Studies on Paraffin-Graphite-Cu PCM Composites for Solar Thermal Storage Applications

In this paper an experimental investigation on the thermal storage capacity for a typical composite mixture of paraffinGraphiteCu PCM composite has been studied. Paraffin wax was used as the base phase change material (PCM) and the paraffin has been mixed with Cu turnings in different ratios 10, 50, 70 and 90 weight percentages and considered as a composite. The thermal charge and discharge capacities of the paraffincopper composite were tested and reported. The Paraffin copper PCM composite was found to have higher heat transfer capacity when compared to pure paraffin as PCM material. The heat charge and discharge performance of the Paraffin was found to be high, when the Cu turnings were mixed with paraffin in a smaller ratio of 10 weight percentage when compared with other weight percentage mixtures of copper. The shiny black colour nature of graphite has been considered to provide a better absorption. The paraffin-Cu composite mixture was studied for different weight percentage 10, 20, and 30 mixture of Graphite powder. It was found that 20 weight percentage mixture of the graphite with paraffin-Cu had considerable better heat energy storage potential because of its expected good heat transfer property and the results have been presented. These composite (paraffinGraphiteCu) sample were encapsulated in heat exchanger pipe of .02m diameter sealed at both ends of length 0.3m were subjected to thermal charging and discharging capabilities. From the observation it is noted that heat exchanger pipes with the PCM composites have higher rate of rise of temperature of 14.7 X 10 -3 C/s, while charging the PCM composite. When compared with the charging performance of pure paraffin, the rate of rise of temperature for the pure paraffin is known to be 6.389 X 10 -3 C/s. So the thermal charging time gets enhanced to more than double while using the PCM-composite as the PCM material for thermal energy storage instead of pure paraffin alone. The rate of fall of temperature of the pure paraffin while discharging was 1.94X10 -3 C/s which was less than the rate of fall of temperature of the best composite 4.167X10 -3 C/s. A best composition of PCM composite has been identified from the present study. The thermophysical properties of the paraffin and paraffin-Graphite-Cu composite are determined through the differential scanning calorimeter (DSC) analysis. Further study is in process to use the PCM-composite in solar water heating application in solar thermal storage utilities.