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Abstract
An implicit finite-difference method is developed to study the effect of variable fluid properties on laminar convection for upflow of air in the entrance region of a heated vertical concentric annulus. Fluid properties are assumed to vary with temperature according to power-law relations. Computations have been made with a radius ratio of 0.2S, and typical results are obtained for pure forced convection with air as the working fluid. The walls of the annulus are subjected to UHF or UWT boundary conditions. The effects of variation of air properties on the local Nusselt number and friction factor are found to be slight at locations close to the channel entrance and far downstream from it, but the effects are shown to be noticeable in locations that are in between. Fluid property variations can cause a reduction of the ratio of the wall and bulk temperatures by about 6%. It is shown that in UWT, the Nusselt numbers for constant and variable properties do not necessarily merge in the entrance region.