Preparation And Application Of Paraffin-based Composite Phase Change Material

In the selection of phase change materials,paraffin wax is more and more widely used in recent years because of its advantages such as high latent heat and rich phase change temperature,but because paraffin has the disadvantage of difficult to encapsulate and low thermal conductivity,expanded graphite is often used as the carrier material to shape paraffin.Although paraffin / expanded graphite composite phase change material can solve the leakage problem of paraffin wax and improve the thermal conductivity of paraffin wax to a certain extent,the volume of paraffin wax / expanded graphite is larger and there are some limitations in the application of paraffin package.therefore,this paper discusses the minimum mass fraction of expanded graphite to shape paraffin wax,and on this basis,high thermal conductivity particles of silver and copper powder are added to improve the thermal conductivity of the composites.Silver-copper powder / expanded graphite / paraffin composite phase change materials were prepared.In order to prepare composite phase change materials,silver-copper powder was fully dispersed in paraffin wax with a phase transition temperature of 44 ℃,and then the mixed dispersion was loaded into expanded graphite at 65 ℃.The latent heat values of composite phase change materials containing 0%,5%,7%,10%,15% and 20% of expanded graphite were tested and analyzed,and the thermal conductivity and leakage rate of loose phase change materials and compacted phase change materials were also compared and analyzed.Finally,it is determined that the composite ratio of 10%expanded graphite / paraffin composite phase change material is more appropriate,and the composite can maintain a more complete micro-worm structure and a more stable setting state at the same time.The leakage rate of this proportion of composite phase change materials is lower,less than 5%,and the latent heat value is about 14% lower than that of pure paraffin.Then silver-copper powder / 10% expanded graphite / paraffin composite phase change materials containing silver-copper powder with mass fraction of5%,10%,15%,20% and 25% were prepared.at the same time,the thermophysical parameters such as leakage rate,latent calorific value,phase transition temperature,thermal conductivity and thermal stability of the new phase change material were tested and analyzed.The experimental results show that the composite ratio of 15% silver copper powder / 10% expanded graphite / paraffin composite phase change material is appropriate,the composite can maintain a good setting effect,and has little effect on the latent heat value of expanded graphite / paraffin setting material.At the same time,it has high thermal conductivity and good thermal stability,which can meet the requirements of material characteristics in the following application experiments.In order to fully explore the properties of composite phase change materials,a kind of milk bottle with cooling and heat preservation was developed by applying it to doublelayer containers.The composite phase change materials containing different mass fractions of silver and copper powder were filled into the milk bottle model,hot water was added,the temperature changes of hot water and phase change materials in the model were recorded,and the change curve of temperature with time was described.First of all,different ratios of composite materials to hot water are added.According to the temperature curve,when the ratio of composite materials to hot water is 1: 1.5,the comprehensive performance of the milk bottle is better,the cooling time is shorter and the holding time is longer.Under this ratio,the effects of different mass fractions of silver and copper powder on the performance of heat preservation milk bottles were also discussed and analyzed.The comprehensive analysis shows that 15% silver copper powder / 10% expanded graphite / paraffin composite phase change material can make the thermal insulation milk bottle have better performance.on this basis,the cooling rate of the thermal insulation milk bottle is 82.7% higher than that of ordinary milk bottles.at the same time,it has better heat preservation ability.Therefore,15% silver copper powder/ 10% expanded graphite / paraffin composite phase change material is applied to reduce heat preservation milk bottles,so that hot water / milk can not only cool down to the temperature of brewing milk powder in a short time,but also achieve the function of heat preservation at this temperature.Therefore,the proposed composite material can be used in cooling milk bottles.The results show that the milk bottles can meet the needs of rapid cooling to brewing temperature and heat preservation.