Preparation And Modification Of MgCl₂·6H₂O/MgSO₄·7H₂O Based Low Temperature Phase Change Composite Heat Storage Materials

In recent years,the continuous and stable supply of energy-saving and environmentally-friendly renewable energy has become one of the main challenges in solving energy problems.In this paper,MgCl₂·6H₂O is used as the main phase change material,and the effect of MgSO₄·7H₂O on the MgSO₄·7H₂O（MSH）-MgCl₂·6H₂O（MCH）composite phase change material were studied;it is further modified by adding activated carbon（ACC）,the effect of activated carbon on the heat storage capacity,phase transition temperature,subcooling degree and cycle stability of the composite phase change system were studied;on the basis of the MCH-MSH-ACC system,through the reconciling of trace paraffin（PA）,the influence of organic paraffin on the phase change heat storage performance of inorganic salt phase change materials were studied.Draw the following conclusions:（1）The MgSO₄·7H₂O（MSH）-MgCl₂·6H₂O（MCH）composite phase change material system was prepared.The influence of trace MgSO₄·7H₂O（MSH）on the phase changeproperty and kinetic property of the hydration and dehydration process of the phase change material of the composite system were studied,and the research results show:when the mixing ratio of MSH and MCH is 1:19,the MSH/MCH composite system exhibits the smallest degree of supercooling,which better inhibits the phase separation phenomenon,and the phase change enthalpy is stable at254.43k J/kg,which shows good overall performance.（2）Activated carbon with porous structure and good thermal conductivity was used as the additive of the phase change material system,and the effect of activated carbon content on the compatibility,phase change characteristics,thermal decomposition stability and thermal conductivity of the MCH-MSH-ACC composite system were studied.The research results show:adding an appropriate amount of ACC can effectively eliminate the supercooling of the MCH-MSH system and reduce the phase transition temperature of the system.When the added mass fraction of ACC is 3%,the initial and final phase transition temperatures of the MCH-MSH-3.0%ACC system during the heating process are 95.45℃and 102.54℃respectively,and the initial phase transition enthalpy reaches 286.45k J/kg and the stable phase change enthalpy is 260.42k J/kg.And the composite material showed good stable performance in the cyclic test.（3）Organic phase change material paraffin as a strengthening agent to build an organic-inorganic PA/MSH-MCH-ACC composite phase change material system that was coordinated and strengthened by paraffin,and study the effect of paraffin wax on the system stability,heat storage capacity and cycle stability of the organic-inorganic composite phase change material system.The research results show:the prepared new PA/MSH-MCH-ACC composite material has good heat storage performance,good cycle performance and more effective heat utilization rate.When the PA content is0.5%,the heat storage time is the shortest,the heat release time is the longest,and the enthalpy change can reach 321.75k J/kg.And after the cycle test,the phase change enthalpy is stable at 310.25k J/kg.With the increase of PA content,the temperature of the exothermic phase change of the composite system increases,the exothermic time becomes shorter,and the heat storage decreases.It shows that the addition of a small amount of paraffin is beneficial to improve the phase change heat storage performance of the PA/MSH-MCH-ACC system,but the addition of paraffin cannot be too much.Too much paraffin addition will worsen the phase change heat storage performance of the system.The research results of this paper are of great significance for understanding the heat storage principle of heat storage materials and conducting follow-up research.