Flow Patterns and Mode Transitions for Falling-Film on Flat Tubes

The transitional Reynolds numbers for different patterns are available and a proposed transitional map is also provided in this paper. The transition of falling-films on flat tubes is studied in this work. Water and ethylene glycol are used as working fluids, for falling-film experiments conducted under adiabatic conditions, without an imposed vapor flow. The flow patterns are recorded using a high-speed, digital camera over a range of flow rate and tube spacing. The flow patterns are similar to those on round tubes, including sheet, sheet-jet, jet, jet-droplet and droplet flows, but the transitions for ethylene glycol are different–there is no sheet-jet pattern during transition between the sheet and jet flow patterns. The transition threshold increases with tube spacing and the effect of distributor height depends on flow patterns. The transitional Reynolds numbers for different patterns are available and a proposed transitional map is also provided in this paper.