Direct computational simulations and experiments for film condensation inside tubes and channels

This article presents accurate numerical solutions of the full 2D governing equations for steady and unsteady laminar/laminar internal condensing flows of pure vapor (FC-72 and R-113) inside a vertical tube and a channel. The film condensation is on the inside wall of a tube or one of the walls of a channel (the lower wall in case of a downward sloping channel). Both experiments and simulations find that exit condition specifications are important. The computations are able to predict whether or not a steady flow exists with a well-defined and steady natural exit condition. If well-defined natural steady/quasi-steady flows exist-as is shown to be the case for gravity-dominated or strong shear-dominated condensate flows that remain parabolic up to the exit location-the computations are able to predict both the natural exit condition and any point of transition (from stable to unstable or smooth to wavy behavior) that may exist within this zone. Compared to gravity-driven cases, shear-driven cases (zero gravity or horizontal cases) tend to destabilize easily. It is found that only for gravity-driven cases interfacial waves are able to cause a concurrent enhancement in heat transfer rates along with an enhancement in interfacial shear. Also it is found that this enhancement in interfacial wave energy is significant if the condensing surface noise is in resonance with the intrinsic waves.