Prediction of flow and heat transfer in the entry region of concentric cylinders with rotating inner walls

Abstract

In this study, the problem of steady laminar forced convection in the entry region of concentric annuli with rotating inner walls is investigated numerically using fluent code. Due to the axi-symmetry of the problem, a 2D axi-symmetric model is used. Focus is on rotation number (Ro), annulus radius ratio (N) effects on heat transfer characteristics, and the torque required to rotate the inner walls. Air and engine oil were used in the simulation. Reynolds number (Re) of 500 based on inlet velocity and hydraulic diameter is kept constant over the whole range of the considered rotation numbers and radius ratios. The Navier stokes equations together with the energy equation are solved. Two boundary conditions are considered to be imposed: (1) The outer cylinder is adiabatic while constant wall temperature is used at the inner cylinder, (2) The inner and outer cylinders are kept isothermal at constant but different wall temperatures. The torque and the nusselt number are presented for three values of annulus radius ratio, N and three values of rotation number, Ro. Furthermore, the effect of variable viscosity is discussed. The results show that the radius ratio and thermal boundary conditions significantly affect the flow field and heat transfer characteristics. Including the variation of viscosity as function of temperature significantly affects the results for engine oil and almost has no effect on the results for air.