Study On Novel Composite Phase Change Material And Its Application In Packed Bed Heat Storage System

The heat storage technology,as an important approach to enhance the efficiency of heat energy conversion and recovery,has been extensively applied in waste heat recovery and solar energy utilization.It can effectively solve the abandoning wind and light,and promote the consumption of renewable energy.At present,latent heat storage technology is a highly applicable option because of its quasi-isothermal charging/discharging processes and high storage capacity per mass or volume.The development of medium and low temperature phase change materials and the optimization of highly-efficient heat storage equipment are the key to realize the popularization and application of latent heat storage technology in industry.In this dissertation,a novel sodium acetate trihydrate(SAT)-based composite phase change material(CPCM)which is belonged to the medium and low temperature phase change field was developed in order to restrain the supercooling and phase segregation of pure SAT.The experimental results manifest that the addition of 3 wt%carboxymethyl cellulose(CMC)is resultful to constrain phase separation of pure SAT.Supercooling degree of pure SAT is reduced from 30? to 1.1? by adding 4 wt%sodium chloride(NaCl).Nano-copper(Nano-Cu)was furnished to further prevent the supercooling phenomenon of CPCM as well as intensify the heat transfer characteristics of pure SAT,and the CPCM with 0.8 wt%Nano-Cu has a minimum supercooling value of 0.8?.Thermal properties containing thermal conductivity,latent heat and specific heat capacity were systematically analyzed using DSC and thermal properties analyzer.The analysis results demonstrate that a satisfactory thermal conductivity,high latent heat(231.2 J·g^–1)and inclusive of an appropriate specific heat capacity are achieved by the optimum CPCM consisted of SAT,3 wt%CMC,4 wt%NaCl and 0.8 wt%Nano-Cu.Additionally,admirable thermal stability is retained by the CPCM.Based on the above research,structured packed bed heat storage configuration with encapsulated the CPCM,which can realize efficient heat transfer,was investigated through numerical simulation.The heat storage properties of the CPCM was studied,a superior structured packing format was explored,and a detailed parametric investigation of the packed bed heat storage configuration is implemented to analyse the effect of Reynolds number(Re),inlet temperature and Prandtl number(Pr)of the heat transfer fluid.The analysis results indicate:(1)superior heat transfer ability,better heat stoage and release are obtained by the CPCM in contrast to paraffin,and the heat storage energy and average heat storage power of the former are 2.57times and 2.85 times the size of that with the latter,respectively;(2)the packed bed heat storage configuration with face centre cubic packing possesses excellent characteristics,such as high charging rate,low investment cost,large total heat storage energy and stable output temperature,compared with that with body center cubic packing or simple cubic packing;(3)the packed bed with small inlet Re is a favorable option,but the smaller the Re is,the slower the discharging rate is.The discharging rate of packed bed decreases with the increase of inlet temperature,while the heat release process becomes more and more durable by increasing the inlet temperature.In addition,under the consisitent Re,the higher the Pr,the better the heat transfer performance.