Hydrodynamics of free-falling turbulent wavy films and implications for enhanced heat transfer

The evolution of the surface waves for vertical free-falling films with Reynolds number ranging from 440 to 5,100 was measured using multiple-point conductance sensors and a computer-based data acquisition system. The physical and mathematical models describing the free-falling turbulent wavy films with the free surface boundary are presented. The governing equations are solved numerically in the film waves based on the coordinate transformation of the measured time-dependent film thickness data. The results show that the evolution of the surface waves has a remarkably nonlinear nature. The hydrodynamics and velocity profiles at the wavefront, the wave crest, and the wave back-for the solitary waves indicate significant effects of the solitary, surface waves with interior recirculation flow on heat and mass transfer enhancement. A correlation for an average heat transfer coefficient is proposed as a function of the Reynolds and Prandtl numbers based on the measurements.