Experimental Investigation of the Effect of Expanded Graphite on the Thermophysical Properties and the Heating and Cooling Rates of Paraffin Wax in Capsule of Thermal-Energy Storage System

Abstract

Expanded graphite (EG) is a promising component to improve the properties of the phase-change materials (PCMs) for thermal-energy storage (TES) systems. The experimental study of the EG effect on the thermophysical properties of the paraffin wax (PW) and the heating and cooling rates in experimental cell, which is a model of the TES system capsule, is performed. Two samples of the PW-based composite PCM are prepared using different methods: PW/EG#1 and PW/EG#2 containing 0.178 gg 1 and 0.111 gg 1 of EG, respectively. The evacuation during the preparing procedure contributes to more full filling of the EG pores with PW and lower EG content in PCM. The EG presence in PW/EG#1 and PW/EG#2 contributes to the thermal-conductivity enhancement by 800% and 640%, respectively, in the range under the PW melting point (53.5C), and by 930% and 740%, respectively, in the range above 53.5C. Duration of the melting and heating from 48C to 59C of PW within the capsule is found to be of 12.0 min. vs. 1.1 min. and 1.4 min. for the PW/EG#1 and PW/EG#2, respectively. The heating duration from 30C to 40C of PW is of 7.7 min. vs. 1.6 min. for both samples. The 'jump' of the density and thermal-conductivity values are not observed for the PW containing EG during transition of the PW melting point. It will contribute to both the faster smoothing of the temperature field in the capsules of the TES systems containing such PCM and the absence of the linear extensions of capsules.Терморозширений графіт (ТРГ) є перспективним компонентом для по-