Thermoelectric Heat Pump

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the United States national phase of International Patent Application No. PCT/NL2023/050379 filed Jul. 14, 2023, and claims priority to The Netherlands Patent Application No. 2032505 filed Jul. 15, 2022, the disclosures of which are hereby incorporated by reference in their entireties.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a thermoelectric heat pump.

Description of Related Art

Known thermoelectric heat pumps are used to displace heat from a first heat transfer fluid to a second heat transfer fluid, usually counter to the temperature gradient prevailing between the fluids. Because a thermoelectric element applied in thermoelectric heat pumps, also referred to as Peltier element, comprises no moving parts, such heat pumps are often used in special applications wherein it is particularly advantageous that the heat pump is vibration-free and can function without further moving parts or liquids.

It is however a drawback of the known thermoelectric heat pumps that the efficiency achieved is very low. Consequently, the existing heat pumps cannot be utilized effectively in applications wherein greater heat capacities are required, such as for instance in residential or industrial heating installations.

It is now an object of the invention to provide a thermoelectric heat pump whereby one or more of the above stated drawbacks can be reduced or even obviated.

SUMMARY

This object is achieved according to an embodiment of the invention with a thermoelectric heat pump comprising a heat exchanger block with a first channel for flow therethrough of a first heat transfer fluid such as a liquid medium and a separate second channel for flow therethrough of a second heat transfer fluid such as a liquid medium, wherein the heat exchanger block comprises a heat exchange cavity which is hydraulically separated by a partition into a first and a second sub-cavity which are connected to respectively the first and second channel and wherein the first heat transfer fluid in the first sub-cavity is in heat-exchanging contact with a first side of the partition and the second heat transfer fluid in the second sub-cavity is in heat-exchanging contact with a second side of the partition lying opposite the first side, wherein the partition comprises a thermoelectric element with a cold side and a hot side lying opposite thereto and at a distance therefrom, wherein an outer peripheral edge extends between the cold and hot side, which thermoelectric element is configured to transport thermal energy from the cold side to the hot side and wherein the cold side is in heat-exchanging contact with the first heat transfer fluid and wherein the hot side is in heat-exchanging contact with the second heat transfer fluid and wherein each channel is provided with a pump for pumping the respective heat transfer fluid through the channel.

By providing a thermoelectric element between the sub-cavities of heat exchange cavity, wherein the heat transfer fluids in the respective sub-cavities are pumped along the partition by means of a pump, heat can be transported from the first heat transfer fluid to the second heat transfer fluid by conducting a current through the thermoelectric element. Because the respective heat transfer fluids are pumped separately, the flow rate can be chosen such, subject to a temperature difference over the thermoelectric element, that the efficiency of the heat transfer can be increased considerably relative to a heat pump wherein no moving parts, such as for instance a pump, are used. The temperature difference over the thermoelectric element is here preferably kept relatively low for the purpose of further increasing the thermal efficiency. For this purpose the temperature difference over the thermoelectric element is preferably kept below 60% of the maximum temperature difference that the thermoelectric element can achieve.

A liquid medium is preferably used here for one or both of the heat transfer fluids, such as for instance a liquid coolant on the basis of a solution of potassium formate in water. The solution is more preferably substantially or wholly saturated. Such a coolant is favourable because it has a lowered freezing point, while the viscosity and heat capacity are very similar to those of water. In addition, it is environmentally friendly and biodegradable.

The respective channels can be hydraulically connected to further heat exchangers in a closed circuit or be connected directly to the heat transfer fluid which supplies or discharges heat energy.

The direction of the heat transport can be reversed in simple manner by reversing the direction of the electric current through the thermoelectric element. This allows the same heat pump to be utilized for both cooling and heating.

The thermoelectric element can take the form of a single-layer thermoelectric element, but it can also comprise a cascade of two or more thermoelectric sub-elements. Coupling the thermoelectric sub-elements in series enables the temperature difference over a single thermoelectric sub-element to be kept smaller, while a great temperature difference between the first heat transfer fluid and the second heat transfer fluid can still be achieved.

In an embodiment of a heat pump according to the invention the first and second side of the partition are formed by respectively the cold and hot side of the thermoelectric element which are in direct heat-exchanging contact with the respective heat transfer fluids, and wherein the thermoelectric element is mounted sealingly in the heat exchanger block all around the outer peripheral edge by means of a flexible seal lying exclusively against the outer peripheral edge for the purpose of maximizing the heat-exchanging surface of the cold and hot side.

Having the thermoelectric element itself form the partition results in as few losses as possible between the transitions of the materials. The thermoelectric element can for this purpose be provided, if necessary, with a coating or surface treatment which limits or prevents permeability for the heat transfer fluids used. It is highly favourable here to mount the thermoelectric element sealingly in the heat exchange cavity or the heat exchanger block all around in a manner such that the seal does not form any impediment to the heat exchange on the heat exchanging surface of the thermoelectric element. For this purpose the seal is arranged lying only against the outer peripheral edge, whereby the whole heat-exchanging surface is in contact with the respective heat transfer fluids. Giving the seal a flexible form enables thermal shrinkage and/or expansion of the thermoelectric element to be accommodated, whereby excessive mechanical stress in the element can be prevented.

In an alternative embodiment of a heat pump according to the invention the partition also comprises on either side of the thermoelectric element a membrane, which membranes form respectively the first and second side of the partition and wherein a non-hardening thermally conductive paste is arranged between the membranes and the respective adjoining sides of the thermoelectric element for the purpose of being able to accommodate the thermal shrinkage and expansion of the thermoelectric element relative to the membranes.

Enclosing the thermoelectric element between two membranes enables mechanical stress on the element due to any pressure differences between the sub-cavities to be accommodated via the membranes. This considerably increases the lifespan of the thermoelectric element. The membrane can also provide an impermeable seal. A thermally conductive paste is supplied between the thermoelectric element and the membranes for the purpose of reducing the transmission losses between the materials. By applying a non-hardening paste the thermoelectric element can shrink and/or expand without mechanical stress due to mutual friction. The thermoelectric element is therefore not wedged tightly between but merely enclosed by the two membranes, wherein relative movement between the thermoelectric element and the membranes is still possible. The paste thus functions not only as thermal conductor, but also as mechanical buffer and lubricant.

In a preferred embodiment of a heat pump according to the invention the outer peripheral edge of the thermoelectric element lies clear all around.

When the thermoelectric element lies clear all around, the thermoelectric element is wholly uncoupled and the mechanical stress on the element is thus reduced to maximum extent. This ensures a long useful life of the element.

Another embodiment of a heat pump according to the invention is a heat pump wherein the heat-exchanging surface of the first and second side of the partition is larger than the heat-exchanging surface of the respective sides of the thermoelectric element, and wherein the whole heat-exchanging surface of the sides of the thermoelectric element lie against and preferably lie centrally relative to the heat-exchanging surface of the respective sides of the partition.

Having the whole heat exchanging surface of the sides of the thermoelectric element lie against the respective membranes forming the partition prevents thermal stress from occurring in the element or in the heat-exchanging surface of the element due to non-uniform heat transfer. The thermal element preferably lies centrally relative to the partition so that a uniform transfer is obtained and space is also created along the edges of the partition, on which a seal can be arranged without the seal interfering with the heat exchange.

Yet another embodiment of a heat pump according to the invention is a heat pump wherein the flow of the heat transfer fluids in the sub-cavities is laminar and distributed homogeneously over the heat-exchanging surface of the partition.

By providing a laminar flow in the sub-cavities a highly uniform and homogeneous distribution of the liquid flow over the partition is obtained. This results on one hand in an increased transfer and on the other in a highly homogeneous surface temperature of the partition, whereby thermal stresses can be prevented to further extent. In order to increase the heat transfer microvortices can be generated at the partition, wherein the flow in the sub-cavities is substantially laminar, but turbulent at the heat exchanging surface.

Another embodiment of a heat pump according to the invention is a heat pump comprising at least two thermoelectric layers between the cold side and the hot side.

Applying a cascade of two or more thermoelectric layers or thermoelectric sub-elements enables the temperature difference over a single thermoelectric layer to be kept smaller, while a great temperature difference between the cold side and the hot side of the thermoelectric element can still be realized. The thermoelectric layers act as serial steps in the heat transfer direction. The working range of the thermoelectric layers can thus be further optimized.

Yet another embodiment of a heat pump according to the invention is a heat pump wherein an intermediate membrane is arranged between two adjacent thermoelectric layers.

Application of an intermediate membrane enables thermal shrinkage and/or expansion of the adjacent thermoelectric layers to be accommodated. A thermally conductive paste is preferably arranged here between the thermoelectric layers and the intermediate membrane. The intermediate membrane can for instance be a copper layer. The intermediate membrane can also serve as thermal buffer and ensure a homogeneous distribution of the heat.

In yet another embodiment of a heat pump according to the invention at least one of the two adjacent thermoelectric layers is constructed from a plurality of thermoelectric sub-elements, preferably constructed from more thermoelectric sub-elements than the other, adjacent thermoelectric layer is constructed from.

Because the intermediate membrane also conducts heat, the intermediate membrane can also be used to conduct heat from a plurality of parallel thermoelectric sub-elements forming part of a thermoelectric layer to the adjacent layer. An additional advantage is that if a thermoelectric sub-element were to fail, the heat can be conducted to another, still active sub-element through the conductive intermediate membrane.

The layers can then optionally also be constructed from different quantities of thermoelectric sub-elements which are arranged in parallel. It is thus possible to opt for every layer for thermoelectric sub-elements with suitable characteristics for that layer, also if the characteristics of the different layers do not correspond directly.

Also according to the invention is an embodiment of a heat pump wherein the heat-exchanging surface of each of the thermoelectric layers is substantially the same.

By making the heat-exchanging surface of the thermoelectric layers substantially identical a compact construction can be obtained, wherein the heat-exchanging surface of the cold side corresponds with the heat-exchanging surface of the hot side. The heat generation of the hot side of the thermoelectric element can here be regulated inter alia by varying the flow rate of the second heat transfer fluid, so that thermal saturation of thermoelectric layers close to the hot side can be prevented.

In yet another embodiment of a heat pump according to the invention the heat pump comprises a housing provided with a plurality of heat exchanger blocks, wherein the housing comprises a first manifold for hydraulically connecting the first channels to each other and comprises a second manifold for hydraulically connecting the second channels of the heat exchanger blocks to each other.

By arranging a plurality of heat exchanger blocks in a housing the capacity of the heat pump can be increased in simple manner. The housing serves here as manifold for hydraulically connecting the heat exchanger blocks. A plurality of heat pumps can optionally also be placed in series or in parallel.

A pair of heat exchanger blocks can also be coupled such that the second sub-cavity is shared between the two heat exchanger blocks.

Another embodiment of a heat pump according to the invention is a heat pump wherein the heat exchanger blocks are thermally insulated from each other.

By thermally insulating the heat exchanger blocks from each other undesired losses can be prevented. The insulation can be obtained here by for instance intermediate air chambers or insulating material. The whole housing can optionally also be further insulated.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the invention are further elucidated with reference to the accompanying drawings.

FIG. 1 is a schematic cross-section of an embodiment of a heat exchanger block of a first embodiment of a heat pump according to the invention.

FIG. 2 is a cross-sectional view of a second embodiment of a heat pump according to the invention.

FIG. 3 is a perspective view of a third embodiment of a heat pump according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a schematic cross-section of an embodiment of a heat exchanger block 1 of a heat pump according to the invention. The first channel 2 and the second channel 3 are hydraulically separated from each other and are hydraulically connected to respectively the first sub-cavity 4 and the second sub-cavity 5. The flow direction is designated in both sub-cavities 4, 5 with an arrow, although a different relative orientation of the flow direction can also be opted for. A partition 6 separates the first 4 and a second sub-cavity 5. A thermoelectric element 7 is arranged in the partition 6. The element 7 is arranged between a first membrane 8 and a second membrane 9 and transports thermal energy in the form of heat in the direction of arrow 10, so from the first sub-cavity 4 to the second sub-cavity 5. In practice it will often be opted for to orient heat exchanger block 1 such that arrow 10 is opposite to the force of gravity, so that optimal use can be made of the heat rising. Membranes 8, 9 close the sub-cavities 4, 5 off from each other hydraulically and are provided with seals 11. The seals 11 are arranged outside the heat-exchanging surface of the membranes 8, 9 which is in direct contact with sub-cavities 4, 5. The cold side 12 lies against first membrane 8 and a thermally conductive paste (not shown) is arranged between the transition. The hot side 13 lies against second membrane 9, and a thermally conductive paste is also arranged on this transition. This makes element 7 able to expand and shrink without being subjected to heavy mechanical stress. The free space 14 formed around the peripheral edge of element 7 also provides for the space required for the expansion.

FIG. 2 shows a cross-sectional view of a second embodiment of a heat pump 20 according to the invention. In this embodiment two heat exchanger blocks 21, 22 are combined, wherein the second sub-cavity 23 is shared by the two heat exchanger blocks 21, 22. The first channels 24, 25 debouch in the respective sub-cavities 26, 27. The membranes 28 seal the sub-cavities 23, 24 and 25 and enclose the respective thermoelectric elements 29, 30. The direction of operation of the first thermoelectric element 29 is opposite to the direction of operation of the second thermoelectric element 30. The empty space 31 between membranes 28 provides space for expansion of the elements 29, 30. In housing 32 a manifold 33 is formed which connects the first channels 24, 25 hydraulically to each other.

In another interpretation of the cross-section of FIG. 2 a third embodiment of a heat pump according to the invention is shown. In this embodiment the direction of operation of heat exchanger block 22 is reversed relative to the second embodiment, whereby the two heat exchanger blocks 21, 22 are connected in series. The second sub-cavity 23 of the first heat exchanger block 21 simultaneously forms the first sub-cavity 23 of the second heat exchanger block 22. Sub-cavity 23 is connected hydraulically to a separate third channel which is not hydraulically connected to respectively first channel 24 and second channel 25. The third channel is preferably also provided with a pump. The thermoelectric elements 29, 30 therefore have the same direction of operation in this embodiment. The first heat transfer fluid, this forming the coldest medium, flows in first channel 24. A third heat transfer fluid, this having an average temperature, flows in sub-cavity 23. The second heat transfer fluid, this having the highest temperature, flows in second channel 25. Owing to this structure, the temperature difference over the respective thermoelectric elements 29, 30 can be kept low and a great temperature difference can still be achieved between the first and the second heat transfer fluid. The third heat transfer fluid transports the energy between the two thermoelectric elements 29, 30. The third heat transfer fluid is preferably pumped turbulently.

FIG. 3 shows a perspective view of a fourth embodiment of a heat pump 40 according to the invention. Heat pump 40 is provided at the head with a supply conduit 41 and return conduit 42 which are connected hydraulically to respectively supply and discharge manifolds which are hydraulically connected by the first channels. Supply 43 and return conduits 44 are connected hydraulically to respectively supply and discharge manifolds which are hydraulically connected by the second channels. Housing 45 is formed by an assembly of ten double heat exchanger blocks 46, which are composed as shown in FIG. 2. Electric wires 47, 48 are provided per heat exchanger block 46 for the purpose of supplying the current required for the thermoelectric elements.