THE STUDY OF THE ENHANCEMENT OF HEAT TRANSFER DUE TO BUOYANCY UNDER THE CONDITION OF MIXED CONVECTION IN A VERTICAL ANNULAR PASSAGE

摘要

In this paper, the enhancement of heat transfer due to buoyancy is studied under the condition of mixed convection of water flowing downwards or upwards through a long vertical passage of annular cross-section with a uniformly heated inner surface and an adiabatic outer one. Measurements of heat transfer have been reported in addition to the results of velocity and turbulence using LDA. Under buoyancy-opposed conditions, the velocity near the heated surface is reduced, turbulence is increased and the effectiveness of heat transfer is enhanced. Computational simulations of the experiments have been performed and some results are presented and compared with measurements. The formulation used solved the Reynolds-averaged equations for two-dimensional buoyancy-influenced, axi-symmetric turbulent flow and energy transfer in conjunction with a low Reynolds number k-ε model. Observed behavior is satisfactorily reproduced.