Transitional flow regime heat transfer in a horizontal annular passage associated with mixed convection and non-uniform wall temperature boundary condition

Abstract

In this experimental study, hydrodynamic and thermally developing flow associated with mixed convection was examined in the transitional flow regime for a horizontal concentric annular passage. The test facility, which consisted of a counter-flow heat exchanger having an annular diameter ratio was 0.483 with an inner passage wall diameter of 15.90 mm, was operated at different degrees of longitudinal Wall Temperature Uniformity (WTU) for heated flow applications using a conventional annular inlet geometry type. The degree of WTU is described in this paper as a ratio of the wall temperature (value in Kelvin) at the outlet to the wall temperature (value in Kelvin) at the inlet of the inner surface of annular passage. Three different degrees of WTUs of 0.99, 0.975 and 0.965 were examined. Critical Reynolds numbers based on heat transfer were analyzed. It was found that the degree of WTU have an influence on critical Reynolds number and the heat transfer coefficient. A model which takes into account WTU is proposed to predict heat transfer in the transition regime.