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Thermal Modeling and Performance Investigation of a Double-Stage Metal Hydride-Based Heat Transformer

In this manuscript, a two-dimensional thermal model of a double-stage metal hydride-based heat transformer (DS-MHHT) working with LaNi4.7Al0.3, LaNi5, and MmNi4.6Al0.4 (low-/intermediate-/high-pressure hydride alloy) is presented. The performance of the DS-MHHT is predicted by solving the conjugate heat and mass (hydrogen) transfer equations in cylindrical coordinates. The variation in reaction bed temperature, hydride concentration, and equilibrium pressure over a complete cycle is presented. Further, the variation in heat transfer fluid (HTF) temperature at the outlet of the reaction bed and the net amount of heat exchange between the reaction bed and the HTF over a cycle is presented. The performance of the DS-MHHT, such as coefficient of performance (COP HT), specific heating power (SHP), and second law efficiency (η E) is estimated at different heat output (T H), heat input (T M), and heat rejection (T L) temperatures. The effect of half-cycle time on COP HT, SHP, total heat output, and amount of hydrogen exchanged between the paired reactors is also presented. COP HT and SHPwere found to increase with T M while η E decreased with T M.