Study of natural convective heat transfer of nanofluids in cubical enclosure

Abstract

This thesis reports a study on natural convection heat transfer and fluid flow in a square cavity and cubical enclosure filled with Cu–Water nanofluid which is investigated numerically. The current geometry is analyzed numerically using finite element method. One vertical wall of the cavity is hot, the opposite one is cold and the rest of the walls are adiabatic. In this thesis, a finite element method for steady-state incompressible natural convection flows has been developed. The physical problems are represented mathematically by different sets of governing equations along with the corresponding boundary conditions. The non-dimensional governing equations are discritized by using Galerkin weighted residual method of finite element formulation. The numerical results are reported for the effect of Rayleigh numbers from 103 to 106, solid volume fractions 0, 0.02, 0.05, 0.08, 0.1, 0.15, 0.2 and average Nusselt number. The results of this investigation reveal that heat transfer rate is always higher for nanofluid than base fluid. Also clear water moves rapidly than nanofluid. The effects of coefficient of heat transfer are analyzed. In addition natural convection of Cu-water nanofluid in a square cavity with circular disk is investigated numerically. Also natural convection of Cu-water nanofluid in a cubical cavity is investigated. The variable thermal conductivity and variable viscosity models are compared to both the Maxwell-Garnett model and the Brinkman model. It is found that at high Rayleigh numbers the average Nusselt number is more sensitive to the viscosity models than to the thermal conductivity models. The results show highest heat transfer enhancement in the conduction dominated flow regime, where the enhanced thermal properties of nanofluids play an important role. When convection is the dominant heat transfer mechanism, using nanofluids yields a smaller increase in heat transfer efficiency. The obtained results are presented in terms of streamlines and isotherms, heat transfer characteristics, Nusselt numbers for various Rayleigh numbers and for different solid volume fractions of nanoparticles. The results show that the Nusselt numbers increase with the increasing of Rayleigh numbers. Comparisons with previously reported investigations are performed and the results show excellent agreement.