| At present,phase change energy storage technology is a research hotspot to improve energy recovery and utilization,and it is also a key step in achieving sustainable energy development.As a phase change material with a large latent heat value and a suitable phase change temperature,in the energy storage field,sodium formate has brightly prospects,but it as well has the common weakness of low thermal conductivity of organic PCMs.This article studied sodium formate of different manufacturers and purity,and identified a sodium formate for follow-up research.Using the three-step method of "impregnation,briquetting and sintering",expanded graphite with different contents(0wt.%,5wt.%,10 wt.%,15 wt.% and 20 wt.%)was added to pure sodium formate to prepare a new type of stable sodium formate/expanded graphite composite phase change materials,and examined and researched the thermophysical properties and thermal stability of the PCMs.The test results showed that sodium formate and expanded graphite are only physically combined and have good chemical compatibility.Sodium formate can be well adsorbed on the porous structure of EG.Appending the expanded graphite reduces the latent heat value and also enhances the crystallization temperature and the thermal conductivity of the PCMs.As the percentage of EG raises from 0wt.% to20 wt.%,the latent heat value of the composite phase change material decreases from338.1J/g to 211.5J/g,and the thermal conductivity increases from 0.134W/(m·K)to0.199 W/(m·K),the crystallization temperature rise from 220.89? to 243.34?.The TG test shows that the sodium formate/expanded graphite composite PCMs has good thermal durability in the 200-300?.The parameters of the PCMs with an expanded graphite content of 5wt.% were selected for the next study.In addition,a heat accumulator was designed to exchange the heat of the fluid in the pipeline with the heat of the PCMs in the shell.A representative two-dimensional cross-sectional model of the heat accumulator was chose,and the model was used to simulate the characteristics of the PCMs during the solidification process and melting process using Fluent software.The changes in the liquid fraction,average temperature and outlet temperature of the PCMs are researchd.The conclusion demonstrated that in the period of the melting endothermic process,the mean temperature and outlet temperature of the PCMs enhance rapidly in the early stage and then gradually level off.The melting speed of the composite phase change material is first slow,then fast and then slowly increases;During the solidification exothermic process,the outlet and average temperature of the PCMs first decrease relatively quickly,and then decrease slowly.The solidification speed of PCMs is very fast,and then with the appearance of solid PCMs,the resistance improves and the solidification speed also slows down.A single variable way is served to simulate the phase transition process of the regenerator with disparate temperature and the velocity of the fluid,and then the PCMs characteristics of the regenerator are studied.And we found that during the melting process,the higher the inlet temperature,the faster the PCMs will melt.The greater the inlet velocity,the faster the outlet temperature rises;during the solidification process,the lower the inlet temperature of the heat transfer oil,the faster the solidification of the composite phase change material,and the faster the outlet temperature and the average temperature of the PCMs drop.The greater the inlet flow rate of the oil,the faster the outlet temperature will drop.The results of theoretical analysis can provide the reference basis for energy storage devices designed and operated in industry. |
PDF Full Text Request