Research On Thermal Performance Improvement Of Nano-Al₂O₃/Si₃N₄ Hybrid Paraffin Phase Change Microcapsules

In the context of the era of emission peak and carbon neutrality,the research on refined utilization of energy has received extensive attention.The Phase change microcapsules are that phase change material wrapped by wall material,so that the phase change material can achieve the purpose of energy storage and release by absorbing and releasing heat during phase change process,and at the same time solve the leakage problem of the phase change material in the actual application process.Conventional phase change microcapsules often use polymer organic wall materials,which hinders the heat absorption and desorption efficiency.High thermal conductivity nanomaterials were hybridized with microcapsule organic wall materials to obtain phase change microcapsules with high thermal conductivity.In electronic field,hybrid paraffin phase change microcapsules can be used as heat-absorbing and heat-dissipating materials.In field of construction,hybrid paraffin phase change microcapsules can be used as temperature-regulating materials to achieve the purpose of energy saving and emission reduction.In this paper,in view of problems of poor thermal conductivity of Conventional phase change microcapsules,the thermal conductivity of microcapsules can be improved by incorporating high thermal conductivity nanomaterials into the wall material.Firstly,Nano-Al₂O₃/Si₃N₄hybrid paraffin phase change microcapsules were prepared by in-situ polymerization using high thermal conductivity nanomaterials as wall modifiers.The microscopic morphology,thermal conductivity,heat storage performance,thermal stability and chemical structure were investigated.Secondly,the paraffin phase change microcapsules were optimized by studying the effect of the content of nano thermally conductive materials on the encapsulation rate and thermal properties of microcapsules.Finally,the wall material hybridization mechanism and thermal conductivity enhancement mechanism of paraffin phase change microcapsules were analyzed.The main work and research results of this paper are as follows:1.Encapsulation Index of Nano-Al₂O₃/Si₃N₄Hybrid Paraffin Phase Change Microcapsules.Compared with ordinary paraffin phase change microcapsules,Surface roughness and encapsulation rate of hybrid phase change microcapsules increase with the ccontent of nano thermal Conductive materials When the content of Nano-Al₂O₃was 14wt%,the encapsulation rate of Nano-Al₂O₃hybrid paraffin phase change microcapsules reached the highest of 81.7%.When the content of Nano-Si₃N₄was 3%,the encapsulation rate of Nano-Si₃N₄hybrid paraffin phase change microcapsules reached the highest of 81.2%.2.Heat storage properties of Nano-Al₂O₃/Si₃N₄hybrid paraffin phase change microcapsules.The phase change temperature of Nano-Al₂O₃/Si₃N₄hybrid paraffin phase change microcapsules ranges from 30℃to 32℃.When the content of Nano-Al₂O₃is 14wt%,the phase change latent heat and phase change temperature of the microcapsules are 121.5J/g and 31.6℃,respectively.When the content of Nano-Si₃N₄is 3wt%,the phase change latent heat and phase change temperature of the microcapsules are 120.8J/g and 31.0℃,respectively.3.Thermal conductivity of Nano-Al₂O₃/Si₃N₄hybrid paraffin phase change microcapsules.When the content of Nano-Al₂O₃is 0wt%～10wt%or the content of Nano-Si₃N₄is 0wt%～4wt%,the thermal conductivity of paraffin phase change microcapsules increases rapidly.When the content of Nano-Al₂O₃is 10wt%or the content of Nano-Si₃N₄is 3wt%,the thermal conductivity reaches a critical value,and then the growth tends to be stable.Compared with Micro PCMs,the thermal conductivity of paraffin phase change microcapsules with Nano-Al₂O₃ content of 10% and Nano-Si₃N₄content of 3wt%increased by 56.8%（0.2487W/m·K）and 47.9%（0.2346W/m·K）,respectively,and has good thermal stability.4.Mechanism of Nano-Al₂O₃/Si₃N₄Hybrid Paraffin Phase Change Microcapsules.Nano-Al₂O₃/Si₃N₄and melamine urea-formaldehyde resin constitute an organic-inorganic hybrid wall material,which improve the thermal conductivity of the wall material,and high thermal conductivity nanomaterials can be evenly distributed in wall material to form a network structure,so that the heat transfer channel inside and outside the microcapsules is formed,which fundamentally improves the thermal conductivity and heat transfer efficiency of the paraffin phase change microcapsules.