Study On Heat Transfer Enhancement Of Horizontal Shell-and-Tube Latent Thermal Energy Storage Unit

Latent thermal energy storage(LTES)technology can solve the contradiction between energy supply and demand in time and space.The application prospect of this technology is very broad.However,due to the low thermal conductivity of commonly used phase change materials(PCMs),especially organic phase change materials,the storage/release rate of LTES devices in the practical application is a little low,and sometimes it is difficult to meet the requirements of system.Therefore,it is necessary to carry out the research on heat transfer enhancement of LTES devices,especially the research on LTES units.Based on the literature review of LTES technology,this paper selects a horizontal Shell-and-Tube LTES unit as the research object,and focuses on the research of new heat transfer enhancement method for natural convection.The research method of this paper is mainly numerical simulation,assisted by experimental verification.Based on enthalpy-porous method,a three-dimensional numerical model of LTES unit is established.An experimental platform of LTES unit is also designed and built.The accuracy of the numerical model is verified by comparing the experimental results,literature results and numerical simulation results.On this basis,numerical simulation method is used to reveal the heat transfer mechanism of the LTES unit during melting and solidification process.The inlet temperature of heat transfer fluid(HTF)and the ratio of inner and outer diameter of the unit are two key factors which can influence the natural convection intensity,the effects of these two key factors on the heat transfer performance of the LTES unit are slso analyzed.It is found that the heat transfer mechanism in the melting process goes through a process from heat conduction to natural convection and then to heat conduction again.During solidification process,heat transfer mechanism is dominated by heat conduction.Natural convection has a great influence on the melting process,which can strengthen heat transfer,but has little influence on the solidification process.Eccentric layout is a new heat transfer enhancement method for natural convection,this paper focuses on the influence of eccentricity on the heat transfer performance of the melting and solidification process of LTES unit.From the perspective of Melting-Solidification cycle,an index for evaluating the heat transfer performance of the whole cycle,namely the full-cycle average heat transfer rate,is defined,and different eccentricities are optimized and analyzed.It is found that the eccentric layout will enhance the natural convection in the melting process,but inhibit the heat conduction in the solidification process meanwhile,when compared with central layout.For solidification process,when eccentric puls reverse layout is adopted,the heat transfer performance can be improved to a certain extent,when compared with eccentric layout alone.For the whole Melting-Solidification cycle,when the eccentricity is small,the heat transfer performance will be enhanced,but when the ccentricity is large,the heat transfer performance will be inhibited.In the structure design of LTES unit,it is necessary to select the appropriate eccentricity within the range of eccentricity which can enhance heat transfer performance.The research in this paper can provide guidance for the structural design of LTES unit,so as to enhance its heat transfer performance and promote the wide application of LTES technology.