Analysis of three-dimensional natural convection of nanofluids by BEM

In this paper we analyse flow and heat transfer characteristics of nanofluids in natural convection flows in closed cavities. We consider two test cases: natural convection in a three-dimensional differentially heated cavity, and flow around a hotstrip located in two positions within a cavity. Simulations were performed for Rayleigh number values ranging from 10(3) to 10(6). Performance of three types of water based nanofluids was compared with pure water and air. Stable suspensions of Cu, Al2O3 and TiO2 solid nanoparticles in water were considered for different volume fractions ranging up to 20%. We present and compare heat flux for all cases and analyse heat transfer enhancement attributed to nanofluids in terms of their enhanced thermal properties and changed flow characteristics. Results show that, using nanofluids, the largest heat transfer enhancements can be achieved in conduction dominated flows as well as that nanofluids increase the three-dimensional character of the flow field. We additionally examine the relationship between vorticity, vorticity flux and heat transfer for flow of nanofluids. The simulations were performed using a three-dimensional boundary element method based flow solver, which has been adapted for the simulation of nanofluids. The numerical algorithm is based on the combination of single domain and subdomain boundary element method, which are used to solve the velocity-vorticity formulation of Navier-Stokes equations. In the paper we present the adaptation of the solver for simulation of nanofluids. Additionally, we developed a dynamic solver accuracy algorithm, which was used to speed up the simulations. (C) 2010 Elsevier Ltd. All rights reserved.