SBIR-STTR Award

This project will develop improved metal hydride materials for a new hydride heat pump that is environmentally clean and potentially twice as efficient as the best current systems. New thermodynamic processes have been developed for hydride heat pumps that are significantly more efficient and utilize no chlorofluorocarbons (CFCs), which must be phased out of use by 1995. The best current refrigerators operating with less damaging hydrochlorofluorcarbon (HCFC) refrigerants have a coefficient of performance or COP = 1.5, while the proposed new hydride heat pump has a theoretical COP = 3.3. Current research has demonstrated that hydride heat pumps are feasible and very promising, but improved hydride materials are needed to achieve their full potential. Improved hydride heat exchangers are needed that have more rapid heat transfer and hydrogen flow. Hydrides have low thermal conductivity so that rapid heat transfer into and out of the hydride bed is difficult. Also, hydride particles tend to become smaller and compacted during use and this blocks the free flow of hydrogen into and out of the hydride bed. In Phase I the approach to the improved hydride materials involves coating the metal hydride particles with a thin layer of copper and then compressing the coated particles into porous heat exchangers which can provide more rapid and effective heat transfer and hydrogen flow. When developed, this technology will allow nearly a 50Wo reduction in the electric power required by refrigerators/freezers, air conditioners, and heat pumps used in both domestic and commercial applications including vehicles. The new system will be smaller, weigh less, and cost about the same as conventional refrigeration equipment. The system does not require CFCs or HCFCs, so it is inherently clean and has no adverse environmental impact. Anticipated Results /Potential Commercial Applications as described by the awardee:Phase I will develop, build, and test improved hydride materials and heat exchangers optimized for a new high performance hydride heat pump. Based on the positive results of preliminary research, it is anticipated that the research will develop improved hydride materials and highly effective hydride heat exchangers that will allow nearly the full potential of the more efficient hydride heat pump to be realized.

An efficient hydride reactor is necessary to allow an environmentally clean hydride heat pump to achieve its potential to be twice as efficient as current systems. A practical and cost effective method of coating hydride particles with high thermal conductivity copper and then compressing and sintering them into porous powder metal hydride (PMH) compacts with improved heat transfer was developed in Phase I. Thermal conductivity, k = 7.5 W/møC was measured on green PMH compact pellets, a factor of 18 better than that of uncoated hydride particles. Transient analysis of reactor performance with a numerical code indicates only k = 5 W/møC is required to achieve an adequate heat transfer rate for the heat pump. Further optimization of the PMH compacts is needed to improve thermal conductivity to 10 W/møC which will provide excellent heat pump performance. Phase I results are highly promising. Phase II will further develop the PMH compacts into the shape of disks that can be press fit into a hydride reactor. The PMH compact disks will have grooves to improve hydrogen flow and win have thermal conductivity of at least 10 W/møC. PMH compact disks with embedded high thermal conductivity fibers will be explored as composite structures with high thermal conductivity and strength. Hydride reactors with these PMH compact disks will be built and tested for thermal performance. The numerical analysis code for heat driven hydride reactors will be rewritten to describe the more promising compressor driven hydride heat pump. The performance of the hydride heat pump including electric energy consumption, cooling rate, coefficient of performance, weight, volume, cost, and life cycle cost will be predicted and compared both with the experimental test data and with performance data of conventional vapor compression systems.Anticipated Results/Potential Commercial Applications as described by the awardee: Optimized hydride reactors will allow the environmentally clean hydride heat pump to provide a nearly 50% reduction in the electric power required by refrigerator/freezers, air conditioners, and heat pumps, used in both domestic and commercial applications including vehicles. The new system will be smaller and have lower life cycle costs than conventional systems. The system is inherently clean and has no adverse environmental impact. These advantages provide a strong incentive to develop the hydride heat pump to its full potenti