Analysis of heat and mass transfer in the passive solar thermal storage of MgCl2·6H2O hydrated salt embedded with copper foam on sieve plates

Abstract

A novel passive solar thermal storage with MgCl₂·6H₂O (Magnesium chloride hexahydrate) hydrated salt as porous media on sieve plates is proposed, in which the serpentine flow channel around sieve plates and several flowing slots in each salt layer are set to enhance the convective between the airflow and hydrated salt layer, besides, the porous copper foam embedded in hydrated salt bed will enlarge the thermal conduction in salt beds. Combining the Prout-Tompkins equation with Clausius-Clapeyron relation accounts for the kinetics characteristics of endothermic dehydration (i.e. hydrated salt loses its water content) in hydrated salt layer where the local thermal non-equilibrium occurs. The double energy equations together with Darcy relation are employed to describe the heat and flow in porous salt bed, and to analyze the effects of the salt bed structure, straight-shaped slots and porous copper foam in salt layer as well as the inlet airflow velocity on the conversion extent of MgCl₂·6H₂O salt and the heat storage characteristics in the passive solar thermal storage reactor during dehydration. In comparison to the salt layer without slot, more than 18% rise of conversion rate happens in the salt bed with n = 12 slots. The higher average conversion rate of MgCl₂·6H₂O, more uniform distribution and larger heat storage rate in the salt layer embedded with copper foam occur than that without, and the amount of heat storage rises slightly with the slot number above n = 6 for the current mode. The simulations accord with the published experiment data. All results can be considered into the promotion and application of the passive solar thermal storage of MgCl₂·6H₂O salt hydrate.