Effect of Sine-Squared Thermal Boundary Condition on Augmentation of Heat Transfer in a Triangular Solar Collector Filled with Different Nanofluids

Abstract

Numerical study of heat transfer phenomena has become a major field of research nowadays. In engineering applications, different boundary conditions arise which have various effects on heat transfer characteristics. For the present work, a triangular-shape cavity has been analyzed for the sine-squared thermal boundary condition which is common in practical cases. The augmentation of heat transfer has been done by introducing a nanofluid inside the cavity. Different solid volume fractions (φ = 0, 0.05, 0.1, 0.2) of water-CuO, water-Al₂O₃, and water-TiO₂ nanofluid have been tested for the cavity with a wide range of Rayleigh number (Ra = 10⁵–10⁸) and for dimensionless time (τ = 0.1 to 1). The Galerkin weighted residual finite-element method has been applied for the numerical solution, and numerical accuracy has been checked by code validation. The heat transfer augmentation for different nanofluids has been done in the light of local (Nu_L) and overall Nusselt number (Nu_av), and the results have been presented with streamline, isotherm, and related contours, in graphs and charts. It has been found that variable boundary condition has significant effect on flow and thermal fields and increase of solid volume fraction enhances the heat transfer.