Thermal Performance Analysis Of Double-layer Phase Change Material Wall

In this paper,for the problem that single phase change material(PCM)can not meet the energy-saving requirements of winter and summer in buildings,it is proposed to simultaneously fill two PCMs with different phase transition temperatures into the foundation wall enclosing structure(the internal matrix material).The two-layer PCM composite wall is formed in different or different positions of the base material.In this paper,the sensible heat capacity method is used to discretize the mathematical model by finite difference method.The MATLAB software is used to calculate and analyze the double-layer PCM wall with different structures in the typical summer hot and cold winter climate.After the variable temperature hot box experiment,the thermal properties of the PCM are considered in the material selection to ensure that the relevant thermal performance meets the requirements.For walls with PCM,the standard error of experimental and analog values is less than 1°C,and the maximum relative error is less than 7%.The values calculated by MATLAB are generally in good agreement with the experimental values and can be used for engineering calculation of related heat transfer problems.The optimal phase change temperature range of the ideal PCM is explored by using the attenuation multiple as the index,and the most suitable PCM is selected from the actual PCM as the research object of this paper.The actual PCM wall thermal performance is compared to the ideal PCM wall thermal performance.The thermal performance of PCM in summer and winter conditions is discussed by changing the placement of the two PCMs.After comparing and analyzing the thermal performance of four different wall envelope structures,it is found that the PCM can adjust the indoor temperature change,and the adjustment effect of the PCM position in the wall on the indoor temperature is also different.Studies have shown that in any of the four different wall envelopes,when any type of PCM is placed on theoutermost or innermost side of the wall,it will cause a large fluctuation in indoor temperature and a poor temperature regulation effect.When the wall envelope is composed of cement mortar,insulation material,block material and lime mortar from the outside to the inside,the two PCMs are placed slightly on the inside of the wall(the PCM with lower phase transition temperature is at a higher phase transition temperature).The wall temperature adjustment effect is best.For a wall containing PCM,the specific heat of the PCM will fluctuate greatly within a certain temperature range,so the corresponding heat transfer is nonlinear,so the thermal performance cannot be accurately described by the attenuation factor and the delay time.A new evaluation index was proposed: PCM utilization.The research shows that when considering both winter and summer,when PCM1 and PCM2 are located slightly on the inner side of the wall(PCM1 is located inside PCM2),the wall has the largest attenuation factor and the longest delay time.The solidification utilization rate of PCM1 in winter and the melting utilization rate of PCM2 in summer are between 0 and 100%.Both PCMs have more room for state change,and the thermal performance of the wall is the best.