Thermal storage achievement of paraffin wax phase change material systems with regard to novolac aerogel/carbon monofilament/zinc borate form stabilization

Abstract

Recently, the development of thermal conductive phase change composites (PCCs) to overcome the limitation of low thermal conductivity and easy leakage of organic phase change materials (PCMs) has led to the wide application of these materials. In this study, a novolac aerogel-based composite was employed as porous support for the encapsulation of paraffin to fabricate a new class of high-performance PCCs. Carbon monofilaments and zinc borate were incorporated into the aerogel as the heat conduction network. Furthermore, zinc borate can act as a flame retardant and nucleation agent. The nanocomposite aerogels were synthesized using the sol-gel technique and then the molten paraffin was impregnated into systems. The structure and thermal properties of the nanocomposite aerogels and PCCs were characterized. Fortunately, no shrinkage was observed during aerogel synthesis. SEM images showed the formation of novolac colloids on the surface of carbon fiber. The presence of conductive fillers results in an enhancement of the thermal conductivity of novolac aerogel. Moreover, the thermal conductivity of fabricated aerogels was predicted using a modified series-parallel model for porous composite structures. Furthermore, more porosity and larger pore size of aerogels by incorporation of filler have led to a significant increase in paraffin absorption capacity. So that the highest impregnation was reached to 364.5 wt% that belongs to AC15Z15 sample. The form-stable PCMs had negligible paraffin leakage upon phase change process (less than 1.4 wt%). In addition, the leakage of PCMs composite was less than 2.59 wt% after heating for 10 h showed outstanding cycle stability of synthesized PCCs. The phase transition temperature and phase change enthalpy of PCCs were in the range of 85–96 °C and 33.94–41.85 J/g, respectively. Moreover, the latent heat of PCCs is in the range of pure paraffin, achieving high energy storage capacity. This type of PCMs system in nanostructure can be used in electrical industry for free cooling of electrical coils in this temperature range.