Study On The Preparation And Thermal Conductivity Of Phase Change Composite Material

Phase change materials?PCMs?have been widely used in the thermal storage system,but most of them have poor thermal conductivity and easy to leak.The diadvantage of PCMs could be solved by adding heat conductive materials or preparing stereotypical phase change composites.In this paper,copper foam,boron nitride and nitrided boron aerogel acted as supporting materials respectively.Paraffin,stearic acid,polyethylene glycol and the solar salt?mixture of potassium nitrate and sodium nitrate?were selected as phase change materials.Scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,X-ray diffraction?XRD?,differential scanning calorimetry?DSC?and thermogravimetric analysis?TGA?and thermal analysis method were applied to test and characterize the supporting material,phase change material and phase change composite material.Also,the paper emphasized on the study of thermal property and thermal stability of the phase change composite materials.Part I:The surface roughness of copper foam was increased by oxidation,and then was modified by vapor deposition.A series of phase change composite materials were prepared by vacuum impregnation and atmospheric pressure impregnation with modified copper foam as supporting material,paraffin or stearic acid as phase change materials.SEM shown that the phase change materials were well adsorbed on the surface of the copper foam.XRD proved that the copper-based phase change composite materials were physical combined without chemical reaction,but the crystallinity of the phase change material was reduced.The DSC and TG proved that the prepared phase change composite materials have good thermal stability and thermal storage ability,and the latent heat of phase change nearly unchanged after 100 cycles of cold and heat.The thermal conductivity of the phase change composite material was tested by a laser thermal conductivity meter.The results showed that the thermal conductivity of the phase change composite material is several times higher than that of the pure phase change material and the thermal conductivity of the prepared phase change composite material has been greatly improved.Part II:Hexagonal boron nitride was selected as the heat transfer material,and ultrasonic method was used to peel the boron nitride.A series of phase change composite materials were prepared by mixing boron nitride and stripped boron nitride with a certain amount of solar salt.The appearance of the stripped boron nitride nanoscale was observed through TEM,and the thickness of the nanoscale was 1.118 nm after the atomic force microscope tested.XRD confirmed that boron nitride,stripped boron nitride and solar salt are physically complex.DSC showed that the prepared boron nitride phase change composite has high latent heat and good thermal stability.Thermal conductivity of the phase change materials was tested by laser thermal conductivity meter.Thermal conductivity of the phase change composite materials increased with increasing of boron nitride and stripping boron nitride,which improved that thermal conductivity of the phase change composite materials can be efficiently enhanced by boron nitride.By contrast,thermal conductivity of the phase-change materials was improved by the ultrasonic peeled boron nitride,furthermore,the phase change material's thermal conductivity was still excellent after 50 thermal cycles,which shown that the peeled boron nitride has higher thermal stability.Part III:The boron nitride aerogel was prepared as the supporting material to adsorb stearic acid,polyethylene glycol and paraffin respectively to fabricate the phase change composite material.SEM and TEM observations shown that the boron nitride aerogel is a three-dimensional structure,and the phase change material is adsorbed in the channel and the outer surface of the boron nitride aerogel.DSC shown that the phase change material supported by the boron nitride aerogel has higher latent heat within 144.74 J g^-1 to 146.2 J g^-1,which proved that the phase change composite material has good heat storage ability.