Heat transfer in a rotating twin-pass trapezoidal-sectioned passage roughened by skewed ribs on two opposite walls

An experimental study of heat transfer in a radially rotating twin-pass trapezoidal-sectioned duct with two opposite walls roughened by 45 degrees staggered ribs was performed. Two channel orientations of 0 degrees and 45 degrees from the direction of rotation were tested. At each Reynolds number of 5000, 7500, 10000, 12500, and 15000, local Nusselt numbers along the centerlines of two rib-roughened surfaces with five different heating levels were acquired at rotating numbers of 0, 0.1, 0.3, 0.5, 0.7, and 1. A selection of experimental results illustrates the isolated and interactive influences of convective inertial, Coriolis, and rotating buoyancy forces on local and centerline-averaged heat transfers. The isolated Coriolis force-effect improves heat transfer over two unstable surfaces of the rotating twin-pass channel. The rotating buoyancy effect undermines local heat transfer, but its influence is alleviated when the rotating number increases. At rotating number of 0.7 and 1, the rotating buoyancy force acting with counter-flow manner considerably impairs local heat transfer in the end-region of the first passage with radially outward flow. With the rotating numbers in the range of 0.1 to 1, the heat transfer differences between the two channels with orientations of 0 degrees and 45 degrees are in the range of 5-26%. As a strategic aim of the present study, heat transfer correlations are derived to evaluate the centerline-averaged Nusselt numbers over two rib-roughened surfaces that permit the individual and interactive influences of convective inertia, Coriolis force, and rotating buoyancy to be quantified. As the full-field spatial heat transfer variations in the present rotating channel are not measured, the local heat transfer results generated by the present study are limited to the locations measured.