CFD And Numerical Heat Transfer Of Non-Newtonian Fluid Using Unstructured Mesh In Eccentric Annuli

Both of flow with heat transfer of non-Newtonian fluids and flow in eccentric annuli are widely applicable in the industries of food production, mechanical engineering, petroleum engineering and chemical engineering. The experimental or numerical investigation of the relevant problems is of significant practical importance, while to a large extent challenging. Flow of non-Newtonian fluid in an eccentric annulus has attracted quit a lot of attention recent years due to the practical significance and the complexity of the fluid and flow channel. The finite volume method (FVM) is used in this paper to study the flow and heat transfer of various fluids in complex channels in unstructured meshes.Generation of an unstructured mesh is much not easier than that of structural grids. Using an unstructured mesh, the transformation of coordinate does not have to be done.in the mathematical formulation. The irregularity of the mesh makes it difficult to study the individual control volumes (CVs) directly. Variables in each CV are represented by the values at the center of the CV, respectively, which nicely leads to the dominant importance of the mesh fineness to the accuracy of the results. This kind of irregular mesh can be used for different complex ducts besides the eccentric annuli investigated in the paper. Some other irregular channels are studied after the validation of fully developed laminar flow in the regular channels. With respect to the flow in eccentric annuli. the effects of different eccentricities and aspect ratios on the velocity, temperature distribution and values of friction factors and Nusselt numbers are discussed in detail.The power law model based on Ostwald-de Waele relationship was used to model the non-Newtonian fluids. Different shear-thinning (n=0.6,0.8) and shear-dilatants (n=1.2,1.6, 1.8) fluids are studied and compared each other. According to the Ostwald-de Waele relationship, the viscosity of non-Newtonian fluids is highly non-linear and affected by the velocity of the fluids. Therefore, the discretization of the viscosity is important while difficult too. A cell-based central method is introduced for the discretization of viscosity in this paper. The velocities involved in the viscosity are calculated by projecting them to the axis-directions of the coordinate system. In fact, as the power index gets closer to 1, the non-linearity of viscosity decreases, as well as the time needed for convergence.