Effect of pressure on slugging in steam/water two-phase flow in a large diameter horizontal pipe

Flow pattern transition from separated (stratified or wavy) flow to intermittent (plug or slug) flow has been experimentally investigated for steam/water two-phase flow in large diameter (180 mm and 87 mm) horizontal pipes at pressures between 3.0 and 12.0 MPa. In comparison with the Mandhane's flow pattern map, present results indicate that the transition takes place at much higher liquid flow rates for large diameter pipes at pressures below 6.0 MPa. The results are also similar to the air/water data obtained at near atmospheric pressures in pipes of comparable diameters, and are reasonably well predicted by the currently available transition criteria. At pressures higher than 9.0 MPa, slug flow was not observed. The disappearance of slug flow at higher pressures can not be explained by the theories on which most transition criteria are based. (author)