Preparation And Properties Of Nano/Micro-particles Composite Magnesium Nitrate Hexahydrate Composite Phase Change Thermal Storage Materials

Salt hydrate is one kind of the important materials for the mid and low phase change materials due to its high heat storage capacity per volume,constant phase transition temperature,low cost and so on,which has a good prospect in the building heating in China.In this thesis,magnesium nitrate hexahydrate?MNH?has been chosen as the object owing to its suitable phase change?89.57 ^oC?and high heat fusion(157.3kJ·kg^-1)for the building heating.The effects of?MNH?and different additives and contents on the properties of MNH based composite phase change materials were studied,which combines theoretical analysis with experimental research.The thermal performance and photo-thermal properties of phase change materials directly determine the heat transfer efficiency of the system and the utilization rate of renewable clean energy.Therefore,the effects of additives on the thermal performance and photo-thermal properties of MNH based composite phase change materials were studied.Blending 3%sodium carboxymethyl cellulose?CMC?,the viscosity of composite phase change materials increases from 0.18 to 163.86 mPa·s,effectively improving the phase separation problem.Compared with nanosilver and nanocopper,carbon nanosphere and graphite nanoplates can reduce effectively the supercooling degree.After blending 1.5%graphite nanoplates,the supercooling degree decreases from23.12 of pure MNH to 2.98 ^oCThe addition of graphene not only effectively improves the thermal conductivity of MNH composite phase change material,but also effectively increases its photo-thermal conversion performance.The value for the absorption capacity of graphene is 78.14%,significantly higher than 46.54%of MNH and 28.65%of CMC.With the increase of graphene content,the absorption capacity of the composite phase change material is higher.Meanwhile,as the optical absorption capacity of MNH in the region of ultraviolet light and near-infrared light is higher than that of graphene,when blending 5%graphene,MNH based composite phase change material has the absorption capacity of 79.12%,higher than that of pure graphene?78.14%?.Compared to graphene,Ti₄O₇ has higher light absorption capacity,which is 87.73%.Due to the absorption capacity is much higher than MNH and CMC,therefore,with the increase of Ti₄O₇ mixed mass fraction,the composite phase change materials of sunlight absorption capacity also gradually increases,when the value for blended graphene mass fraction is 10%,the composite phase change materials has photo-thermal storage efficiency of 78.6%.The new photo-thermal salt hydrate phase change materials are very promising materials for solar-to-thermal conversion and energy storage.