Microencapsulated dimethyl terephthalate phase change material for heat transfer fluid performance enhancement

Micro-phase change materials (micro-PCMs) are proposed to increase the thermal conductivity and the thermal energy storage capacity of a heat transfer fluid (HTF). In this work, we have selected dimethyl terephthalate (DMT) to be used as a PCM for performance enhancement of a synthetic oil in the temperature range of approximately 100 to 170 C. Silicon dioxide (SiO2) was used as the microencapsulant, because of its desirable properties as containment material, including thermal stability. The SiO2-coated DMT micro-PCM was characterized to determine relevant properties and its suitability for HTF performance enhancement. The SiO2-coated DMT was found to completely disperse in the synthetic oil, Therminol SP, silicone oil, at and above 100 degrees C. FTIR, thermal diffusivity and differential scanning calorimetry measurements were carried out on the materials, and these tests demonstrated that the coated particles can be used for HTF enhancement in the temperature range of 100-170 degrees C and potentially higher temperatures if pressurized pipes/vessels are utilized. Using the measured thermal diffusivity and known data for density and specific heat capacity, the thermal conductivity of the micro-PCM was calculated. Our calculations indicate that both the thermal conductivity and the thermal energy storage heat capacity of the HTF would be enhanced by the addition of this micro-PCM. It is expected that the thermal conductivity increase will enhance the heat transfer of the fluid when in use at temperatures above and below the melting temperature of the PCM. At the melting point, the latent heat of the PCM will increase the thermal energy storage capacity of the fluid. Copyright (C) 2016 John Wiley & Sons, Ltd.