Climbing film, flooding and falling film behavior in upflow condensation in tubes

Upflow condensation in vertical tubes is complicated by the relative magnitude of the opposing vapor shear and gravity. This study examines the different flow regimes for condensation of FC-72 in a vertical tube using both high-speed video imaging and detailed heat transfer measurements. Four regimes are identified, falling film, where the condensing film drains downwards by gravity opposite to low velocity vapor flow, oscillating film, corresponding to film flow oscillating between upwards and downwards, flooding, where film begins to be sheared upwards by the vapor core, and climbing film, where high vapor velocity causes the film to be sheared upwards. The four flow regimes are well segregated in a flow regime map based on dimensionless superficial velocities of the vapor and liquid. The condensation heat transfer coefficient is shown to decrease axially because of gradual thickening of the film, except for high mass velocities, where turbulence and intensified interfacial waviness cause downstream heat transfer enhancement. An annular flow model is constructed, which shows fair predictions for the climbing film regime. The predictive accuracy of the model is influenced by flow oscillations occurring downstream of the climbing film region and inability of the model to account for interfacial waves.