The influence of gravity on developing forced, laminar flow in a vertical isothermal tube was investigated by means of a numerical analysis and an associated experiment. Numerically predicted velocity profiles and Nusselt numbers for combined forced–free convection with Gr/Re = −30 are compared with their counterparts for pure forced convection, Gr/Re = 0, for air with Re = 500. The analysis was performed for both the uniform irrotational and the fully developed velocity entrance models. Velocity profiles were measured in a vertical-tube apparatus designed to provide an approximately uniform entrance velocity using air as the test fluid. These are compared with numerical predictions based on test conditions.

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