Flow regimes and void fractions during condensation of hydrocarbons in horizontal smooth tubes

• High-speed flow visualization of condensing hydrocarbons in horizontal tubes.
• Flow regimes classified.
• Void fraction measured.
• New multi-regime drift flux model developed.

Phase change in hydrocarbons is of interest to the petroleum, refining, and chemical processing industry, as well as in HVAC and in organic Rankine power cycles. An experimental investigation of flow regimes and void fractions during condensation of propane flowing through smooth horizontal tubes with internal diameters of 7.0 mm and 15.0 mm was conducted. Measurements were made over mass fluxes ranging from 75 to 450 kg m−2 s−1, operating pressures ranging from 952 to 1218 kPa, and nominal vapor qualities ranging from 0.05 to 0.95. Results from this experimental study are compared with predictions from correlations in the literature, and agreement and differences are interpreted and discussed. Appropriate flow regime transition criteria between the wavy and annular flow regimes are highlighted. Detailed analyses of the video frames are also used to develop a new multi-regime void fraction model that uses the drift flux model framework. The model provides improved agreement with the experimental results when compared to correlations from the literature, and predicts the trends with mass flux, tube diameter and pressure well.