Thermal conductivity enhancement of phase change materials with form-stable carbon bonded carbon fiber network

Abstract

Carbon bonded carbon fiber (CBCF) monoliths were prepared from graphite fibers with high thermal conductivity, to promote heat transfer and to stabilize the shape of phase change material (PCM). The CBCF monoliths with density from 0.09 to 0.39g/cm3 were filled with paraffin wax to form PCM composites. Due to the anisotropy of the CBCF material, the PCM composites had varied thermal conductivities with their directions. Results showed that the in-plane thermal conductivity of the PCM composites was markedly improved by 18 to 57 times over the pure wax, depending on the density of CBCF composites, while the out-of-plane thermal conductivity was also increased by 3.7 to 5.5 times. In addition, the improvements in thermal conductivity showed almost linear relationship with the volume fraction of carbon fibers in the PCM composites. The charging time of the composites with the high CBCF density was reduced to one quarter of pure paraffin, while the discharging time was about one sixth. The apparent enthalpy of PCM composites was found to vary with the loadings of paraffin wax, by differential scanning calorimetry (DSC). After 40cycles, the wax loadings in the PCM composites were retained at 56–70%.