Effect of Surfactants on Gas Holdup in Shear-Thinning Fluids

Abstract

In this study, the gas holdup of bubble swarms in shear-thinning fluids was experimentally studied at superficial gas velocities ranging from 0.001 to 0.02 m⋅s −1 . Carboxylmethyl cellulose (CMC) solutions of 0.2 wt%, 0.6 wt%, and 1.0 wt% with sodium dodecyl sulfate (SDS) as the surfactant were used as the power-law (liquid phase), and nitrogen was used as the gas phase. Effects of SDS concentration, rheological behavior, and physical properties of the liquid phase and superficial gas velocity on gas holdup were investigated. Results indicated that gas holdup increases with increasing superficial gas velocity and decreasing CMC concentration. Moreover, the addition of SDS in CMC solutions increased gas holdup, and the degree increased with the surfactant concentration. An empirical correlation was proposed for evaluating gas holdup as a function of liquid surface tension, density, effective viscosity, rheological property, superficial gas velocity, and geometric characteristics of bubble columns using the experimental data obtained for the different superficial gas velocities and CMC solution concentrations with different surfactant solutions. These proposed correlations reasonably fitted the experimental data obtained for gas holdup in this system.

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

“…Figure 1 summarizes two recognized effects of adding surface‐active substances in a gas–liquid two‐phase flow. The surface‐active substances reduce the mobility of the gas–liquid interface and inhibit bubble coalescence, thus increasing the gas holdup and mass transfer area, in an effect called the “Marangoni effect.” 10,11 According to our previous work, the bubble coalescence time in a surfactant‐water system controlled by the Marangoni effect can be thousands of times larger than that in a pure water system, due to the significant effect of surfactants on hydrodynamics and mass transfer 12,13 . The other recognized effect is the increased drag force.…”

“…10,11 According to our previous work, the bubble coalescence time in a surfactant-water system controlled by the Marangoni effect can be thousands of times larger than that in a pure water system, due to the significant effect of surfactants on hydrodynamics and mass transfer. 12,13 The other recognized effect is the increased drag force. The adsorbed surfactant molecules are swept to the trailing pole of a rising bubble and create the Marangoni stress at the interface.…”

Bubble size distribution and gas holdup in bubble columns employing non‐Newtonian liquids: A CFD study

“…[ 6,23 ] The bubble number density and hydrodynamics are influenced by the gas flow rate. [ 11 ] Li et al [ 24 ] found the gas holdup to be directly proportional to and the concentration of aqueous carboxymethyl cellulose (CMC) solution. Anastasiou et al [ 4 ] used CFD and reported bubble cluster formation at lower velocities and the onset of the heterogeneous regime with bubble coalescence at higher velocities.…”

“…Xing et al [ 31 ] used the population balance model (PBM) and found that bubble Sauter mean diameter (SMD) was overpredicted because the liquid viscosity affected breakage models more than the coalescence models. Li et al [ 24 ] observed a lower gas holdup with an increase in the shear‐thinning property of the liquid. Moreover, the gas holdup increased with liquid viscosity due to the reduction in bubble rise velocity and the consequential increase in bubble residence time.…”

“…Factors such as bubble wakes, bubble coalescence and breakage, liquid vortexes, and so on result in a heterogeneous spatial-temporal distribution of bubble size and gas holdup. [15] Several researchers [4,10,[16][17][18][19][20][21][22][23][24] developed correlations for the gas holdup in bubble columns employing non-Newtonian liquids. The following sections allude to the major research done in studying the effect of gas flow rate, liquid viscosity, yield stress, and sparger bubble size on the BSD and gas holdup in bubble columns containing shear-thinning non-Newtonian liquids.…”