Correlation of Interfacial Friction Coefficients for Predicting Countercurrent Flow Limitation at a Sharp-Edged Lower End of Vertical Pipes

One-region (1-R) sensitivity computations with the annular-flow model were carried out for countercurrent flow limitation (CCFL) at a sharp-edged lower end in vertical pipes to generalize the prediction method for CCFL there (i.e., predicting effects of diameters and fluid properties on CCFL characteristics). In our previous study, we selected a correlation of interfacial friction coefficients, f_i, with a function of average void fraction which gave a good prediction of the trend for air–water CCFL data, and we modified it to get good agreement with steam–water CCFL data under atmospheric pressure conditions, but it failed to predict CCFL reasonably at high pressure conditions. We recently found a Russian report on CCFL data at high pressure conditions, by which we improved the f_i correlation using the dimensionless diameter and the viscosity ratio or density ratio of gas and liquid phases to get good agreement with CCFL data at high pressures. The improved f_i correlation with the viscosity ratio and the improved f_i correlation with the density ratio gave similar computed results, but the number of adjustment functions was one for the density ratio and two for the viscosity ratio (i.e., minimum value of two functions).