Study On Dynamic Heat Insulation Mechanism And Performance Optimization Of Phase Change Composite Wall

The research on the application of Phase Change Material(PCM)to building wall mainly focuses on the temperature regulation of building envelope in cold area.However,the research on the application of phase change wall in the building exterior wall insulation in summer is not deep,especially in the area of small temperature difference between day and night in summer.In this paper,based on the principle of phase change heat transfer,the dynamic heat insulation characteristics and performance optimization of composite phase change wall in hot summer and warm winter zone are studied.The whole cycle dynamic heat insulation of the Composite Phase Change Wall is analyzed in hot summer and warm winter zone.According to the characteristics of melting heat absorption and solidification heat release of PCMs layer,the phase change heat transfer of PCMs layer in the phase change cycle is analyzed.In this paper,a full-cycle dynamic heat insulation model of composite phase change wall is proposed;In full cycle dynamic thermal insulation mode,the effects of phase change time,phase change temperature,thermal conductivity,latent heat of phase change and heat release direction of solidification on the thermal insulation performance of PCM composite phase change wall were studied.The mathematical model of the whole cycle dynamic heat transfer of the composite phase change wall is established.Based on the mathematical differential equation and The First Law of thermodynamics,the equivalent enthalpy method is used to establish the enthalpy equation for calculating the phase change time of the PCM layer;A simplified "parallel + series" dynamic heat transfer model is put forward,and a heat transfer mathematical model is established under the full cycle dynamic heat insulation model of the Composite Phase Change Wall,the differential governing equations of heat transfer are solved numerically by using the separation variable method and the equivalent heat capacity method.The preparation and characterization of composite phase change materials for thermal insulation were carried out.Based on the concept of full-cycle dynamic thermal insulation of Composite Phase Change Wall,the principle and method of selecting PCM and its load base to meet the thermal insulation requirements are presented,the optimum ratio(2:98,1:8:1)and the maximum adsorption rate of the carrier group to the sepiolite are 57.14%,the demagnesization rate of the sepiolite is 45.63% after acid(hydrochloric acid)modification,and the sepiolitebased composite phase change material is prepared,the phase change temperature and latent heat are 40.94/39.7 °C and 120.3/122.5 J/g respectively Based on the improved T-history method,the specific heat,thermal conductivity and latent heat of PCM in solid and liquid state are measured and calculated,and the basic parameters of PCM and its composites are obtained,it provides basic data for theoretical calculation of full cycle dynamic thermal insulation mathematical model of PCM layer.The reliability of the full cycle dynamic thermal insulation mathematical model is verified,and the factors affecting the thermal insulation performance are analyzed.The Composite Phase Change Cement Board was prepared,the testing platform for the thermal insulation performance of the Composite Phase Change Wall was set up,and the testing scheme was worked out,the reliability of the mathematical model for the full cycle dynamic heat insulation of the Composite Phase Change Wall is verified,the maximum deviation is 9.8%.The effects of phase change latent heat,phase change temperature,thermal conductivity and PCM thickness on the thermal insulation performance of PCM composite phase change wall are studied.The structure optimization scheme of PCM layer on the composite phase change wall is proposed.The PCM layer structure optimization scheme(namely PCM1 layer + air layer +PCM2 layer)based on the hollow plate is proposed,and the double-layer PCM plate is applied to the test platform,the average temperature difference between the Test Chamber and the Reference Chamber is 6.5 °C(East),7.2 °C(south),9.3 °C(West)and 5.2 °c(north),respectively,the maximum deviation between the measured value and the theoretical value is1.4%,which is within the acceptable range.The reliability of the calculation method is verified The influence of different phase change temperature and heat conduction on the dynamic thermal insulation performance of double-layer Composite Phase Change Wall was studied.