Experimental Study Of The Thermophysical Properties Of Medium Or Low Temperature Phase Change Materials

Because of the disparity between energy supply and demand,heat storage technology plays a crucial role in new energy application and waste heat recovery.The heat storage technology,can be classified as latent heat storage,sensible heat storage,thermochemical heat storage and absorptive heat storage.Among the four heat storage technology,latent heat storage has received much attention in recent decades because it has merits such as large heat capacity,and no siginificant temperature variation in the process of phase transition.Phase change materials have a predominant role in heat storage technology.This paper focused on experimental study of two kinds of phase change materials.The first one was ternary molten salts consisting by calcium nitrate,sodium nitrate and potassium nitrate.The results showed that the mixture（Ca（NO3）2:NaNO3:KNO3=32:24:44,wt%）has the best performance for latent heat storage and its enthalpy is 67 J/g and melting point is about 80℃.The specific heat capacity,viscosity,thermal conductivity,thermal decomposition and cycle stability of the molten salts were also measured.The thermophysical properties including the low manufacturing cost showed that the molten salts have great potential application in thermal storage systems.The other one was barium hydroxide（Ba（OH）₂.8H₂O）and its melting point is 78℃and its latent heat is 572 KJ/L.Although it has large heat capacity,it shows siginificant supercooling phenomenon and phase separation during its cooling process.This study used sodium borate、copper powder、calcium fluoride、calcium chloride and calgon as nucleating agents to suppress the supercooling phenomenon of barium hydroxide.In addition,the experiment also used gelatin to suppress the phase separation of barium hydroxide.The experimtal results indicated that the addition of 5%sodium borate、1%copper powder、1%calcium fluoride、1%calcium chloride and 1%calgon can reduce the supercooling degree and the addition of 1%gelatin can hinder the phase separation effectively.The thermal conductivity、cycle stability and specific heat capacity were also measured in the experiment.The favorable thermal stability、large heat capacity and low price showed that barium hydroxide（Ba（OH）₂.8H₂O）is a good candidate for phase change materials.