Numerical Simulation Of Heat Transfer Characteristics Of Phase Change Heat Storage And Exchange Device

China is rich in industrial waste heat resources,but it has the characteristics of dispersion,instability,intermittence and so on,so it is difficult to recycle.Therefore,exploring new technologies to recycle industrial waste heat and improving energy efficiency is an important direction of current energy conservation and emission reduction work.The phase change material has high heat storage density and good heat stability.The shell and tube heat storage and exchange device is simple in structure and widely used.The combination of the two can better recover and utilize intermittent industrial waste heat,and solve the problem of uneven distribution of energy supply and demand in time and space.It is of practical significance to realize the efficient recovery and transformation of intermittent industrial waste heat.The research of this paper is aimed at the recovery and utilization of low-temperature industrial waste heat,so it is very important to select phase change materials with suitable temperature range,large latent heat of phase change,good thermal stability,non-toxic and pollution-free,and low economic cost.Based on the above factors,combined with the temperature conditions that may be applied to building heating system in the future,this paper chooses paraffin as the research object.The density,thermal conductivity,specific heat capacity,viscosity,phase change temperature and phase change latent heat of the selected paraffin sections were studied experimentally.The melting process of phase change material was simulated by FLUENT software,and the heat transfer mechanism of paraffin during phase change process was explored.The numerical simulation results show that the whole upper part of paraffin melted faster than that of the lower part under the influence of natural convection.The melting rate is mainly divided into three stages: emergence,exuberance and weakening.Due to natural convection,the vigorous melting period of paraffin is about half of the melting time.A set of liquid comparison and temperature field simulation data were obtained for reference.A shell and tube type phase change heat storage and exchange device is designed.The heat energy stored in the phase change material paraffin is converted and output by the heat carrier water in the tube.A three-dimensional unit model is established to simulate the heat transfer characteristics of the phase change heat storage and exchange device during the phase change process of melting heat storage and solidification heat release,and analyze the liquid ratio,temperature field and temperature change of the heat transfer medium of the phase change material under certain working conditions.The simulation results show that the outlet temperature of the heat carrier water in the heat exchange tube increases rapidly at the initial stage of heat storage,then slows down and the heat exchange effect is stable.At the beginning of solidification exothermic process,the solidification rate of liquid phase change material paraffin is very fast,and then the solidification rate gradually slowed down with the increase of heat transfer resistance.By changing the water temperature and the inlet velocity of the heat carrying fluid,18 sets of comparative working conditions were set to simulate the heat transfer characteristics of the shell and tube phase change heat storage and exchange device.The numerical simulation results show that when the inlet water temperature is higher,the melting time ofphase change material is earlier and the complete melting time is shorter during the process of melting and heat storage.The faster the inlet velocity is,the higher the outlet temperature is,and the outlet temperature increases continuously with the melting and heat storage process.In the process of solidification and heat release,the complete solidification time of paraffin is affected by the inlet temperature and inlet velocity,but it does not change with the same gradient.The influence of the inlet temperature of the heat carrier fluid is more significant than that of the inlet velocity for the outlet temperature,which further affects the heat transfer efficiency of the phase change heat storage and heat exchange device.The research results are helpful to optimize the design of shell and tube phase change heat storage and exchange device and provide theoretical reference.