Inhibition Of Bubble Coalescence Research Articles

Effect of Surfactants on Inertial Cavitation Activity in a Pulsed Acoustic Field

It has previously been reported that the addition of low concentrations of ionic surfactants enhances the steady-state sonoluminescence (SL) intensity relative to water (Ashokkumar; et al. J. Phys. Chem. B 1997, 101, 10845). In the current study, both sonoluminescence and passive cavitation detection (PCD) were used to examine the acoustic cavitation field generated at different acoustic pulse lengths in the presence of an anionic surfactant, sodium dodecyl sulfate (SDS). A decrease in the SL intensity was observed in the presence of low concentrations of SDS and short acoustic pulse lengths. Under these conditions, the inhibition of bubble coalescence by SDS leads to a population of smaller bubbles, which dissolve during the pulse "off time". As the concentration of surfactant was increased at this pulse length, an increase in the acoustic cavitation activity was observed. This increase is partly attributed to enhanced growth rate of the bubbles by rectified diffusion. Conversely, at long pulse lengths acoustic cavitation activity was enhanced at low SDS concentrations as a larger number of the smaller bubbles could survive the pulse "off time". The effect of reduced acoustic shielding and an increase in the "active" bubble population due to electrostatic repulsion between bubbles are also significant in this case. Finally, as the surfactant concentration was increased further, the effect of electrostatic induced impedance shielding or reclustering dominates, resulting in a decrease in the SL intensity.

The Effect of Surface-Active Solutes on Bubble Coalescence in the Presence of Ultrasound

The sonication of an aqueous solution generates cavitation bubbles, which may coalesce and produce larger bubbles. This paper examines the effect of surface-active solutes on such bubble coalescence in an ultrasonic field. A novel capillary system has been designed to measure the change in the total volume resulting from the sonication of aqueous solutions with 515 kHz ultrasound pulses. This volume change reflects the total volume of larger gas bubbles generated by the coalescence of cavitation bubbles during the sonication process. The total volume of bubbles generated is reduced when surface-active solutes are present. We have proposed that this decrease in the total bubble volume results from the inhibition of bubble coalescence brought about by the surface-active solutes. The observed results revealed similarities with bubble coalescence data reported in the literature in the absence of ultrasound. It was found that for uncharged and zwitterionic surface-active solutes, the extent of bubble coalescence is affected by the surface activity of the solutes. The addition of 0.1 M NaCl to such solutes had no effect on the extent of bubble coalescence. Conversely, for charged surface-active solutes, the extent of bubble coalescence appears to be dominated by electrostatic effects. The addition of 0.1 M NaCl to charged surfactant solutions was observed to increase the total bubble volume close to that of the zwitterionic surfactant. This suggests the involvement of electrostatic interactions between cavitation bubbles in the presence of charged surfactants in the solution.

Inhibition of Bubble Coalescence in Aqueous Solutions. 1. Electrolytes

The inhibition of bubble coalescence has been studied in dilute 1:1 and 2:1 electrolyte solutions. All electrolytes studied were found to inhibit coalescence, with anions dominating the inhibition at concentrations below 0.01 M and cations dominating the inhibition at higher concentrations.

Surface Tension of Aqueous Solutions of Electrolytes: Relationship with Ion Hydration, Oxygen Solubility, and Bubble Coalescence

The surface tension of aqueous solutions of simple inorganic electrolytes (36 in total) have been measured by the maximum bubble pressure method as a function of electrolyte concentration up to 1M.In most cases the surface tension increased, however in a minority of cases, certain combinations of cations and anions had a negligible effect or decreased surface tension. Results were analysed in terms of surface tension/electrolyte concentration gradients (d(Δγ)/dc) and this parameter was found to correlate with the entropies of ion hydration, Jones–Dole viscosity coefficients and dissolved oxygen gradients. Calculation of Gibbs surface deficiencies for selected electrolytes were carried out using the raw surface tension data. Discussion of the surface tension/electrolyte concentration gradients was extended to the mechanism of inhibition of bubble coalescence by electrolytes. The Gibbs–Marangoni effect did not provide a satisfactory explanation for the inhibition of coalescence for all electrolytes and from the present study we suggest that dissolved gas (microbubble) gradients between macroscopic bubbles plays an important role in the coalescence process.

Surface Tension and Bubble Coalescence Phenomena of Aqueous Solutions of Electrolytes

The inhibition of bubble coalescence by electrolytes beyond a critical transition concentration has been assessed by the relationship between transition concentration and surface tension gradients of electrolytes (d(Δγ)/dc) and gas solubility. The correlation between transition concentration and [d(Δγ)/dc] -2 was mediocre (0.74), suggesting that the Gibbs-Marangoni effect cannot fully account for inhibition of bubble coalescence. Preliminary bubbling experiments on mixed electrolytes supported this conclusion. A much better correlation was found between the transition concentration and gas solubility (represented by the exponential decay coefficient of O 2 solubility with increasing electrolyte concentration). Hence, the inhibition of bubble coalescence may be linked with the decreased dissolved gas concentration in the electrolyte solution

Effect of liquid coalescing properties on mass transfer, heat transfer and hydrodynamics in a three-phase fluidized bed

The most important difference between pure water and the liquids used in industrial reactors may be their coalescing properties, i,e. their ability either to promote or to hinder the coalescence of gas bubbles. Experimental techniques were developed for the simultaneous measurement of gas-liquid mass transfer, particle-liquid mass transfer and particle-liquid heat transfer. Salt could either promote or inhibit bubble coalescence, depending on its concentration. The effects on the gas holdup of coalescence inhibition and gas distribution were correlated with the “bubble slip velocity”. Coalescence inhibition reduced particle-liquid mass and heat transfer. There was no analogy between heat and mass transfers. Coalescence inhibition greatly affected gas-liquid mass transfer.

High Cell Density Computer Control of Candida utilis Yeast Production on Molasses

C. utilis was continuously grown at cell densities of 76 to 80 g/l with yields of 0.46 to 0.55 g cell/g sugar, in a 10.5 m3 jet loop fermenter provided with a computer system for on line data acquisition and molasses flow rate feedback control. Infered ethanol production rate was employed as control variable to keep high conversion yields while maintaining high volumetric productivity (10.1 to 10.7 g/l h). Molasses addition control was useful to accommodate moderate gas holdup and OTR oscillations due to bubble coalescence inhibition and antifoam shot additions required for foam control. However, results suggest that improved fermentation process control will result, if gas holdup variations are minimized. A gas holdup control scheme is proposed including a differential pressure transmitter to indirectly measure gas holdup and provide an output signal to control antifoam addition. Advantages of such approach would be a more stable fermentation process continuously operating to maximum OTR and productivity.

Inhibition of bubble coalescence by the electrolytes

Coalescence frequency and coalescence time were measured in electrolyte solutions. Marrucci model was acceptable to predict the coalescence time of one pair bubble in the dilute solution of electrolytes. Transition concentration decreased with increase of bubble forming frequency. This tendency was same as the results in low molecular alcohol solution. For a bubble column study, the effects of electrolyte on the gas holdup and bubble characteristics were invstigated. The inhibition effect of bubble coalescence of the K2SO4 was slightly higher than that of the KCI at a same ionic strength. In this work, transition concentration was 0.36 kmol/m3, which is larger than the value predicted in pair bubble study.

INFLUENCE OF LIQUID PROPERTIES ON THE DETERMINATION OF THE VOLUMETRIC MASS TRANSFER COEFFICIENT WITH THE HYDRAZINE METHOD

Abstract The oxidation of hydrazine in aqueous solution by atmospheric oxygen in presence of a homogeneous catalyst (copper tetrasulphophthalocyanine) is well suited for the determination of volumetric mass transfer coefficients. In contrast to other chemical methods the hydrazine oxidation permits to vary coalescence behaviour of the liquid phase by adding electrolytes or organic compounds, because without these solutes the reaction liquid does not inhibit bubble coalescence. With appropriate high molecular additives the hydrazine method can also be used for mass transfer measurements in liquids of high viscosity. Compared to the dynamic method the hydrazine method as a steady state method is far less influenced by systematic errors originating from the evaluation model. For this reason the application of the hydrazine method for testing semi-industrial and industrial gas-liquid contacting devices should be especially attractive.

Inhibition of bubble coalescence by solutes in air/water dispersions

Measurement of bubble size distributions in bubble column by a photoelectric probe showed that both electrolyte and organic solutes affect coalescence behaviour of aqueous solutions drastically within a narrow concentration range, changing from quick coalescence as in pure water to coalescence restraining. Besides the electrolytes NACl, Na 2SO 4, Al 2(SO 4) 3, NaOH, organic compounds from homologous series ( n-alcohols, diols, ketones, carboxylic acids), detergents, saccharose, and carboxymethylcellulose have been used as solutes. Rough relationships between concentrations for coalescence restraining and molecular properties can be given (ionic strength for electrolytes, number of C-atoms in homologous series of organic compounds), but no exact equations based on a theory of coalescence. For the n-alcohols (C 1-C 8), specific surface areas were calculated from experimental mean bubble diameters (Sauter diameters) and measured gas hold-up and compared to volumetric mass transfer coefficients from literature. Concentration dependence of the two types of data showed surprisingly good agreement with regard to the fact that the mass transfer data had been obtained in a gas-liquid contacting device (stirred vessel) quite different to the reactor used in this work (bubble column).