Performance enhancement of surface heat exchangers enabled by graphene aerogel based PCM array architectures

The compactness of the heat exchanger serves as a crucial factor, especially in vehicles. One method is to reject heat directly through the exposed area to the ambient air, known as a surface heat exchanger. However, the constraints imposed on the air side of the surface heat exchanger represent a significant impediment to the further enhancement of its thermal performance. A surface heat exchanger integrated with graphene aerogel/paraffin wax composite phase change materials (CPCMs) is proposed to eliminate the problem. This exploits the temperature-invariant characteristic of CPCMs during endothermic melting, increasing the average heat transfer temperature difference within the surface heat exchanger and serving as an additional heat sink. In this article, the benefits of using CPCMs are demonstrated and a detailed investigation is performed considering the effects of operating conditions and thermophysical properties of CPCMs. The obtained results demonstrate that surface heat exchangers incorporating CPCMs achieve a 14.60 % higher heat transfer rate compared to finned ones under an air convective heat transfer coefficient of 110 W·m⁻²·K⁻¹ and a liquid inlet velocity of 0.03 m·s⁻¹. It is further found that surface heat exchangers with CPCMs can meet the requirements of different operating conditions by modifying the thermal conductivity and latent heat of the CPCMs. Through a comprehensive analysis, the heat transfer per unit mass of the surface heat exchanger with CPCMs is 40.50 % higher than that of the base surface heat exchanger during the operation period of the CPCMs. Additionally, the operating period of CPCMs is 2.55 times longer than the recovery period.