Effect of concave and convex side-wall curvature on natural convective heat transfer in trapezoidal enclosures

Focusing on the enhancement effects of fluid flow alteration on natural convective heat transfer in enclosures, this study presents a numerical investigation about natural convection behavior inside the concave and convex shaped trapezoidal-based enclosures. The side walls of a two-dimensional standard isosceles trapezoidal enclosure (TE) were modified to constitute concave and convex enclosures based on the reference geometry. Regarding the wall curvature, three different concave (C1, C2, and C3) and three different convex (V1, V2, and V3) enclosures were examined in terms of natural convective heat transfer, considering three different Rayleigh numbers (Ra=104, 105, and 106). The governing equations of the problem was solved by finite volume based commercial software, and the heat transfer performance was discussed over dimensionless streamline and temperature contours, as well as quantified by average Nusselt numbers (Nu). The numerical outcomes revealed that the curvature of side walls have significant effects on buoyancy-driven fluid flow and heat transfer. The fluid flow was squeezed and restricted in concave enclosures, particularly at high Ra, while double longitudinal circulations were generally formed in convex enclosures. Hence, utilization of concave enclosures led to a significant decrease in Nu, approaching 45%, while the convex-shaped enclosures resulted in a remarkable improvement in Nu, which can reach up to 18.6% depending on the Ra, compared to the reference enclosure. Regarding the outcomes of the work, convex-structured enclosures were found to be superior for enhancing heat transfer and were recommended for engineering applications such as cooling of electronics, solar thermal energy and relevant heat exchangers.