Performance analysis of multi-salt sorbents without sorption hysteresis for low-grade heat recovery

Three types of consolidated compact composite multi-salt sorbents are studied, which are mixtures of NH4Cl, CaCl2 and MnCl2 with different proportions. The Clapeyron curves under non-equilibrium conditions and isobaric sorption/desorption curves are tested. The multi-salt sorbents show combining properties of NH4Cl, CaCl2 and MnCl2 at different temperatures. One distinguished feature of these three types of multi-salt sorbents is the disappearance of sorption hysteresis. However, there are some differences in cycle sorption quantities, which may influence refrigeration and energy storage performances for different types of multi-salt sorbents. The behaviors of different types of sorption working pairs are analyzed for continuous sorption refrigeration cycle and energy storage system. Results indicate that the multi-salt sorbents are more suitable for variable temperature heat source and low-grade heat recovery than single salt sorbents. The NH4Cl/CaCl2/MnCl2 mixture with the mass ratio of 1:3:2 generates more cooling power than the other two with similar coefficient of performance (COP), while the multi-salt sorbent with the mass ratio of 3:2:1 is optimal for the thermochemical sorption energy storage system. Analysis of exergy efficiency and exergy destruction also shows that the multi-salt sorbents adapt better for low temperature low-grade heat.