Velocity, Temperature, and Turbulence Measurements in Air for Pipe Flow With Combined Free and Forced Convection

Abstract

Experimental results are presented for velocity and temperature profiles and for the turbulence quantities vz′ t′ and vzt, for up-flow of air in a vertical pipe with constant heat flux at Reynolds numbers of 5000 to 14,000. The measurements show that, with increasing heat flux, superimposed free convection effects cause marked distortion of the flow structure at low Reynolds numbers, with the velocity maximum moving from the tube center to a position near the wall. The axial turbulence intensity, vz′, is depressed by increasing heat flux while the temperature intensity, t′, first decreases and then rises, with a shift in the position of the peak intensity away from the wall. On the basis of an analysis developed for heated turbulent flow, the turbulent shear stress and heat flux distributions are calculated from the experimental results. As the flow field becomes appreciably distorted on heating, it is found that the turbulent shear stress becomes very small, while the heat flux distribution suggests an increase in the width of the viscous sublayer.