Combined free and forced convection for a laminar steady flow in a horizontal tube

It is well known that free convection is caused by the buoyancy forces of a laminar steady flow in a heated pipe. However, this experimental investigation shows that free convection occurs when the temperature differences between air in a room and water in an unheated pipe are large. Under such experimental conditions, cross-sectional distributions of axial velocities are measured for water as a parameter of ReRa of the Rayleigh and Reynolds numbers. Furthermore, numerical analysis is also presented, and the calculated results are qualitatively compared with the above experimental data of axial velocities and experimental ones in the case of air reported by Mori et al. (1964).