Experiments on heat transfer to transpired turbulent pipe flows

Abstract

Local heat transfer results were deduced from measurements on turbulent flow of air in a porous-walled tube. Hydrodynamically developed, room temperature air was ducted to the entrance cross section of the tube, and heated air was injected through the tube wall. The experiments were performed for inlet Reynolds numbers of the main flow ranging from 4000 to about 65 000 and for injection Reynolds numbers (based on the tube diameter and injection velocity) of approximately 25, 50, 100 and 200. The local Nusselt numbers in the presence of injection were generally lower than those for a solid-walled tube, with the reductions being most marked at low values of the local main flow Reynolds number. It was found that the local Nusselt numbers in the downstream region of the tube could be correlated by local parameters, the local main flow Reynolds number and the injection Reynolds number, without separate dependence on the inlet Reynolds number and the axial position. At small values of the inlet Reynolds number and high rates of injection, a partial laminarization of the flow was evidenced by very low values of Nusselt number in the initial portion of the tube.