Investigation into Bubble Size Distribution and Transient Evolution in the Sparger Region of Gas−Liquid External Loop Airlift Reactors

Abstract

It is well-known that the gas sparger can play an important role on the transient evolution of bubbles and bubble size distribution (BSD) in gas-liquid external loop airlift reactors (EL-ALRs). Therefore, the main subject of the present work was to study the influence of sparger design and process parameters on the transient evolution of bubbles and bubble size distribution (BSD) in the sparger region of the considered EL-ALRs. For this purpose, both detailed measurements and prediction of the size of bubbles produced at the sparger were carried out in EL-ALRs with different size and sparger structure parameters. The unique set of BSD curves were obtained by analyzing a large amount of bubbles with a measurement based on an image analysis technique. Additionally, Colella's model of BSD evolution in bubble columns was further developed by implementing a detailed physical model for predicting the initial BSD at the sparger applied to gas-liquid EL-ALRs where the model input is only based on design/process parameters. A validation of the model was carried out using data from gas-liquid EL-ALRs with different size and sparger design parameters. In order to provide more deep insight for transient evolution of bubbles at the local scale in the sparger region, the computational fluid dynamics (CFD) code Fluent 6.2 was used. The transient evolution of bubbles was simulated in the sparger region of gas-liquid EL-ALR. The simulating results of bubble size are in good agreement at the lower gas velocity with the experimental data in the sparger regions of TU-A and TU-B. With increasing gas flow rate, the difference between simulations and experimental values for bubble size increases. The simulations underestimate bubble size at high gas flow rate.

Comprehensive experimental investigation of counter-current bubble column hydrodynamics: Holdup, flow regime transition, bubble size distributions and local flow properties

“…It is worth noting that the BSD at the sparger depends on many design parameters (i.e., the hole of the sparger and the flowrate) as reported by Hur et al (2013) and Geary and Rice (1991). For example, a sensitivity analysis made by Cao et al (2009) using the Geary and Rice (1991) model showed that increasing hole flowrate or decreasing hole dimensions lead to larger bubbles, whereas an increasing number of holes results in smaller bubbles detaching from the sparger.…”

“…The data obtained by sampling only the bubbles freshly detached from the sparger (Fig. 30a) can be compared with the correlations of Polli et al (2002) and by Cao et al (2009). These correlations are based on non-dimensional numbers-the "dimensionless bubble diameter" d w and the "dimensionless velocity" N w :…”

“…Cao et al (2009) and Polli et al (2002) assumed that d w is well estimated with the dimensionless correlation of Miyahara et al (Miyahara and Hayashino, 1995) for values of N w lower than 14 and 10, respectively. For higher N w , their correlations are obtained by fitting experimental values with an exponential function, as suggested by Miyahara and Hayashino (1995).…”

Computational fluid dynamics modelling of large-scale bubble columns: from the mono-dispersed to the pure heterogeneous flow regime

“…The inlet bubble size was assumed to have a log-normal distribution with a constant variance about the mean value. The Cao et al [18] correlation was used to calculate the inlet mean bubble size, whereas the variance was determined from the experimental data.…”