Paraffin/porous-graphite-matrix composite as a high and constant power thermal storage material

A new supported phase change material (PCM) made of paraffin impregnated by capillary forces in a compressed expansed natural graphite (CENG) matrix i s presented. High loads of paraffin were obtained: from 65% to 95% weight d epending upon the bulk graphite matrix density. Composite PCM/CENG thermal conductivities were found to be equivalent to those of the solo graphite ma trix: from 4 to 70 W m(-1) K-1 instead of the 0.24 W m(-1) K-1 of the pure paraffin. Thermal Fewer and capacity of the composite are theoretically com pared to those of conventional systems in the casi: of two usual external g eometries: tubes and spherical hollow nodules. The CENG induced a decrease in overall solidification time and a stabilization of the thermal storage p ower. An optimization procedure of the composite composition was proposed a ccording to the antagonistic behaviours of the thermal power and the therma l capacity with respect to the CENG content. Within tile usual external hea t transfer coefficient range, the estimated CENG matrix optimized densities fell within the practicable range. (C) 2001 Elsevier Science Ltd. All righ ts reserved.