Thermal Modeling and Performance Investigations of Metal Hydride Based Heat Pumps

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The use of Chloro-Fluro-Carbon refrigerants (CFCs) is a significant source of pollution to the global environment and an attempt is being made to minimize this problem through the promotion of the alternative refrigeration and air-conditioning systems. One of the most promising alternatives is the use of hydrogen as a refrigerant in the thermally driven metal hydride based heating and cooling systems. These systems provide a wide operating temperature range and use low grade thermal energy (e.g., waste heat from industries, heat from the exhaust flue gases and solar energy) to produce high quality thermal energy and cooling outputs. Further, these systems are environment friendly, contain no moving parts, have a compact construction and offer noise free operation. Absorption and desorption of hydrogen to/from the metal hydride are exothermic and endothermic reactions, respectively. The performance of such devices highly depends on the rate at which the heat is removed/supplied from/to the metal hydride beds. Development of an efficient and economic design of such devices requires highly sophisticated computational methods. Therefore, it is necessary to carry out the mathematical modeling before conducting the expensive experiments. Many investigators have predicted the heat and mass (hydrogen) transfer characteristics of metal hydride beds [e.g., Mayer et al. (1987), Groll et al. (1987, 1993), Gopal and Murthy (1992, 1995)] using various simplifying assumptions, such as, the use of one-dimensional model without considering the effect of hysteresis and plateau slope in the pressureconcentration- temperature (PCT) curve, neglecting the variation in the heat transfer fluid temperature along the axial direction of the reactor, etc. Such simplified models reported in the literature have limited scopes. Further, there is a lack of literature on thermal modeling of metal hydride heat pump (MHHP)....
Supervisor: P. Mutthukumar & Anupam Dewan