Molten Salt/spinel-based Composite Phase Change Heat Storage Materials Prepared By In-situ Reaction Process

The properties and the current research status of phase change heat storage materials are introduced. Moreover, the preparation and properties of high-temperature composite phase change heat storage materials are also discussed. The factors of molten salt/spinel high-temperature composite phase change heat storage materials by in-situ sintering process are discussed. The influences of molten salt content, mixture ratio of molten salt and different additive graphite on the performance of molten salt/spinel high-temperature composite phase change heat storage materials are studied.Molten salt/MgAl2O4 spinel high-temperature composite phase change heat storage materials are prepared by in-situ sintering process, which is based on spinle ceramic substrate raw materials of magnesia and corundum powder, and molten salt as reaction medium. The influences of sintering temperature, different magnesia/alumina proportion and kinds of molten salt on the performance of molten salt/spinel phase change heat storage material are investigated. The materials are characterized by XRD and SEM. The result show that, the preparative materials show the better performance using KCl-KF complex salt as phase change materials at theoretical ratio when the appropriate sintering temperature is 1000℃.The influences of molten salt content on the performance of molten salt/spinel high-temperature composite phase change heat storage materials are studied. The materials'latent heat is measured by DSC thermal analysis, thermal conductivity is detected by laser flash method,and the flexural strength of the materials is also studied in the heating process. The results show that prepared materials show better heat storage performance, with phase change latent heat of 70.98kJ/kg, heat-storage density of 240 kJ/kg (ΔT = 100℃) under the condition of sintering temperature 1000℃, molten salt content 40%; Thermal conductivity decrease with the molten salt content increase. The flexural strength of samples reaches the maximum at 600℃, which increas with temperature raise.Molten salt/spinel high-temperature composite phase change heat storage materials are prepared by changing the mixture ratio of molten salt, which suit for different melting temperatures. KF content increase, compressive strength and flexural strength of samples decrease, thermal conductivity decrease, respectively.The properties of ceramic substrate are studied after molten salt leaching, and the properties of the encapsulated samples are discussed initially. Results show that ceramic substrate has certain strength after molten salt leaching, and its compressive strength change with content of additive molten salt. Otherwise, evaporation loss of molten salt reduces during cycle using process after coating. The effects of additive graphite on the molten salt/spinel high-temperature composite phase change heat storage materials are studied. The exothermic processes of samples are simulated by input experimental data using ANSYS. The results showed that thermal conductivity of samples is effectively improved by adding graphite, but the increase of graphite content is not helpful for the formation of spinel. Thermal conductivity of samples dominates their exothermic process. The greater thermal conductivity, the faster samples heat transfer, and the smaller temperature difference. Materials with 10% graphite additive reached phase change temperature at 600s, while the materials with no graphite additive need 1000s reach that temperature.