Heat and mass transfer during heating of a hybrid absorption/sensible storage tank

Abstract

A numerical study of heat and mass transport in a tank of aqueous calcium chloride as heat is added to the tank is presented to evaluate the potential of storing water, diluted, and concentrated salt solutions in a single tank to provide sensible and thermochemical (sorption) storage for solar space heating and hot water. An immersed heat exchanger provides the means to sensibly charge the tank while a stable density interface between layers of different salt mass fraction minimizes mass transfer to permit long term storage. Transient simulations are presented over the wide range of conditions expected in practice, as represented in dimensionless form by the Rayleigh number (Ra), buoyancy ratio (N), geometric aspect ratio (a), Lewis number (Le) and Prandtl number (Pr). Correlations of Nusselt number (Nu) and Sherwood number (Sh) for 7×103<Ra<3.3×109, 1<N<26.4, 0.125<a<1, and 15<Le<1.5×104 are in the form Nu=0.45a0.5Ra0.28 and Sh=0.001Ra0.28N−0.69Le1.17.