Experimental and Numerical Study of Heat Transfer Process of Chilled Water Storage Tank

Abstract

Cool thermal energy storage using thermal stratification becomes one of the widespread applications because of the ability to shift the electrical cooling loads from on-peak to off-peak periods and significantly contributes to reducing the capacity of the refrigeration system and operating costs. Seven flow rate tests varying from 1.5 to 7.5 l/min for charging cycle were performed on small-scale vertical cylindrical storage tank equipped with three primary inlet diffusers, an elbow, two-ring linear and radial circular diffusers. The storage tank with inlet diffusers was assessed using temperature distributions and performance measures including thermocline thickness(ht), the half-cycle figure of merit ( ) and equivalent lost tank height (ELH). Commercial finite volume code was used to predict temperature distributions in a stratified water tank model, temperature data acquired from experimental tests and simulation models were compared for validation purpose. The results suggested that the storage tank with two-ring linear circular diffuser produced better performance and higher stratification than two-ring radial circular diffuser for various flow rates by 1.4% , 20.6% ELH and 10.6% ht, and much better than an elbow diffuser by 1.7% , 24% ELH and 31.1% ht, furthermore, the degree of mixing was affected essentially the flow velocity which in turn causes an increase or decrease in thermocline thickness. Temperature distributions obtained from finite volume model are found to be in very close agreement with those obtained experimentally.