THE INTERTUBE FALLING FILM .1. FLOW CHARACTERISTICS, MODE TRANSITIONS, AND HYSTERESIS

When a liquid film falls from one horizontal tube to another below it, the flow may I take the form of discrete droplets, jets, or a continu ous sheet; the mode plays an important role in the wetting and hear tr ansfer characteristics of the film. Experiments are reported that expl ore viscous, surface tension, inertial, and gravitational effects on t he falling-film mode transitions. New flow classifications, a novel fl ow regime map, and unambiguous transition criteria for each of the mod e transitions are provided. This research is part of an overall study of horizontal-tube, falling-film flow and heat transfer, and the resul ts may have important implications on the design and operation of fall ing-film heat exchangers.