Experimental Analysis And Numerical Simulation Of Intermittent Heat Release Of Shaped Phase Chang Materials

Shaping composite phase change materials have the characteristics of large latent heat value of phase change,high thermal conductivity,simple molding,etc.,which make the phase change heat storage technology has high industrial value.It is applicable to power battery temperature control,electronic device thermal management,electric vehicle defrosting and other fields,so it is of great significance to the optimization of phase change heat storage system.Most of the studies are carried out from the perspective of the properties of phase change materials and the optimization of heat exchangers,and lack of the exploration of heat release mode.Therefore,this paper studies the influence of periodic heat release on the performance of phase change heat storage system through the intermittent heat extraction method of heat transfer fluid,and optimates the heat release conditions.Firstly,a cylindrical phase change heat storage unit is prepared using erythritol/expanded graphite composite phase change material,and the relative thermal physical properties of the phase change heat storage unit are measured.The results show that its average phase transition temperature is 117.39?,the phase transition latent heat value is 308.7k J/kg,and the average thermal conductivity is 4.5W/(m·K).The phase transition process is stable without attenuation.On this basis,a phase-change heat storage experiment platform with water as the heat transfer fluid was built,and the single-factor module in the response surface method was used to design the experimental plan,and the phase-change heat storage unit was subjected to periodic heat release experiments.An evaluation system based on the total heat release power,Stephen number,and exergy efficiency of thermal materials.The study found that: the flow rate of the heat transfer fluid and the inlet temperature remain unchanged.When the intermittent time is 20 minutes and the accumulative heat release time of the heat storage unit is 40 minutes,the evaluation indicators all increase with the increase of the operating time,and there is a trend of first increasing and then decreasing.Among them,the emergence of extremum efficiency is about 22% behind the other two indicators.Based on comprehensive considerations,a running time of 7.7min is the best result.Then build a numerical simulation model of the heat storage unit,and firstly study the internal heat self-balance phenomenon of the phase-change heat storage unit during the intermittent system of the phase change heat storage unit.It is found that the heat self-balance can effectively improve the heat release performance of the heat storage unit.The intermittent time of 7min is the most preferable the result of.Then use the BBD module in the response surface method to design a simulation program to explore the effect of running time,heat transfer inlet temperature and flow rate on the heat release performance of the heat storage unit,and find that to=15min,Tin=36.596?,v=0.3m/s It is the combination that makes the evaluation index the best,and the fluid flow rate has the highest sensitivity to the heat release performance.Finally,based on the original model,under the premise of the same quality,the target heat release power is given,and the matching of the qualitative size of the phase change heat storage unit with the heat release power is studied.It is found that every time the qualitative size is reduced by 0.01 m,the heat storage unit The heat release performance is improved by about 18% on average.The research results of this paper are beneficial to further optimize the heat release operation mode of the phase change heat storage system,and the research mode provided also provides new ideas for the optimization of the performance of the phase change heat storage system.