Study On Heat Transfer In Charging Process Of A Cold Storage Tank For Use In Air-Conditioning

Energy is one of the most necessary requirements for social and economic development. The harmonious development of economy, energy and environment is the most important issue to achieve the modernization in China. Although the energy efficiency in our country is much higher than before, it is still apparently lower than that of development countries. Cold storage air conditioning, an effective method for shift peak, which has great social and economic significance can reduce the installed capacity, increase the equipment efficiency and so on.At present the ice cold storage system is more widely applied. The freezing point of water is low, which makes the evaporation temperature, COP and cool capacity of cool-storage air-conditioning much lower than that of conventional air-condition system. In addition, the system is more complex by the doublestage mode refrigeration main machine applied in the air-conditioning mode and ice storage mode. So in this paper, we propose a heat transfer tube with multiple phase change materials (mPCMs) which was applied in a cold storage tank for use in air-condition system to improve the charging performance. The major research efforts are indicated from the following aspects:(1) We have built the physical and mathematical models of the heat transfer tubes. Three selected PCMs were injected into the tubes as the multiple PCMs (mPCMs). The charging process in the heat transfer tubes with the mPCMs was simulated using Ansys Fluent. The models were validated by experiment.(2) The effects of PCM volumetric proportion and the temperature of the heat transfer fluid (HTF) on liquid fraction and temperature distribution in the tubes were investigated.(3) The effects of PCM volumetric proportion on charging capacity and charging rate were discussed by the caparison between the heat transfer tubes with mPCMs and single PCM. The results show that heat transfer tubes with mPCMs have better charging performance. The best PCM volumetric proportion was acquired.(4) The physical and mathematical model of the cold storage tank was built to study the charging process in the cold storage tank with mPCMs. The effects of HTF inlet flow rate on charging capacity, charging rate, temperature distribution in the cold storage tank, outlet temperature and the liquid fraction in the tubes were investigated. The influence of inlet flow rate on charging process was also obtained.This paper proposed heat transfer enhancement method by the use of mPCMs which can effectively increase the charging capacity of the heat transfer tubes and expend the selection of the PCMs. The conclusions obtained in this paper can be used to improve the operation efficiency of the cold storage system and its application in the conventional air conditioning system.