Experimental Study On Heat Storage Properties Of Composite Phase Change Materials

The latent heat storage of phase change materials has the advantages of large heat storage density,small volume of heat storage container,high thermal efficiency and constant during charge/discharge heat,compared to sensible heat storage.It was used for solar energy utilization,building energy saving,waste heat recovery,aerospace and other fields.Composite phase change materials is designed to overcome the shortcomings of pure phase change material and has better energy storage characteristics.Binary composite phase change materials?PCMs?of stearic acid?S18?and stearyl alcohol?C18?are prepared using melt blending method.The composite phase change material can not only overcome the disadvantages of quadratic phase change of stearyl alcohol,but also obtain suitable phase transition temperature.The phase transition temperature of S18-C18 mixture are measured using the method of cooling curves.The eutectic temperature of the binary composite is about 51.6?.The results of T-History method and DSC test show that the phase change latent heat of the eutectic composite phase change materials is about 210 J·g^-1.FT-IR spectra of the eutectic composite show that the compound of S18-C18 is mixed by molecular intro-atomic forces.High-low temperature cycling experiments between 35?and90??800 times?present that no stratification is observed for the composite phase change materials and phase change latent heat is almost unchanged.The phase transition temperature changes no more than 0.6?,and phase transition temperature of PCMs doesn't change after 400 times high-low temperature cycling tests.The thermal stability of the eutectic mixture of S18-C18 is good.The inorganic phase change material sodium acetate trihydrate has the disadvantages of phase separation and supercooling,but it has higher thermal conductivity than that of organic phase change material.Adding 3%nucleating agent?the quality ratio of tetrasodium pyrophosphate decahydrate and disodium hydrogen phosphate dodecahydrate was 2:8?,can make its supercooling degree down to1.79?.And adding 1.5%Carboxymethyl Cellulose?CMC?can be distributed evenly after repeated experiments.The sodium acetate?30%?was mixed with stearic acid and stearyl alcohol?mass ratio is 1:1?.The phenomenon of phase separation of the phase change material can be effectively improved by adding 1.8wt%Carboxymethyl Cellulose?CMC?,2.5%the mixture of span-80 and tween-80?the mass ratio of span-80 and tween-80 is 7:3?.The charge/discharge heat is done using cylindrical heat exchange device,the water flow is 148 L/h,135 L/h and 122 L/h and the temperature difference of inlet and outlet is no more than 1.5?.During the charge heat process of phase change materials,the axial melting time is difference at the same radial distance from the surface of the heat source.It shows that natural convection plays a crucial role during the process of heat transfer.During the discharge heat process of phase change materials,the axial solidification time is almost identical at the same radial distance from the surface of the cold source.It shows that conduction has the important effect for heat transfer.