A direct comparison of three different material enhancement methods on the transient thermal response of paraffin phase change material exposed to high heat fluxes

The thermal performance and energy storage capabilities of a 54 °C organic paraffin wax is be tested and directly compared using three common different thermal conductivity enhancement methods (TCE). These include the use of graphite foam with infiltrated PCM, aluminum foam with infiltrated PCM, and PCM with 10 wt% graphite nanofibers. The applied heat flux varies from 1.93 W/cm2 to 19.3 W/cm2. This allows the study of higher heat flux conditions than any previously studied and the first direct comparison of the effectiveness of these three different methods on the control of the heated base temperature. The performance of the PCM in both the solid and liquid phase as well as the motion of the melt front between the two phases is examined for each TCE configuration.It is found that the selection of enhancement method has a significant effect on the thermal response of the system. The base paraffin consistently shows the development of a superheated liquid layer at the base and Rayleigh-Benard convection currents in the melt region. With the addition of 11 wt% GNF the convection currents at the base are suppressed and the PCM is coupled more closely to the module. The GNF/PCM was more effective at controlling the base temperature than the base paraffin at low power loads, but this effect decreased with increased power loading. The GNF/PCM mixture was less effective at base temperature control when compared to the aluminum or graphite foams. However, the foams are found to improve the heat sink abilities of the system without exhibiting any significant delay to steady-state through effective use of the PCM mass. The results provide much needed valuable insight into the comparative effectiveness of different TCE designs for high power configurations.