Research And Optimization Of Phase Change Heat Storage System For Membrane Seawater Desalination

Energy is an indispensable foundation for human society and economic development.With the continuous development of the economy,China's demand for energy continues to increase.At present,non-renewable energy sources such as oil and coal account for 85% of the world's total energy consumption,and renewable energy sources such as solar energy account for only 15%.Therefore,it is crucial to increase the utilization rate of renewable energy.The phase change storage and discharge device can store and utilize renewable energy such as solar energy to improve energy utilization efficiency.In this paper,the energy release efficiency of the traditional phase change energy storage device is low.The energy release efficiency of the metal ball phase change energy storage tank is improved by using the metal phase change ball internal fins and the paraffin internal graphite filling.And the effects of different flow rates,fins and graphite filling on the exothermic process of the phase change tank under open direct current heat storage and closed loop heat release conditions.The paraffin phase change material was encapsulated by a 304 stainless steel metal spherical shell to prepare a phase change pellet unit having a liquid phase paraffin mass ratio of 95%.A certain number of phase change pellets are filled into a high density polyethylene cylindrical tank filled with water to make a phase change energy storage tank combining the sensible heat of water with the latent heat of the phase change unit.For the application of seawater desalination,a system model of phase change hot water tank and membrane seawater desalination is established,and numerical factors are used to study the factors affecting the heat release efficiency of phase change energy storage tank.Firstly,the changes of paraffin phase change time and outlet water temperature in the phase change unit of the open direct current and closed loop exothermic process of the phase change water tank were studied experimentally under different inlet flow rates.The experimental data show that the paraffin phase change time and the outlet water temperature decrease with the increase of the inlet water flow rate.Based on the standard outlet water temperature,the heat obtained from the inlet water of the open direct current/closed loop exothermic processes of the phase change tank increases with the increase of the inlet flow rate.Secondly,the effect of optimization process on the heat release of the phase change water tank is studied.The effects of different shell materials,the number of different fins in the spherical shell,and the filling rate of different expanded graphite in paraffin on the open direct current and closed loop exothermic processes of the phase change tank were studied bynumerical simulation.Since the thermal resistance of the metal spherical shell accounts for a small proportion of the heat transfer resistance,the simulation results show that the influence of different shell materials on the open direct current and closed loop heat release performance of the phase change water tank is almost negligible.The addition of fins inside the metal ball can quickly transfer the heat in the internal paraffin phase transition to the inter-shell cooling water.Therefore,the addition of fins can effectively improve the heat release efficiency of the phase change water tank.The simulation results show that the phase change water tank is open.In the open direct current exothermic process,when the number of fins is 6,the maximum optimized ratio of heat release is 1.133.In the closed loop heat release process of the phase change water tank,when the number of fins is 6,the maximum optimized ratio of heat release is 1.020;In addition,the paraffin wax filled with expanded graphite can effectively improve the thermal conductivity of the paraffin wax.The simulation results show that when the filling rate is 5%,the average liquid fraction of paraffin is 7.6%.Finally,the effects of phase change water tank optimization on freshwater production of coupled seawater desalination systems were studied.The study found that the seawater desalination rate increased from 261.2g to 335.8g when the phase change water tank was used compared to the empty water tank.In addition,in addition to the optimized design of adding 6fins inside the ball,the amount of seawater desalination increased from 436.3g to 541.1g.This study has certain guiding significance for improving the utilization efficiency of solar energy and improving the efficiency of solar-powered desalination system.