Comparative optimization of the thermal performance for H2 – Metal hydride heat storage and heat pump systems

Abstract

Metal hydride is very promising in hydrogen storage and simultaneously the thermal effect in the reversible hydrogenation process makes it possible in heat storage and heat pump area. The interaction of H₂ – Metal – hydride pair and its further applications need comprehensive thermodynamic design and performance optimization. Therefore, this work makes thermodynamic comparative research of heat storage and heat pump systems by adopting H₂ – Metal-hydride pair. According to the investigation, the thermodynamically optimal charging-discharging temperatures ($T_{m1},T_{m2}$), the heat source temperature ($T_{h1}$) and the ambient temperature ($T_{c1}$) meet the relationship of $T_{m1}{T}_{m2}=T_{h1}{T}_{c1}$ for the heat storage system. Given the operating pressure (p), there exists a well-matched temperature (T) range to maximize the exergy performance of metal hydride heat storage system. Meanwhile, the running p-T is positively correlated, e.g., when the charging pressure is set at 0.2 MPa to 0.3 MPa, the well-matched T varies from 307 K to 317 K. When the discharging pressure is set at 0.4 MPa to 0.7 MPa, the well-matched T varies from 304 K to 320 K. For the metal hydride heat pump system, the optimal performance lies in maximizing the transported heat. Given the operating T, there exists a well-matched pressure range for the heat sink device, e.g., for the heat releasing process, when operating T is set at 353 K, 363 K, 373 K, 383 K and 393 K, the well-matched p are 2.3 MPa, 3.3 MPa, 3.8 MPa, 4.6 MPa and 6.1 MPa. Both the heat storage and heat pump performances are also affected by the operating pressure – temperature −transported heat, presenting improved region and degraded region. The optimal thermodynamic criterion and the matchability of the operating parameters provide a theoretical guidance for the MH-based thermodynamic system design and operation.