EP2578741B1

EP2578741B1 - Thermoelectric heat pump, heat exchanger, household appliance and method for operating a household appliance

Info

Publication number: EP2578741B1
Application number: EP11183858.7A
Authority: EP
Inventors: Ian David Dr. Hopkin; Jonathan Jayne; David Thomas
Original assignee: DBK David and Baader GmbH
Current assignee: DBK David and Baader GmbH
Priority date: 2011-10-04
Filing date: 2011-10-04
Publication date: 2017-04-12
Anticipated expiration: 2031-10-04
Also published as: DK2578741T3; EP2578741A1; PL2578741T3

Description

The invention relates to a thermoelectric heat pump, a heat exchanger, a household appliance, especially a dishwasher, and a method for operating such household appliance.
In DE 10 2008 043 554 A1 a dishwasher is disclosed. It has an interior in which the dishes to be washed have to be arranged. Through a rinsing device disposed in the interior the dishes are supplied with water for cleaning. For draining the water from the interior a sump pit is provided in the bottom area of the dishwasher. Moreover, a heater is provided to heat the water prior to introducing it to the interior. For the purpose of saving energy the water can be heated to low temperature only, e.g. 30°C. For drying the dishes after the rinsing operation an energy-efficient sorption drying system is provided. It includes a tank in which reversibly dehydrogenizable drying material, for instance zeolite, is arranged. The tank comprises an inlet connection for an inlet passage connected to the interior of the dishwasher for feeding process air from the interior to the tank and an outlet connection for an outlet passage equally connected to the interior for discharging the process air from the tank. Process air is conveyed via a fan disposed in the inlet passage from the interior through the inlet passage to the tank and from there through the outlet passage into the interior again. The process air passes through the drying material, whereby the humid process air coming from the interior of the dishwasher is dried. The drying by the drying agent is carried out in an exothermal manner, thereby thermal energy being released by the drying agent when the humidity of the process air is absorbed. The released thermal energy in turn results in heating the process air guided to the interior through the inlet passage, thus increasing the capability of the process air of absorbing humidity. At the end of the drying operation a particular liquid quantity is stored in the drying material. During a new rinse cycle when the dishwasher is equipped with new dishes the drying material is then dried at the start of the rinsing process. For this purpose, the process air is conveyed again through the fan from the interior of the dishwasher through the inlet passage to the tank. For heating the process air a heater is provided in the tank upstream of the drying material, wherein heated process air then dries the drying material by the absorption of humidity. Subsequently, the process air flows through the inlet passage into the interior where it condenses at the dishes and gives off heat, thereby thermal energy being recovered for the rinsing operation.
It is a drawback of this solution that a large tank is required for holding the drying material which is complex in terms of devices. The drying material furthermore forms a significant flow resistance for the process air, which results in a considerable pressure drop when the process air flows along the drying material; therefore an extremely powerful fan has to be used. Moreover an additional heater is required for heating the drying material. Drying the drying material in a new rinse cycle in addition leads to the drawback of a considerable prolongation of rinse programs of the dishwasher. On the whole, a dishwasher of this type requires very complex devices and is cost-intensive.
Document DE 10 2004 055926 A1 discloses a tumble dryer including a drying unit. The latter includes a Peltier element having a cooling portion and a heating portion. Humid and warm air conveyed from a drying chamber of the tumble dryer is cooled by the cooling portion of the Peltier element and is subsequently heated in the heating portion. In addition, a heat pipe is provided. A heat flow of the Peltier element is tapped by the heat pipe via a heat conducting element and is supplied to the cooled air.
In document DE 20 2009 005871 U1 a heat exchanger for a tumble dryer is illustrated. In this case thermoelectric elements are arranged for cooling air flowing through flow passages and for heating said air. The upstream and downstream thermoelectric elements are connected to be thermally conducting through a heat conducting element in the form of a plate.
Document US 5 649 372 A includes two sensors for sensing an air humidity of an air flow of a tumble dryer and a sensor for sensing a temperature of the air flow is provided.
US 2006/254623 A1 illustrates a dishwasher in which a heat pipe is provided for removing heat from an air flow upstream of a condenser and for re-supplying the heat to the air flow downstream of the condenser.
In US 2009/049843 A1 a Peltier element is disclosed for the supply and discharge of heat of a drying unit of a tumble dryer.
Document US 2009/044576 A1 shows a tumble dryer. Process air discharged from the tumbler drum is divided into first and second passages in a waste air passage. In one passage a heater for heating the process air is arranged and in the other passage a cooler is arranged.
WO 2010/003936 A1 shows a tumble dryer comprising a drying drum. Warm and humid process air flows through a passage from the drying drum to an evaporator for cooling and dehumidifying. After that the process air is heated via a condenser and is returned to the drying drum. The evaporator and the condenser are interconnected via a cooling circuit including a refrigerant. After having absorbed heat from the process air in the evaporator, the refrigerant is compressed in a compressor, whereby it is heated. Then heat is discharged by the refrigerant to the process air via the condenser. After that, the refrigerant is further cooled through capillaries. Above the evaporator the refrigerant is then reheated by the warm process air. A heat pipe is employed for cooling the compressor.
EP 2 372 012 A1 is prior art according to Article 54(3) EPC and shows a tumble dryer comprising a drying device with a condenser having a thermoelectric heat pump, in particular a Peltier element, for cooling the condenser and/or the process air. A waste heat of the heat pump is discharged via a heat pipe.
In WO 2010/140334 A1 a tumble dryer is shown.
In DE 103 34 792 A1 a dishwasher is illustrated comprising a Peltier element for cooling and subsequently heating process air.
Compared to this, the object underlying the invention is to provide a thermoelectric heat exchanger for a dishwasher which allow for an energy-saving dishwasher having an inexpensive design that is simple in terms of devices. It is another object of the invention to provide an energy-saving household appliance, especially a dishwasher, having an inexpensive design that is simple in terms of devices. Furthermore, it is the object of the invention to provide a method for such household appliance which permits an energy-saving operation.
The objects are achieved as regards the heat exchanger in accordance with the features of claim 1 as regards the household appliance in accordance with the features of claim 6 and as regards the method in accordance with the features of claim 8.
In accordance with the invention, process air of a dishwasher can be cooled by a thermoelectric heat pump for the dishwasher, wherein waste heat being formed by the cooling operation is advantageously discharged by a heat pipe. For cooling the process air Peltier elements are provided, for instance. The cooling of the process air is especially carried out during a drying operation of dishes arranged in the dishwasher. By cooling of the process air a liquid absorbed by the same is condensed. By arranging a heat pipe the waste heat, for instance, can be flexibly returned to the process air after cooling for energy recovery. An inexpensive dishwasher having a simple design in terms of devices with low energy consumption can be manufactured with such heat pump.
One or more fins are mounted to the heat pipe so that the latter is capable of giving off the waste heat discharged by the same to a medium surrounding the heat pipe in a more efficient fashion. The heat pump including the heat pipe and the fin can be easily incorporated in a dishwasher as a unit. At least one fin is brazed or pressed, for instance, with the heat pipe.
In accordance with the invention, a heat exchanger for a dishwasher comprises a cooling section having a heat pump according to the invention for cooling process air flowing through the heat exchanger. Such heat exchanger has an extremely inexpensive and simple design in terms of devices, which when used in a dishwasher results in an equally inexpensive dishwasher simple in terms of devices. Moreover a dishwasher including such heat exchanger can be used in an energy-efficient manner when the heat pipe, for instance, recovers the waste heat discharged by the same to the dishwasher in the drying operation.
For feeding the waste heat to the process air the heat exchanger has a heating section downstream of the cooling section which can be heated via the heat pipe. A heat exchanger of this type constitutes an extremely compact unit which can be easily built into the dishwasher.
The cooling section and/or the heating section of the heat exchanger can have at least one layer including a plurality of flow passages through which the process air is guided. The cooling section and the heating section are preferably thermally substantially separated from each other. A water drain for discharging condensed liquid from the cooling section can then be provided between the cooling section and the heating section.
A layer is preferably formed by two walls arranged at a parallel distance from each other between which the flow passages are formed. Advantageously plural layers can be superimposed in this case.
At least part of the neighboring flow passages of the layer are advantageously in fluid communication with each other, whereby process air can flow from one flow passage to the other flow passage so as to avoid the heat pump, for instance, that constitutes a flow resistance.
The at least one Peltier element of the heat pump is arranged between the flow passages of the cooling section, wherein a hot side of the Peltier element is thermally insulated against the process air at least in sections so as to prevent waste heat of the Peltier element from being recirculated to the process air in the area of the cooling section. By arranging the Peltier element in the area of the flow passages heat can be efficiently discharged by the process air by when the latter circulates around the Peltier element.
For the discharge of waste heat in the area of the heating section of the heat exchanger the heat pipe opens into this area, especially between the flow passages, thereby the process air being capable of circulating around the latter.
The communication of the flow passages is provided preferably in the area of the Peltier element and/or in the orifice area of the heat pipe, as the Peltier element as well as the heat pipe constitutes a flow resistance and the process air can spread over the flow passages in these areas.
The flow passages between the walls are formed, for instance, by fins that are V-shaped and/or disposed at a parallel distance and extend approximately perpendicularly to the walls.
So that a large area of the volume flow of the process air can circulate around the heat pipe the latter penetrates the flow passages at least in sections in the area of the heating section approximately transversely to the direction of flow.
In accordance with the invention, a household appliance which is especially a dishwasher comprises a useful area to and from which process air can be supplied and discharged via a flow path in the form of a fluid passage. In said fluid passage advantageously a heat exchanger according to the invention is disposed which results in a dishwasher having an inexpensive and extremely simple design in terms of devices that can be employed in an energy-efficient manner.
In order to be able to adjust the thermal capacity of the heat exchanger in the dishwasher in an energy-efficient manner, a temperature and/or an air humidity sensor are provided in the fluid passage upstream and/or downstream of the heat exchanger. Thus, for instance a temperature and a relative air humidity of the process air can be detected before the latter enters the heat exchanger and by the detected values the dew point and the dew point temperature of the process air can be determined by way of psychrometric theory, for example by an electronic control unit (ECU), and thus the cooling section can be operated with a predetermined cooling capacity sufficient to result in the condensing of the humidity in the process air. In this way an unnecessarily high cooling capacity at low temperatures is avoided, which is energy-saving. It is imaginable to provide this also in a tumble-drier, for instance, including such thermoelectric heat pumps.
A method according to the invention for the household appliance according to the invention comprises the step of:

controlling a thermal capacity of the heat exchanger in response to a dew point temperature of the process air, especially a dew point temperature upstream of the heat exchanger.

The method can additionally comprise the steps of:

detecting a temperature and an air humidity of the process air upstream and/or downstream of the heat exchanger;
calculating the dew point temperature of the process air based on the detected temperature and air humidity of the process air. After that the thermal capacity of the heat exchanger is controlled.

Other advantageous developments of the invention are the subject matter of further subclaims.
Hereinafter the invention will be explained in detail by way of schematic drawings in which

Figure 1 shows a schematic cross-sectional view of a dishwasher according to an embodiment;
Figure 2 is a perspective view of a heat exchanger according to a first embodiment;
Figure 3 is a perspective view of a heat pump according to an embodiment;
Figure 4 shows a front view of part of the heat pump according to a first embodiment;
Figure 5 is a perspective exploded view of a heat exchanger according to a first embodiment;
Figure 6 is a perspective view of parts of the heat exchanger according to a second embodiment;
Figure 7 is a top view of the heat exchanger according to Figure 6;
Figure 8 is a perspective view of parts of a heat exchanger according to a third embodiment;
Figure 9 shows a top view and a side view of a heat pump according to a second embodiment;
Figure 10 is a perspective view of a heat pump according to a third embodiment; and
Figure 11 shows a wiring diagram of the dishwasher according to the embodiment.

Figure 1 illustrates a dishwasher 1 in a schematic longitudinal sectional view according to an embodiment. It comprises a machine housing 2 including an interior 4 for receiving dishes. The interior 4 is accessible via a tilting door 6 pivoted to the machine housing 2 for loading and unloading the dishwasher 1 with the dishes. In the interior 4 two dish cages 8 and 10 can be arranged for receiving the dishes which are movable out of the interior 4 approximately horizontally when the tilting door 6 is opened. For introducing water to the interior and for supplying water to the dishes during the rinsing operation a first rinsing arm 12 is provided approximately in the center of the interior 4 below the dish cage 10 and a second rinsing arm 14 is provided in the bottom area of the interior 4 below the dish cage 8. These arms are connected to a water source and mounted in the interior 4 in a conventional fashion.
After a rinsing operation during which the dishes have been cleaned with water to which dish detergents and/or rinse agents have been added, the dishes are dried. For this purpose a heat exchanger 16 including a heat pump 18 is provided which is arranged outside the interior in a bottom area 19 of the dishwasher 1. It serves for cooling process air so that the liquid absorbed by the process air is condensed. Further, the process air is re-heated via the heat exchanger 16 after cooling. The process air is tapped through an outlet connection 20 by the interior 4 and is guided via an inlet passage 22 extending outside the interior 4 to the heat exchanger 16. A fan 24 is provided in the inlet passage 22 for conveying the process air. After the process air has passed the heat exchanger 16, it is guided through an outlet passage 26 communicated with the interior 4 via an inlet connection 28, whereby the process air flows from the outlet passage 26 into the interior 4. The outlet connection 20 is formed approximately closely to the bottom of the interior 4 above the lower rinsing arm 14, while the inlet connection 28 is formed in an upper area of the interior 4 above the upper rinsing arm 12. The heat exchanger 16 centrally further includes a water drain 30 or sump pit for discharging condensed water which is connected to a waste water connection, for instance, via an outlet passage 32. The heat exchanger 16 is explained in detail in the following Figure 2.
Figure 2 shows in a perspective view the heat exchanger 16 of the dishwasher 1 of Figure 1 in accordance with a first embodiment. It includes a cooling section 34 on the left in Figure 2 for cooling the process air and a heating section 36 on the right for heating the process air. The sections 34 and 36 are thermally insulated from each other by a thermal insulator 38 disposed between the sections 34 and 36. The insulator 38 in addition includes the water drain 30, see also Figure 1. The heat exchanger has two layers 40 and 42 each of which includes a plurality of flow passages 44 and 46 for guiding the process air 48 - represented in Figure 2 by a plurality of arrows. The flow passages 44 and 46 of a respective layer 40 and 42 are restricted at their upper and lower areas by a wall. The wall is formed by plates, wherein both the cooling section 34 includes three plates 50, 52 and 54 and the heating section 36 includes three plates 56, 58 and 60. The plates 50, 52, 54 and 56, 58, 60 are arranged at a parallel distance from one another and extend in the flow direction of the process air 48. Between the upper plates 50 and 56, resp., and the central plates 52 and 58, resp., the flow passages 44 are formed and between the central plates 52 and 58, resp., and the lower plates 54 and 60, resp., the flow passages 46 are formed. Each of the flow passages 44 and 46 is constituted by a plurality of fins 61 and 63, resp., extending perpendicularly to the plates 50 to 60.
For cooling the process air 48 in the cooling section 34 a heat pump 62 and 64, respectively, having two respective Peltier elements is associated with a respective layer 40 and 42 of the cooling section 34. Such Peltier elements are sufficiently known from the state of the art and are disclosed, for instance, in the document WO 2007/138064 A1 for a dishwasher; therefore hereinafter more detailed explanations are dispensed with. The heat pumps 62 and 64 are described below in more detail. The Peltier elements penetrate a respective layer 40 and 42, resp., over the entire width thereof transversely to the direction of flow of the process air 48 and are arranged approximately in the center of a respective layer 40 and 42, resp., in the cooling section 34. Waste heat of the Peltier elements is discharged through heat pipes 66 and 68 and is supplied to the heating section 36 of the heat exchanger 16 with the heat pipes 66 and 68 passing through the latter. The heat pipe 66 is associated with the upper heat pump 62 in Figure 2 and the heat pipe 68 is associated with the lower heat pump 64. In Figure 2 only the portion of the heat pipes 66 and 68 projecting from the heat exchanger, which is U-shaped, is visible. A first leg 70 of the heat pipes 66 and 68 penetrates the cooling section 34 between the Peltier elements. Another leg 72 of the heat pipes 66 and 68 penetrates a respective layer 40 and 42 of the heating section 36 substantially transversely to the direction of flow of the process air 48 and centrally of a respective layer 40 and 42. The heat pipes 66 and 68 per se are known equally sufficiently from the state of the art, which is therefore referred to for further explanations.
During use of the heat exchanger 16 the process air 48 to be cooled is guided from the interior 4 of the dishwasher 1 of Figure 1 to the heat exchanger 16 and flows through the flow passages 44 and 46 of the layers 40 and 42 of the cooling section 34. The process air 48 circulates around the Peltier elements of the heat pumps 62 and 64, respectively, whereby the process air is cooled and condenses humidity entrained by the same. The condensed water then flows to the water drain 30, the layers 40 and 42 being appropriately configured. The waste heat generated by the Peltier elements then arrives via the heat pipes 66 and 68 to the heating section 36 of the heat exchanger 16. The cooled process air 48 then continues to flow after the cooling section 34 through the heating section 36 with the heat pipes 66 and 68, whereby the waste heat is discharged to the process air 48 and the latter is heated. In the area of the cooling section 34 the fins 61 and 63 of the layers 40 and 42 additionally serve as absorbing surfaces of heat of the process air 48 and in the heating section 36 additionally serve as heat transfer surfaces of the waste heat from the heat pipes 66 and 68 to the process air 48. Behind the heat exchanger 16 the dried and heated process air is recirculated to the interior 4 of the dishwasher 1 of Figure 1.
The heat pipes are thermally insulated outside the heating section 36 so that the waste heat is discharged to the ambience substantially only in the heating section 36.
Figure 3 schematically shows in a perspective view the heat pump 62 and 64, resp., of Figure 2. The heat pipes 66 and 68 open with their end portions leading away from the Peltier elements into a heat spreader 78 via which heat is discharged over a large area from the heat pipes 66 and 68 and to which process air 48 of Figure 2 is supplied. The heat pipes 66 and 68, resp., penetrate the heat spreader 78 approximately centrally with their legs 72. A heat spreader 80 and 82, resp., is likewise associated above and below the Peltier elements of the heat pumps 62 and 64, thus the Peltier elements being sandwiched between the heat spreaders 80 and 82.
In Figure 4, the thermoelectric heat pump 62 or 64, respectively, of Figure 2 is illustrated in a schematic cross sectional view. The heat pumps 62, 64 comprise a heat sink 84 consisting preferably of aluminium or copper and having a roughly rectangular cross section. On the top and bottom faces of the heat sink 84, Peltier elements 86, 88 each are arranged which are adapted to be supplied with current via electrical connections that are not illustrated. A respective cool side 90 and 92 of the Peltier elements 86 or 88, respectively, points away from the heat sink 84, while a hot side 94 and 96 of the Peltier elements 86 or 88, respectively, abuts on the heat sink 84. The width of the Peltier elements 86 and 88 is somewhat smaller than that of the sink 84, and the Peltier elements 86, 88 are arranged approximately centrally with respect to the heat sink 84. A heat spreader 80 or 82, respectively, having a rectangular cross section abuts on a respective cool side 90 or 92 of the Peltier elements 86 or 88, respectively. The heat spreader 80, 82 may be an individual heat spreader or may be formed directly by the cold side heat sink 44, 46, eliminating the need for the additional component. A width of the heat spreaders 80, 82 is somewhat larger than the width of the heat sink 84. Insulation elements 98 are arranged between the heat sink 84 and the respective heat spreader 80 and 82 next to the Peltier element 86 or 88, respectively. Further insulation elements 100 are arranged between the heat spreaders 80 and 82. A left and a right side face of the heat sink 84 are thermally insulated from the environment by the insulation elements 100. The pipe section of the heat pipe 62 or 64, respectively, extends through the heat sink 84 approximately centrally.
Figure 5 shows the heat exchanger 102 in an exploded view according to a second embodiment. For convenience, only some portions of the heat exchanger 102 in the cooling section 34 are shown. The fins 104 and 106 of the layers 40 and 42, resp., are formed substantially V-shaped with respect to each other in contrast to the fins of Figure 2. A plurality of fins is integrally combined into modules 108. Crests 110 formed by two respective adjacent fins, two of which are provided with a reference numeral in Figure 5, extend approximately in the direction of flow of the process air and are substantially adjacent to the plates 50, 52 and 54 in the mounted state. The modules 108 are connected to the plates 50, 52 and 54 in a force-fit, form-fit and/or adhesively joined manner. A width of the modules 108 in the direction of flow is formed such that the heat pumps 62 or 64 can be disposed there between. The heat pumps 62 and 64, resp., do no longer penetrate the respective layer 40 and 42, resp., in contrast to the heat exchanger 16 of Figure 2, but are arranged centrally of a respective layer. The heat pipes 66 or 68 are guided transversely to the direction of flow between modules 108 to an edge area of the heat exchanger 102 and do not project from the same in contrast to Figure 2. In the edge area the heat pipes 66 and 68 then extend further in the direction of flow along the modules 108 to the heating section 36. The heating section 36 can be formed, substantially corresponding to the cooling section 34, to have plural modules of fins between which the heat pipes 66 and 68, resp., are guided through.
Figure 6 shows a portion of the heat exchanger according to a third embodiment. Here the upper layer 40 is represented in which a plurality of fins 114 arranged in V-shape is provided in the cooling and heating sections 34 and 36 so as to form flow passages. The heat pump 62 is arranged centrally in the cooling section 34 between the fins 114, wherein, in contrast to the previous embodiments, two heat pipes 116 and 118 extend in the direction of flow of the process air 48 to the heating section 36 and thus are substantially shorter as a whole. The heat pipes 116 and 118 are arranged at a parallel distance from each other and then open centrally into a heat spreader 120 disposed in the heat section 36.
Figure 7 shows a strongly simplified representation of a top view on the heat exchanger 112 of Figure 6. For convenience, the insulator 121 of Figure 6 is not shown here. The flow passages 122 formed by the fins 114, only some of which are provided with a reference numeral for easier reference, are in multiple fluid communications with one another. The fluid communication takes place through rows of openings 124 to 130. The openings 124 are formed upstream approximately ahead of the heat pump 62 in the cooling section 34 and the openings 126 are formed downstream approximately behind the heat pump 62. The openings 128 are formed upstream ahead of the heat spreader 120 in the heating section 36 and the openings 130 are formed downstream behind the heat spreader 120. Through the openings 124 to 130 the process air 48 represented by plural arrows in Figure 7 can be spread comparatively uniformly to the flow passages 122 passing the heat pump 62 so as to by-pass the heat pump 62 constituting an obstacle to flow.
Figure 8 shows a fourth embodiment of the heat exchanger 132, the layer 40 being represented in sections. Fins 134 are disposed in the heat exchanger 132 at a parallel distance from each other and are connected to the plate 52 in the cooling section 34 via a common holding plate 136. The fins 134 may also be of a folded fin construction so that plate 136 is not required. Fins 137 of the heating section 36 are fixed to the heat pipe 138, on the other hand. The U-shaped heat pipe 138 extends in the cooling section 34 with the first leg 140 approximately transversely to the fins 134 outwardly from the heat pump 62 approximately centrally in the cooling section 34. In the outermost flow passage 142 the heat pipe 138 then extends with its connecting portion 144 between the leg 140 and the further leg 146 from the cooling section 34 to the heating section 36. The leg 146 then extends transversely to the flow direction centrally through the heating section 36. Fins 137 of the heating section 36 are fixed to the leg 146 of the heat pipe 138 in that the latter penetrates each of the fins 137 centrally through a through bore 151 introduced to the same and is pressed or welded, for instance, with the same. For increasing an heat exchange surface between the process air and the fins 137 of the heating section 36 the fins are bent at their longitudinal side facing away from the central plate 52 and having an angular portion 152, whereby they have an L-shaped cross section to improve the thermal contact with plate 58 and 60.
Figure 9 shows the heat pump 62 of the heat exchanger 132 in top view and side view. In the upper top view it is visible that the heat pipe 138 completely penetrates the heat pump 62. It is further visible in Figure 9 that the heat pump 62 forms a unit with the heat pipe 138 and the fins 137 fixed to the leg 146 which can be easily inserted in a heat exchanger 132 according to Figure 8.
Figure 10 constitutes the heat pump 154 according to a further embodiment. It includes two L-shaped heat pipes 156, 158. They have a respective leg 160, 162 extending away from the heat pump 154 in the direction of flow of the process air, the legs extending at a parallel distance approximately centrally of a respective layer 40, 42, see Figure 2. The respective other legs 164 and 166 of the heat pipe 156 and 158 extend substantially transversely to the direction of flow of the process air and face away from each other. The legs 164 and 166 extend approximately centrally of a respective layer 40 and 42 of the heating section 36, see e.g. Figure 2. At the legs 164 and 166 extending away from each other five, or any other suitable number, respective fins 168 and 170 are fixed at a parallel distance from each other. A respective fin 168 and 170 has a central through bore 172 and 174 through which the respective heat pipe 156 and 158 is guided. The fins 168 and 170 are then fixed to the heat pipes 156 and 158 in a force-fit, form-fit and/or adhesively joined manner, for example by a soldering, pressing or adhesive connection.
Figure 11 shows a simplified diagram of the dishwasher 1. It includes, in contrast to the dishwasher 1 of Figure 1, an additional air heater 176 disposed downstream of the heat exchanger 16 in the outlet passage 26. Thus the process air 48 can be further heated, before it enters the interior 4 of the dishwasher 1 again. This can benefit the system in conditions when the ambient conditions are cold so that the drying air is easily saturated. Increasing the air temperature reduces the relative humidity for a given specific humidity and thus makes the drying more efficient.
For the electric supply of the dishwasher 1 a power supply 178 is provided at which the heater 176 is connected electrically via wires 180 and the heat exchanger 16 is connected via electric wires 182. A power flow in the wires 180 and 182 can be switched on and off by a respective switch 184 and 186. The switches 184 and 186 are controlled via an Electronic Control Unit (ECU) 188. Plural sensors are connected to the same. A sensor 190 is arranged upstream of the heat exchanger 16 in the inlet passage 22 for measuring the temperature and the air humidity of the process air in this area. The measuring signals of the sensor 190 are then guided through a measuring line 192 to the ECU 188. In the outlet passage 26 between the heat exchanger 16 and the heater 176 another sensor 194 which is connected to the ECU 188 via a measuring line 196 is arranged for measuring the temperature and the air humidity of the process air. Downstream of the heater 176 in the outlet passage 26 a sensor 198 equally provided for measuring the temperature and the air humidity of the process air is arranged which is connected to a measuring line 200 to the ECU 188. A temperature in the cooling section 34 of the heat exchanger 16 is detected via a sensor 202 and in the heating section 36 via a sensor 204 each of which is connected to the ECU 188 via a measuring line 206 and 208. Furthermore a sensor 209 is provided for measuring the temperature of the ambient air which is connected to the ECU 188 via a measuring line 211. The ECU 188 then controls the electric switches 184 and 186 via a respective control wire 210 and 212 in response to the detected measuring signals. For the electric supply of the ECU 188 the latter is connected to the power supply 178 via electric lines 214. In the ECU 188 a control algorithm is deposited which uses psychometric theory to determine the optimum operating point and whether the heater 176 is required during the drying cycle. Cooling of the process air then is controlled by the ECU 188 by switching on or off the power supply 178 via the switch 186. The heater 176 is equally controlled by switching on or off the power supply 178 via the electric switch 184.
There is disclosed a dishwasher comprising a rinsing chamber for cleaning dishes. For drying rinsed dishes by process air the latter can be discharged from the rinsing chamber and can be dried and heated via a heat exchanger. Downstream of the heat exchanger the process air is supplied to the rinsing chamber. The heat exchanger includes a heat pump for cooling and drying the process air, wherein waste heat of the heat pump is discharged through a heat pipe.

List of reference numbers:

1: dishwasher
2: machine housing
4: interior
6: door
8: dish cage
10: dish cage
12: rinsing arm
14: rinsing arm
16: heat exchanger
18: heat pump
19: bottom area
20: outlet connection
22: inlet passage
24: fan
26: outlet passage
28: inlet connection
30: water drain
32: outlet passage
34: cooling section
36: heating section
38: insulator
40: layer
42: layer
44: flow passage
46: flow passage
48: process air
50: plate
52: plate
54: plate
56: plate
58: plate
60: plate
61: fin
62: heat pump
63: fin
64: heat pump
66: heat pipe
68: heat pipe
70: leg
72: leg
78: heat spreader
80: heat spreader
82: heat spreader
84: heat sink
86: Peltier element
88: Peltier element
90: cool side
92: cool side
94: hot side
96: hot side
98: insulation element
100: insulation element
102: heat exchanger
104: fin
106: fin
108: module
110: Crest
114: fin
116: heat pipe
118: heat pipe
120: heat spreader
121: insulator
122: flow passage
124: rows of openings
126: rows of openings
128: rows of openings
130: rows of openings
132: heat exchanger
134: fin
136: holding plate
137: fin
138: heat pipe
140: leg
142: flow passage
144: connecting portion
146: leg
152: angular portion
154: heat pump
156: heat pipe
158: heat pipe
160: leg
162: leg
164: leg
166: leg
168: fin
170: fin
172: bore
174: bore
176: heater
178: power supply
180: wires
182: electric wires
184: switch
186: switch
188: Electronic Control Unit
190: sensor
192: measuring line
194: sensor
196: measuring line
198: sensor
200: measuring line
202: sensor
204: sensor
206: measuring line
208: measuring line
210: control wire
212: control wire

Claims

A heat exchanger, in particular for a household appliance, comprising a cooling section (34) including a thermoelectric heat pump (18) for cooling process air flowing through the heat exchanger (16),
wherein process air (48) can be cooled by said heat pump and waste heat occurring by cooling is discharged through a heat pipe (66, 68), and wherein downstream of the cooling section (34) a heating section (36) with the heat pipe (66, 68) is provided by which the process air (48) can be heated,
wherein the cooling section (34) and the heating section (36) include at least one layer (40, 42) having a plurality of flow passages (44, 46) through which the process air (48) is guided,
wherein at least one Peltier element (86, 88) of the heat pump (18) is arranged between flow passages (44, 46) in the area of the cooling section (34),
wherein a hot side (94, 96) of the Peltier element (86, 88) is thermally insulated at least in portions vis-à-vis the flow passages (44, 46) so as to prevent waste heat of the Peltier element from being recirculated to the process air in the area of the cooling section,
wherein the heating section (36) includes a plurality of fins (137) which are mounted to the heat pipe (138) so as to form flow passages of the heating section (36).
The heat exchanger according to claim 1, wherein the layer (40, 42) is formed by walls (50, 52, 54; 56, 58, 60), in particular two walls, arranged at a parallel distance from each other.
The heat exchanger according to claim 1 or 2, wherein at least part of the flow passages (44, 46) of the layer (40, 42) adjacent to each other are in fluid communication with each other.
The heat exchanger according to claim 3, wherein the fluid communication of the flow passages (122) is substantially provided in the cooling section (34) in the area of the heat pump (64) and/or in the heating section (36) in the orifice area of the heat pipe (116, 118).
The heat exchanger according to any of the preceding claims, wherein the heat pipe (138) penetrates the flow passages in the area of the heating section (36) approximately transversely to the direction of flow of the process air.
A household appliance comprising a useful area (4) to and from which process air (48) can be supplied and discharged via a flow path (22, 26), wherein a heat exchanger (16) according to any one of claims 1 to 5 is arranged in the flow path (22, 26).
The household appliance according to claim 6, wherein upstream and/or downstream of the heat exchanger (16) in the flow path (22, 26) a sensor (190, 194, 198) is provided for measuring a temperature and an air humidity of the process air (48).
A method for operating a household appliance in accordance with claims 6 or 7, comprising a useful area (4) to and from which process air (48) can be supplied and discharged via a flow path (22, 26), wherein the heat exchanger (16) is arranged in the flow path (22, 26) comprising the cooling section (34) including the heat pump (18) for cooling process air flowing through the heat exchanger (16), wherein waste heat occurring by cooling is discharged through the heat pipe (66, 68) comprising the step of:
- adjusting a temperature of the heat exchanger, in particular a thermal capacity of the heat exchanger (16), in response to a dew point temperature of the process air (48).
A method according to claim 8, comprising the additional steps of:
- detecting a temperature and an air humidity of the process air (48) upstream and/or downstream of the heat exchanger (16);

- calculating the dew point temperature of the process air (48) on the basis of the detected temperature and air humidity of the process air (48).