AbstractThis paper describes an experimental measurement of temperatures at the free liquid interface of distilled water films falling vertically downwards on the outside surface of a copper tube heated internally by a countercurrent circulating liquid. An infrared radiometer was used for the temperature measurements. A prediction for these temperatures is made by solving numerically the governing equations of momentum, continuity and energy. Experimentally estimated temperature profiles were employed as the wall temperature boundary conditions. Internal turbulence eddies and surface wave celerity were considered in the numerical solution by using the eddy diffusivity profile of Mills and Chung. Good agreement between experiment and theory was obtained