Heat pump metal hydride

DOE, through Brookhaven National Laboratories, has recently issued a contract for an industrial team to design, build, and test a prototype metal hydride heat pump for residential, commercial or industrial applications. This three-year program is intended to assess the commercial viability of this technology. 

Metal hydride sorbers were in a composition of experimental installations [4, 5] based on the metal hydride heat pump. Here we shall consider in detail features of one of installations for cold generation [4] (Fig. 3) using waste heat - hot water with temperature 80-90°C - as an energy source simulator. 

The main units of installation are sorbers forming two units of a metal hydride heat pump. Sorbers of the first unit are modular-type. Modules of the first unit sorbers have seven thin-walled steel tubes 25 mm in diameter. When installation works, water is run through a sorber case and flow around external surface of modules heating or cooling them. 

Astahov, B.A., Afanasjev, V.A., Bokalo, S.J., et al. (1999) Creation of smallsized refrigerating installations with a metal hydride heat pump. - 6th NATO Int. Conf. Hydrogen Material Science and Chemistry of Metal Hydrides ", ICHMS 99. Abstract Book of NATO International Conference. Katsiveli, Yalta, Ukraine, September 02-08, 1999, 306-307 (in English and Russian). 

Suda, S., Recent advancements of metal hydride heat pump developments. Chemical Engineering (Japan), 1983, 18 p. 1-29. 

The reversibility of the metal-hydrogen reaction (Eq. l) and the heat of chemical reaction (Eq. 2) provides the basis for hydride heat pumps. These devices are closed units in which hydrogen serves as an energy carrier between two or more hydride beds. By selecting appropriate hydriding alloys, heat sources and heat sinks, heat can be pumped over wide temperature differentials with no moving parts except possibly check valves. 

Application of hydride heat machines (the HHM - the hydride heat pump (HHP), a refrigerator, a heat transformer, the compressor, the accumulator of hydrogen) is justified there where there are sources of low-potential energy or a plenty of wasted heat is not used. Systems hydrogen-metal hydrides promote improvement of ecological conditions and introduction of cleaner hydrogen technologies. 

Shanin, Yu.I. (2002) Simulation of hydride heat pump operation with reference to vehicle refrigerating devices. - In Veziroglu TN, Zaginaichenko SY, Schur DV, Trefllov VI editors/Hydrogen Materials Science and Chemistry of Metal Hydrides. NATO science series. Series II Mathematics, Physics and Chemistry, 82, 97-106. 

Hydrogen-storage alloys (18,19) are commercially available from several companies in the United States, Japan, and Europe. A commercial use has been developed in rechargeable nickel—metal hydride batteries which are superior to nickel—cadmium batteries by virtue of improved capacity and elimination of the toxic metal cadmium (see BATTERIES, SECONDARYCELLS-ALKALINe). Other uses are expected to develop in nonpolluting internal combustion engines and fuel cells (qv), heat pumps and refrigerators, and electric utility peak-load shaving. 

There are two basic cycles for heat pump operation conventional (15) and temperature upgrading (3, J/[). It is convenient to visualize the operation of these cycles by following the changes in pressure and temperature of each alloy on a Van t Hoff plot. For ease of narration, these curves are idealized. Many engineering properties of metal hydrides must be considered in a detailed explanation (e.g., hysteresis, plateau slope, cyclic stability, etc.). The two cycles are shown in Figure 17. 

Sheft, I. Gruen, D.M. and Lamich, G. "HYCSOSiA Chemical Heat Pump and Energy Conversion System Based on Metal Hydrides" 1979 Status Report, Angonne National Laboratory Report ANL-79-8. 

Ternary Metal Hydrides as Chemical Heat Pumps... 

To choose metal hydride pairs efficiently for heat pump operation, the relationships among the thermodynamic quantities that govern Reaction 1 and the values for Th, Tm, and T should be established. Three examples for the relationships between thermodynamic quantities of Mi and M2 are shown in Figure 3. These are the only possibilities that simultaneously satisfy the condition P(M2) > P(Mi) for any given 1/T > 0. 

Many AB5 hydrides have AH 8 kcal so that at 0-100°C (of interest for chemical heat pump action), the hydrogen dissociation pressures change roughly by one order of magnitude. This implies that a metal hydride pair could function in the heat pump mode even if their enthalpies were exactly the same, provided... 

For successful use of metal hydrides as chemical heat pumps, alloy systems should allow for changes in the free energies of formation continuously over a wide range. Given a particular hydride, it would be possible to specify AH and AS of a second hydride to reach a given Th and Tj. Recent work in our laboratory has shown that LaNi5 xAlx alloys provide a close approach to such a system (27). 

Metal hydrides that have a linear dependence of In P vs 1/T can be used in chemical heat pump systems. General equations were developed to relate the thermodynamic variables of the hydrides to the chemical heat pump operating temperatures. A series of hydrides with variable thermodynamic properties were prepared from alloys of composition LaNi5-x Alx (x = 0-1.5). 

Suda, S., Komazaki, Y., Narasaki, H., Uchida, M. (1991) Development of a double-stage heat pump experimental and analitical surveys, J Lesson-Common Metals, 172-174,1092-1110 Energy conversion systems using metal hydride, Z. fur Physikalische Chemie Neue Folge. 1989,164, 1463-1474. 

Shanin, Yu.I. (1997) Choice of hydrides for two-stage hydride chemical heat pumps. - In abstract book 5th international conference "Hydrogen materials science and chemistry of metal hydrides . (ICHMS 97) (Katsiveli, Yalta, Ukraine, September 02-08, 1997), p. 256. (In Russian and English). 

Hot water thermostat, tank of cooling water, pumps for water pumping, gas and hydraulic main pipes and control instrumentation are parts of installation beside sorbers. Units of installation operation have cyclic character. In the first half-cycle, hydrogen is absorbed by metal hydride of a low-temperature sorber. Released heat is removed by flowing water with temperature 10-15°C. Hydrogen in a low-temperature sorber comes from a high-temperature sorber, where it is desorbed due to heating by hot water. 

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