Mechanisms of efficient heat transfer in n-octadecane/silica phase change microcapsules: A molecular dynamics study

In this paper, a paraffin (n-octadecane) / silicon dioxide (SiO2) three-layer model was constructed. Langevin temperature control method was used to set heat sources at different temperatures, and the effects of different temperature differences and different core/shell ratios on heat transfer were simulated respectively. It is found that in the initial stage of heat transfer, the influence of temperature difference on the temperature rise of C18H38 layer is not obvious, but with the progress of heat transfer, its influence is gradually enhanced. The reduction of temperature difference will lead to a decrease in the heat exchange rate. The excellent thermal conductivity of the shell allows it to rapidly attain the temperature of the heat source, thereby facilitating swift heat transfer to the internal phase change material (PCM). The heating rate of the PCM is directly proportional to the temperature differential between the shell and its external environment. In addition, the change of shell thickness has a certain influence on the heating rate of PCM. Although the increase of core/shell ratio can slightly increase the heating rate of C18H38 layer and optimize the temperature distribution, the shell thickness is not the main factor affecting the thermal resistance of the whole phase change microcapsule because the thermal conductivity of the shell material is much higher than that of PCM.