Intermittent flow parameters from void fraction analysis

Two-phase horizontal intermittent flow in straight pipes is experimentally investigated. A new procedure is proposed to characterize the flow through the statistical analysis of the instantaneous cross-sectional averaged void fraction obtained by means of ring impedance probes. The algorithm, based on the statistical analysis of the void fraction records, allows the main intermittent flow parameters, such as slug frequency and length, time average void fraction, minimum and average liquid film height to be evaluated. The procedure is validated through flow visualizations, as obtained from a fast digital video camera. Experiments on air-water horizontal flows in 40 mm and 60 mm inner diameter pipes are performed. The operating conditions cover the 0.3-4.0 m/s and 0.6-3.0 m/s gas and liquid superficial velocity ranges, respectively. An extensive comparison with literature data shows a general agreement with present measurement. The reliability of both the instrumentation and the signal analysis procedures allows new correlations for minimum and average liquid film height in stratified regions to be proposed. Finally proper dimensionless numbers were applied to correlate frequency data in a wide range of superficial velocity values