Study On Phase Change Material Latent Heat Mechanism For Air-conditioning And Direct-contact Cool Storage Tank Heat Transfer Performance

In recent years, considerable attentions have been devoted to the development of thermal energy storage system air-conditioning for district cooling purposes in order to save energy and reduce electrical cost, particularly during peak hours in summer. It can solve the pressure of power supply and demand from the electricity peak-valley effectively. The major application is ice storage air-conditioning in cool storage air-conditioning, however the lower evaporating temperature of ice storage air-conditioning leads to decreasing the coefficient of performance and the larger thermal resistance of heat exchange tube leads to losing energy. Therefore, there are two big problems needed to resolve in the field of cool storage air-conditioning currently: on the one hand, how to find a phase change material (PCM) with high phase change latent heat value and compatible phase change temperature; on the other hand, how to overcome the lower heat exchange efficiency and the serious energy dissipation in the process of charging and discharging. This paper presents research and analysis aiming at the existing two big problems. Find out the influence factors of the phase change latent heat value size by means of mechanism analysis of phase change latent heat to PCM. Add water as heat transfer fluid (HTF) and PCM as cool storage material, using the direct contact cool storage tank to processing charging experiment.Firstly, this paper selects various organic PCM to measuring the cooling curve in different proportion. Preliminary finding out three groups organic mixture PCM which with compatible phase change temperature and without obvious sub cool temperature. The experiment of oxidation modification esterification modification graft modification are processing to the three groups PCM. Traversing the thermal physical property of the modified PCM through differential scanning calorimetry (DSC) and fourier transform infrared spectroscopy (FTIR). The experimental results show that the modified PCM joining up polar group successful. But the material chain length taking place easily, moreover molecular weight、molecular structure and molecular polarity have crucial influence on intermolecular forces and the latent heat value of phase change material.Secondly, this paper builds up the physics model and mathematical model of direct contact cool storage tank and taking simulation study of total charging process. Study on the great influences of inlet flow rate and inlet temperature of HTF、inlet flow rate of cool storage material on outlet temperature of HTF. At the initial stage of charging process, the outlet temperature of HTF grows up faster, and then tends to slow, and finally transfer to a constant value.Finally, this paper studies on the the heat exchange performance of direct contact cool storage tank through setting up small size direct contact cool storage tank and changing the nozzle location of cool storage material. Furthermore, studing the influence of nozzle location on temperature field distribution in cool storage tank and mass heat exchange coefficient. The influences of inlet flow rate and inlet temperature of HTF、inlet flow rate of cool storage material on mass heat exchange coefficient are also investigated. There are some errors when the experiment value is compared with the emulation value, it shows that the variation trend is consistent. The research shows that the mass heat exchange coefficient is a relatively stable constant value under a certain condition, and adopts the bottom nozzle can gain the largest mass heat exchange coefficient. Its value increases with the increasing of cool storage material velocity, however the influence of nozzle location reduces gradually when the velocity reaches2.8m/s. The mass heat exchange coefficient is proportional to the inlet floe rate of HTF and is inversely proportional to the inlet temperature of HTF.This paper presents theoretical direction to improving the phase change latent heat of PCM and the heat exchange efficiency of cool storage tank through researches the phase change latent heat mechanism and direct contact heat exchange performance. It possesses significant reference value in the field of cool storage air-conditioning.