An Experimental Study of Gas Holdup in Two-Phase Bubble Columns With Foaming Liquids

Minimum superficial gas velocity for onset of foaming

“…Laimbock [6] has observed that a minimum superficial gas velocity should be reached to initiate foaming of molten glass. The same observations have been made for different aqueous solutions [7][8][9][10][11][12], as well as for molten steel [1,[13][14][15][16][17][18]. Fig.…”

“…The Weber number is commonly used in the studies of bubble coalescence [11,19,21] and represents the ratio of the inertial forces to the surface tension forces [19]:…”

“…For gas-liquid systems, the flexibility of the bubble/liquid interface leads to negligible particle-particle interaction forces and the above expressions for the drift-flux and for the superficial gas velocity for onset of foaming j m in the different flow regimes are still valid for values of the void frac- tion α very close to unity, including foams or dense packing regimes [4,23,25]. Moreover, the drift-flux model has been validated for gas-liquid bubbly flow featuring void fraction close to unity such as foams [4,11,[23][24][25][26]. Therefore, the drift-flux model can be used with confidence for predicting the onset of foaming since ideally, the onset of foaming corresponds to the situation when bubbly or churn-turbulent flow regimes with low void fraction prevail and coexist with only a single layer of packed bubbles accumulating at the free surface as shown in Fig.…”

“…Additional data were obtained from the literature [11]. The minimum superficial gas velocity for onset of foaming j m was determined experimentally by extrapolating the data for the steady-state foam thickness H ∞ as a function of the superficial gas velocity j g and by assuming a linear relationship [i.e.…”

“…Note that the shape of the bubbles derived from Ishii's criteria agree with different models based on other dimensionless numbers than the viscosity number (see [27], p. 27). Even though no transition criteria between the distorted bubble and the churn-turbulent regimes has been given, experimental data reported by Pino et al [11] were assumed to feature a churn-turbulent regime as described by the authors. The radii of the bubbles for data reported by these researchers were found based on the following correlation relating the bubble radius to the gas flow rate [see [4], Eq.…”