Investigation of bubble diameter and flow regime between water and dilute aqueous ethanol solutions in an airlift reactor

Abstract

In this study, the effect of ethanol addition into pure water and its concentration on bubble diameter, gas hold-up and flow regimes were investigated in an airlift reactor. Air and water with ethanol (concentration ranging from 0%-1%, v/v) were as dispersed and continuous phases, respectively. Superficial gas velocity was considered as an effective parameter. Bubble size distribution was measured by photography and picture analysis at various concentrations of ethanol and various velocities of gas. Alcohol concentration enhancement caused bubble diameter to decrease. Furthermore, the bubbles diameter in pure water was nearly 4 times higher than that of ethanol with concentration of 1% (v/v) and also was 3.4 times higher than that of ethanol with concentration of 0.25% (v/ v) at the highest aeration gas velocity inlet. For ethanol solutions in lower superficial gas velocity, a homogenous flow regime was observed. This trend continued to inlet gas velocity of about 0.4 cm/s. The transition flow regime occurred after this datum although in pure water, a homogenous flow regime was observed up to a superficial gas velocity of 0.7 cm/s. The gas hold-up in dilute ethanol solutions were more than (around 2 times) that of pure water and increased with increasing concentration of ethanol in those solutions.

Marangoni effect on hydrodynamics and mass transfer behavior in an internal loop airlift reactor under elevated pressure

“…Therefore, the interpretation based on Andrew's model cannot explain the phenomenon that the gas holdup changes greatly with ethanol concentration, although the predicted ethanol concentration corresponding to the peak gas holdup is reasonable. Besides, the volcano‐shaped relationship between the gas holdup and ethanol concentration can hardly be attributed only to the surface tension as claimed in some literatures since the surface tension decreases monotonically with ethanol concentration 40–42 …”

“…Note that the correlation of α g from Moraveji 17 uses the average bubble diameter d b , which is less measured in literatures, so we regard d b as 1.0 mm 32,40 for the data sets without d b measurement.…”

“…Figure 15 shows that the empirical correlations in the literature had large deviation with the same experimental data sets as in Figure 14. Note that the correlation of α g from Moraveji 17 uses the average bubble diameter d b , which is less measured in literatures, so we regard d b as 1.0 mm 32,40 for the data sets without d b measurement.…”

“…Besides, the volcano-shaped relationship between the gas holdup and ethanol concentration can hardly be attributed only to the surface tension as claimed in some literatures since the surface tension decreases monotonically with ethanol concentration. [40][41][42] The computational fluid dynamics (CFD) incorporating population balance model (PBM) has been demonstrated to be effective for prediction of the hydrodynamics and mass transfer in a gas-liquid two-phase flow. Due to the complexity of the gas-liquid two-phase flow in the presence of surfactants, there is not yet a complete model that couples the Marangoni effect to predict hydrodynamics and mass transfer.…”

CFD Simulation of Scale Influence on the Hydrodynamics of an Internal Loop Airlift Reactor

“…Park et al used an airlift bioreactor in which the top and bottom of the draft tubes were covered with stainless steel sieves for the production of itaconic acid by Aspergillusterreus [10]. Sajjadi et al investigated the effects of ethanol addition to pure water and its concentration enhancement on the bubbles diameter, gas holdup and flow regime in a split-cylinder airlift bioreactor [11]. They found that an increase in alcohol concentration reduces the bubble diameter.…”