Preparation And Properties Study Of Binary Composite Shaping Phase Change Material

Phase change energy storage technology is a technology that uses phase change materials to store heat by absorbing or releasing a large amount of latent heat during the phase change process.The material accompanies change in the state of matter during the phase transition,but the temperature of phase change materials is constant.It can store sensible heat and latent heat at the same time and provide high unit mass heat storage capacity,greatly improve energy efficiency.At present,this technology has been widely used in solar photovoltaic solar thermal systems.Most of researches focused on the study of heat transfer medium phase change fluid.However,the application of shaped phase change materials in systems is less well studied.And some researchers propose a new type of phase change material can be filled between PV panels and copper tubes,which can not only store excess heat during the day,but also reduce the temperature of the panel and its temperature fluctuations.This paper proposed to the problems that the low thermal conductivity and leakage of phase change materials,as well as the small range of phase change temperatures of single phase change materials.Conducted the experiments of composite shaped phase change materials based on a large number of literature research.The paper selects the phase change materials with the phase change temperature of about 25 °C and 50 °C,respectively.Melting and mixing the two into binary phase change materials,which expands the temperature range of phase change energy storage.To select the material ratio suitable for solar PV/T system by analyzing the thermal physical properties of binary phase change materials.Then,the expansion graphite,a support material with good thermal conductivity,was added to adsorb the phase change material.Thereby improving the phenomenon of low thermal conductivity and easy leakage of the phase change material.The experiment adds 5～20% of expanded graphite with different mass fractions,and comprehensively investigates the thermal physical properties,adsorption and stability of five composite phase change materials.To determine the optimal amount of expanded graphite in the docosane-lauryl alcohol /expanded graphite composite shaped phase change material,which provided theoretical data support for the subsequent application of shaped phase change materials in solar PV/T heat collection system.The main conclusions of this paper include:(1)The docosane-lauryl alcohol is prepared by melt mixing method.It’s DSC curve presents two phase transition peaks,and it’s phase change temperature range is 20～50 °C,basically covering the working temperature range of the solar PV/T system.According to the DSC test results,when the docosane mass content is 60%,the phase change latent heat value is the largest,reaching 243.8k J/kg.In addition,the area ratio of the two phase transition peaks under this ratio is more suitable for the subsequent applications in PV/T solar energy collection system.(2)In the preparation of expanded graphite,the temperature is too high or the time is too long will destroy its internal pore structure,so the experiment uses single variable method to investigate the optimal expansion temperature and expansion time.The experimental results show that when the expansion temperature is 900 °C and the expansion time is 60 s,the expansion effect is the best.Moreover,the scanning electron microscopy observation is found that the expanded graphite is loose and porous worm-like and has a strong adsorption capacity.(3)Analyzing the scanning electron microscopy and infrared spectroscopy test of the composite shaped phase change materials,we found its physical compatibility and chemical compatibility are both good.At the same time,the DSC test,thermal conductivity test,adsorption test and thermal cycle test are also carried out on the 5 proportions of composite materials.The results show that when the amount of expanded graphite is 15%,the composite material basically reached the adsorption saturation state,and it has high latent heat of phase change and thermal conductivity.The experimental results also show that it has good stability after 50 cycles.