Numerical And Experimental Study On Ice-on-coil Storage Tank

With energy supplies intense increasingly and environmental protection being concerned on particularly, requirement of energy utilization technology enhances endlessly. Thermal energy storage technology, which helps to shift peak load on electricity, has benefit of the optimization of the existing power system of energy utilization structure, research of the cool-storage air conditioning technology has important practical significance.Ice thermal energy storage technology is used widely in the present, ice storage tank, which heat transfer performance is directly related to the performance of the ice storage system, is a very important component. This paper mainly focus on heat transfer performance of ice-on-coil storage tank. Research works mainly include the following two aspects:(1) Have established the model of ice storage tank on the basis of certain assumptions and simulated by ANSYS software to study on geometric parameters of the storage tank, such as coil layouts, diameter and space, and the influence of inlet temperature of refrigerating medium for heat transfer characteristics of the ice storage tank, as well as the influence of coil diameter for flow resistance of refrigerating medium; (2) Have designed ice storage tank particllarly and built ice storage test-bed of air-conditioning system, as well as carried study on heat transfer characteristics of the ice storage tank according to the simulation results.According to the simulation and experiment, the main results were as follows:(1) For the U-shaped coil, tubes in-line arrangement, which not only simplified layouts and enhanced the heat transfer characteristics, but also met the requirements of uniform temperature pattern, was better than staggered style to the performance of ice storage tank; (2) For U-tubes in-line arrangement, initial temperature of refrigerating medium, coil diameter and space, had a great influence on heat transfer characteristics, larger space was benefit to improving heat transfer characteristics of ice storage tank with the same diameter and number of tubes when ice storage tank volume was certain. It is believed larger diameter was tried to choose if the conditions permitted; (3) Coil diameter had less impact on flow resistance; (4) Temperature stratification of ice storage was significant and subcooled temperature was larger with the minimum temperature of-3℃, the maximum temperature of-0.9℃, and phase transition temperature of-2.2℃in freezing processes; (5) Adding mass fraction of 0.25% of borax to the water was able to reduce 0.2℃of subcooled temperature and increase 0.1 of COP, thus that adding a certain amount of borax was benefit to heat transfer and improving heat transfer performance of ice storage tank; (6)The rate of temperature change for inlet and outlet was closely related to melting process, In certain stage, difference in temperature between inlet and outlet of refrigerating medium maintained steady at 8℃.