Study On Preparation And Thermal Properties Of Paraffin Microcapsules And Their Modified Materials

In recent years,to alleciate the environmental pressure caused by wood drying,wood solar drying technology has been concerned.In order to meet the application requirements of the thermal storage unit of wood solar drying system,response surface method was used to optimize the preparation process of paraffin microcapsules.And the influence of experimental factors on the encapsulation and thermal properties of paraffin microcapsules was investigated.On the other hand,carbon nanotubes（CNTs）and zirconium carbide（Zr C）nanoparticles were used to modified paraffin microcapsules to further enhance the thermal properties.And the influence of nano-materials on thermal conductivity,phase change performance,thermal storage and release time and photo-thermal conversion performance were investigated.The results are as follows:（1）The optimal preparation process conditions of paraffin microcapsules:HLB value of composite emulsifier is 10,mass ratio of SDS to paraffin is 3.25:100,mass ratio of water to paraffin is 1.8:1, mass ratio of core material to wall material is 1.6:1.The obtained paraffin microcapsules showed smooth surface,dense spherical structure.The thermal conductivity is 0.1526W/（m·K）,latent heat is 105.93J/g.（2）The preferred preparation process conditions of CNT-paraffin microcapsules:mass ratio of PSS （sodium 4-styrene sulfonate）to paraffin microcapsules is 4:100,mass ratio of NH₂-CNT（aminated carbon nanotubes）to paraffin microcapsules is 15:100,assembly time of PSS is 2h,and assembly time of CNT（carbon nanotube）is 3h.The results showed that the prepared CNT-paraffin microcapsules performed low particle size and the entangled CNTs were observed on surfaces.Latent heat is 76.69J/g and thermal conductivity is 0.2066W/（m·K）,which is 36.28%higher than that of paraffin microcapsules.（3）Zr C nanoparticles were doped in the wall material of paraffin microcapsules to prepare the microcapsules modified by different concentration of KH550-Zr C nanoparticles.When the mass fraction of KH550-Zr C nanoparticles is 4%,the obtained Zr C-paraffin microcapsules showed a small particle size and uniform distribution.The thermal conductivity is 0.4962W/（m·K）,which increased by 225.16%compared with paraffin microcapsules.The latent heat is 121.74J/g,which increased by 87.08%compared with paraffin microcapsules.In addiation,Zr C-paraffin microcapsules exhibited good heat storage and release performance.It only took 34min in rasing from 25℃to 80℃,which decreased by 47.69%compared with that of paraffin microcapsules.（4）The addition of Zr C nanoparticles makes Zr C-paraffin microcapsules show good photo-thermal conversion performance.The results show that paraffin microcapsules with 4%mass fraction of KH550-Zr C nanoparticles behave good light absorption in the full-spectral.The light absorption capibiliy is 70.23%,which increased by 247.67%compared with that of paraffin microcapsules. Under solar radiation,the heat storage capacity of 4%Zr C-paraffin microcapsules is 83.17J/g,which is 250%higher than that of paraffin microcapsules and the photo-thermal conversion efficiency is47.72%.