WO2002013282A1

WO2002013282A1 - Thermoelectric heat pump

Info

Publication number: WO2002013282A1
Application number: PCT/IT2001/000438
Authority: WO
Inventors: Vincenzo Picone
Original assignee: Peltech S.R.L.
Priority date: 2000-08-09
Filing date: 2001-08-07
Publication date: 2002-02-14
Also published as: ITMI20001863A1; IT1318752B1; ITMI20001863A0

Abstract

The solid sate thermoelectric device for a thermoelectric heat pump includes an array of thermoelectric couples electrically connected in series and thermally connected in parallel so that all the hot and cold sides of the thermoelectric couples are separately arranged on opposite surfaces of the thermoelectric device and is characterised in that the thermoelectric couples are supported on a flexible polymeric substrate made of polyimide, polyethylene naphtalate, polyaryl heteroketone, polysulphon, polypheniloxide or polyphenilsulphur. The flexible polymeric substrate is wound in a cylindrical or spiral configuration so as to form a hollow core of the thermoelectric device. Alternatively, the flexible polymeric substrate is arranged in a configuration having a polygonal cross section so as to form a hollow core of the thermoelectric device.

Description

THERMOELECTRIC HEAT PUMP

TECHNICAL FIELD

The present invention generally relates to the field of thermoelectric devices used for cooling and heating purposes in the civil, industrial, automotive, nautical, aeronautical, aerospace and military sectors.

Thermoelectric cooling and heating is generally based on the Peltier effect. This is a phenomenon whereby heat is liberated or absorbed at a junction of two dissimilar metals or a junction of a metal and a semiconductor when an electric current is passed through the junction. The junction becomes hot or cold depending on the direction in which the current is passed through the junction. The Peltier effect is reversible, i.e. if the direction of the electric current is reversed, the cold junction becomes hot and the hot junction becomes cold. It has been found that the Peltier effect is magnified by using metal-semiconductor junctions rather than metal-metal junctions.

In the following, the term "thermoelectric device" generally designates a solid state device that makes use of the Peltier effect _,f°^r heating or cooling a material substance. The term "thermoelectric element" generally designates a metallic conductor or a semiconductor forming the element of a junction. The term "thermoelectric couple" designates a combination of two dissimilar thermoelectric elements forming a junction. The term "thermoelectric cell" designates an array of thermoelectric couples electrically connected in series.

BACKGROUND ART

As known, solid state thermoelectric devices based on the Peltier effect are commercially available since 1960 and thenceforward great investments have been made into the development of suitable materials for the purpose of increasing the efficiency and performance of such devices.

Initially, the thermoelectric elements were made of a metallic conductor, whereas at present the modern semiconductor technology permits thermoelectric elements to be made of Bi₂Te₃, PbTe, SiGe and SiSb with N-type and P-type doping.

Notwithstanding the use of these materials it is not yet possible to substitute the thermoelectric devices for the conventional refrigeration systems and therefore at present special high performing thermoelectric elements are being developed.

Thermoelectric devices known in the art and available on the market comprise thermoelectric cells built in a planar configuration, but there are also known thermoelectric devices comprising thermoelectric cells built in a cylindrical configuration. In the prior art thermoelectric devices having thermoelectric cells built in a planar configuration the thermoelectric couples are assembled between a pair of plane substrates made of alumina or the like via a solder layer. In the prior art thermoelectric devices having thermoelectric cells built in a cylindrical configuration the thermoelectric couples are assembled on a flexible plastic material substrate which is subsequently deformed in a cylindrical shape.

The structure of the prior art thermoelectric devices has the disadvantage of limiting the maximum size of each thermoelectric cell because of the chemical and physical properties of materials used for the substrates which cannot withstand high thermal gradients. Therefore, the construction of thermoelectric devices having a capacity greater then 0.5 kW always requires a great number of small modules of thermoelectric cells which may occupy a great surface, in particular when built in a plane configuration.

Therefore, the thermoelectric cells having a cylindrical configuration or similar are preferred. International Application Document WO 00/49664 annexed hereto describes a thermoelectric device having a circularly or spirally wound configuration.

DISCLOSURE OF THE INVENTION

The present invention relates to a solid state thermoelectric device for a thermoelectric heat pump including an array of thermoelectric couples electrically connected in series and thermally connected in parallel so that all the hot and cold sides of the thermoelectric couples are separately arranged on opposite surfaces of the thermoelectric device and is characterised in that the thermoelectric couples are supported on a flexible polymeric substrate made of polyimide, polyethylene naphtalate, polyaryl heteroketone, polysulphon, polypheniloxide or polyphenilsulphur, said flexible polymeric substrate being wound in a cylindrical or spiral configuration so as to form a hollow core of the thermoelectric device.

According to another embodiment of the present invention, the solid state thermoelectric device for a thermoelectric heat pump including an array of thermoelectric couples electrically connected in series and thermally connected in parallel so that all the hot and cold sides of the thermoelectric couples are separately arranged on opposite surfaces of the thermoelectric device is characterised in that the thermoelectric couples are supported on a flexible polymeric substrate made of polyimide, polyethylene naphtalate, polyaryl heteroketone, polysulphon, polypheniloxide or polyphenilsulphur, said flexible polymeric substrate being arranged in a configuration having a polygonal cross section so as to form a hollow core of the thermoelectric device.

According to the present invention, the thermoelectric device comprises a first heat exchange tube arranged inside the hollow core of the thermoelectric device and a second heat exchange tube arranged outside the hollow core of the thermoelectric device, said first heat exchange tube being provided with turbulence generating means on its inner surface or inside its hollow space for producing a turbulent flow of a heat exchange fluid therethrough and said second heat exchange tube being provided with heat exchange fins on its outer surface.

According to the present invention the thermoelectric device comprises coupling means at its end portions for permitting its first exchange tube to be connected to a pipe line through which a heat exchange fluid is passed.

The present invention also relates to a thermoelectric heat pump comprising a plurality of thermoelectric devices the two end portions of which are connected to a first and second manifold, respectively, through which a heat exchange fluid is distributed to the thermoelectric device, said thermoelectric heat pump being provided with fan means for producing a flow of cooling air through the heat exchange fins of each thermoelectric device.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will now be described in more detail in connection with the accompanying drawings, wherein: Figure 1 is a partial cross sectional view of a first embodiment of the thermoelectric cell according to the present invention,

Figure 2 is a partial cross sectional view of a second embodiment of the thermoelectric cell according to the present invention,

Figure 3 is a partial cross sectional view of a third embodiment of the thermoelectric cell according to the present invention,

Figures 4A and 4B are a front and rear view, respectively, of the thermoelectric cell of Figures 1 and 2, Figure 5 is a cross sectional view of a first embodiment of a thermoelectric device built using the thermoelectric cells of Figures 1 and 2,

Figure 6 is a cross sectional view of a second embodiment of a thermoelectric device built using the thermoelectric cells of Figures 1 and 2,

Figure 7 is a cross sectional view of a third embodiment of a thermoelectric device using the thermoelectric cell of Figures 2 or 3,

Figure 8 is a perspective view of the third embodiment of the thermoelectric cell according to the present invention, Figure 9 is a side elevation view of a thermoelectric device using the thermoelectric cells according the first, second and third embodiment of the present invention,

Figure 10 is a longitudinal cross sectional view of the thermoelectric device of Figure 9, Figure 11 is an assembly view of turbulent flow generating means of a heat exchanger used in the thermoelectric device of Figure 9,

Figure 12 is a front elevation view of a heat exchanger built with a plurality of thermoelectric devices of Figure 9,

Figure 13 is a rear elevation view of the heat exchanger of Figure 12.

BEST MODE FOR CARRYING OUT THE INVENTION Referring to Figure 1 of the drawings, there is shown a first embodiment of the thermoelectric cell of the present invention. According to this embodiment the thermoelectric cell comprises a pair of flexible laminates each consisting of a layer of polymeric material, for example polyimide PI available on the market under the trademark Kapton MT®, polyethylene naphtalate PEN available on the market under the trademark Kaladex®, polyaryl heteroketone PEEK available on the market under the trademarks Ultrapek® or Kadel®, polysulphon PSU, polyphenyloxide PPO, polyphenylsulphur PPS, and a layer of metallic material, for example copper.

The two laminates are mutually and directly joined together by means of an adhesive resin with a high coefficient of heat transmission, for example an epoxy resin or an acrylic resin containing a silver or metal oxide filler. The connections for the thermoelectric elements are made on the metallic material layer of the laminates via an etching process. Numeral 10 designates the connections onto which the N-type and P-type thermoelectric elements 11 and 12 respectively are soldered by using an eutectic tin alloy. The thickness of the connections 10 will vary depending on the electric power to be supplied to the thermoelectric device and preferably it should range from 100 to 400 microns.

Numeral 13 designates the layer of polymeric material of the laminates and numeral 14 designates the adhesive material joining together the laminates. Preferably, the thickness of the layer of polymeric material of the laminates should range from 25 to 150 microns.

The purpose of the adhesive material 14 is to pack the hollow core of the thermoelectric device and even the contacting surfaces of the two laminates, in order to prevent formation of air bubbles and to level of possible surface imperfections. Another purpose of the adhesive material 14 is to assure a good transmission of heat. To this purpose, a thermosetting resin, for example an epoxy resin containing a finely ground metallic element filler should be used. The resin is spread with a scraper in order to limit the quantity of material deposed and to form a thin layer, preferably having a thickness not greater than 10 to 15 microns. The resin should be formulated so as to simultaneously and completely set during the final soldering operation of the thermoelectric couples.

Figures 4A and 4B show the thermoelectric cell of Figure 1 in a plane condition. Numerals 16 and 17 designate the terminals allowing connection of thermoelectric cell to a power source not shown in the drawings. As illustrated, the thermoelectric couples are arranged on a portion only of the laminate, the remaining portions L1 , L2, L3 and L4 being provided for permitting the laminates once attached to be deformed into a cylindrically wound configuration or a spirally wound configuration so as to form a hollow core of the thermoelectric device as taught by the pending International Application WO 00/49664 and shown in Figures 5 and 6 of the drawings.

Referring to Figure 2 of the drawings, there is shown a second embodiment of the thermoelectric cell of the present invention.

According to this second embodiment, the thermoelectric cell comprises a flexible laminate consisting of a layer of polymeric material, for example the same polymeric used in the first embodiment, and two layers of metallic material, for example copper, each arranged on the two opposite faces of the layer of polymeric material. The laminate is deformed into a cylindrical configuration or a spiral configuration so as to form a hollow core of the thermoelectric device as taught by the pending International Application WO 00/49664.

The connections for the thermoelectric elements are made on the metallic material layer of the laminates via an etching process.

Numeral 10 designates the connections onto which the N-type and P-type thermoelectric elements 11 and 12 respectively are soldered by using an eutectic tin alloy. The thickness of the connections 10 will vary depending on the electric power to be supplied to the thermoelectric device and preferably it should range from 100 to 400 microns.

Numeral 13 designates the layer of polymeric material of the laminate. The thickness of the layer of polymeric material 13 of the laminate should be chosen so as to assure on the one hand a good mechanical strength and on the other hand an effective transmission of heat. Preferably, the thickness of the layer of polymeric material should range from 25 to 150 microns.

Figures 4A and 4B show the thermoelectric cell of Figure 2 in a plane condition. The thermoelectric cell is subsequently deformed into a cylindrically wound configuration or a spirally wound configuration so as to form a hollow core of the thermoelectric device as shown in Figures 5 and 6 of the drawings. Referring to Figure 3 of the drawings, there is shown a third embodiment of the thermoelectric cell of the present invention. According to this third embodiment the thermoelectric cell comprises a rigid laminate consisting of a layer of ceramic material, for example alumina or similar, and two layers of metallic material, for example copper, each arranged on the two opposite faces of the layer of ceramic material.

Numeral 10 designates connections onto which the N-type and P- type thermoelectric elements 11 and 12 respectively are soldered by using an eutectic tin alloy and numeral 15 designates the rigid layer of ceramic material.

Also in this third embodiment the thickness of the connections 10 should range from 100 to 400 microns and the thickness of the layer of ceramic material 15 should range from 25 to 150 microns.

As shown in Figures 7 and 8 of the drawings, a plurality of thermoelectric cells according to the second or third embodiment are cascaded in series thermally and arranged so as to form a hollow core of the thermoelectric device having a polygonal cross section.

Referring to Figures 5, 6 and 7 of the of the drawings, numeral 18 designates the heat exchange fins provided on the external heat exchange tube designated by numerals 19, 22 and 24, respectively. Alternatively to the heat exchange fins 18, provision may be made for other heat exchange means known in the art. Numerals 20, 23 and 26 designate the internal heat exchange tube around which the thermoelectric cells are arranged. Numeral 21 designates the passage for the heat exchange fluid to be cooled or heated by means of the thermoelectric device.

Referring to Figures 9 and 10 of the drawings, there is shown the thermoelectric device of Figures 5, 6 or 7 used as a module for example in the construction of a heat pump. The capacity of the thermoelectric device may range from 0.3 to 2.5 kW depending on the design specifications required for obtaining a high efficiency of thermal exchange and on the intended use of the heat pump.

The thermoelectric device is provided with couplings for connecting it to a pipe line. Numeral 27 designates a screw-type coupling. Of course, other kinds of couplings may be also used. Numeral 28 designates two closure elements made of polymeric material which thermally insulate the hollow core of the thermoelectric device and also form the body thereof. The polymeric material from which the covers 28 are made may be polytetrafluorethylene, polyvinylidene fluoride, polyamide 6.6 with glass fibre or high density polyethylene filler according to the kind of fluid to be cooled or heated and to the design specifications. Turbulent flow generating means designated by 33 are provided inside the hollow core of the thermoelectric device for increasing the heat exchange efficiency of the thermoelectric device. Means 33 consist of a first series of disks designated by 29 for distributing the heat exchange fluid along the walls of the hollow core and, intercalated therewith, a second series of disks designated by 31 for uniformly distributing the temperature inside the heat exchange fluid.

With reference to Figure 11 of the drawings, there is shown in more detail the configuration of the disks 29 and 31. Disks 29 are provided with a series of radial grooves 30 formed on their surface. Because the disks 29 are in thermal contact with the surface of the interior heat exchange tube 20,23,26 the grooves 30 increase the surface contacted by the heat exchange fluid and cause a turbulent flow to be generated. Conversely, disks 31 have a smooth surface and are provided with a central bore designated by 32 through which the heat exchange fluid is passed. Disks 31 are also in thermal contact with the surface of the interior heat exchange tube 20,23,26 and their purpose is to uniformly distribute the temperature inside the fluid. Generally, disks 31 will have a thickness smaller than that of the disks 29 since they serve as intervening elements. The diameter of the passage 32 for the heat exchange fluid may vary according to the properties of the heat exchange fluid and the design specifications of the thermoelectric device. Both the disks 29 and 31 may be made of the same metallic material, for example aluminium. Referring to Figures 12 and 13 of the drawings, there is shown a modular heat pump formed of a plurality of thermoelectric devices having a predetermined capacity. The thermoelectric devices are in fluid communication with two manifolds designated by 34 and 40, respectively. The manifolds distribute the heat exchange fluid through the thermoelectric devices. Numerals 35 and 36 designate the heat exchange fluid outlet and inlet, respectively, of the modular heat pump. Numeral 38 designates a pair of thermocouples which are provided for controlling the temperature of the heat exchange fluid at the inlet and outlet of the modular heat pump. The thermocouples are generally connected to a control unit, not shown in the Figure, which is provided for controlling the power supplied to the heat pump through cables 37 according to the heat load. The modular heat pump may be attached to a support by means of fittings which are designated by 41 in Figure 12. A flow of air is produced through the heat pump by means of fans designated by 44. The rating of the fans 44 and the dimension of the paddles designated by 42 depend on the required design specifications. The number of fans shown in Figure 13 is not binding to the purposes of the present invention. Numeral 43 designated the power supply terminals provided for the fan motors. The supply voltage may be equal of different to that used for supplying the heat pump depending on the required design specifications. Numeral 45 designates the air duct wherein the fans 44 are mounted. The air duct may be made of a metallic or polymeric material.

The capacity of the thermoelectric devices which form the modular heat pump may range from 0.3 to 2.5 kW depending on the design specifications required for obtaining a high efficiency of thermal exchange and on the intended use of the heat pump. In this way the heat pump may have a high capacity and at the same time be very compact in size.

Claims

1 ) A solid state thermoelectric device for a thermoelectric heat pump including an array of thermoelectric couples electrically connected in series and thermally connected in parallel so that all the hot and cold sides of the thermoelectric couples are

5 separately arranged on opposite surfaces of the thermoelectric device, characterised in that the thermoelectric couples are supported on a flexible polymeric substrate made of polyimide, polyethylene naphtalate, polyaryl heteroketone, polysulphon, polypheniloxide or polyphenilsulphur, said flexible polymeric o substrate being wound in a cylindrical or spiral configuration so as to form a hollow core of the thermoelectric device.

2) A solid state thermoelectric device for a thermoelectric heat pump including an array of thermoelectric couples electrically 5 connected in series and thermally connected in parallel so that all the hot and cold sides of the thermoelectric couples are separately arranged on opposite surfaces of the thermoelectric device, characterised in that the thermoelectric couples are supported on a flexible polymeric substrate made of polyimide, 0 polyethylene naphtalate, polyaryl heteroketone, polysulphon, polypheniloxide or polyphenilsulphur, said flexible polymeric substrate being arranged in a configuration having a polygonal

5 cross section so as to form a hollow core of the thermoelectric device.

3) A solid state thermoelectric device for a thermoelectric heat pump according to claims 1 or 2, characterised in that the thermoelectric device comprises a first heat exchange tube arranged inside the hollow core of the thermoelectric device and a second heat exchange tube arranged outside the hollow core of the thermoelectric device, said first heat exchange tube being provided with turbulence generating means on its inner surface or inside its hollow space for producing a turbulent flow of a heat exchange fluid therethrough and said second heat exchange tube being provided with heat exchange fins on its outer surface.

4) A solid state thermoelectric device for a thermoelectric heat pump according to claim 3, characterised in that it comprises coupling means at its end portions for permitting its first exchange tube to be connected to a pipe line through which a heat exchange fluid is passed.

5) A thermoelectric heat pump, characterised in that it comprises a plurality of thermoelectric devices the two end portions of which are connected to a first and second manifold, respectively, through which a heat exchange fluid is distributed to the thermoelectric device, said thermoelectric heat pump being provided with fan means for producing a flow of cooling air through the heat exchange fins of each thermoelectric device.