M. Prakash Maiya

Parametric studies on a metal hydride based single stage hydrogen compressor

Abstract Influence of operating parameters such as heat source and sink temperatures, operating pressures, pressure ratios, cycle time, and bed parameters such as overall heat transfer coefficient, bed thickness and thermal conductivity, on the performance of a single stage hydrogen compressor is presented. Coupled heat and mass transfer and reaction kinetics are considered for the analysis. An AB2-type alloy, Ti0.98Zr0.02V0.43Fe0.09Cr0.05Mn1.5 is chosen as an example. At a given pressure ratio, the hydrogen throughput increases with hot fluid temperature and decreases with increase in cold fluid temperature. Optimum values of thermal conductivity and overall heat transfer coefficient exist for any given hot and cold fluid temperatures. Among the variables studied, heat transfer fluid temperature, bed thickness and supply pressure are found to exert significant influence on the compressor performance.

Performance analysis of a single stage four bed metal hydride cooling system, part A: influence of mass recovery

The concept of mass recovery in metal hydride systems is studied with a single stage multi-bed cooling system as example. Mass recovery results in variation of bed temperatures due to removal or addition of heat of desorption or absorption respectively. Coefficient of performance and cold output increase while required heat input decreases for the mass recovery cycle. Thus mass recovery between hydride reactors is found to improve system performance compared to that of a basic system.

Performance analysis of a single stage four bed metal hydride cooling system, part C: influence of combined heat and mass recovery

The effects of combined heat and mass recovery on the performance of a single stage multi-bed metal hydride cooling system is studied. A combined recovery cycle which effectively utilizes the advantages of both heat recovery and mass recovery is described. Reduction in sensible heating and cooling requirements along with increased hydrogen desorption results in improvement of coefficient of performance. Operating temperatures exert significant influence on the performance of combined recovery cycle. It is found that combined recovery is more effective at lower heat source temperatures and also at higher intermediate temperatures.

Parametric studies on a heat operated metal hydride based water pumping system

Abstract The principle of metal hydride based thermal sorption compressor is adapted for water pumping application. Desorption of hydrogen at high pressure and its absorption at low pressure by a metal hydride are used to expand and contract a bellow which pumps an equivalent amount of water. A part of the pumped water is used to cool the bed to facilitate the absorption process, simultaneously yielding warm water. A parametric study is carried out for mischmetal alloy (MmNi4Al) at various pump heads, warm water temperatures, dead volumes of bellow and heat loss through bellow. It is observed that hydride based water pumping is suitable for ‘low discharge and high head’ conditions, particularly due to its capability to heat a portion of pumped water.

Metal hydride water pumping system for low head-high discharge applications

Abstract A metal hydride water pumping system for low head and high discharge applications is analyzed. A gear system converts the large desorption to absorption pressure differential into large volume displacement. A parametric study is carried out for LaNi 5 alloy for various pump heads, absorption temperatures and gear ratios. It is observed that higher the desorption temperature, the higher is the optimum desorption pressure maximizing the specific water discharge.

Analysis of a metal hydride cold storage module

The concept of using metal hydrides in cold storage modules is discussed. Refrigeration can be stored in such modules at ambient temperature for subsequent cooling applications. Analysis of a system based on ZrMnFe/LaNi5 is done for various operating conditions and its performance characteristics are presented. Optimum heat source temperatures to yield maximum COP are computed. In view of the high cost of hydrogen valves, cold storage module without hydrogen valve is also comparatively studied.