Vertical upward and downward churn flow: Similarities and differences

Investigation of downward two-phase flows received less attention compared to the vertical upward flows. Downward flows are found in many industries and facilities including; oil/gas production, nuclear industry and petroleum refinery/production facilities such as evaporators, chemical reactors and distillation towers. A thorough understanding of the flow dynamic characteristics occur in such transportation lines, process plants and units is very crucial in terms of design, operation, production and safety. In the current work, air-water two-phase churn flow in a 34 mm I.D. pipe was investigated for two configurations of vertical upward (51 cases) and downward (48 cases). Several conductance probes and pressure transducers were used to measure cross-sectional averaged void fraction time series, and pressure drop along the pipe, respectively. The main objectives of the work were to investigate the similarities and dissimilarities between vertically upward and downward churn flow and specifically understand how gravity could affect the behavior of liquid structures present within the flow. To quantify this, different parameters such as Probability Density Function, distribution coefficient in the drift-flux model, structural velocity, slippage number, dimensionless pressure gradient etc. were used. It was noticed that in both configurations, dimensionless pressure gradient and slippage number demonstrated a strong correlation with the mixture Froude number. There were, however, discrepancies in Probability Density Functions (PDFs) and structural velocities of flow in the two orientations.