BACKGROUND

The present invention relates, in general, to thermoelectric cooling systems. More specifically, the present invention relates to modular or distributed thermoelectric devices.

Thermoelectric cooling systems are reliable, lightweight, and an environment- friendly alternative to traditional vapor compression systems. For cooling purposes, conventional thermoelectric cooling systems use one or more thermoelectric devices in conjunction with a DC power source. While cooling a chamber, a thermoelectric device transfers heat from a cold side of the thermoelectric device to a hot side of the

thermoelectric device.

In the conventional thermoelectric cooling systems, the hot side of the

thermoelectric device is attached to a heat sink, which has a plate made of a metallic material and fins to dissipate heat to the ambient. Heat from the thermoelectric device is transferred to a base and the fins of the heat sink. As the size of the thermoelectric device (and thus the contact area between the thermoelectric device and the heat sink) is small as compared with the size of the heat sink, the heat transfer from the hot side of the thermoelectric device to the heat sink is not efficient. Due to spreading thermal resistance of the base of the heat sink, the center of the heat sink (where the

thermoelectric device is attached) is the hottest as compared with edges of the heat sink. Thus all the fins of the heat sink are not equally used to dissipate the heat. The fins near the center of the heat sink transfer more heat than those near the edges. This results in the heat sink with a high spreading thermal resistance. As a result, there is a large temperature difference between the heat sink and the hot side of the

thermoelectric device.

Ideally, the temperature of the heat sink and the hot side of the thermoelectric device should be close to the ambient temperature to reduce the temperature differential across the thermoelectric device and thereby to maximize the coefficient of performance of the thermoelectric cooling system. Accordingly, there is a need for a compact and cost effective thermoelectric cooling system which can efficiently transfer the heat from the thermoelectric device to the heat sink.

While various systems and methods have been developed for thermoelectric cooling systems, there exists a need for further contributions in this technology area.

SUMMARY

The present invention provides an efficient thermoelectric cooling system.

The thermoelectric cooling system includes a plurality of thermoelectric devices, one or more heat sinks connected to a hot side of the thermoelectric devices, and one or more cold sinks connected to a cold side of the thermoelectric devices. In an

embodiment of the present invention, the cold sides of the thermoelectric devices are connected to one cold sink. In another embodiment of the present invention, the cold side of each thermoelectric device is connected to an individual cold sink. The cold side of the thermoelectric devices is connected to a chamber which contains a fluid to be cooled. In an embodiment of the present invention, the heat sink includes one or more heat pipes. The heat pipes have insulating sections and act as thermal diodes. Thus, the thermoelectric cooling system can use both conventional aluminum heat sinks and heat pipes to increase the efficiency of heat transfer. When the thermoelectric devices are switched on, they extract heat from the fluid and transfer the heat from the cold side of the thermoelectric devices to a hot side of the thermoelectric devices. Heat sinks dissipate the heat from the thermoelectric devices to the ambient. When heat pipes are used in the themioelectric cooling system, the backflow of heat to the fluid is prevented when the thermoelectric devices are switched off.

In an embodiment of the present invention, the heat pipes are embedded into a plate made of a metallic material to reduce the spreading thermal resistance of the heat sink.

In an embodiment of the present invention, the thermoelectric devices are manufactured by dividing a large thermoelectric device into a number of small

thermoelectric devices. For example, the large thermoelectric device is divided into two, four, six, or eight modular thermoelectric devices. In an embodiment of the present invention, the large thermoelectric device is divided into four modular thermoelectric devices with a square shape and an equal surface area. In another embodiment of the present invention, the large thermoelectric device is divided into four modular thermoelectric devices with a rectangular shape and an equal surface area. The modular thermoelectric devices are attached to the heat sink.

The thermoelectric devices are electrically connected either in parallel or in series so that the thermoelectric cooling system can operate at a specified operating DC voltage and current.

Use of the plurality of thermoelectric devices changes the heat flux incident on the heat sinks from a concentrated source to a distributed source. This further reduces the spreading thermal resistance of the heat sink and minimizes the temperature difference between the heat sink and the hot side of the thermoelectric devices. Thus, the

coefficient of performance of the thermoelectric cooling system is enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred embodiments of the present invention will hereinafter be described in conjunction with the appended drawings that are provided to illustrate, and not to limit the invention, wherein like designations denote like elements, and in which:

FIG. 1 illustrates a cross-sectional view of a state-of-the-art thermoelectric cooling device;

FIG. 2 illustrates a cross-sectional view of a thermoelectric cooling device, in accordance with an embodiment of the present invention;

FIG. 3 illustrates a cross-sectional view of a thermoelectric cooling device, in accordance with another embodiment of the present invention;

FIG. 4 illustrates a cross-sectional view of a thermoelectric cooling device, in accordance with yet another embodiment of the present invention;

FIG. 5 illustrates a top view of modular thermoelectric devices, in accordance with an embodiment of the present invention;

FIG. 6 illustrates division of a thermoelectric device into modular thermoelectric devices, in accordance with an embodiment of the present invention; FIG. 7 illustrates a top view of modular thermoelectric devices, in accordance with another embodiment of the present invention;

FIG. 8 illustrates temperature distribution along edges of a modular thermoelectric device, in accordance with an embodiment of the present invention;

FIG. 9 illustrates temperature distribution along edges of a modular thermoelectric device, in accordance with another embodiment of the present invention;

Fig. 10 illustrates a cross sectional view of a thermoelectric cooling device, in accordance with yet another embodiment of the present invention;

Fig. 11 illustrates a top view of the thermoelectric cooling device, in accordance with an embodiment of the present invention;

FIG. 12 illustrates a cross-sectional view of a thermoelectric cooling device, in accordance with yet another embodiment of the present invention;

FIG. 13 illustrates a detailed view of segmented thermoelectric devices, in accordance with an embodiment of the present invention;

FIG. 14 illustrates a detailed view of segmented thermoelectric devices, in accordance with another embodiment of the present invention; and

Fig. 15 illustrates a cross sectional view of a thermoelectric cooling device, in accordance with yet another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Before describing the embodiments in detail, in accordance with the present invention, it should be observed that these embodiments reside primarily in

thermoelectric cooling devices. Accordingly, the system components have been represented to show the specific details that are pertinent for an understanding of the embodiments of the present invention, and not the details that will be apparent to those with ordinary skill in the art.

FIG. 1 illustrates a cross-sectional view of a state-of-the-art thermoelectric cooling device 100.

Thermoelectric cooling device 100 contains a heat pipe 102 connected to a hot side of a thermoelectric device 104. Heat pipe 102 is connected to thermoelectric device 104 through a Thermal Interface Material (TIM) (Not shown in the figure). Thermoelectric device 104 is connected to a chamber 106 (only one side of chamber 106 is shown to focus on a wall of chamber 106). Chamber 106 contains a fluid 108 that needs to be cooled. A metal standoff 110 connects a cold side of thermoelectric device 104 to a cold sink 124 which is in contact with fluid 108 in chamber 106.

A first plate 112, a second plate 114, and screws 1 16 hold heat pipe 102 to the hot side of thermoelectric device 104. Heat pipe 102 is soldered to first plate 112, which is made of copper or copper alloy. Screws 116 are made of an insulating material such as ceramic or hard plastic material to prevent the heat flow from the hot side of thermoelectric device 104 to fluid 108.

Heat pipe 102 is connected to metal fins 1 8. Further, a heat sink fan 120 is positioned proximal to metal fins 118. Heat sink fan 120 facilitates transfer of heat from metal fins 118 to the ambient.

When thermoelectric device 104 is switched on, it cools fluid 108 through a cold sink 124 that comprises an extended fin structure. The hot side of thermoelectric device 104 is at a higher temperature than the metal fins 118. The heat extracted by

thermoelectric device 104 from fluid 108 is conducted to metal fins 118through heat pipe 102.

Chamber 106 has a cold fan 122 that helps in transferring heat from the fluid 108 to thermoelectric device 104. Further, cold fan 122 aids in maintaining a uniform temperature within chamber 106.

FIG. 2 illustrates a cross-sectional view of a thermoelectric cooling device 200, which is used to cool fluid 108 contained in chamber 106, in accordance with an embodiment of the present invention.

In an embodiment of the present invention, thermoelectric cooling device 200 comprises modular thermoelectric devices 202 to cool fluid 108. Further, in an

embodiment of the present invention, modular thermoelectric devices 202 present in thermoelectric cooling device 200 are manufactured by splitting a single thermoelectric device. The total number of thermocouples in all modular thermoelectric devices 202 present in thermoelectric cooling device 200 is equal to the number of thermocouples in the single thermoelectric device. Moreover, in an embodiment of the present invention, the combined cooling power of modular thermoelectric devices 202 has approximately the same cooling power of the single thermoelectric device. In an embodiment of the present invention, the number of thermocouples in each of modular thermoelectric devices 202 is less than 100. Table 1 illustrates a comparison of configuration and properties of modular thermoelectric devices 202 derived from the single thermoelectric device.

Where,

Imax is the maximum current that can enable cooling of a thermoelement;

Qmax is the maximum cooling power of a thermoelectric device; and

ΔΤ _m ax is the maximum temperature difference between the cold side and the hot side of a thermoelectric device.

In various embodiments, modular thermoelectric devices 202 are electrically connected either in parallel or in series configuration. If modular thermoelectric devices 202 are connected in parallel configuration, they are operated with a common DC voltage. On the other hand, if modular thermoelectric devices 202 are connected in series configuration they are operated with a common DC current. A plate 204 and screws 116 connect metal fins 118 to the hot side of preferably each of modular thermoelectric devices 202. Plate 204 and metal fins 118 form a heat sink. Metal standoffs 110 connect a cold side of preferably each of modular thermoelectric devices 202 to chamber 106. Further, an insulating material 126 is provided to prevent the flow of heat from the heat sink to cold sink 124. The insulating material 126 is made of styrofoam or any other thermally insulating foam. The assemblies of modular

thermoelectric devices 202, screws 116, metal standoffs 110 are enclosed in

Polypropylene (PP) Cartons 206. In an embodiment of the present invention, metal fins 118 and cold sink 124 are present in a modular form. That is, thermoelectric cooling device 200 has metal fins 118 and cold sink 124 in a modular format with one set of metal fins 118 and one set of cold sink 124 corresponding to preferably every modular thermoelectric device 202. Modules of metal fins 118 and cold sink 124, and modular thermoelectric devices 202 are assembled together to form thermoelectric cooling device 200.

When the thermoelectric cooling device 200 is switched on, it cools the fluid 108 through the cold sink 124. The heat extracted by each of modular thermoelectric devices 202 from the fluid 108 is conducted to metal fins 118. The presence of a plurality of modules of thermoelectric devices instead of a single thermoelectric device improves heat transfer from the hot side of the modular thermoelectric devices 202 to plate 204 and metal fins 118. Further, spreading thermal resistance of plate 204 and the

associated temperature rise at the hot side of modular thermoelectric devices 202 are reduced significantly.

FIG. 3 illustrates a cross-sectional view of a thermoelectric cooling device 300, in accordance with another embodiment of the present invention.

In this embodiment of the present invention, thermoelectric cooling device 300 comprises modular thermoelectric devices 202 to cool fluid 108. A plate 302 and screws 116 hold metal fins 118 to the hot side of preferably each of modular thermoelectric devices 202. Metal standoff 110 connects the cold side of preferably each of modular thermoelectric devices 202 to chamber 106. Further, insulating material 126 is provided to prevent the flow of heat from the heat sink to the cold sink 124. In an embodiment of the present invention, fan 304 is provided to increase the heat flow from metal fins 118 to the ambient, and fan 306 is provided to increase the heat flow from fluid 108 to cold sink 124. Preferably, all modular thermoelectric devices 202 share fan 304 at the hot side and fan 306 on the cold side, thus making thermoelectric cooling device 300 compact in design. Alternatively, in another embodiment of the present invention, multiple fans with small blade diameters are used at the hot side and the cold side of modular thermoelectric devices 202 to increase the reliability of thermoelectric cooling device 300.

In an embodiment of the present invention, metal fins 118 and cold sink 124 are present in a modular form. That is, thermoelectric cooling device 300 has metal fins 118 and cold sink 124 in a modular format with one set of metal fins 118 and one set of cold sink 124 corresponding to preferably every modular thermoelectric device 202. Modules of metal fins 118 and cold sink 124, and modular thermoelectric devices 202 are assembled together to form thermoelectric cooling device 300.

FIG. 4 illustrates a cross-sectional view of a thermoelectric cooling device 400, which is used to cool fluid 108 contained in chamber 106, in accordance with yet another embodiment of the invention.

In this embodiment of the present invention, thermoelectric cooling device 400 comprises modular thermoelectric devices 202 to cool fluid 108.

All components in FIG. 4 are similar to those described in conjunction with FIG. 3 except that instead of plate 302 present in FIG. 3, a plate 402 is provided in FIG. 4. In this embodiment of the present invention, plate 402 has a heat pipe 404 embedded in it. Plate 402 collects heat from the hot side of modular thermoelectric devices 202 and acts as a base for metal fins 118. Heat pipe 404 aids in reducing the spreading thermal resistance of the heat sink. Further, fan 304 enhances the heat flow from metal fins 118 to the ambient, and fan 306 enhances the heat flow from fluid 108 to cold sink 124. In another embodiment, a single wide area vapor chamber (not shown) can be used at the base of metal fins 118 to minimize the spreading thermal resistance of the heat sink.

In an embodiment of the present invention, heat pipe 404 extends out of plate 402

(not shown in the figure) and is connected to metals fins (similar to metal fins 118 described in conjunction with FIG. 1) and a fan (similar to heat sink fan 120 described in conjunction with FIG. 1). This ensures improved heat transfer by heat pipe 404.

In an embodiment of the present invention, metal fins 118 and cold sink 124 are present in a modular form. That is, thermoelectric cooling device 400 has metal fins 118 and cold sink 124 in a modular format with one set of metal fins 118 and one set of cold sink 124 corresponding to preferably every modular thermoelectric device 202. Modules of metal fins 118 and cold sink 124, and modular thermoelectric devices 202 are assembled together to form thermoelectric cooling device 400.

FIG. 5 illustrates a top view of modular thermoelectric devices 202, in accordance with an embodiment of the present invention.

A plurality of modular thermoelectric devices 202 are provided that improves the coefficient of performance of the thermoelectric cooling device because of improved heat transfer and reduces the spreading thermal resistance of the heat sink.

Plate 204 (not shown in Fig. 5) and screws 116 hold the hot side of each of modular thermoelectric devices 202 to metal fins 118. In an embodiment of the present invention, screws 116 are made up of an insulating material such as ceramic or hard plastic material to prevent the backflow of heat. In another embodiment of the present invention, screws 116 include a combination of metallic materials and insulating standoffs made up of insulating materials, which include but are not limited to ceramic, Delrin, and Nylon. Screws entirely made of metals are preferably not used in the invention as they may contribute to thermal leakage between the heat sink and the cold sink.

In another embodiment of the present invention, the assembly of the

thermoelectric cooling device is accomplished by using a conductive epoxy material to attach the different components such as the plate (204, 302, or 402), modular

thermoelectric devices 202, metal standoff 110, and cold sink 124. The thermoelectric cooling device assembled using the conductive epoxy material eliminates the need for screws and insulating grommets and reduces the parasitic thermal leakage. It also provides a better thermal interface between the various components. The conductive epoxy material can be either a thermoset or a thermoplastic material with embedded metals such as silver or other high thermal conductivity material such as boron nitride or forms of carbon particles. In another embodiment of the present invention, a combination of the conductive epoxy material and screws 116 are used to assemble the

thermoelectric cooling device. FIG. 6 illustrates division of a thermoelectric device 600 into modular thermoelectric devices 602, in accordance with an embodiment of the present invention.

In this embodiment of the present invention, thermoelectric device 600 is divided into four smaller thermoelectric devices 602 with a square shaped cross-section and an equal area using a method such as cutting. In another embodiment, thermoelectric device 600 is divided into eight smaller modular thermoelectric devices.

Multiple modular thermoelectric devices 602 aid in an efficient heat transfer from the hot side of modular thermoelectric devices 602 to metal fins 118. As a result, the spreading thermal resistance of the heat sink is reduced.

FIG. 7 illustrates a top view of an arrangement of modular thermoelectric devices

702, in accordance with another embodiment of the present invention.

A plurality of modular thermoelectric devices 702 are provided that improves coefficient of performance of the thermoelectric cooling device because of improved heat transfer.

Modular thermoelectric devices 702 have an equal area and a rectangular cross- section. Plate 204 (not shown in Fig. 7) and screws 116 hold the hot side of modular thermoelectric devices 702 to metal fins 118. In an embodiment of the present invention, screws 116 are made up of an insulating material such as ceramic or hard plastic material to prevent the backflow of heat. In yet another embodiment, the hot side of each modular thermoelectric device 702 is attached to metal fins 118 by means of conductive epoxy material.

FIG. 8 and FIG. 9 represent temperature distribution curves across edges of modular thermoelectric devices, and illustrate that modular thermoelectric device 702 with a rectangular cross-section has a greater temperature differential across it as compared with modular thermoelectric devices 602 with a square cross-section.

FIG. 8 illustrates temperature distribution across a top surface 802 and a bottom surface 804 of modular thermoelectric device 602 that has a square cross-section, in accordance with an embodiment of the present invention.

Top surface 802 is in contact with plate 302 while bottom surface 804 is in contact with cold sink 124. T _am bient indicates the temperature of the ambient. A curve 806 represents temperature distribution along the line AA' on the top surface 802 (or temperature distribution at the hot side of the thermoelectric device). As depicted in the figure, the temperature at the midpoint of top surface 802 is significantly higher as compared with the temperature at the edges of top surface 802.

Similarly, a curve 808 represents temperature distribution along the line AA' on bottom surface 804 (or temperature distribution at the cold side of the thermoelectric device). As depicted in the figure, the temperature at the midpoint of bottom surface 804 is lower than the temperature at the edges of bottom surface 804. Hence the

temperature differential ΔΤ _max (temperature difference between the cold side and the hot side) is much larger at the center of modular thermoelectric device 602 than at its edges.

FIG. 9 illustrates temperature distribution across a top surface 902 and a bottom surface 904 of modular thermoelectric device 702 that has a rectangular cross-section, in accordance with another embodiment of the present invention.

When modular thermoelectric device 702 is used in a thermoelectric cooling device, top surface 902 is in contact with plate 302, and bottom surface 904 is in contact with cold sink 124. Thus, top surface 902 represents the hot side of the thermoelectric device and bottom surface 904 represents the cold side of the thermoelectric device. A curve 906 represents temperature distribution along the line BB' on top surface 902 (or the temperature distribution at the hot side of the thermoelectric device).

The temperature distribution curves 806 and 906 illustrate that variation of temperature across the top surface is low for modular thermoelectric device 702 (that has a rectangular cross-section) as compared with that of modular thermoelectric device 602 (that has a square cross-section). Thus, the coefficient of performance and the maximum attainable temperature differential is higher for modular thermoelectric device 702 than that of modular thermoelectric device 602.

Similarly, variation of temperature across the bottom surface is also low for modular thermoelectric device 702 as compared with that of modular thermoelectric device 602. Temperature distribution across bottom surface 904 (or the temperature distribution at the cold side of the thermoelectric device) has not been shown in the figure.

In an embodiment of the present invention, thermoelectric cooling devices - 200, 300, and 400 are used for cooling in water coolers or portable coolers.

Multiple modular thermoelectric devices 202, 602, and 702 provide better transfer of heat from the hot side of the thermoelectric devices to the plate, the heat pipe, and the heat sink. Thus, various embodiments of the present invention reduce the spreading thermal resistance of the heat sink. Further, they ensure that the temperature of the heat sink and the hot side of the thermoelectric devices is close to the ambient temperature. Similarly, the temperature of the cold sink and cold side of the thermoelectric devices are very close in various embodiments of the present invention. Hence, the coefficient of performance of the thermoelectric cooling devices described in the present invention is high.

Fig. 10 illustrates a cross sectional view of a thermoelectric cooling device 1000, in accordance with yet another embodiment of the present invention.

Thermoelectric cooling device 1000 comprises two stage modular thermoelectric devices comprising a first thermoelectric device 1002 and a second thermoelectric device 1004. The two-stage thermoelectric cooling devices can provide a large cooling effect and can operate at a wide temperature range such as 0°C to 40°C. A hot side of second thermoelectric device 1004 is thermally connected to a cold side of first thermoelectric device 1002. The two stage modular thermoelectric devices are enclosed in PP Cartons 206. Insulating material 126 is provided to prevent the flow of heat from the heat sink to cold sink 124. In an embodiment of the present invention, insulating material 126 is foam. A modular heat pipe 1006 is present at a hot side of preferably every first thermoelectric device 1002. Modular heat pipe 1006 reduces the spreading thermal resistance of the heat sink and improves heat dissipation of thermoelectric cooling device 1000.

Fig. 11 illustrates a top view of thermoelectric cooling device 1000, in accordance with an embodiment of the present invention. Various elements of thermoelectric cooling device 1000 have been explained in conjunction with FIG. 10. FIG. 12 illustrates a cross-sectional view of a thermoelectric cooling device 1200, in accordance with yet another embodiment of the present invention.

Thermoelectric cooling device 1200 comprises segmented thermoelectric devices 1202 (explained below in conjunction with FIGs 13 and 14).

FIG. 13 illustrates a detailed view of segmented thermoelectric devices 1202 present in thermoelectric cooling device 1200, in accordance with an embodiment of the present invention.

Segmented thermoelectric devices 1202 are placed perpendicular to flattened heat pipes 1302 in an embodiment of the present invention. Flattened heat pipes 1302 have rectangular, elliptical, or circular cross-section. Flattened heat pipes 1302 are soldered to first plate 112, which is made of copper or copper alloy. In another embodiment, flattened heat pipes 1302 are directly attached to segmented

thermoelectric devices 1202 by using a conductive epoxy material or screws.

FIG. 14 illustrates a detailed view of segmented thermoelectric devices 1202 present in thermoelectric cooling device 1200, in accordance with another embodiment of the present invention. Segmented thermoelectric devices 1202 are oriented in the same direction as heat pipes 1302 in this embodiment of the present invention.

FIG. 15 illustrates a cross sectional view of a thermoelectric cooing device 1500.

A hot side of segmented thermoelectric devices 1202 is attached to a first plate 112, which in turn is connected to flattened heat pipes 1302. In an embodiment of the present invention, the width of segmented thermoelectric devices 1202 is 10mm, the width of flattened heat pipes 1302 is 10mm, and centre to centre pitch between flattened heat pipes 1302 is 15mm. It should be appreciated that the width of segmented thermoelectric devices 1202, width of flattened heat pipes 1302, and centre to centre pitch between flattened heat pipes 1302 can be any other suitable value.

First plate 112, second plate 114, and screws 116 hold flattened heat pipes 1302 to the hot side of segmented thermoelectric devices 1202. In an embodiment, the thickness of first plate 1 12 is 1mm. Screws 116 have an insulating standoff 1502 to prevent heat conduction. The cold side of segmented thermoelectric devices 1202 is connected to a metal standoff 1504. Metal standoff 1504 is a metal block with ridges. In an embodiment of the present invention, metal standoff 1504 is made of copper or aluminum and has a height of 25mm. In this embodiment, the height of the ridges of metal stand off 1504 is 12mm. The ridges of metal standoff 1504 include insulating material 126.

It will be apparent to a person skilled in the art that the dimensions of elements such as height width and distance may have any other suitable value. The dimensions mentioned in the various embodiments are illustrative and should not be considered as limitations.

While the preferred embodiments of the invention have been illustrated and described, it will be clear that the invention is not limited to these embodiments only. Numerous modifications, changes, variations, substitutions, and equivalents will be apparent to those skilled in the art without departing from the spirit and scope of the invention.