Effect of Tilt Angle on Pure Mixed Convection Flow in Trapezoidal Cavities Filled with Water-Al2O3 Nanofluid

A numerical study is carried out to investigate the effect of tilt angle of the cavity on mixed convection heat transfer inside two different lid-driven trapezoidal cavities; one having heated wall on short base and another having heated wall on long base. In this investigation, the top wall is maintained at isothermal cold temperature, which is moving in its own plane at a constant speed while a constant high temperature is provided at the bottom surface of the cavity. The cavity is assumed to be filled with water-Al2O3 nanofluid. The governing Navier–Stokes and thermal energy equations and boundary conditions are non-dimensionalised and are solved using Galerkin finite element method. Attention is paid in the present study on the pure mixed convection regime at Richardson number, Ri = 1 where the natural and the forced convection are equally dominated. Parametric investigations are carried out by taking base wall tilt angle from 0o to 45o with a step of 15o and also varying Reynolds numbers from 0.1 to a maximum order of 104 with the corresponding Grashof numbers varying from 0.01 to a maximum order of 108 for Ri = 1. Simulations are carried out by considering both plain fluid (water) and nanofluid with 10% solid-volume fraction of nanoparticles. Flow and heat transfer characteristics are explained using streamline and isotherm contours, and the variation of average Nusselt number of the heated wall and average fluid temperature of the cavity are analysed for different tilt angles.