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An experimental study on air/water flow behaviours in a 101.6 mm i.d. vertical pipe with a serpentine configuration is presented. The experiments are conducted for superficial gas and liquid velocities ranging from 0.15 to 30 m/s and 0.07 to 1.5 m/s, respectively. The bend effects on the flow behaviours are significantly reduced when the flow reaches an axial distance of 30 pipe diameters or more from the upstream bend. The mean film thickness data from this study has been used to compare with the predicted data using several falling film correlations and theoretical models. It was observed that the large pipe data exhibits different tendencies and this manifests in the difference in slope when the dimensionless film thickness is plotted as a power law function of the liquid film Reynolds number.

Interfacial friction is one of the key variables for predicting annular two-phase flow behaviours in vertical pipes. In order to develop an improved correlation for interfacial friction factor in downward cocurrent annular flow, the pressure gradient, film thickness and film velocity data were generated from experiments carried out on Cranfield University's Serpent Rig, an air/water two-phase vertical flow loop of 101.6 mm internal diameter. The air and water superficial velocity ranges used are 1.42-28.87 and 0.1-1.0 m/s respectively. These correspond to Reynolds number values of 8400-187000 and 11000-113000 respectively. The correlation takes into account the effect of pipe diameter by using the interfacial shear data together with dimensionless liquid film thicknesses related to different pipe sizes ranging from 10 to 101.6 mm, including those from published sources by numerous investigators. It is shown that the predictions of this new correlation outperform those from previously reported studies.Interfacial shear in adiabatic downward gas/liquid co-current annular flow in pipes, Experimental Thermal and Fluid Science, Volume 72, April 2016, Pages 75-87. AbstractInterfacial friction is one of the key variables for predicting annular two-phase flow behaviours in vertical pipes. In order to develop an improved correlation for interfacial friction factor in downward co-current annular flow, the pressure gradient, film thickness and film velocity data were generated from experiments carried out on Cranfield University's Serpent Rig, an air/water twophase vertical flow loop of 101.6 mm internal diameter. The air and water superficial velocity ranges used are 1.42-28.87 and 0.1-1.0 m/s respectively. These correspond to Reynolds number values of 8400-187000 and 11000-113000 respectively. The correlation takes into account the effect of pipe diameter by using the interfacial shear data together with dimensionless liquid film thicknesses related to different pipe sizes ranging from 10 to 101.6 mm, including those from published sources by numerous investigators. It is shown that the predictions of this new correlation outperform those from previously reported studies.

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We present an experimental study on the flow behaviour of gas and liquid in the upward section of a vertical pipe system with an internal diameter of 101.6 mm and a serpentine geometry. The experimental matrix consists of superficial gas and liquid velocities in ranges of 0.15 to 30 m/s and from 0.07 to 1.5 m/s, respectively, which cover bubbly to annular flow. The effects on the flow behaviours downstream of the 180° return bend are significantly reduced when the flow reaches an axial distance of 47 pipe diameters from the U-bend. Therefore, reasonably developed flow is attained at this development length downstream of the bend. Other published measurements for large-diameter film thickness show similar trends with respect to the superficial gas velocity. However, the trends differ from those of small-diameter pipes, with which the film thickness decreases much faster with increasing gas flow. As a result, only a few of the published correlations for small pipe data agreed with the experimental data for large pipe film thickness. We therefore modified one of the bestperforming correlations, which produced a better fit. Qualitative and statistical analyses show that the new correlation provides improved predictions for two-phase flow film thickness in large-diameter pipes.

Experimental investigation has been carried out on upward and downward vertical pipes with 180° bends to study gas-liquid two-phase flow behaviours in pipes with serpentine configuration. Wire mesh sensor (WMS) is installed at top and bottom positions of upward and downward sections in order to identify the void fraction distributions. Film thickness probes are employed to obtain circumferential profile of the liquid film thickness at different axial positions along both sections. Further features such as flow patterns are identified by examining the time trace and probability density function (PDF) data. All measurements are conducted for different superficial gas velocities, while superficial liquid velocity is fixed at 1.0 m/s.The study identified that the centrifugal force present in 180° bends caused a flow maldistribution in the adjacent straight sections. It is noted from the time trace and PDF results that the superficial gas velocity has obvious effects on the flow development along different positions of the pipes, where the flow regime varied over whole velocity ranges tested. These results are confirmed by the cross-sectional view and sliced stack images (longitudinal view) of the void fraction distributions. The results also showed that the flow behaviour in upward and downward pipes is affected by bends, although to varying degrees.

We investigate the effect of a return U-bend on flow behaviour in the vertical upward section of a largediameter pipe. A wire mesh sensor was employed to study the void fraction distributions at axial distances of 5, 28 and 47 pipe diameters after the upstream bottom bend. It was found that, the bottom bend has considerable impacts on up-flow behaviours. In all conditions, contour plots of the crosssectional phase distribution measurement using the wire mesh sensor (WMS) show that centrifugal effect of the U-bend causes appreciable misdistribution in the adjacent straight section. However, flow asymmetry significantly reduces at an axial distance of 47D from the U-bend. Flow regime maps generated from three axial locations showed that, in addition to bubbly, intermittent and annular flows, oscillatory flow occurred particularly when gas and liquid flow rates were relatively low. At this position, the mean void fractions were in agreement with those from other large-pipe studies.Comparisons were made with existing void fraction correlations. Among the correlations surveyed, drift flux-type correlations were found to give the best predictive results.