Study On Heat Storage Performance Of Mineral Phase Composite Change Concrete Slabs

When phase change materials are combined with roof building materials,the problems such as high peak temperature of roof in summer,large fluctuation of indoor temperature of roof,large cooling load of the roof layer air conditioner and poor thermal comfort can be solved properly.In this project,the porous structure of diatomite is used to adsorb phase changematerials,forminganewbuilding materialwithtemperatureregulation function..Firstly,SA-MA eutectic systems with different mass ratios were prepared.The diatomite-based shaped phase change materials with different SA-MA composite phase change materials were prepared by liquid phase intercalation method using diatomite modified by roasting and strong alkali.Phase change heat storage concrete slab is made by mixing diatomite-based shaped phase change material with concrete.The step-cooling curve method,SEM,DSC,FT-IR,TG test and thermal stability test were carried out on the materials in the preparation process.At the same time,the thermal insulation performance of the phase change roof is simulated,and the following conclusions were obtained:?1?The lowest eutectic ratio of SA-MA eutectic system is m_SA:m_MA=39:61,The lowest phase transition temperature and phase change latent heat of SA-MA eutectic system are41.7?and 169.6 J/g,respectively,and there is no suppercooling phenomenon.The theoretical calculation mass ratio is the same as the experimental ratio of the test.The maximum error of phase transition temperature measured by theoretical calculation,Step-cooling curve method and DSC method is 1.02?.The FT-IR test method showed that the spectral shape and characteristic peak of SA-MA composite phase change material were consistent with tetradecanoic acid and stearic acid,which proved that there was no chemical reaction in SA-MA composite phase change material.In 600 thermal cycles,the phase transition temperature of the SA-MA eutectic system did not change after 350 cycles,and the phase transition temperature decreased by 1.6 C compared with that before cycles.?2?From the appearance,the PCM mass fraction 15%-55%diatomite-based shaped phase change material has no obvious leakage.According to the step-cooling curve method test,the PCM mass fraction of 15%and 25%of the diatomite-based shaped phase change material has very few PCM,and the duration of the temperature drop curve platform is too short to meet the experimental requirements.The PCM mass fraction reaches 50%or more,and the effect of prolonging the phase transition duration of the shaped phase change materials becomes less and less obvious.According to the principle of economy,the optimum PCM content of diatomite-based shaped phase change materials is 50%.SEM,DSC,FT-IR,TG and thermal stability tests were performed on PCM mass fraction of 50%of diatomite-based shaped phase change materials:SA-MA composite phase change materials are evenly filled in the pore of diatomite and well combined with modified diatomite;The phase transition temperature and phase change latent heat of PCM mass fraction 50%diatomite-based shaped phase change material are 42.45?and 59.88 J/g,respectively;The spectral shape and characteristic peak of PCM mass fraction 50%of diatomite-based shaped phase change material are consistent with SA-MA composite phase change material and modified diatomite.There is no chemical reaction between SA-MA composite phase change material and modified diatomite in diatomite-based shaped phase change material;The diatomite-based shaped phase change material has good thermal stability below 200?and low leakage rate after 400 thermal cycles,which meets the requirements for application in the construction field.?3?The higher the mass fraction of the diatomite-based shaped phase change material,the longer the heat storage and release time of the phase change heat storage concrete slab is,and the temperature delay phenomenon appears on the inner and outer surfaces.The peak temperature of the concrete slab can be effectively reduced by incorporating the diatomite-based shaped phase change material,but as the mass fraction of the diatomite-based shaped phase change material increases,the reduction range decreases.When the mass fraction of the diatomite-based shaped phase change material increases,the temperature difference between the inner and outer surfaces of the phase change heat storage concrete slab increases,but the mass fraction of the diatomite-based shaped phase change material increases to more than 25%,and the temperature difference between inner and outer surface decreases.The leakage rate of phase change heat storage concrete blocks after 400 thermal cycles meets the requirements of long-term use of buildings.According to the economic and thermal performance,the optimum content of the diatomite-based shaped phase change material in the phase change heat storage concrete slab is 25%.?4?Based on the typical summer day in Ganzhou,the numerical simulation method was used to analyze the heat insulation of the phase change roof.Compared with the ordinary roof,the internal surface temperature of the phase change roof is reduced by 2.97?,the temperature fluctuation is small,and the fluctuation of outdoor temperature is delayed by 1h,and the hourly heat flow distribution curve is more gentle.The average heat flux density fluctuation on the inner surface of the phase change roof is reduced by up to 45.9%compared to the normal roof.The position of the phase change layer has a great influence on the roof insulation capacity,and the trend of the heat flux change is basically the same.The phase change layer position is more beneficial to the transmission of the heat insulating amount when the second layer of the roof structure is located.Compared with the ordinary roof,the daily heat is reduced by 20.7%,which reflects the good thermal insulation performance of the phase change roof and the energy saving effect is remarkable.