Numerical Research On Heat Storage Of Paraffin/Aluminum Foam Composite Phase Change Material

Under the background of the energy crisis, new energy vehicles industry has developed rapidly. As the core component of energy storage device in electric vehicles, hybrid vehicles and fuel cell vehicles, high-capacity lithium-ion battery is increasingly subject to widespread attention. Among the evaluations which impact the working performance of the lithium-ion battery, the temperature condition is particularly important. Reasonable temperature environment is the key of improving battery reliability and extending battery life, so the battery effective thermal management is imperative. The thermal management system which uses the phase change materials as working substance has the advantages of high heat storage capacity, small system volume, simple structure and no additional energy cost, and therefore it has broad application prospects.Heat storage properties of phase change materials determine the performance of the pros and cons of the thermal management system, a heat storage experiment system based on phase change materials is built up to study the performance of phase change materials on heat transfer process, and the following aspects are discussed:phase changing response time, the internal temperature distribution in pure paraffin and aluminum foam/paraffin composite phase change material, and fully heat storage time in different heating condition. Seen from the results, comparing with pure paraffin, the temperature distribution in aluminum foam/paraffin composite phase change material has a better uniformity and the fully heat storage time in it is also much shorter. Considering the three heating flux of 7000 W/m2,12000 W/m2, and 15000 W/m2, the fully heat storage time in composite phase change material brings 35.35%,22.14% and 39.90% drop respectively, comparing with that in pure paraffin.Due to the limitations of the experimental measurement points, the change of phase change interface, temperature and velocity, as well as other influence factors on process of heat storage can not be obtained, physical models in line with the true characteristics of the skeleton structure of aluminum foam are established by means of numerical simulation in this paper, also the behavior of it on heat storage process are studied and analyzed in this paper. Face-centered cubic(FCC) and body-centered cubic(BCC) modeling methods are used to build different skeleton structures, and the physical models built are changeable with porosity and pore scale. It is proven that the simulation results are in good agreement with the experimental results. The results show that the phase transition interface changes are related to velocity field and the aluminum foam skeleton structure. The existing of aluminum foam skeleton in composite phase change materials can impact the development of velocity field strongly, but at high Ra number condition, this impact of skeleton will be weakened. The porosity is one of the factors which can influence the heat transition characteristics of composite phase change materials on process of heat storage, the smaller the porosity, the more uniform the temperature distribution in composite phase change materials, at the same time, the thermal conductive rate increases as the porosity decrease in composite phase change materials. Moreover, heat conduction is the main way of heat transfer in composite phase change materials and heat convection in pure paraffin materials, the fact above leads to the results that aluminum foam skeleton pore scale doubling, the maximum rate of fluid will increase to 4 times in the material, simultaneously, the overall heat transfer rate of the composite material will decrease, which means the heat transfer performance of composite phase change materials will be enhanced with the pore scale of aluminum foam skeleton decreasing.