Thermal conductivity enhancement of phase change materials for low-temperature thermal energy storage applications

Low thermal conductivity is the main drawback of phase change materials (PCMs) that is yet to be fully addressed. This paper studies several efficient, cost-effective, and easy-to-use experimental techniques to enhance thermal conductivity of an organic phase change material used for low-temperature thermal energy storage applications. In such applications, the challenges associated with low thermal conductivity of such organic PCMs are even more pronounced. In this investigation, polyethylene glycol (PEG-1000) is used as PCM. To improve the thermal conductivity of the selected PCM, three techniques including addition of carbon powder, and application of aluminum and graphite fins, are utilized. For measurement of thermal conductivity, two experimental methods-including flat and cylindrical configurations-are devised and increments in thermal conductivity are calculated. Melting and solidification processes are analyzed to evaluate melting and solidification zones, and temperature ranges for melting and solidification processes respectively. Furthermore, latent heat of melting is computed under constant values of heat load. Ultimately, specific heat of the PCM in solid state is measured by calorimetry method considering water and methanol as calorimeter fluids. Based on the results, the fin stack can enhance the effective thermal conductivity by more than 40 times with aluminum fins and 33 times with carbon fins. For pure PCM sample, Initiation of melting takes place around 37C and continues to above 40C depending on input heat load; and solidification temperature range was found to be 33.6-34.9C. The investigation will provide a twofold pathway, one to enhance thermal conductivity of PCMs, and secondly 'relatively easy to set-up' methods to measure properties of pure and enhanced PCMs.