Study On Enhanced Heat Transfer Characteristics Of Solar Phase Change Accumulator

Vigorously developing solar energy technology is an important means to alleviate the shortage of resources and environmental pollution caused by traditional fossil energy consumption.Heat storage technology can solve the imbalance of heat supply and demand in time and space caused by the alternation of day and night,season,weather and other factors of solar energy to a certain extent.Phase change heat storage technology has many advantages,such as stable temperature of heat absorption and release,high energy storage density,easy control of phase change process and so on.In this paper,the heat transfer characteristics of the sleeve type solar phase change accumulator were studied by numerical simulation,with the basic structure of the sleeve type solar phase change accumulator and the paraffin added with 10% expanded graphite as the heat storage material.The effects of natural convection caused by gravity,eccentricity of heat transfer tubes and geometric parameters of fins on the heat storage performance of phase change regenerator were investigated.(1)The physical model of the tubular phase change regenerator is established and meshed.The CFD software is used for numerical simulation.The simulation results are in good agreement with the experimental data,and the simulation results are reliable.The results show that the natural convection in the liquid phase region of the phase change material has a significant effect on the heat storage process of the regenerator.The heat storage time of the regenerator considering the natural convection is 16000 s,which is only28% of that without considering the natural convection.(2)With the increase of the eccentricity,the overall heat storage time of the regenerator first decreases and then increases.When the eccentricity e = 40 mm,the heat storage rate is the highest,and the heat storage time is 3900 s,which is 75% shorter than that of the concentric tube regenerator.During the heat release process of the accumulator,the PCM condenses gradually with the heat transfer tube as the center.The offset heat transfer tube makes the condensation of the PCM in the upper part slow down and the overall heat release time longer.Considering the total time of heat storage and release,when the eccentricity e= 40 mm,the shortest total time of heat storage and release is 19000 s.(3)In order to solve the problem of low heat storage and release rate caused by the low thermal conductivity of phase change materials,the heat accumulator with metal fins was simulated.The results show that the appropriate fin height can effectively improve the heat storage efficiency of the regenerator,but has little effect on the heat release process.The optimal fin height in the numerical simulation range of this paper is h = 28mm;When the number of fins is N = 10,the overall heat storage and release efficiency is the highest,and the total heat storage and release time is 8800 s;When the thickness of the fin increases to a certain extent,the heat storage rate will reach the limit,but the heat release rate will continue to accelerate.When the fin thickness c = 4mm,the total time of heat storage and release is the shortest,which is 8400 s.