Study On Application Of Stabilized Capric Acid/stearic Acid Phase Change Material In Thermal Storage Concrete

With the acceleration of urbanization process in China,building energy consumption is becoming more and more serious,the proportion of total energy consumption in the society is increasing and the total volume is gradually rising.Now it has become a hot topic of current social concern about how to reduce building energy consumption.Phase change material(PCM)can store and release energy under specific conditions,so if it is applied to concrete,the concrete can achieve energy transition in different time and space through its phase transition process.In this paper,fatty acid eutectic mixture is used as phase change material(PCM),then the stabilized composite PCM is prepared by adsorption through the porous ceramsite.After being modified in its surface,it is applied as aggregates to the concrete to obtain phase change thermal storage concrete.The mixture of capric acid-stearic acid(CA-SA),capric acid-myristic acid(CA-MA)and capric acid-lauric acid(CA-LA)were subjected to eutectic ratio calculation and phase transition temperature prediction by Schroeder's formula,then step cooling test and DSC test were used to further verify.The results showed that the eutectic ratio(wt%)of CA-SA,CA-MA and CA-LA mixture were respectively 86-14,74-26 and 65-35,phase transition temperatures were respectively 25.6?,21.8?and18.7?.The difference between DSC test and step curve was smaller than the theoretical calculation.Based on the phase transition temperature of building phase change material and the thermal comfort of human body,CA-SA eutectic mixture was selected as PCM.After CA-SA eutectic mixture was suffered multiple melt-solidification cycles,FT-IR analysis found that it could still maintain good compatibility and structural stability.DSC test indicated that phase change temperature was nearly 25?,and phase change latent heat was about 165J/g,it has good thermal stability as before.The stabilized CA-SA PCM was produced by vacuum adsorption method using porous ceramsite as matrix material.It turned out that ceramsite absorbed PCM about60 minutes to steady state,and the mass adsorption rate was up to 31%.SEM showed that a large number of PCMs were adsorbed into ceramsite pores.FT-IR analysis discovered that new characteristic absorption band didnot appear in the infrared spectrogram,ceramsite and PCM were only physically bonded.DSC test showed that the phase transition temperature of stabilized CA-SA PCM was 1?higher than that of PCM,and the theoretical calculation of phase change latent heat was reduced about10.3%.Then sodium alginate reaction,cement slurry and silica sol were used to encapsulate stabilized CA-SA PCM,The results turned out that the encapsulation effects of sodium alginate reaction and cement slurry had different degrees of leakage,but the encapsulation effect of silica sol was still good.Therefore,silica sol was used as a packaging material in this paper.The stabilized CA-SA PCM encapsulated by silica sol were used as aggregates to prepare phase change heat storage concrete.With the extension of curing age,increase of mixing amount of stabilized CA-SA PCM and increase of thermal cycling times,the compressive and flexural strength of phase change heat storage concrete both enhanced.According to heat storage performance test,the heating and cooling rate of phase change heat storage concrete experimental room were lower than the ordinary concrete experimental room,the central temperature difference could be up to 6?,and the effect of heat storage performance was better than that of ordinary experimental room.The volume density of phase change heat storage concrete declined after continuous thermal cycles,but the decreasing level was smaller than the ordinary concrete.When phase change heat storage concretes experienced 600thermal cycles,there were no defects and no leakage in its surface,it had good thermal stability and durability.After thermal calculation,When the concrete layer of202mm external wall was mixed with 4.68kg/m~2 stabilized CA-SA PCM,it could achieve the same thermal insulation effect to 282mm standard external wall,and thermal performance of the external wall was significantly improved.