Combined free and forced convection for laminar steady flow in horizontal tubes

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, the cross-sectional distributions of axial velocities are obtained for water with ReRa (Re : Reynolds number, lia : Rayleigh number) as a parameter. Furthermore, a numerical analysis is also presented, and the calculated results are qualitatively compared with the above experimental data of axial velocities and those reported previously for air.