ABSTRACT:

Thermal energy storage (TES) in a stratified water tank allows cooling or heating capacity to be stored when it is cheap and delivered when it is needed. This paper evaluates such a tank in terms of energy efficiency, storage capacity and discharge behaviour. A small-capacity storage unit for a refrigeration system was designed, developed and fabricated to study thermal stratification at different flow rates, using the thermocline thickness, the figure of merit and the equivalent lost tank height as indicators. A multi-node energy balance, a fully mixed tank model and capacity-based performance equations are presented to describe the tank. The work shows that stratification stores thermal energy with high efficiency and capacity. Tank design, flow rate and inlet temperature are the key factors, and a low inlet velocity, a large temperature difference and wide port spacing limit mixing. Therefore, the paper strongly emphasized the multi-node model, eddy diffusivity, and Froude/Reynolds number relationships as the novel contributions of this paper.