Numerical study on effect of aspect ratio in natural convection with nanofluids in vertical channels asymmetrically heated

A numerical investigation on two-dimensional steady-state natural convection in a vertical channel asymmetrically heated at uniform heat flux with water and alumina (Al2O3) nanofluids is performed to evaluate the effect of the aspect ratio on thermal and fluid dynamic behaviors. The interest in this problem is related to several technological applications such as nuclear systems, bio-nanofluids and solar systems. Nanoparticles have a diameter of 30 nm and four different values of volumetric concentration (0%, 2%, 4% and 6%). The computational domain is made up of the principal channel and two lateral extended reservoirs at the open sections, which simulate the external ambient. The channel is bounded by two vertical parallel plates, one of them heated with a constant heat flux. The twodimensional governing equations are numerically solved with finite volume method by means of the ANSYS-Fluent code. Three different values of the aspect ratio of the channel (5, 10 and 20) are considered. Different values of wall heat flux are considered to cover a range of Rayleigh numbers between 7.0 and 106. Results are presented in terms of velocity, temperature, pressure and stream function. Finally, correlations for the prediction of the average Nusselt number along the heated plate are presented.