Experimental Studies of Interfacial Area in a Horizontal Slug Flow

Abstract The internal flow structure of horizontal slug flow has been experimentally investigated by measuring the local interfacial area concentration, void fraction and interfacial velocity distribution. The four-sensor electroresistivity probe was used to detect the instantaneous interface velocities and interfacial area. Experimental studies were performed on the plug/slug flow regimes with an air-water system. Data were acquired at the axial location of L/D = 253 from the mixing chamber. Four different liquid flow rates in combination with five different gas injection rates were studied. The superficial liquid velocity was varied between 0.55 and 2.20 m/s and gas velocity between 0.27 and 2.20 m/s. With these experimental conditions, the total void fraction, including contributions from small and large slug bubbles, ranged from 10 to 70%. The void fraction measurements were checked against the raw signal data, high speed video recordings, and measurements obtained by the hot film anemometer probe. The agreement between the data was very good, confirming that the four-sensor probe measurements can be performed with a high degree of confidence. In the region of transition between plug and slug flow regime, with an increase in the gas flow rate, the number and contribution of the small follow-up bubbles increased. The increase in the liquid flow rate produced similar effects. The slug bubble frequency also increased with an increase in the gas velocity and also slugs are longer at higher gas flow rates. Total interfacial area concentration profile includes the contribution from both slugs and small follow-up bubbles. Experimental data showed higher interfacial area concentration in the lower part of a slug bubble, with a larger curvature of interface. This is expected, since along the steeper curvature a ratio of local surface area to volume is increasing. Radial profiles of interfacial area concentration for slug bubbles show almost a flat profile in the upper part of slug bubble. The larger values of the total interfacial area concentration indicates that the contribution from the small bubbles is increasing. Experiments showed that in the plug/slug flow regime, contribution from the increasing number of small bubbles to the interfacial area concentration is substantial in upper part of the horizontal channel.