Thermal analysis of the mixture of n-octadecane and carbon nanotubes is carried out and influence of carbon nanotubes concentration on thermal characteristics of the mixture is investigated. The multi physics numerical code is used to analyze the micro-images obtained from the experiment and characterize the thermal properties accordingly. An experiment is carried out to validate the molten state of the phase change material; in which case, aluminum frame is used to fill n-octadecane and 9% carbon nanotubes prior to the experiment. It is found that liquidus isocline recorded from the experiment is in good agreement with their counterpart obtained from the simulations. The homogeneous and heterogeneous models are introduced in the simulations in line with the experimental conditions. The homogeneous model incorporating effective properties predicts earlier melting time than that of the heterogeneous model, which is associated with the high values of effective thermal conductivity predicted by the mass based analysis and assumption of continuous connection of carbon nanotubes in the homogeneous model. Local discontinuity in the carbon nanotube connections suppress the heat conduction in the phase change material, which in turn results in locally delaying of melting of n-octadecane, as observed in the heterogeneous model. (C) 2015 Elsevier Ltd. All rights reserved.