This paper describes an experimental study of heat transfer to hydrodynamically fully-developed, falling viscous liquid films inside a 25.9 mm i.d., 560 mm long, heated tube. Time-averaged heat transfer coefficients were determined for water, 50% aqueous glycerine, and 75% aqueous glycerine over a range of Reynolds numbers from 31 to 3700 and Prandtl numbers from 5 to 200. The fluctuating wall temperature was found to correlate directly with the passage of roll waves, a sharp drop in temperature occurring at wave fronts and a minimum occurring at wave backs. A simple model is presented to estimate the increase in heat transfer that occurs as a single wave passes, indicating that a maximum should occur at a wave front. The results are consistent with the fluctuating wall temperature measurements, if allowance is made for the thermal capacitance of the tube wall.
Fore, L.B., Witte, L.C., Roll-Wave Effects on the Heating of Viscous Liquid Films, National Heat Transfer Conference, ASME, New York, NY, HTD-Vol. 314, pp. 23-30, August, 1995.