Simulation And Analysis Of Phase Change Process For Latent-Heat Insulating Packages

In recent years, with the growth of global traffic for cold chain food, the problem of being out of cold chain was more and more prominent. Insulating box with PCM can effectively solve the "last mile" cold chain problem.it was needed to design the temperature control packaging system in the cold chain according to the transport environment, and insulation materials, phase change materials, the size of the products were the main factors affecting the performance of temperature control packaging. In this paper, the latent-heat rectangular temperature control packaging system was discussed. Furthermore, the effect of convective heat transfer between solid and liquid on the holding time was studied. Besides, different sizes of rectangular products were builded and its actual holding time was analysed.The contents mainly include the followings:(1) Temperature control packaging models were established and analysed with Comsol Multiphysics and the corresponding experiments were designed to verify the accuracy of the models. The results show that the holding time of the simulation was advanced 2.70% ?13.32%than the measured time, which proved that the model was safer and could accurately simulate the internal temperature of the system. Furthermore, the models of convective heat transfer under constant temperature condition and variable temperature condition were established respectively, and its influence on holding time of EPS insulating boxes were analyzed, the results showed that the holding time was shortened by 14.06% under the condition of constant temperature, and the holding time was shortened by 12.52% under the condition of variable temperature.(2) The phase change model was established based on heat transfer law and fluid flow law,and the influence of the viscosity of PCM on the holding time was analyzed. The results showed that the holding time decreased with the increase of the viscosity, when the viscosity reached the critical value, the holding time become longer as the viscosity increases, and when the viscosity was increased so that the PCM had solid properties, the holding time remained constant.(3) The finite element simulation of phase change process was carried out, and the shape and movement of solid-liquid interface were analyzed.Forthermore, rectangular products with different size were constructed and its error between actual holding time(when the phase transition interface contacted the product) and effective holding time(when the PCM was completely melted) for EPS and EPP insulating boxes under constant temperature condition and variable temperature condition were analysed.The results showed that when the size of the products was the same, the effect of ambient temperature on the error was not significant, and the average error between the actual holding time and the effective holding time was 31.3%?33.01% in EPS insulating box and 33.21%?34.42% in EPP insulating box.