COOLING APPARATUS

Abstract

The invention relates to a portable cooling vented apparatus, comprising: an array made of one or more thermoelectric cooler(s), each thermoelectric cooler having a cold side and a hot side, the cumulative cold sides and the cumulative hot sides of all the thermoelectric coolers define cold and hot sides of the array, respectively; one or more heatsinks at the hot side of the array; and at least one reservoir configured to supply liquid to the heatsink(s), by being adjoined to the heatsink(s) and/or with the aid of one or more liquid channels connected to said reservoir and installed in the interior of the cooling apparatus in proximity to, or within, said heatsink(s); wherein the apparatus is open to the surroundings.

A method of cooling using a thermoelectric cooler is also provided.

Claims

1. A portable cooling vented apparatus, comprising: an array made of one or more thermoelectric cooler(s), each thermoelectric cooler having a cold side and a hot side, the cumulative cold sides and the cumulative hot sides of all the thermoelectric cooler(s) define cold and hot sides of the array, respectively; one or more heatsinks at the hot side of the array; and at least one reservoir configured to supply liquid to the heatsink(s), by being adjoined to the heatsink(s) and/or with the aid of one or more liquid channels connected to said reservoir and installed in the interior of the cooling apparatus in proximity to, or within, said heatsink(s); wherein the apparatus is open to the surroundings.

2. A portable cooling apparatus according to claim 1, wherein the reservoir is in the form of a liquid-absorbing layer attached to the heatsink(s).

3. A portable cooling apparatus according to claim 1, wherein the reservoir is in the form of a container, wherein the liquid channel(s) is(are) tube(s) connected to the container, with one or more drippers along the length of the tube(s), directed onto the hot side.

4. A portable cooling apparatus according to claim 1, further comprising a liquid impermeable layer separating between the hot side and the cold side of the array.

5. A portable cooling apparatus according to claim 1, further comprising a heat dissipating layer, which is attached to the cold side of the array.

6. A cooling apparatus according to claim 3, further comprising one or more pumps, for assisting in conveying a liquid coolant from the container to the drippers.

7. A portable cooling apparatus according to claim 3, further comprising a recycling reservoir and recycling liquid channels, for accumulating excessive liquid coolant, and returning the excessive coolant to the container.

8. A cooling apparatus according to claim 7, further comprising one or more pumps for assisting in returning excessive liquid coolant from the recycling reservoir to the container.

9. A portable cooling apparatus according to claim 6, wherein said one or more pumps operate based on pressure applied by the user.

10. A portable cooling apparatus according to claim 1, wherein the hot side is at least partially uncovered or covered with a gas-permeable cover, such that when vapors are formed in the hot side, these vapors escape to the surroundings.

11. A portable cooling apparatus according to claim 1, combined with a garment.

12. A portable cooling apparatus according to claim 1, for use within a cooling box, a chair cushion, a helmet or a bike handle.

13. A portable cooling apparatus according to claim 1, comprising a liquid channel in the form of a narrow piece of wettable material emerging from the liquid reservoir and in contact with the heatsink.

14. A portable cooling apparatus according to claim 13, wherein the liquid channel has one end that is immersed in the liquid tank, to enable liquid flow along the channel by capillary action.

15. A portable cooling apparatus according to claim 13, wherein said liquid channel has a serpentine-like shape, curving in alternate directions on the heatsink.

16. A method of cooling using a thermoelectric cooler, comprising passing an electric current through the thermoelectric cooler from a DC power supply, to create a cold side and a hot side, drawing off heat from the hot side with the aid of one or more heatsink(s) coupled to the hot side, characterized in that liquid coolant is delivered to the heatsink(s) whereby said liquid evaporates and vapors formed escape to the surrounding environment.

17. A method according to claim 16, wherein the liquid coolant is delivered to the heatsinks by supplying the liquid coolant to a liquid-absorbing layer attached to said heatsinks.

18. A method according to claim 16, wherein the liquid coolant is delivered to the heatsinks by causing one or more liquid streams to flow in one or more tubes equipped with drippers directed to said heatsinks or to the liquid-absorbing layer attached to said heatsinks.

19. A method according to claim 16, wherein the liquid coolant is delivered to the heatsinks by causing one or more liquid streams to flow from a liquid reservoir by capillary action.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In the drawings:

[0033] FIG. 1 illustrates in a schematic form the structure of a first embodiment of the present invention;

[0034] FIG. 2 illustrates in a schematic form the structure of a second embodiment of the present invention;

[0035] FIG. 3 illustrates in a schematic form an embodiment of the apparatus of the invention, as combined with a shoe;

[0036] FIG. 4 illustrates in a schematic form the structure of the Peltier array;

[0037] FIG. 5 shows a cooling apparatus which includes a top main reservoir and a bottom recycling reservoir;

[0038] FIG. 6 shows another cooling apparatus with a bottom recycling reservoir and a top main reservoir;

[0039] FIG. 7 shows the measured ΔT between the cold side and the ambient air with and without a water spray on the heatsink; and

[0040] FIG. 8 shows the measured ΔT between the cold side and the ambient air with and without a water spray on the heatsink, while a fan was used.

[0041] FIGS. 9A-9C show a cooling apparatus in which a liquid-absorbent layer soaked with liquid coolant is attached to the heatsinks to deliver the liquid to the heatsinks.

[0042] FIG. 10 illustrates the performance of a cooling device with the aid of ΔT versus power plot, measured based on the operation of a cooling apparatus designed according to FIGS. 9A-9C.

[0043] FIGS. 11A and 11B show another variant of the cooling device of the invention (front and side views, respectively.

[0044] FIGS. 12A and 12B show another variant of the cooling device of the invention (front and back views, respectively.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0045] The present invention provides a portable, energetically efficient, and light-weight apparatus that includes an array of (one or more) TEC units (hereinafter also referred to as “Peltier plates”). As will be discussed in more details hereinafter, the inventors have found that the manner in which the portable Peltier-based cooling apparatuses of the prior art is used, could be improved. In one aspect, while such prior art devices use heatsinks to cool their hot side of the Peltier plates, the capability of these heatsinks to disperse heat to the environment is limited, unless large and bulky heatsinks are used, and this limitation results in a reduction in the overall mobility of the apparatus. The inventors suggest an evaporation-based use of coolant in order to further cool the heat-sinks, and significantly improve the overall efficiency of the apparatus. Moreover, the use of coolant (such as water or any other coolant or mixture of coolants with or without solid particles dispersed in them) eliminates any necessity for pre-freezing. The adding of frozen particles to the coolant, if used, can further intensify the cooling.

[0046] In another aspect, the inventors have found that operating the Peltier plates with a low voltage, lower than the typical operating point of the Peltier plates, is advantageous. While this reduction of voltage somewhat reduces the cooling of the plates to an acceptable extent, such a reduction results in a significant improvement to the overall efficiency of the apparatus. In this respect, the inventors have found that operating close to the maximal coefficient of performance is preferable.

[0047] In view of the above structural and design differences compared to prior art apparatuses, the apparatus of the invention can operate based on a small-size and light-weight battery for a relatively longer time.

[0048] When used to cool a body part, such as for therapeutic or recreational purposes, the portable apparatus of the invention may be combined with a clothing item (such as, a shoe, a shirt, a pillow, etc.) or worn directly on a body part. The portable apparatus of the invention may also be used for other purposes, such as for cooling of food, for air conditioning, for cooling a chair in a vehicle, for cooling a motorcycle vest, motorcycle handlebars or any other uses.

[0049] The Peltier plates in the array may be connected in parallel, in series, or in a combination of series and parallel. Each plate in the array has a cold side and a hot side. One or more heatsinks are attached to the hot side of the array to assist in the heat dissipation. Coolant (such as water or any other flowing medium that can go through phase transition) is spilled on the heatsinks to facilitate an accelerated heat dissipation. The coolant may be spilled using one or more of liquid drippers, nozzle sprays, or any other mechanism capable of dispensing liquid on the heatsinks (for the sake of brevity, all will be referred hereinafter as “drippers”). The coolant evaporates and thus contributes to the cooling of the hot sides of the Peltier plates, thereby facilitating the cooling effect of the apparatus.

[0050] FIG. 1 is a general-schematic view of a cooling apparatus 100 according to one embodiment of the invention. A series of Peltier plates 105 are arranged in a two-dimensional array form, and are electrically connected in parallel, in series, or in a combination of series and parallel. The plates 105 are preferably also connected mechanically by flexible strips, discrete wires to provide higher strength. Alternatively, single or several flexible TECs, which are currently being developed in various places, may be used instead of the rigid ones to add to the flexibility. In case more than one TEC is used, heat dissipating layer 120 may be added to diffuse the cold environment between the TEC-s. Layer 120 may also be used to allow a different touch or feel of the cold side. A liquid impermeable layer 125 (such as fabric or any other medium that is impermeable to coolant) may also be used to mechanically connect the plates and separate between the hot (wet) sides and the cold (dry) sides of the array. The fact that each of the plates 105 is of relatively small dimensions (typically from a few square millimeters and up to hundreds of square millimeters) enables the user a flexibility to adapt the cooling surface 120 of the array to the surface of the cooled region. In some embodiments, each of the Peltier plates may be reduced even to a 1×1 micron size, which is the smallest Peltier plates currently known in the art. The collection of all the cooling sides 105c of the Peltier plates 105, together with the heat dissipating layer 120 forms, in combination, a roughly unified cooling surface. In order to provide an improved temperature distribution on the cooled object, while compensating for the gaps between the plates 105, the cooling layer 120 may be made of a thermal-conducting layer (for example, carbon fiber, strengthened carbon, simple cloth, etc.). A series of heatsinks 107 are attached to the hot sides 105h of the Peltier plates 105. Alternatively, a series of discrete heatsinks 107 may be used, each being attached separately to a single or several hot sides 105h of a Peltier plates 105.

[0051] One or more liquid drippers (or nozzles) 111 are provided to wet the heatsinks 107 with coolant. The coolant evaporates on the heatsink, thereby it accelerates the heat dissipation and the total cooling of the series of hot surfaces of the Peltier plates, thus facilitating the cooling effect of the entire apparatus 100. The one or more liquid drippers 111 are connected to a liquid channel 106 which is connected to a main reservoir (in this case a top main reservoir) 113, i.e., a container that contains the coolant substance. In one embodiment, the liquid channel 106 includes a valve 109 that is configured to enable or disable the flow of the coolant to the liquid drippers 111. The number of liquid drippers 111 may vary. There may be one liquid dripper 111 per each plate 105, there may be several liquid drippers 111 per each plate 105, or there may be one liquid dripper per several of plates 105.

[0052] The term “liquid channel” refers herein to any mechanism for carrying out a liquid flow, such as a tube, an open channel, or similar.

[0053] Throughout this application, similar reference numbers appearing in the various embodiments relate to components of similar functionalities, respectively.

[0054] In the embodiment of FIG. 1, the main reservoir 113 is located at the top of the apparatus 100. In another embodiment 300 shown in FIG. 2, the main reservoir 313 is located at the bottom of the apparatus. Pump 319 is used to raise the liquid towards drippers 311. For a sake of brevity, the additional components whose function is similar to those of FIG. 1, will not be discussed in more details.

[0055] FIG. 5 shows a cooling apparatus 500 which includes a top main reservoir 513 and a bottom recycling reservoir 514.

[0056] Apparatus 500 is similar to the apparatus 100 of FIG. 1, however, with two reservoirs. Excessive coolant which is dropped over the heatsinks and not evaporated is accumulated within the bottom recycling reservoir 514 for recycling. One or more check valves 516 are repeatedly opened to allow the recycled coolant to flow back into the top main reservoir 513.

[0057] FIG. 6 shows a cooling apparatus 600 with a bottom recycling reservoir 614 and a top main reservoir 613. The apparatus further includes a compact pump 619. Pump 619 is substantially made of two components: a ferromagnetic core 618, an electric coil 617, an upper check valve 616a and a lower check valve 616b. The ferromagnetic core may be made, for example, of iron. Ferromagnetic core 618 has a diameter somewhat smaller than the internal diameter of liquid channel 615, and is located within the liquid channel (in contact with the recycled coolant). When electric current flows through coil 617, core 618 is pushed up, thereby also pushing the recycled liquid, that opens both check valves 616a and 616b (that are normally closed, and are configured to open upon a flow of liquid (in this case in the up direction). When the current is off, core 618 sinks down to rest on the lower check valve and both check valves 616a and 616b close.

[0058] As will be discussed in more details hereinafter with respect to FIG. 3, when the apparatus is combined with a garment article which covers the hot side (such as a shoe), ventilation holes may be provided in the garment such that the evaporated coolant is removed from the apparatus (such as 310 in the shoe shown in FIG. 3) while improving the overall efficiency of the heat removal. Another option is to condense the coolant that is evaporated and recycle it.

[0059] FIG. 2 shows an embodiment 300 with a bottom reservoir. The embodiment 300 is essentially identical to the embodiment 100 of FIG. 1, however, while in the embodiment of FIG. 1 the reservoir 113 is positioned at the top of the apparatus, in the embodiment of FIG. 2 the reservoir 313 is positioned at the bottom, while pump 319 is used to raise the coolant into liquid channel 306, and spray or drizzle (or dispense in any other way) it via one or more of the nozzles 311.

[0060] The embodiments of FIGS. 1 and 2 preferably recycle the coolant, in order to save weight and coolant volume. In the embodiment of FIG. 1, a pump (not shown) may be used to lift the excess of coolant that was not evaporated and drained into a lower reservoir (also not shown) to the top reservoir 113. In the embodiment of FIG. 2, the pump 319 lifts the coolant towards the nozzles 311, from which the liquid goes back down by gravity, thus completing the recycling process. In some embodiments, the user's movement assists in raising the liquid up with a further assistance of one or more check valves, replacing the pump. For example, the pressure applied by the user's foot may assist in pumping the coolant upwards towards the nozzles. Other random motions may also raise the liquid through the check valves.

[0061] FIG. 3 schematically shows a side view of a shoe which is integrated with a cooling apparatus 300 such as shown in FIG. 2. The apparatus 300 cools down the lower part of a wearer's leg (the Achilles tendon, the ankle, and the foot). The shoe 400 contains a series of Peltier plates 305 with their cold side facing the leg, and one or more check valves 403. Check valve 403 allows coolant to drain into the lower reservoir 313. When the leg is lifted up, the spring 402 lowers the pressure in the lower reservoir 313. This facilitates the entry of the drained liquid through the check valve 403. A check valve 404 is opened when the foot is down allowing the liquid to go up into the nozzles 311. The shoe 400 does not need an electrical pump for its operation, as each step of the user applies a force on the bottom section of the shoe, which causes a dose of liquid to flow from reservoir 313 upward through liquid channel 306 towards liquid drippers 311 (only one liquid dripper 311 is shown, for the sake of brevity). The liquid is sprayed to cool the heatsink 307 and excessive of it falls downwards. Additional elements, such as a control unit, a switch, and a pump may also be included within the shoe 400 (but are not shown, for the sake of brevity). The battery is also not indicated, as it may be included within the shoe, or external to the shoe or can be used in combination with solar panels. Ventilation holes 310 are provided such that at least a portion of the evaporated coolant is removed from the apparatus while improving the overall efficiency of the heat removal. The coolant can be added through the sealable opening 405.

[0062] FIG. 4 illustrates a structure of TECs array, according to an embodiment of the invention. The exemplary array 200 has 25 Peltier plates 202.sub.1,1 to 202.sub.5,5 that are arranged in rows and columns. Each of the series of the plates 202 is mechanically connected with a coolant liquid impermeable fabric 225 (or any other medium that is impermeable to the coolant). The impermeable fabric 225 can be connected at any place between the Peltier plates, but placing it between the wet (hot) side of the plate and the dry (cold) side can serve two purposes: separating the hot and the cold sides, and separating the wet and the dry sides. Alternatively, separate thermal insulator and coolant impermeable materials may be used. Each of the Peltier plates 202 is connected to a battery or a power supply via positive and negative lines 208 and 210, respectively. The Peltier plates may be connected either in a parallel form, in a serial form, or a combination of serial and parallel connections. The example of FIG. 4 shows a combined connection in which the plates in each row are connected in series, while all the 5 rows are connected in parallel. Preferably, the exact type of electrical connection which is selected is the one which optimizes the energy consumption and cooling. The structure of all the connected plates forms a roughly unified cooling array. The cooling array may contain an ON/OFF switch (not shown), and optionally also a cooling regulator or control system (not shown), such as a potentiometer, for regulating the level of cooling by adjustment of the DC voltage that is applied on the plates or several batteries, that can be switched ‘on’ or ‘off’ so that the number of batteries that are ‘on’ determine the voltage level on the Peltier plates.

[0063] As noted above, the present apparatus is designed to provide a prolonged cooling. It is known that the coefficient of performance (COP) of Peltier plates has a maximum at some low power, i.e. low voltage and current (the exact values of which depends on the type of the plate). The COP is the ratio between amount of heat transferred by the Peltier plates and the energy consumption of the plate. Other prior art cooling devices (either stationary or portable) tend to use a much higher power and low COP so that the cooling rate will be maximal regardless of the COP efficiency. In this invention, however, the tendency is to use a relatively low power (low voltage and current) and to be closer to the COP maximal value. This provides higher energetic efficiency and longer working time. The cooling rate can still be rather high due to the evaporation of the coolant that adds to the cooling rate.

[0064] It is expected that with a battery having dimensions similar to those of a conventional portable phone, the apparatus may provide a cooling temperature which is more than 10° C. lower than the ambient temperature, and this cooling may be provided to a duration up several hours.

[0065] It should be noted that the one or more of the containers (top or bottom) may be located external to the apparatus. Moreover, the array may include one or more Peltier plates. For the sake of brevity, the term “array” is used herein even when only one Peltier plate is included within the array.

[0066] In some alternatives, the type of heatsinks and liquid channels may vary. For example, the heatsink may be in a form of a wet fabric, where coolant is dripped on the fabric. In another alternative, the tubing may partially or entirely pass through internal liquid channels within the heatsinks. This can eliminate the need for external drippers as the liquid oozes/seeps out of the pores in the heatsinks.

[0067] Another embodiment is using TECs that only have a wet cloth as a heat sink, or a solid heat sink that is made with pores into which liquid can enter and from which liquid can evaporate.

[0068] As explained above, the cooling device is designed to benefit from a phase transition of a liquid coolant delivered at the hot side of the TEC array. When the liquid coolant is supplied to the hot side of the TEC array, it removes heat, transforming into vapors (the quantity of heat removed is known as latent heat of evaporation). The cooling device of the invention is configured to enable the escape of these vapors, such that the heat generated is released away from the device, dissipating in the environment.

[0069] Suitable liquid coolants include, in addition of course to water, a mixture of water and isopropyl alcohol or ethylene glycol or any other substance or combination of substances that undergo liquid to vapor phase transition at temperatures close to room temperature. Latent heat of water at 28° C. is 2434.6 kJ/kg, the latent heat of ethylene glycol at the same temperature is 1057 kJ/kg and the latent heat of isopropyl alcohol at this temperature is 748.8 kJ/kg. The mixture of each of these alcohols with water creates a heat of vaporization (latent heat) that is between the corresponding two numbers. The advantage in mixing them comes from the increase in the rate of evaporation.

[0070] FIGS. 9A-9C illustrate another approach to the supply of the liquid coolant to the hot side of the TEC array, namely, an alternative to a design consisting of main tubing and drippers which drip the coolant onto the hot side, shown in previous drawings. FIG. 9A is a top view of the cold dry side of the TEC array, consisting of six TECs arranged in two parallel rows, electrically connected to a power source. A top view of the hot side of the TEC array is illustrated in FIG. 9B, showing the heatsinks deployed on the hot side of the TECs. The liquid coolant is supplied to the heatsinks with the aid of a liquid-absorbing layer attached to the heatsinks (e.g., a porous material whose pores can be filled up with the liquid coolant, for example, a sponge soaked up with the liquid coolant). FIG. 9C shows a side view of a cooling device 900 based on the “sponge” variant of the invention. Numerals 905, 905c and 905h indicate the thermoelectric modulus and its cold and hot sides, respectively. Heatsinks 907 (e.g., made of a plate with fins or pins, e.g., an aluminum plate, or any other geometry that allows an increase in the surface area and allows contact with a liquid) are placed on the hot side 905h, partially surrounded by the liquid absorbing layer 915, which is about 0.01 to 100 mm thick, depending on the intended use of the cooling device. Liquid impermeable layer 925, e.g., made of nylon or other flexible cloth that is impermeable to the coolant liquid used, prevents coolant liquid occupying the pores of layer 915 from crossing into the TEC array zone. Note that heat dissipating layer 920 is provided in the spaces between each individual TECs. It is seen that heatsinks 907 extend above the surface of the liquid absorbing layer 915, reaching a liquid permeable cover 916, to let vapors, generated in the cooling device upon evaporation of the liquid coolant, escape. For example, the ventilation function is achieved with cover 916 in the form of a net, or a sheet made of nylon mesh or a plastic cover or other materials with ventilation holes uniformly distributed over the sheet.

[0071] Another aspect of the invention is a method of cooling using a thermoelectric cooler, comprising passing an electric current through the thermoelectric cooler from a DC power source, to create a cold side and a hot side, drawing off heat from the hot side with the aid of one or more heatsink(s) coupled to the hot side (e.g., heatsinks in the form of a plate with fins or pins), wherein the cold side and hot side are separated by a liquid impermeable layer, characterized in that a liquid coolant is delivered to the heatsink(s), whereby said liquid evaporates and vapors formed escape to the surrounding environment (for example, through openings provided in a cover applied onto said heatsinks, or by partially or fully exposing the heatsinks to the surrounding environment).

[0072] Suitable TECs are usually square or rectangular in shape with length and width in the ranges of 10 to 40 mm and 10 to 40 mm, e.g., of 15 to 30 mm and 15 to 30 mm, respectively, including TECs of low quality, namely, high resistivity TECs, e.g., of 0.00375 to 0.00625 ohm/mm.sup.2, for example, of 1.95 ohm for 20 mm×20 mm TEC (nominal resistance). Either a single or a multistage TEC may be used.

[0073] A satisfactory cooling efficiency was measured when operating at voltages and currents of 0.5 V to 2 V, and 0.1 Amp to 0.5 Amp, respectively, with a fairly cheap, low quality (high resistivity) TEC; the resulting power consumption was usually about 0.05 to 1 Watt per a single TEC plate of 20×20 mm.

[0074] For example, we used an array of six TEC plates of 20×20 mm arranged in two parallel rows (three plates in each row). The rows were 10 mm spaced apart. The distance between the edges of a pair of adjacent TEC plates in a row was 10 mm. We glued a 21 mm×21 mm heatsinks with pins of 15.2 mm to the TECs and used the extra 1 mm margin to glue a vinyl tablecloth which served two purposes: (a) it was a water barrier that made sure that the cold side is dry; (b) it provided a structural base connecting the array. The vapors generated during operation were allowed to flow to the surrounding air without any restrictions.

[0075] As pointed out above, the liquid coolant can be delivered to the heatsinks by supplying the liquid coolant to a liquid-absorbing layer attached to said heatsinks, e.g., a sponge or a cloth soaked up with the liquid. Alternatively, the liquid coolant is delivered to the heatsinks by causing one or more liquid streams to flow in one or more tubes equipped with drippers/sprayers/nozzles directed to said heatsinks, or directed to the liquid-absorbing layer attached to said heatsinks, or by directly incorporating the liquid coolant into the heatsink (e.g., tubes installed internally within the heatsink, such that liquid coolant emerges from within the heatsinks, e.g., in the form of drops which undergo evaporation).

[0076] Another variant of the cooling device is based on using a liquid tank for delivering liquid to the heatsink through a liquid channel provided by a long narrow piece of wettable material with good liquid holding capacity and good liquid mobility, that is attached to the heatsink. This variant of the invention benefits from a combination of a liquid tank, that can supply liquid continuously to the heatsink, and the use of liquid-absorbing material in contact with the heatsink, that can wet the heatsink directly. In the description that follows, we refer to water as an example of the liquid that can be used, but aqueous mixtures are also meant to be included.

[0077] One design of the cooling device according to the variant set forth above is illustrated in FIGS. 11A and 11B. FIG. 11A shows heatsink 1, consisting of a plate (e.g., with the shape of a quadrangle such as a rectangle or a square, made of aluminum) with a plurality of fins 2 protruding from one face of the plate. The geometry shown in FIG. 11A is based on deploying the fins in rows and columns over one face of the plate, to cover about 30 to 70% of total area of the face of the plate 1. Water is held in, and supplied from, tank 4 that is adjacent to, or contiguous with at least one edge of heatsink 1, with a water channel in the form of a long narrow piece of wettable material with good water holding capacity and water mobility, e.g., a sponge strip, or a strip made of a suitable cloth (akin to clothes used in the manufacture of wet wipes), emerging from tank 4 and lying on the face of plate 1. For example, by capillary action, water moves along channel 3, from one end of the channel that is immersed in tank 4, to the opposite end. Water channel 3 has an appropriate geometry to maximize the contact of the water passing therethrough with the heatsink and at the same time maximize water evaporation to the surroundings.

[0078] For example, in FIG. 11A, water channel 3 has a serpentine-like shape, e.g., it rests on the surface of the heatsink and curves in alternate directions, in the spaces between the columns of the fins. Water channel 3 can touch and wet fins 2 directly, such that the contact of water channel 3 and heatsink 1 result in evaporation of water to the open atmosphere. Other useful geometries include a tree-like shape, i.e., with branches made of the wettable material distributed over the surface of the heatsink.

[0079] FIG. 11B is a schematic side view of the cooling device. It is seen that water tank 4 is placed beneath heatsink 1. The TEC 5 is attached to one face of the heatsink 1, whereas fins 2 and water channel 3 are provided on the opposite face of the heatsink 1. Water channel 3 is deployed in the spaces between the columns of fins, creating the serpentine-like shape that is seen in FIG. 11A.

[0080] As pointed out above, water channel 3 consists of a long, narrow piece of wettable material (good water mobility) with good water holding capacity. For example, the total length of the piece(s) of wettable material lying on the heatsink is at least twofold (e.g., threefold) longer than the side of the heatsink; the width of the piece(s) of the wettable material preferably does not exceed the height of the fins disposed on the heatsink; the thickness of the piece(s) of the wettable material preferably does not exceed the spacing between adjacent fins; the water holding capacity is at least two times, e.g., three times, the dry weight; and good water mobility indicates that the liquid channel enables capillary rise of water.

[0081] By way of example, when the area of the heatsink is roughly 4 cm.sup.2, the length of the water channel could be roughly from 4 cm to 13 cm, with width of 1 to 10 mm. The volume of water tank 3 is from 3 ml to 30 ml.

[0082] Thus, according to a preferred variant of the invention, there is provided a portable cooling apparatus comprising a liquid channel in the form of a narrow piece of wettable material emerging from the liquid reservoir and in contact with the heatsink. That is, the liquid channel has one end that is immersed in the liquid tank, to enable liquid flow along the channel by capillary action onto and along the heatsink.

[0083] FIGS. 12A and 12B show a modification of the cooling device of FIGS. 11A and 11B, i.e., with greater number of components as compared to the configuration of FIG. 11, i.e., two water tanks 4 and the three heatsinks 1. A heatsink with the TEC 5 attached to one of its faces is placed between two other heatsinks (i.e., the same plates with fins protruding from one of their faces, but without TEC being glued to the opposite face, as shown in FIG. 12B). That is, each of two opposing sides of the central square-shaped heatsink (the one equipped with a TEC) is aligned with a side of an adjacent heatsink. The set-up consisting of the three heatsinks can be assembled with the aid of flexible aluminium wires 6, glued or attached with a heat conducting material very close to the edges (top and bottom, respectively) of the square plates to join the three heatsinks. Akin to the design of FIG. 11, a sponge strip 3 rests on one face of the heatsink (the one with fins 2 deployed thereon), curving in alternate directions to create a serpentine-shaped path for the water to flow through and contact with the heatsink to maximize water evaporation. The experimental results reported below indicate the devices of FIGS. 11 and 12 both achieve good cooling effect.

[0084] Technological advantages of the present invention include a long period of operation, as opposed to the short duration of the melting prior art devices. Also, there is no necessity for a pre-operation stage. The operation of the apparatus of the invention is immediate compared to the prolonged freezing required for prior art devices.

[0085] Several experiments were performed that show advantages of the present invention, as reported in the experimental section below.

EXAMPLES

Example 1

[0086] A system with a top reservoir of 20 ml was prepared. The system dripped water at flow rate of 1.8 ml/min on a row of 3 heatsinks that were connected to 3 TECs. The water was collected at a lower reservoir from which it was recycled back to the top reservoir. Three 20 mm×20 mm×3.6 mm TECs were of model FPH1-7104NC, produced by Qinhuangdao Fulianjing Electronic Co., Ltd, China. Three 21 mm×21 mm×15.2 mm heatsinks of model H/S HO-HB-1106, produced by Antou Resource Inc., China, were supported on vinyl sheet. The three TECs were connected in series to a DC source which supplied 1.8 Volts and 0.19 Ampere—0.6 Volts on each TEC, or 0.114 Watts on each TEC. The temperature on the cold side of one of the TECs was measured. It was assured that the temperature remained stable for at least 20 minutes. The experiment was repeated with and without a fan. For the experiment with the fan, one fan was used, that faced the heatsink of the one TEC whose cold side temperature was measured. The fan drew a 5.25 Volts and 53 milli Ampere (0.278 Watt).

[0087] FIG. 7 is a bar diagram showing the measured ΔT between the cold side and the ambient air with and without a water spray on the heatsink. FIG. 8 is a bar diagram showing the measured ΔT between the cold side and the ambient air with and without a water spray on the heatsink, while a fan (as mentioned above) was used. The results of the experiments clearly indicate the beneficial effect gained from the evaporation of the liquid applied onto the hot side, i.e., an improved cooling.

Example 2

[0088] A single 20 mm×20 mm×3.6 mm TEC of model FPH1-7104NC, produced by Qinhuangdao Fulianjing Electronic Co., Ltd, China was glued to a single 21 mm×21 mm×15.2 mm heatsinks of model H/S HO-HB-1106, produced by Antou Resource Inc., China. The glue used was PRIMA-SOLDER™ (EG8020) produced by AI Technology, Inc. The sides of heatsink were partially covered with an absorbent cloth (Sano sushi cleaning cloths), by sewing it to the pins of the heatsink. The lower part of the cloth, which extended beyond the heatsink, was immersed in small puddle of water (1 ml, this amount of water reservoir was more than sufficient for the whole experiment). The water soaked by the cloth provided a continuous supply of liquid coolant throughout the experiment. The TEC was connected to a DC power source which was set on 0.7 Volts and 0.15 Ampere. The TEC cooled its colder side and its temperature was allowed to stabilize for 20 minutes. The stable temperature was recorded. The power supply was then set on 0.9 Volts and 0.21 Ampere and again the new temperature of the cold side of the TEC was recorded after 20 minutes. Similarly, the power supply was set on 1.2 Volts and 0.33 Ampere and the stable temperature of the cold side of the TEC was recorded. The results are shown in FIG. 10, as ΔT versus power plot (ΔT being the temperature difference between the cold side and ambient temperature).

Examples 3A and 3B

[0089] Devices were assembled based on the configurations shown in FIGS. 11 and 12 and were tested to determine their efficiency (Examples 3A and 3B, respectively).

[0090] As water reservoir, a tank with a shape of rectangular parallelepiped made of plastic was used (a single tank in the device of Example 3A, two tanks positioned one next to each other in Example 3B). The volume of each tank was 9 ml. Each tank had a 1 mm wide 6 mm long opening through which a strip of cloth of about 6 mm wide and roughly 200 mm long was passed (commercially available from Sano, Israel, multi-use cleaning cloth). Four of the six inner walls of the tank were covered by the cloth, such that the corners of the tank had a cloth touching them or placed very close to them, to enable an efficient drain off the water held in the tank.

[0091] A heatsink consisting of 20 mm×20 mm×9 mm anodized aluminium plate was used (purchased from Mouser Electronics). The fins protruding from one face of the aluminium plate were 6.5 mm high. The space between fins located in adjacent columns was 3 mm. A 15×15 mm TEC (purchased from Mouser Electronics) was glued (PRIMA-SOLDER™ (EG8050) purchased from AiTechnology) to the opposite face of the aluminium plate.

[0092] The device that was assembled and tested in Example 3A consisted of a single heatsink placed atop of a single water tank. In the device that was assembled and tested in Example 3B, the heatsink with the TEC attached to one of its faces was placed between two other heatsinks (i.e., the same anodized aluminium plates with fins protruding from one of their faces, but without TEC being glued to the opposite face, as shown in FIGS. 12A and 12B). That is, the opposing 20 mm sides of the central heatsink (the one with the TEC) are aligned with a 20 mm side of an adjacent heatsink. The set-up consisting of the three heatsinks was assembled with the aid of two 0.0403″ aluminium wires, that were glued very close the edges (top and bottom, respectively) of the square heatsinks plates using the same thermal glue, to join the three pieces. There was a 4 mm separation between edges of the central heatsink and edges of the adjacent heatsinks.

[0093] The cloth running from the opening in the top of the tank was formed into a serpentine-like shape, curving in alternate directions over the heatsink(s), as shown in FIGS. 11A and 12A, so that at least one side of every fin was in contact with the cloth. The tank was filled with water; water flow by capillary action occurred, from the tank through the cloth to the heatsink.

[0094] Then, the TEC was connected to a power source, and the temperature was measured. Water evaporated from the sponge attached to the heatsink and from the continuously wetted heatsink to the ambient environment. The room was at 25° C. and at a voltage of 0.5 V and 1.15 Amp, the temperature of the cold side of the TEC went down to 12° C. and 8° C., for Examples 3A and 3B, respectively, and remained stable for the duration of the experiment (77 minutes).