Slug flows of gas and shear-thinning fluids in horizontal pipes

Experiments on slug flow are carried out with air and three solutions of carboxymethylcellulose (CMC)(0.05, 0.1 and 0.2% w/w) in a 44.2 mm ID horizontal pipe. The lengths, velocities and frequency of passage of the large bubbles are obtained through a high-speed digital camera. The gas fraction and length of liquid slugs are also estimated. Pressure changes along the pipe are measured with a differential pressure transducer. Particle Image Velocimetry is used to obtain the mean velocity of the continuous liquid field in the film and slug regions. The combination of tested gas and liquid superficial velocities and of distinct fluid rheology results in 48 different experimental conditions. The flow behavior is found to be strongly dependent on the rheological properties of the continuous phase. In particular, the gas volume fraction within the liquid slug (a = 1 - Rs), the passage frequency of the large bubbles (vt) and the pressure changes are increased. New expressions are proposed for a and vt to account for the rheology of the liquid phase. Predictions of the flow parameters obtained through two modified mechanistic models are compared with the experimental data. The friction coefficient expression proposed by Anbarlooei et al. (Phys. Rev. E, 92(6), 5-9, 2015) is also tested. The impact of the proposed modifications on the calculated properties of slug flow is assessed; typical RMS-errors of less than 15% are obtained for parameter predictions.