Mass transfer during sensible charging of a hybrid absorption/sensible storage tank

Abstract

A concept for long term thermochemical storage based on absorption of aqueous CaCl2 is described and evaluated during sensible charging operation. The novelty of the desiccant storage tank is that strong and diluted salt solutions as well as water are stored in one vessel. An immersed heat exchanger and manifold provide the means to charge the tank without mixing solutions of different CaCl2 mass fraction. The ability to heat the tank via natural convection, while minimizing mass transfer between regions of different salt mass fraction, is elucidated via optical measurements of the velocity and CaCl2 mass fraction distributions in a 1500 liter prototype tank. Over a wide range of the dimensionless parameters that govern mixing, the mass transfer between layers of differing CaCl2 mass fraction is low, typically with Sherwood numbers less than 100, and temperature stratification is maintained. Projected time scales for long term storage exceed 100 days.