Experimental study of interfacial parameter distributions in upward bubbly flow under vertical and inclined conditions

Radial distribution of interfacial parameters for air–water bubbly flow in a circular tube (i.d.50 mm) was investigated experimentally under vertical and inclined conditions with the help of double optical fiber probe method, including the local Interfacial Area Concentration (IAC), bubble frequency and void fraction. The ranges of superficial gas and liquid velocities are 0.002∼0.037 m/s and 0.072∼0.569 m/s, respectively. The inclination angles are 5°, 15° and 30°. The core peak, wall peak, intermediate peak and transition distribution types were observed for vertical upward flow. Under inclined condition, bubbles congregate toward the upper part of the tube, resulting in the asymmetrical distributions of the local interfacial parameters. Comparing with that of vertical flow, the central broad peak leans to the upper part of the tube, and its value increases as the inclination angle increases. Accordingly, with increasing of the inclination angle, the peak near the lower wall weakens gradually, even disappears, whereas, the one near the upper wall of the tube boosts up. The interfacial parameters increase diametrically from ri/R = −0.84 to the peak location in upper part of the inclined pipe, of which higher slope is observed as the inclination angle increases. The Sauter mean diameter is influenced by the gas and liquid velocities as well as the inclination angles. The asymmetrical distributions of interfacial parameters under inclined condition are induced by the radial component of buoyancy force.

► Effects of Inclination angle on interfacial parameter distribution are studied.
► Void fraction, bubble frequency and IAC have similar radial distributions.
► Different typical profiles are influenced by inclination angles in different ways.
► Interfacial parameter profiles are correlated with Sauter mean diameters.
► Radial component of buoyancy determines the asymmetrical distributions.