THERMAL TRANSPORT IN TURBULENT COUETTE FLOWS IN CONCENTRIC ANNULI FORVARIOUS PRANDTL NUMBERS

A theoretical study is performed to investigate turbulent flow and hea t transfer characteristics in a concentric annulus with an axially rot ating inner cylinder (circular Couette flow) or with a streamwise movi ng inner cylinder (parallel Couette flow). The two-equation k-epsilon model is employed to determine turbulent viscosity and turbulent kinet ic energy. The Reynolds stress and turbulent heat flux are expressed b y Boussinesq's approximation. The governing boundary layer equations a re discretized by means of a control volume finite difference techniqu e and numerically solved using a marching procedure. Emphasis is place d on the effect of the Prandtl number of a fluid on the velocity and t hermal fields. It is found from the study that (I) an increase in the ratio of inner core moving velocity to fluid flow velocity causes an a ttenuation in the turbulent kinetic energy, resulting in a substantial deterioration in heat transfer performance; (2) in contrast, an incre ase in the Taylor number, ie., the inner core rotational velocity, cau ses an amplification of turbulent kinetic energy, resulting in a subst antial enhancement in the Nusselt number; and (3) both heat transfer c haracteristics in items I and 2 are amplified with an increase in the Prandtl number.