Thermal conductivity of eicosane-based phase change materials was enhanced by suspending highly-conductive silver nanoparticles. Three batches of solid eicosane-silver samples with mass fractions (0, 1, 2, 3.5, 5, 6.5, 8 and 10 wt%) of nanoparticles were obtained under three different solidification routes: ice-water bath, room temperature and oven solidification. The transient plane source technique was used to measure the thermal conductivity at different temperatures starting at 10 °C and ending close to the melting point of each sample. Results showed an increase in the value of thermal conductivity as the temperature increased, and when close to melting point, a sharp rise in thermal conductivity was observed. Also, the oven solidification route samples exhibited the highest values while the ice-water samples showed the least increase.For samples with an additive loading greater than 2 wt%, a non-monotonic relationship was obtained between the thermal conductivity and the weight fraction of Ag nanoparticles, 2 regardless of the method of solidification. In addition to thermal conductivity measurement, the latent heat of fusion of the samples was investigated, utilizing differential scanning calorimetry.Results exhibited a decrease in the latent heat and the melting point of the samples as the additives loading increased due to the decrease in the number of molecules of eicosane in the samples.

The present study deals with a theoretical investigation of a close-contact melting (CCM) process involving a vertical cylinder on a horizontal isothermal surface, where the liquid phase is a non-Newtonian viscoplastic fluid that behaves according to the Bingham model. Accordingly, a new approach is formulated based on the thin layer approximation and different quasi-steady process assumptions. By analytical derivation, an algebraic equation that relates the molten layer thickness and the solid bulk height is developed. The problem is then solved numerically, coupled with another equation for the melting rate. The new model shows that as the yield stress increases the melting rate decreases and the molten layer thickness increases. It is found that under certain conditions, the model can be reduced to a form that allows an analytical solution. The approximate model predicts an exponential dependence of both the melt fraction and the molten layer thickness. Comparison between the numerical and analytical solutions shows that the analytical approximation provides an excellent estimation for sufficiently large values of the yield stress. Dimensional analysis, which is supported by the analytical model results, reveals the dimensionless groups that govern the problem. For the general case, the melt fraction is a function of two dimensionless groups. For the analytical approximation, it is shown that the melt fraction is governed by a single dimensionless group and that the molten layer thickness is governed by two dimensionless groups.