Mixed convection of air with Prandtl number 0.7 in eccentric horizontal annuli is numerically investigated. The inner cylinder is at a higher temperature while the inner and outer cylinders can be rotated either clockwise or counter-clockwise with a constant angular velocity. The effects of various parameters such as the eccentricity of the annulus and the Rayleigh number are studied using a three-dimensional model. The Navier-Stokes Equations, along with the energy equation are solved in an orthogonal-structured grid of bipolar coordinate system employing a finite volume method based on the SIMPLE algorithm. Here, both steady and unsteady results are presented in two separate codes. Three-dimensional considerations lead to a complicated flow pattern whereas Taylor vortices have a major role on heat and flow characteristics. It is shown that the axial component of velocity in some configurations has a considerable value, therefore, flow pattern and heat transfer characteristics change in comparison with two-dimensional approach. Eccentricity leads to a different flow pattern in the upper and lower parts of the annulus. Mean and local heat transfer results are obtained. The physics of the flow underlying the observed heat transfer behavior is revealed by the velocity vectors and the isotherm plots of the numerical solutions. Results show that flow and heat transfer are strongly influenced by eccentricity of the inner cylinder and Raleigh number, and that three- dimensionality consideration is inevitable.

Keywords