Experimental And Numerical Investigation Of The Latent Heat Thermal Storage Unit With PCM Packing At The Inner Side Of A Tube

In recent years,latent heat thermal storage systems(LHTS)have been extensively studied to solve the problem of mismatch between time and place of energy supply and demand.For latent heat thermal storage systems,the core of the technology lies in phase change thermal storage materials and phase change regenerators.Most of the previous studies are focusing on the systems with the phase change materials(PCM)packing outside the tube.The characteristics of a LHTS with the PCM packing at the inner side of a tube has been rarely reported.In this paper,a visualized experimental device for horizontal phase-package phase change thermal storage unit is built.The development of the phase interface during the melting and solidification process of the LHTS unit and the influence of different working parameters on the heat storage and discharge performance are studied.The results show that the temperature of the heat exchange fluid has a great influence on the heat storage time of the unit.The charging time is shortened by 61.5% when the temperature of the heat transfer fluid in the heat storage process increases by 14.5%,and the discharging time was shortened by 42.7% when the heat exchange fluid temperature during the heat release process is reduced by 26.9%.In contrast,the heat transfer fluid flow has a much smaller effect on the performance of the LHTS unit.The charging time is reduced by 7.5% when the heat transfer fluid mass flow rate in the heat storage process is increased by 86.0%,and the discharging time is reduced by 2.4% when the heat fluid mass flow rate in the heat release process is increased by 73.3%.In the past,the performance comparison of the tube and shell package structures was carried out at a material filling rate of 50%.In some practical applications,it is desirable to package more phase change materials in a limited space to store more heat.In order to make the comparison more closed to practical application,this paper verifies the accuracy of the numerical model by experimental data,and use this numerical method to tube and shell package phase under different filling rates of phase change materials(40%~90%).The thermal storage performance of the variable thermal storage unit is compared.The results show that the tube package phase change thermal storage unit has better comprehensive performance when the filling rate is greater than 62%.Therefore,in the space-constrained practical application,the tube package phase change thermal storage unit has advantages.In order to optimize the structure of the tube LHTS unit,the thermal storage performance of the horizontal and vertical elliptical tube package phase change thermal storage unit was simulated.The results show that the horizontal elliptical tube structure has better comprehensive performance.Compared with the circular structure,although the horizontal elliptical tube structure increases the heat exchange area by 5.2%,it can shorten the storage and release time by 10.2% and 11.01%,respectively.On the basis of the horizontal elliptical tube phase change thermal storage unit,the numerical simulation was used to simulate the heat storage and release of the tripletube package phase change thermal storage unit with the outer tube as a horizontal ellipse and the inner tube as a circular,horizontal ellipse and vertical ellipse.The results show that the triple tube structure can effectively improve the heat storage and release performance of the tube LHTS unit,and the performance is optimal when the inner tube structure is horizontally ellipse.Compared with the circular tube structure,the structure can shorten the heat storage time by 40.9%,shorten the heat release time by 59.2%,increase the average storage and release power per unit mass of materials by 118.3%,and reduce the temperature unevenness of the heat storage and discharge process by 29.6%.8.6%.