Studies of mixed convection in vertical tubes

The early study of convective heat transfer considered the branches of forced and free convection independently with only passing reference to their possible interaction. In fact the two are extreme cases of the general condition of “mixed” or “combined” forced and free convection where both mechanisms operate simultaneously. The present contribution aims to provide an up-to-date review of those works concerned with mixed convection heat transfer in vertical tubes. The review is divided into two sections, the first dealing with laminar flow, and the second with turbulent flow; further subdivisions are made according to whether the work is theoretical or experimental. Comparisons between theory and experiment are made where possible, expressions defining the conditions for onset of buoyancy effects are presented and equations for determining heat transfer are given. The paper ends with some general comments and recommendations. The survey is restricted to fluids of moderate Prandtl number; mixed convection in liquid metals can display very different characteristics which will be discussed in a future paper.