Highly porous copper foam coated with graphene flakes and silver nanowires to cool overheated solar air heaters

Abstract

Solar air heaters (SAHs) transfer radiative heat to the air flowing under irradiated panels. However, excessive heating can induce thermal stresses and cause malfunctioning of solar devices. Thus, a method to cool the panels is essential. We developed a highly effective method for cooling an overheated solar collector panel by increasing the surface area using a highly porous metal foam supersonically sprayed with graphene flakes (G) and silver nanowires (AgNWs). Notably, convective cooling via the textured surface only reduced the surface temperature without affecting the total amount of solar heat collected at the radiated side. The effect of G/AgNW texturing and the highly porous metal foam on cooling was assessed. The best G/AgNW-coated foam afforded a temperature reduction of ΔT = 18 °C and a 25.3% increase in heff compared with the bare case. In addition, G/AgNW texturing significantly increased the amount of solar heat collected, with a temperature increase of ΔT = 81 °C, because the G/AgNW surface promoted the trapping of radiative heat waves, similar to the perfect black body of a Helmholtz jar. Therefore, augmentation with a G/AgNW layer is recommended for both the solar heat collecting and convective cooling sides of an SAH panel.