Development of an efficient static-type ice thermal energy storage vessel using a low concentration aqueous solution

Abstract

If an aqueous solution with low concentration is used for static-type ice-storage-vessels, even when a large amount of solution (aqueous ethylene glycol in this study) is solidified and bridging of ice developed around cold tubes occurs, the pressure increase can be prevented by the existence of a continuous liquid phase in the solid-liquid two-phase layer (mushy layer) which opens to an air gap at the top of a vessel. Therefore, one can continue to solidify an aqueous solution after bridging occurs, achieving a high ice packing factor (IPF) which is defined as the ratio of mass of created ice to initial mass of water in a vessel. In the present study, experiments using small-scale test cells have been conducted with initial concentration, C ₀, of aqueous ethylene glycol ranged from 0 mass % to 5.0%. It was seen that the IPF obtained using the solution with C ₀≤1.0% is much greater than the IPF of 65%–70% using pure water for which the solidification must be stopped before bridging, and that a large pressure increase is not observed during solidification of the solution with C ₀≥0.5%. Therefore, if we use the solution with 0.5%≤C ₀≤1.0%, we can probably obtain a large IPF without a large pressure increase for real ice-storage-vessels.