Experimental assessment of the gap width effect on turbulent flow and forced convective heat transfer around a single rod suspended in a channel

Abstract

The present work presents the experimental campaign carried out to assess the convective heat transfer around a single rod suspended in a rectangular channel under axial turbulent flow. The distance between the rod and the upper wall of the channel forms a rod-wall gap, whose width, d, can be varied. The experiments were performed for the dimensionless gap widths that yield W/D = 1.050, 1.100, 1.150 and 1.200. Hot-wire anemometry was used to measure mean velocities, the RMS velocity fluctuations and the velocity spectra. The rod is equipped with a heated cell that provides the local temperature and convective heat transfer coefficient distributions around the rod’s surface. The local convective heat transfer distribution is in good agreement with the literature. The lowest value for the heat transfer coefficient was not found right in the narrow gap for W/D = 1.050, but, slightly away from the gap. As W/D increases, the minimum local convective heat transfer coefficient occurred closer to the narrowest gap width. The Reynolds-Colburn analogy was investigated for all configurations through the measured convective heat transfer coefficient and the skin friction distributions. A linear relationship was found between the Stanton number and the skin friction coefficient. Moreover, data scattering was seen to decrease significantly when the local velocity was used instead of the global one. It suggests that the heat transfer process is governed, mainly, by the local parameters.