Investigation On Heat Transfer Performance Of Internally Finned Tube Thermal Storage Tank With Leaves-like Channels

In the field of refrigeration and air-conditioning, Latent heat thermal storage technology used in conventional air-conditioning system have received greater attention because of its vietues, such as the possibility of utilizing original chilling unit and air-conditioning system directly, smaller cold energy loss, larger COP. Higher requirements of phase change material has been put forward to, larger latent heat, lower cost, and higher thermal efficieney are the main development aspects. Organic materials have become the hot researchnig subject because of the characteristic of no super-cooling and no chromatography. However, organic phase change material usually has lower thermal.conductivity, the increased thermal resistance leaded by the freezed PCM layer inside the heat trasfer suface makes the charging and discharging process worsen, the charging and discharging rate will be decreased consequently, which is a major drawback for its application and development. Therefor, improving charging and discharging rate and uniformity in latent thermal storage system has become the focus of related research both home and abroad.Adding fins in the latent heat thermal storage system is an easy and effective method for heat transfer enhancement of PCM. The main characteristic is to increase heat transfer coefficient through enlarging the area of the heat transfer surface, achieving the aim of heat transfer enhancement. Internally Finned tube with leaves-like channels was chosed as encapsulation container, heat transfer performance of the thermal storage system is investigated numerically and experimentally. The major research efforts and achievement are as follows:(1) Acccording to the structural characteristics of the tube and heat transfer characteristics of PCM, heat transfer model of the finned tube thermal storage system is developed, and heat transfer performance has been studied by numerical calculation. During charging and discharging process, we have significantly analyzed the effects of fins, temperature of heat transfer fluid on freezing and melting characteristic, and compared different fin number effect on heat transfer enhancement. The numerical result indicates that temperature of heat transfer fluid has great impact on the total freezing time and the total melting time, and the heat transfer of PCM is enhanced by adding the number of finns.(2) Heat transfer model of thermal storage tank usable in conventional air-conditioning has been developed, and dynamic characteristic of charging and discharging process of the thermal storage system were simulated. Effect of inlet temperature, flow rate of heat transfer fluid, number of the tube and initial temperature on charging and discharging process has been studied. The simulation result indicates that inlet temperature, number of the tube and initial temperature have great impact on on the cold thermal energy stored and cold thermal energy released, the increase of flow rate of heat transfer fluid helps to heat transfer process and reduce the charging and discharging time, but it did not have great impact on the cold thermal energy stored and cold thermal energy released.(3) An experimental apparatus for thermal storage tank was built, heat transfer characteristic of PCM during phase-change and charging performance were investigated experimentally. Numerical calculation results were validated by comparing with the experiment results, the comparison show good agreement between numerical and experimental results.The conclusion drawn from numerical simulation and experimental investigation has instructional efect on deeper theoertic study and practical application, and will provide theoretical guides for designing, performance simulaton and management of thermal storage tank usable in conventional air-conditioning.