Performance Analysis And Optimization Of Household Phase Change Heat Storage Tank

The current situation of resource scarcity and environmental pollution puts forward higher requirements for energy utilization.Exploiting the renewable energy is an important way to achieve sustainable development.In the field of renewable energy utilization,solar thermal utilization technology has been widely used.However,due to the constraints of weather,day and night changes and seasons,solar radiation is discontinuous and unstable,which affects the efficiency of solar light and heat utilization.The hot water storage tank,as a heat storage device in the utilization of solar heat,can adjust load fluctuations and store hot water,effectively improving the influence of meteorological parameters on the utilization of solar heat.Ordinary hot water storage tanks use water as the heat storage medium,and the heat is stored in the form of sensible heat,which has disadvantages such as low heat storage density and large water tank volume.To solve this problem,a combination of phase change material and heat storage tank was proposed.A method of combining phase change materials with hot water storage tanks was proposed.Utilize the characteristics of high heat storage density of phase change materials and approximately constant temperature during phase change to increase the energy storage density and decrease the volume of the watre tank,and also reduce the influence of solar radiation instability on the utilization of solar heat,improve the effective utilization rate of solar heat.First,by comparing and analyzing the physical parameters of various phase change materials and the structural characteristics of different phase change hot water storage tanks,combining with domestic domestic hot water related specifications and standards,it was determined that the phase change water tank was made of paraffin as the heat storage material,and the paraffin was placed on the outside of the water tank.Revit and COMSOL Multiphysics were used to establish the physical model and numerical model of the phase change hot water storage tank respectively.After confirming the correctness of the numerical calculation model with experimental data,the heat storage and release process of the phase change hot water storage tank was simulated.Based on the simulation results,the optimization method of the water tank structure was proposed.The simulation results show that the heat storage process of the water tank with phase change layer is obviously prolonged,while the heat release process is firstly prolonged and then shortened with the increase of the thickness of phase change layer.In the process of heat storage,with the increase of the thickness of PCM,the average temperature of PCM decreases,the liquid phase ratio difference between top and bottom increases,and the tendency of liquefaction at the bottom of the phase change layer decreases obviously.During the heat release process,the phase change trend of phase change materials with different thicknesses is similar,it decreases at the beginning of the exotherm and then increases.Compared with other simulation conditions,when the thickness of the phase change layer is 30 mm,the rate of decrease in water temperature is the smallest,and the exothermic process is extended by about 5 hours.In addition,the provision of a ring-shaped metal separator inside the phase change layer can improve the operating characteristics of the phase change hot water storage tank.In the heat storage process,the increase in the number and thickness of the annular baffle is beneficial to the melting process and the utilization of latent heat,but also prolongs the heat storage process,increases the cost and the weight of the device.During the exothermic process,adding a metal separator can increase the liquid phase ratio.But the thickness of the separator is not as thick as possible.When the number of separators is fixed,the ring-shaped separator with a thickness of 5 mm has a stronger effect on promoting the liquefaction of the phase change material and maintaining the water temperature than the ring-shaped separators with the thickness of 2 mm and 10 mm.Finally,the energetic dissipation is used to evaluate the performance of the phase change hot water storage tank before and after the structural optimization.During the exothermic process,the phase change material can release latent heat at almost constant temperature to maintain the water temperature,and the temperature difference between water and the phase change material has little change,the absolute value of energetic dissipation rate of the optimized tank is also small.Therefore the effect of the latent heat to keep the water temperature is more obvious.The energetic dissipation analysis verifies the effectiveness of the metal baffle in improving the heat storage and release performance of the phase change tank from the perspective of energy storage quality.