Studies on thermodynamic performance of three stage sorption heat transformer

Abstract

In the present study, a novel four alloys three-stage hydrogen based sorption heat transformer (4A – HSHT) is proposed to achieve higher heating output and efficiency with wide range of operating temperatures. The 4A – HSHT system can able to produce multiple heating outputs compared to conventional single stage metal hydride heat transformer (MHHT) with higher COP. The screening of metal hydrides is carried out to identify the best suited working pair for 4A – HSHT which results in the pair of La0.9Ce0.1Ni5 – MmNi4.4Al0.6 – LaNi4.7Al0.3 – MmNi3.7Co0.7Mn0.3Al0.3 hydrides for operating temperature range of 180 °C for heating output, 140 °C for heat supply and 45 °C for heat sink. The thermodynamic performance of 4A – HSHT is investigated using experimentally measured pressure concentration isotherm (PCI) and thermodynamic properties of chosen metal hydrides. The thermodynamic performance i.e. COP, specific heat output and heating capacity are estimated as 0.75, 81.8 W/kg and 0.9 kW, respectively for 2.75 kg of each alloy with 64 min of cycle time followed by the discussion on effects of heating output temperature on COP and specific heat output. The detailed flow chart demonstrating the methodology of material selection and thermodynamic simulation is presented. In addition, the various issues related to the implementation of practical devices based on metal hydride sorption systems are discussed including recent developments.