Figure 5 . Probability
density function of bubble size at different liquid viscosities andUSG =27.6 mm/s.
Transport coefficients determine the performance and efficiency of a
bubble column and are sensitive to the bubble size and void fraction.
Bubble size and void fraction are heavily depended on the operation
regime, which sets the dominant fluidic mechanisms within a gas-liquid
system. The rest of this paper is structured as such to study the bubble
size and void fraction with respect to the operation regimes i.e.,
homogenous and heterogeneous.
3.2 Homogeneous
regime
In this section bubble size and void fraction were studied in the
homogenous operation regime, which features a linear trend between the
void fraction and the gas superficial velocity as well as a direct
correlation between bubble size and gas superficial velocity.
Homogeneous bubbly flow is characterized by the absence of breakage and
coalescence and a Gaussian BSD; therefore, any attempt to scale the
bubble size should include the pore size (rp ) and
the gas superficial velocity (USG ) in the
parameter space. The present work also includes the liquid properties
(i.e. surface tension σ , liquid viscosityμL , and liquid densityρL ), and gravity (g ) to scale the bubble
size in the homogenous regime. Using dimensional analysis, the scaled
bubble size was expected to be dependent on the Froude number
(Fr ), Weber number (We ), and Reynolds number (Re );
see Equations (5)-(7).
Figure 6 validates the correlation for predicting bubble size
(d32 ) in homogeneous regime (see Equation 8)
against experimental bubble size data. Results show that in the
homogenous regime the proposed correlation predicts the bubble size. In
Equation (8) the power exponents were found following the recommendation
from Kazakis et al.,40 which argues that the sparger
material effects correlations of this type due to the sensitivity of
bubble size to pore dimensions in homogeneous bubbly flow. The power law
functional form between the aforementioned non-dimensional terms (see
Equations 5-7) was first suggested by Akita and
Yoshida;24 in addition, in Equations (5)-(7) the
exponents were obtained empirically.40