Abstract:
An air conditioner for an automobile includes two pairs of hydrogen storage cells. Each cell includes a hydride-forming material, which absorbs hydrogen while generating heat, and releases hydrogen while absorbing heat. One pair of cells operates as an air conditioner, absorbing heat from the interior of the automobile and discharging heat to the outside. The other pair of cells is regenerated by supplying heat from the engine exhaust to one of the cells, while allowing heat generated at the other cell of the pair to be discharged to the outside. A system of valves is arranged such that one cell pair is always functioning as an air conditioner while the other cell pair is being regenerated.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a heat pump for cooling an automobile. The heat pump is driven by waste heat from the engine. The present invention eliminates the need for a compressor. In conventional air conditioners, a compressor consumes a significant part of the engine horsepower. The present invention also eliminates the need for chlorofluorocarbons, which destroy ozone in the upper atmosphere. 
     A typical heat load for an automobile air conditioner is 12,000 BTU per hour. It takes about 18,000 BTU per hour to drive the heat pump of the present invention. A typical engine produces about 11 pounds of exhaust gas at 500° C. per horsepower-hour. Thus, if the engine is operating at 20 horsepower, and the gas is cooled by 200° C., the amount of heat produced by the engine, per hour, is 
     
         (20 hp)(11 lb/hp/hr)(200° C.)(0.45 Btu/lb/°C.), 
    
     where 0.45 Btu/lb/°C. is the specific heat of air. The above expression equals 19,800 Btu per hour, which is sufficient to drive the heat pump. 
     An essential component of the heat pump of the present invention is the hydrogen storage cell described in U.S. Pat. No. 4,599,867. The cell comprises a nest of metal fins that are traversed by tubes that carry a heat transfer fluid. The fins are coated with a metal hydride or with a metal capable of forming a hydride. Also essential to this heat pump is U.S. Pat. No. 4,799,360, entitled &#34;Method of Binding a Metal Hydride to a Surface&#34;. The disclosures of the above-cited patents are incorporated by reference herein. 
     SUMMARY OF THE INVENTION 
     In the preferred embodiment, the present invention includes two pairs of hydrogen storage cells. All of the cells are substantially identical, and can be constructed according to the teachings of the above-cited patents. The cells are connected, in a manner to be described, with first, second, and third heat exchangers. The first heat exchanger continuously absorbs heat from the interior of the automobile. The second heat exchanger continuously rejects heat to the ambient air outside of the automobile. The third heat exchanger continuously absorbs heat generated by the engine. A heat transfer fluid circulates between the cells and the heat exchangers. There is also a hydrogen conduit connecting the two cells of each pair. 
     The invention also includes an arrangement of valves for routing the flow of heat transfer fluid between the heat exchangers and the hydrogen storage cells. The connections are made as follows: 
     
         ______________________________________      During any  During the next      interval of time                  interval of time______________________________________First exchanger:        First cell of the                      First cell of        first pair    the second pairSecond exchanger:        Second cell of the                      Second cell of the        first pair, and                      second pair, and        first cell of the                      first cell of the        second pair   first pairThird exchanger:        Second cell of the                      Second cell of the        second pair   first pair.______________________________________ 
    
     The operation of the apparatus is summarized as follows. The first exchanger absorbs heat from the interior of the automobile, and this heat is conveyed to the first cell of the first pair of cells. When the cell absorbs heat, it releases hydrogen, and this hydrogen is conveyed to the second cell of the first pair of cells. The hydrogen is absorbed by this second cell, which generates heat, and this heat is discharged to the outside by the second heat exchanger. 
     While the first cell pair is operating as an air conditioner, the second cell pair is being regenerated. Heat from the engine exhaust is absorbed by the third heat exchanger, which conveys this heat to the second cell of the second pair of cells. This second cell releases hydrogen which is conveyed to the first cell of the second pair of cells. The latter cell absorbs the hydrogen, releasing heat, and this heat is discharged to the outside by the second heat exchanger. 
     Periodically, the valves are switched to their second position. In the second position, the second cell pair is connected to do the air conditioning and the first cell pair is regenerated, in the same manner as described above. Then, after a predetermined interval, the valves are switched again to their first position. Because the valves are continuously switched back and forth, at predetermined intervals, the air conditioner can operate without interruption. 
     It is therefore an object of the invention to provide an air conditioner for an automobile, in which the air conditioner uses the principle of hydriding and dehydriding to pump the heat. 
     It is another object to provide an air conditioner for an automobile that is driven by waste heat in the exhaust gas. 
     It is another object to provide an air conditioner for an automobile, wherein the air conditioner includes two pairs of hydrogen storage cells, and wherein one cell of each pair is always being regenerated, so that the air conditioner can operate substantially without interruption. 
     It is another object to provide a heat pump that can be driven by waste heat from any source. 
    
    
     It is another object to provide a heat pump that is compact. 
     Other objects and advantages of the invention will be apparent to those skilled in the art, from a reading of the following brief description of the drawings, the detailed description of the invention, and the appended claims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram showing the essential components of the invention, wherein the valves are shown in the first of two possible positions. 
     FIG. 2 is a schematic diagram, similar to FIG. 1, showing the valves in the second of two possible positions. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     When a metal absorbs hydrogen to form a hydride, heat is evolved. Conversely, when the hydride evolves its hydrogen, heat is absorbed. A metal hydride heat pump requires two hydrides. If the hydrides are at the same temperature, one of the hydrides must exert a higher pressure of hydrogen than the other hydride. Conversely, for a hydride at a given temperature, there exists another temperature, different from the first, such that another hydride operating at this second temperature will exert the same pressure as the first. Thus, the high-pressure hydride can evolve hydrogen at a low temperature, and absorb heat, while the evolved hydrogen is being absorbed by the low-pressure hydride at some higher temperature, where the heat is being rejected. In the present case, the lower temperature is somewhat below that inside the automobile, and the higher temperature is somewhat above that of the air outside the automobile. 
     A pair of hydrogen storage cells therefore can function as an air conditioner, as follows. One of the cells absorbs heat from the interior of the automobile, thereby giving off hydrogen. The evolved hydrogen is absorbed by the other cell, thereby causing that cell to release heat. If the heat given off by the second cell is discharged to the outside, there is a net transfer of heat from the interior to the exterior of the automobile. 
     In the arrangement described above, the hydrogen must periodically be evolved from the second hydride and reabsorbed into the first hydride. This process is called regeneration. Regeneration must be driven by heat available at a temperature above that of the ambient air. In the present invention, the engine exhaust is the source of this high temperature heat. To accomplish regeneration, the second hydride is heated, indirectly, by the engine exhaust, and the first hydride is cooled, indirectly, by the ambient air. 
     To provide continuous cooling, it is necessary to have first and second pairs of hydrogen storage cells. One pair performs the cooling while the other pair is being regenerated. At all times, heat is being absorbed continuously from the air inside the automobile, continuously rejected to the outside air, and continuously absorbed from the exhaust. The heat transfer is accomplished most efficiently by providing first, second, and third heat exchangers, one for each heat transfer task. Each exchanger operates at a constant temperature, so that it does not impose a parasitic cooling load when the hydrogen storage cells alternate between cooling and regeneration. It is only necessary to reroute the flow when the cells switch from cooling to regenerating. 
     FIG. 1 shows the essential components of the invention in schematic form. There are four hydrogen storage cells, identified by reference numerals 10, 11, 12, and 13. Cells 10 and 11 form the first pair of cells, and cells 12 and 13 form the second pair. Cells 10 and 11 are connected by a hydrogen conduit, represented symbolically by dotted line 60. Cells 12 and 13 are similarly connected by a hydrogen conduit represented by dotted line 61. The construction of all of the hydrogen storage cells can be as described in U.S. Pat. No. 4,599,867. 
     Cells 10 and 12 are designated as the first cells of their respective pairs; cells 11 and 13 are the second cells of their pairs. In the figures, the pairs are identified by numbers (e.g. &#34;Pair 1&#34;) and the cells within a pair are identified by letters (e.g. &#34;Cell A&#34;). 
     There are three heat exchangers 20, 21, and 22. Exchanger 20 absorbs heat from the air inside the automobile. Exchanger 21 rejects heat to the outside air. Exchanger 22 absorbs heat from the engine exhaust. These exchangers can be of the type resembling automobile radiators, i.e. a nest of fins traversed by heat transfer tubes, but are not limited to a particular structure. 
     There are five valves, 30, 31, 32, 33, and 34, for routing the flow of the heat transfer fluid. FIG. 1 shows these valves in a first of two positions. There are also four check valves 35, 36, 37, and 38, which permit the fluid to flow in only one direction. There are three pumps 40, 41, and 42 for circulating the heat transfer fluid. 
     At the interval of time captured in FIG. 1, the cells and exchangers are connected as follows: 
     Cell 10 with exchanger 20 
     Cell 11 with exchanger 21 
     Cell 12 with exchanger 21 
     Cell 13 with exchanger 22 
     During this time interval, heat from the interior of the automobile is absorbed by exchanger 20, and transferred to cell 10. Cell 10 absorbs this heat and gives off hydrogen. The hydrogen is conveyed to cell 11, the second cell of the pair. Cell 11 absorbs the hydrogen while releasing heat, and this heat is conveyed to exchanger 21, which transfers the heat to the outside. Thus, cells 10 and 11, the first cell pair, function as an air conditioner. 
     At the same time, cells 12 and 13, the second cell pair, are being regenerated. Heat from the engine exhaust is absorbed by exchanger 22 and transferred to cell 13, the second cell of the second pair of cells. When heat is applied to cell 13, the cell gives off hydrogen, which is conveyed to cell 12, the first cell of the pair. Cell 12 absorbs the hydrogen, and gives off heat, and this heat is conveyed to exchanger 21, which transfers the heat to the outside. 
     During the next interval of time, the cells and exchangers are connected in this way: 
     Cell 10 with exchanger 21 
     Cell 11 with exchanger 22 
     Cell 12 with exchanger 20 
     Cell 13 with exchanger 21 
     This arrangement is shown in FIG. 2. In FIG. 2, the reference numerals are unchanged, as the components are the same. The only difference is in the position of the three-way valves. 
     In the valve position shown in FIG. 2, heat from the automobile interior is absorbed by exchanger 20 and conveyed to cell 12. This heat is absorbed by cell 12, which generates hydrogen. The hydrogen is conveyed to cell 13, which absorbs the hydrogen, and gives off heat. This heat is discharged to the outside, through exchanger 21. 
     At the same time, as shown in FIG. 2, heat from the automobile exhaust is absorbed by exchanger 22, and conveyed to cell 11. This heat is absorbed by cell 11, which gives off hydrogen, and the hydrogen is carried to cell 10. Cell 10 absorbs the hydrogen, and gives off heat which is discharged to the outside through exchanger 21. 
     Thus, in FIG. 2, cells 12 and 13 comprise the pair which is doing the cooling, and cells 10 and 11 comprise the pair which is being regenerated. 
     The valves are periodically switched from the position shown in FIG. 1 to the position shown in FIG. 2, and back. Thus, at all times, there is one pair of cells doing the air conditioning and the other pair of cells being regenerated. 
     The same heat transfer fluid circulates through all of the cells and exchangers in FIGS. 1 and 2. Advantageously, this is the same glycol-water mixture that is used for engine coolant. In one embodiment, hot coolant from the engine could be used to drive the heat pump. 
     It would be possible to reconstruct FIGS. 1 and 2 so that each of the four cells has its own heat exchanger. The exchangers connected to cells 10 and 12 would alternate between being contacted with cool air inside the automobile and warm air outside the automobile. Cooling the mass of the exchanger imposes a parasitic load on the heat pump. The exchangers connected to cells 11 and 13 would alternate between outside air and exhaust gas. 
     There are several reasons to prefer the arrangement of FIG. 1: 
     1. There are three exchangers instead of four: 
     2. The parasitic load for cooling two exchangers is eliminated; 
     3. Only one exchanger must withstand hot, corrosive exhaust gas; 
     4. Each exchanger can be optimally sized to do just one task; and 
     5. Valves for routing heat transfer liquid are smaller and cheaper than valves for routing gases. 
     The five two-position three-way valves in FIG. 1 are the minimum number of valves needed to prevent the mixing of liquids circulating at different temperatures. Consider the circuit of cell 10, exchanger 20, and pump 40, in FIG. 1. All of the liquid emerging from cell 10 must return to the circuit via line 50. There is only a small amount of inout surge through line 51, because the lines are completely filled with liquid, and because there is no return path for the liquid. The same applies to the circuit of cell 13, exchanger 22, and pump 41. And, no liquid can escape from the circuit that comprises cells 11 and 12 in parallel, pump 42, and exchanger 21. It is important to prevent warmer liquid from mixing with the cold liquid that is circulating through cell 10, because this would create parasitic heat load. Check valves 35, 36, 37, and 38 are needed to prevent this mixing. 
     In the position represented by FIG. 2, fluid flows in line 51, but does not flow from cells 11 and 12 towards pump 42, because there is again no return path for the fluid. 
     Note that each of the heat exchangers 20, 21, and 22 is operating at a constant temperature, and does its heat transfer task continuously. If the heat exchangers were not at constant temperatures, one would need to expend energy to change the temperatures of the ex-hangers, and to do so would be wasteful. 
     This heat pump is not limited to cooling automobiles. Trucks, ships, and army tanks also need cooling. Some commercial buildings have waste heat that could drive a heat pump. 
     Although the invention has been described with respect to the particular embodiment shown, it is understood that other variations are possible. The invention is not limited by the types of valves or by the specific construction of the hydrogen storage cells. As stated above, other circuit topologies could be used. These and other modifications should be deemed within the spirit and scope of the following claims.