Performances of a variety of low-Reynolds number turbulence models applied to mixed convection heat transfer to air flowing in a vertical tube

The study reported here is concerned with mixed convection heat transfer to air flowing upwards in a vertical tube. Computational simulations of experiments from a recent investigation have been performed using an 'in-house' code which was written specifically for variable-property, developing, buoyancy-influenced flow and heat transfer in a vertical passage. The code incorporates a selection of two-equation, low Reynolds number turbulence models. The objective of the study was to evaluate the models in terms of their capability of reproducing the effects on turbulent heat transfer of non-uniformity of fluid properties and buoyancy. Direct comparisons have been made between results from the experimental investigation and those obtained by computational modelling for a range of conditions. The trends of impairment and enhancement of heat transfer owing to the influence of buoyancy found in the experiments were captured to some extent in the simulations using each of the models. However, none reproduced observed behaviour correctly over the entire range of buoyancy influence.