Study On Fin Structure Optimization And Heat Transfer Characteristics Of Phase Change Of Heat Storage Unit

In the face of increasingly severe energy problems,it is imperative to optimize the energy consumption structure,save energy,reduce emissions,improve energy utilization and adhere to the road of sustainable energy development.Low temperature waste heat is abundant in our country.its recycling is an important measure to improve energy utilization,but the cost of cross-region and cross-season utilization is higher,and the technical difficulty is greater.However,thermal storage technology can effectively solve the contradiction of mismatch between heat supply and demand in time and space.Phase change thermal storage technology is one of the most promising technologies in thermal storage,which has the advantages of high thermal storage density,compact structure,flexible design and approximately constant working temperature.However,the thermal conductivity of the phase change material is low,and most of the engineering applications adopt the means of adding fins to enhance heat transfer.Therefore,the optimized design of the fin structure of the phase change heat storage unit is crucial,which directly affects the enhanced heat transfer effect of the system.Based on this,this paper took the recovery and utilization of low temperature waste heat by phase change heat storage technology as the background,and took the horizontally placed shell and tube type phase change heat storage unit with longitudinal fins as the research object.Designed a new fin structure,and optimized its internal structure by different methods.Studied and analyzed the phase change heat transfer characteristics of PCM melting process and the influence law of fluid parameters on heat transfer performance by numerical simulation method and experimental method,and verified and analyzed the reasonable reliability of numerical simulation and fin structure optimization.In this paper,firstly,the heat transfer structures of longitudinal rectangular,conical and Tshaped fins and the heat transfer structures of light tubes(without fins)were studied by numerical simulation respectively,keeping the same fin height and area and using RT35 as the phase change material.The simulation results showed that the melting rate of PCM in the upper part of the shell was the fastest,and the PCM in the bottom area of the shell was the most difficult to melt.The new T-shaped fin structure had the best heat transfer performance,and the highest PCM liquid fraction was 4.5 times higher than that of the optical tube heat transfer structure.The T-shaped fin structure was then designed to optimize the bionic configuration,and it was founded that double T-shaped fin structure had the best heat transfer performance.The orthogonal experimental optimization design and RSM optimization design were carried out to analyze the degree of influence of fin structure parameters on the heat transfer process:total fin height H>fin T-shaped aspect ratio L/W>fin end height H3>double T-height ratio H1/H2.In addition,the RSM optimized structure showed the best heat transfer properties.Further research analyzed the influence of fin arrangement direction,clamping angle and combination of RSM optimized structure and fluid temperature on the heat transfer process.It was found that the PCM melting rate was faster when placed in reverse and the fin clamping angle in the lower part of the shell affected the PCM melting process more strongly.The PCM liquid fraction of the forward-combined fins that occupied 0.8%more space can be improved by up to 16.4%over its original structure.In addition,the PCM phase change heat transfer performance increased almost proportionally with increasing fluid temperature.Finally,the reasonable reliability of numerical simulation and fin structure optimization were verified by experimental study.The results showed that the heat transfer performance of the phase change heat storage unit increased with the increased of fluid temperature and flow rate,and the influence of fluid temperature on heat transfer performance of heat storage unit was far greater than that of fluid flow rate.The total melting time of PCM of forward-placed fin was the least,which was 45%less than that of the original T-shaped fin structure.The average heat storage power was the highest,which increased by 42.8%compared with the original T-shape structure.