The heat transfer enhancement of low temperature airflow foam effect in the ice storage charging process

Abstract

Phase change cold storage, as an energy-saving application, was widely used in central air-conditioning system of commercial building to fit the intermittent and the changing cooling load. Ice storage with different container structures was developed, but the low charging efficiency and non-linear energy storage rate were difficult to match the dynamic change of cooling load and the energy-saving strategy of the chiller system, and increased the energy consumption and the complexity of the ice storage air-conditioning system control. Low temperature airflow (LTA) was introduced into water in the low temperature environment. Gas, liquid and solid coexisted in the phase transformation process, and the process of heat and mass transfer underwent complex changes. The effects of these changes on phase transformation were studied by experiment. It was found that porous frozen body was generated with a large number of microchannels inside. The porous structure dispersed the airflow into isolated bubbles, and foam generated. Foam enlarged the heat transfer area and prolonged the contact time between LTA and phase change material (PCM), sharply improving the heat transfer efficiency, and strengthening the heat transfer between PCM and its geometry boundary. When the air flow rate was 25 L/min, the freezing rate increased by 4 times than that of freezing without LTA. This study concluded that it was simple, practical and efficient to introduce LTA into PCM considering the heat transfer enhancement of the foam effect. It will have a prosperous application in ice storage system.