Laminar convection with buoyancy in tube flows with a surrounding liquid medium

The laminar flow and heat transfer within a horizontal tube surrounded by a liquid medium are studied both numerically and experimentally. Emphasis is given to flow regimes where a buoyant effect on the forced flow is exhibited within the tube. Two different boundary conditions are investigated. When the surrounding liquid dictates its temperature to the wall, the boundary is assumed to be isothermal (boundary condition of the first kind). When the outside liquid is not constantly replaced, natural convection occurs around the tube wall, creating a temperature gradient along the surface of the tube. A large-scale experimental facility is constructed and approximately 100 tests are carried out over a wide range of operating conditions. The secondary flow effects are verified qualitatively by direct visualization of the flow, using a dye-injection method. A three-dimensional numerical model is used to analyze the flow behavior and the heat transfer in a short horizontal tube. Both experimental and theoretical results demonstrate that the flow is complex and three dimensional.