, such as,
for example, those sold in Italy by company Thermal Technology or in China by companies
Senphus and CIT Solution (Hong Kong).
[0040] The plates 32, 33 divide the cross-section of the collector 28 into three portions:
an upper one 36, a central one 37, and a lower one 38, into which the air to be heated
during the drying cycle is canalized.
[0041] Furthermore, according to a preferred embodiment, also the inner wall of the collector
28 is coated with carbon, so that it can absorb the infrared radiations emitted by
the carbon wires 34, 35 and then, once heated, emit infrared radiations itself.
[0042] The same also applies to the region of the wall of the chamber 1 where the shell
21 is applied, which is preferably also coated with carbon, thus providing a radiating
effect similar to that of the inner wall of the same shell 21.
[0043] The above-described clothes dryer operates as follows.
[0044] The drying air is enriched with water vapour after having lapped the laundry load
to be dried in the chamber 1; the humid air is sucked in by the impeller 25, which
delivers it into the collector 28, where it is heated by the heater 30 as it flows
in the channels 36, 37 and 38.
[0045] More in particular, at the initial stage the carbon wires 34, 35 quickly reach the
normal operating temperature of 80-110 °C, so that the air blown by the impeller will
be heated, at this stage, mainly by convection as it laps the hot wires 34, 35.
[0046] A part of the heat emitted by irradiation by the carbon wires 34, 35 is absorbed
by the inner wall of the collector 28, which, as aforesaid, is made of or coated with
a material such as carbon or the like, suitable for the intended purpose.
[0047] As the air becomes more and more humid, the heat component supplied to it by irradiation
increases, in that infrared rays interact with the water molecules scattered in the
air flow; the temperature of the latter increases as well, so that, on the whole,
the temperature inside the shell 21 will increase.
[0048] In this condition, the inner wall of the collector, as it heats up, will also emit
radiations in the infrared range, thereby contributing to increasing the energetic
efficiency of the drying air heating system because, as a matter of fact, the whole
device will contribute to heating the air.
[0049] The same will occur for the plates 32, 33 that support the wires 34, 35, which are
also made of a material suitable for emitting radiating energy in the range of the
operating temperatures of the heating device 10.
[0050] In other words, it can be said that inside the heating device 30, and in particular
in the region of the collector 28, the conditions are created for a cavity (for physics
theories on this matter, see "https://en.wikipedia.org/wiki/Black_body"), in which
radiating thermal energy is produced: the dimensions and shape of such a cavity can
be optimized as a function of the resonance frequency of the infrared radiations emitted
therein, thus maximizing the air heating effect.
[0051] This ensures a high level of energetic efficiency, with clear advantages in terms
of consumption.
[0052] Similar considerations also apply to other possible variants of the invention, such
as those intended for implementation in washing/drying machines, i.e. not only the
clothes dryers of the previous example.
[0053] One of these variants is shown in Figures 4 and 5, which show a heating device 40
for heating the air flow in a washing/drying machine, not shown in the drawings for
the reasons explained above.
[0054] The heating device 40 comprises an essentially concave outer body or shell 41, preferably
made of a material suitable for emitting radiations in the infrared range (i.e. radiations
comprised in the range from infrared to ultraviolet, with wavelengths of 10
-1 to 10
2 µm) in the temperature range of 80 °C to 150°C.
[0055] As in the previous example, the shell 41 may be made of or coated with carbon, and
internally accommodates a radiating plate 42; the latter is also made of an appropriate
material, i.e. a material that can provide maximum irradiation of thermal radiations
in the range of operating temperatures of the heater 40.
[0056] The choice of the material for the plate will depend on several factors, such as
the required mechanical strength, the dimensions and weight of the heating device
(also related to the air flow circulating therein), its shape (the device may also
have a cylindrical geometry), and the like.
[0057] On the radiating plate 42 a heating wire 45 made of carbon fiber is wound, which
is similar to those already described; the winding of the wire 45 is such as to cover
substantially the entire plate, though this will depend, as a general rule, on the
required heat.
[0058] For example, solutions may be conceived with two wires 45 wound on one plate 42,
whether close to each other or at a predetermined distance.
[0059] In general, it can be said that the length of the heating wire 45 and its winding
pitch on the plate 42 will depend on the required thermal exchange with the air circulating
in the heating device 40; the air is supplied by an impeller (not shown in the drawings)
at a rate and in humidity conditions that may vary according to the case (i.e. between
different machines) and during the same drying cycle.
[0060] In the heating device 40, the plate 42 with the carbon wire 45 wound thereon extends
transversally relative to the body 41, thus dividing the section thereof into two
portions: an upper portion 46 and a lower portion 47, crossed by a corresponding air
flow (indicated by the arrows in Figure 6).
[0061] In the light of the above explanation, it is easy to understand the operation of
the heating device 40, since it is similar to that of the previous case referring
to a clothes dryer.
[0062] In fact, the device 40 is arranged in the drying air circuit of a washing/drying
machine, external to the tub 1.
[0063] In order to heat the air that flows in the device 40, the carbon-fiber wire 45 is
electrically powered, so that it will heat up to temperatures of approximately 80-130
°C.
[0064] The air flowing through the device 40 will be heated not only because it laps the
hot wire 45, but also through the effect of the radiating heat emitted by the plate
42 and by the shell 41, in accordance with the same principles already explained.
[0065] In this manner, the efficiency of the thermal exchange occurring in the device 40
is increased, all conditions being equal, compared to normal heaters using traditional
electric resistors.
[0066] From what has been described hitherto, it can be understood how the heating method
of the invention can solve the addressed technical problem.
[0067] In fact, thanks to the use of electric resistors made of carbon fibers, boron fibers
or the like, it is possible to exploit the performance of these materials, in terms
of rapidity in reaching the required working temperatures and low consumption, for
making heating wires 34, 35 and 45 which are better, from an energetic efficiency
viewpoint, than the normal electric resistors currently included in household appliances.
[0068] This is due to the use of the heating wire 34, 35 and 45 made of carbon, which, as
aforesaid, the power supplied thereto being equal (a few hundreds of W), can reach
operating temperatures (between 100 and 200 °C) in a shorter time while consuming
less power than normal resistors made of tungsten or the like as commonly used in
household appliances.
[0069] This effect can be further enhanced by using sheathless heating wires 34, 35 and
45: this will ensure direct contact between the carbon fiber and the air to be heated,
thus improving the thermal exchange by convection between them.
[0070] This is made possible also by the fact that the wires 34, 35 and 45 are supported
by respective plates 32, 33, 43 in a raised condition within the section of the respective
heating devices 20 and 40, so that any moisture deposits will concentrate on the bottom
of the body 21, 41, without impregnating the carbon fibers of the wires.
[0071] Moreover, the raised condition ensures a better exploitation of the thermal irradiation
of both faces of the plate 32, 33 and 43, so that both the upper air flow and the
lower air flow will be involved.
[0072] In addition, by exploiting the characteristics of carbon as regards the emission
of radiating thermal energy, in particular in the infrared range, it is possible to
increase the performance of the heating method according to the invention.
[0073] In fact, the invention teaches to use also this form of energy as an integration
to the one exchanged by convection with the hot resistors 34, 35 and 45, so as to
maximize the energetic efficiency.
[0074] To this end, by appropriately selecting the relevant process parameters, i.e. temperature
of the heating carbon wires 34, 35 and 45, air speed and/or flow, heat to be provided
for the drying cycle, it will be possible to determine the best wavelength for achieving
the desired heating.
[0075] This also allows designing heating devices 20, 40 with shapes and dimensions suitable
for the intended purpose.
[0076] It must finally be pointed out that the above-described principles of the invention
can be extended to other household appliances wherein an aeriform fluid needs to be
heated for drying a load or for other purposes.
[0077] This is the case, for example, of dishwashers, wherein a final step of drying the
load (dishes, flatware, glasses, etc.) is executed, during which the resistor heats
the air inside the wash tub, thus causing the water deposited on the load to evaporate
until it is completely dry.
[0078] Air heating can be provided, at least partly, by the heat generated by one or more
electric resistors made of carbon, carbon fiber or the like, by current dissipation
(Joule effect) and/or by irradiation in the infrared range, which interact with the
water molecules deposited on the crockery and/or with steam molecules.
[0079] The electric resistors may be incorporated into a covering that covers, at least
partially, the outer walls of the tub, so as to heat them by conduction, and hence
heating by convection the inner volume of the tub that contains the crockery to be
dried.
[0080] The inner surface of the dishwasher door, which acts as a tub closing wall, may also
be covered in the same way.
[0081] If the whole outer surface of the tub is not covered, i.e. if only some predefined
surfaces are covered, the uncovered surface (e.g. the rear surface of the tub) will
be colder and will act as a condensing surface promoting condensation of steam in
the form of condensed water drops, which will then slide by gravity into the sump
of the dishwasher, to be finally evacuated by the drain pump.
1. Method for heating an aeriform fluid in a household appliance, such as a clothes dryer,
a washing/drying machine, a dishwasher or the like, characterized in that it uses at least one resistive heating element (34, 35; 45) made of a material suitable
for providing thermal energy by electric dissipation and irradiation throughout the
range of fluid heating temperatures.
2. Method according to claim 1, wherein the heating element (34; 35; 45) is made of carbon,
carbon fiber or the like.
3. Method according to claims 1 or 2, wherein the heating element (34, 35; 45) is a wire.
4. Household appliance, such as a clothes dryer, a washing/drying machine, a dishwasher
or the like, comprising a chamber (1) for treating the load, a circulation circuit
(10) for circulating air taken in from the chamber (1) and then reintroduced therein,
heating means (30; 40) for heating the air along the circulation circuit (10), characterized in that the heating means comprise at least one element (34, 35; 45) made of carbon, carbon
fiber or the like, which is adapted to provide the drying air with thermal energy
by convection and/or irradiation.
5. Household appliance according to claim 4, wherein at least one of said carbon elements
(34, 35; 45) is of the resistive type.
6. Household appliance according to claims 4 or 5, comprising a heating device (30; 40),
wherein the heating device comprises at least one wire (34, 35; 45) made of carbon,
carbon fiber or the like, supported by a plate (32, 33; 42) extending along the path
(36, 37, 38; 46, 47) followed by the air to be heated.
7. Household appliance according to claim 6, wherein the plate (32, 33; 42) is of the
radiating type, and is adapted to irradiate within the infrared range at air drying
temperatures.
8. Household appliance according to any one of claims 4 to 7, wherein an air heating
device (30; 40) associated with the load treating chamber (1) comprises an external
shell (21; 41), a portion of which houses said at least one element (34, 35; 45) made
of carbon, carbon fiber or the like, which is adapted to provide the drying air with
thermal energy, wherein at least said portion of the shell (21; 41) is made of, or
internally coated with, a material suitable for irradiating within the infrared range
at air drying temperatures.
9. Household appliance according to claim 8, wherein the material used for making or
coating the shell (21; 41) comprises carbon, carbon fiber or the like.