Buoyancy and Property Variation Effects in Turbulent Mixed Convection of Water in Vertical Tubes

Abstract

Friction factor and heat transfer coefficient behavior are investigated experimentally under mixed convection conditions in aiding and opposing transition and turbulent flow of water (4000 < Re < 9000 and Bo < 1.3). With increasing buoyancy influence, the friction factor increases by as much as 25 percent in aiding flow, while it decreases by as much as 25 percent in opposing flow (GrΔT < 7·106). The effects of temperature-dependent viscosity variations are also included in the analysis (0.5 < μw/μb < 1.0). When they are taken into account, the increase in the friction factor due to buoyancy forces alone in upward flow becomes larger. The friction factor behavior is compared with previous studies in the literature. Our experimental data agree well with some of the previous experiments described in the literature. The heat transfer coefficient was also measured under the same experimental conditions; the heat transfer coefficient monotonically increases in opposing flow by as much as 40 percent, and first decreases by 50 percent and then recovers in aiding flow with increasing buoyancy influence.