Flow behavior of liquid falling film on a horizontal rotating tube

Falling liquid film on outside surface of a horizontal tube is an important and commonly used heat transfer process in heat exchangers. Experimental study has been conducted to investigate the effect of the rotation speed of the tube on the falling film mode transitions, film thickness and dimensionless wavelength. Experiments have been indicated that, when a liquid falling film falls on a horizontal rotating tube, the transition starts at low Reynolds number. To avoid instable falling film during rotation of the tube, the tube speed of rotation should not exceed the maximum speed of rotation. The value of the film thickness has been slightly decreased by increasing the rotation speed. A reduction of the film thickness was observed at about 12% for water film at Reynolds number of 285 and 300 rpm rotating speed. A clear reduction of the dimensionless wavelength, λ∗, has been occurred due to the increase of the rotating speed of the tube for high viscosity fluids. On the other hand, a small effect has been observed for low viscosity fluids (water and mixture of 50% water and 50% ethylene glycol).