EP3040472A1

EP3040472A1 - Household appliance heating method and related drying or washing-drying machine

Info

Publication number: EP3040472A1
Application number: EP15197235.3A
Authority: EP
Inventors: Giovanni Bombardieri; Paolo Filipponi; Aldo Liberatore
Original assignee: Indesit Co SpA
Current assignee: Whirlpool EMEA SpA
Priority date: 2014-12-31
Filing date: 2015-12-01
Publication date: 2016-07-06

Abstract

The invention relates to a method for heating air in a clothes dryer, a washing/drying machine (1) or a dishwasher, wherein a resistive heating element (5) made of carbon fiber is used.

The heating element is a wire (5) that provides thermal energy by electric dissipation and irradiation throughout the range of air heating temperatures.

The heater (10) is housed in a shell (21) also coated with or made of carbon, thus forming a radiating cavity and increasing the thermal efficiency of the system.

The invention also relates to a household appliance implementing the heating according to the method.

Description

The present invention relates to a method and an apparatus for heating a fluid, intended in particular for household appliances.
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.
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.
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.
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.
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.
In this frame, the Applicant's attention has focused on reducing the energy consumption for air heating in such household appliances.
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.
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.
This type of resistor has proven to be effective and reliable over time, although it has a few drawbacks.
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.
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.
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.
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.
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.
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.
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 .
However, the Applicant does not know of any application to household appliances, in particular for heating fluids in household appliances in dynamic conditions.
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.
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.

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.
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.
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.
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.
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.
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.
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.
One end of the latter is configured with a lobe 23 that houses an impeller 25, driven by an electric motor 26.
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.
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.
As Figure 3 clearly shows, the heater 30 comprises a pair of support plates 32, 33 for respective heating resistors 34, 35.
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.
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 10² µm) in the temperature range of 80 °C to 150°C.
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.
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).
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.
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 mm²; the diameter of the carbon wires will depend on the heat to be supplied, and hence on the current required for obtaining it.
To this end, the heating carbon wires 34, 35 preferably have no sheath, for improved thermal exchange.
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).
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.
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.
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.
The above-described clothes dryer operates as follows.
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.
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.
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.
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.
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.
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.
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.
This ensures a high level of energetic efficiency, with clear advantages in terms of consumption.
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.
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.
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 10² µm) in the temperature range of 80 °C to 150°C.
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.
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.
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.
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.
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.
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).
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.
In fact, the device 40 is arranged in the drying air circuit of a washing/drying machine, external to the tub 1.
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.
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.
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.
From what has been described hitherto, it can be understood how the heating method of the invention can solve the addressed technical problem.
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.
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.
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.
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.
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.
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.
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.
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.
This also allows designing heating devices 20, 40 with shapes and dimensions suitable for the intended purpose.
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.
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.
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.
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.
The inner surface of the dishwasher door, which acts as a tub closing wall, may also be covered in the same way.
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.

Claims

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.
Method according to claim 1, wherein the heating element (34; 35; 45) is made of carbon, carbon fiber or the like.
Method according to claims 1 or 2, wherein the heating element (34, 35; 45) is a wire.
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.
Household appliance according to claim 4, wherein at least one of said carbon elements (34, 35; 45) is of the resistive type.
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.
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.
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.
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.