The titration of clay minerals I. Discontinuous backtitration technique combined with CEC measurements

Evolution of liquid holdup profile in a standing foam formed by whipping and stabilized by sodium caseinate in the presence of xanthan gum when subjected to 16 and 29g centrifugal force fields was measured using magnetic resonance imaging for different pH, ionic strength, protein and xanthan gum concentrations. Drainage resulted in the formation of a separate liquid layer at the bottom at longer times. Foam drainage was slowest at pH 7, lower ionic strength, higher protein and gum concentrations. Foam was found to be most stable at pH 5.1 near the isoelectric point of protein, lower ionic strength and higher protein and xanthan gum concentrations. A predicted equilibrium liquid holdup profile based on a previous model (G. Narsimhan, J. Food Eng. 14 (1991) 139) agreed well with experimental values at sufficiently long times. A proposed model for velocity of drainage of a power law fluid in a Plateau border for two different simplified geometries was incorporated in a previously developed model for foam drainage (G. Narsimhan, J. Food Eng. 14 (1991) 139) to predict the evolution of liquid holdup profiles. The model predictions for simplified circular geometry of Plateau border compared well with the experimental data of liquid holdup profiles at small times. At longer times, however, the predicted liquid holdup profile was larger than the observed, this discrepancy being due to coarsening of bubble size and decrease in foam height not accounted for in the model. A Newtonian model for foam drainage under predicted drainage rates did not agree with the experimental data.     

Liquid drainage in single plateau borders of foam

This paper reports on an investigation of the influence of the interfacial shear viscosity on the liquid drainage in single Plateau borders of foam. The simplified Navier-Stokes equation governing the liquid flow is solved for the liquid velocity by the numerical computational method. The numerical results show significant influence of the interfacial shear viscosity on the liquid velocity in the Plateau border. Comparison of the numerical results for the average velocity over the cross-section area of the Plateau border to the available analytical solution shows that the available analytical solution underestimates the average velocity. New, simple yet accurate correlations for the dependence of the average velocity on the radius of the cross section of the Plateau border, the pressure gradient, and the interfacial shear viscosity are obtained using the asymptotic analysis and the numerical data.     

Film junction effect on foam drainage

Foam drainage is modelled by the flow of liquid through Plateau borders (PBs) that are the liquid channels resulting from the merging of three liquid films separating the gas bubbles. Available models generally neglect the influence of these films. Yet, within drainage conditions, experimental observations indicate a strong coupling of these films with the channels. We consider the influence of films on foam drainage through their effect on the cross-section geometry of the channels. More precisely, we assume that the Plateau border cross-section is enclosed by three circular arcs that are not always tangent but instead exhibit a non-zero contact angle θ as it has been observed experimentally. The liquid flow through the channels is studied using numerical simulations whose parameters are θ and the Boussinesq number, Bo, that reflects the surface shear viscosity of the interface. We show that, for values of Bo relevant for foam drainage conditions, a slight increase of θ results in a strong decrease of the average liquid velocity.     

Decay of standing foams: drainage,coalescence and collapse

A summary of recent theoretical work on the decay of foams is presented. In a series of papers, we have proposed models for the drainage, coalescence and collapse of foams with time. Each of our papers dealt with a different aspect of foam decay and involved several assumptions. The fundamental equations, the assumptions involved and the results obtained are discussed in detail and presented within a unified framework.Film drainage is modeled using the Reynolds equation for flow between parallel circular disks and film rupture is assumed to occur when the film thickness falls below a certain critical thickness which corresponds to the maximum disjoining pressure. Fluid flow in the Plateau border channels is modeled using a Hagen-Poiseuille type flow in ducts with triangular cross-section.The foam is assumed to be composed of pentagonal dodecahedral bubbles and global conservation equations for the liquid, the gas and the surfactant are solved to obtain information about the state of the decaying foam as a function of time. Homogeneous foams produced by mixing and foams produced by bubbling (pneumatic foams) are considered. It is shown that a draining foam eventually arrives at a mechanical equilibrium when the opposing forces due to gravity and the Plateau-border suction gradient balance each other. The properties of the foam in this equilibrium state can be predicted from the surfactant and salt concentration in the foaming solution, the density of the liquid and the bubble radius.For homogeneous foams, it is possible to have conditions under which there is no drainage of liquid from the foam. There are three possible scenarios at equilibrium: separation of a single phase (separation of the continuous phase liquid by drainage or separation of the dispersed phase gas via collapse), separation of both phases (drainage and collapse occurs) or no phase separation (neither drainage nor collapse occurs). It is shown that the phase behavior depends on a single dimensionless group which is a measure of the relative magnitudes of the gravitational and capillary forces. A generalized phase diagram is presented which can be used to determine the phase behavior.For pneumatic foams, the effects of various system parameters such as the superficial gas velocity, the bubble size and the surfactant and salt concentrations on the rate of foam collapse and the evolution of liquid fraction profile are discussed. The steady state height attained by pneumatic foams when collapse occurs during generation is also evaluated.Bubble coalescence is assumed to occur due to the non-uniformity in the sizes of the films which constitute the faces of the polyhedral bubbles. This leads to a non-uniformity of film-drainage rates and hence of film thicknesses within any volume element in the foam. Smaller films drain faster and rupture earlier, causing the bubbles containing them to coalesce. This leads to a bubble size distribution in the foam, with the bubbles being larger in regions where greater coalescence has occurred.The formation of very stable Newton black films at high salt and surfactant concentrations is also explained.     

Liquid drainage through aqueous foam: study of the flow on the bubble scale

Macroscopic properties of foams are highly dependent on the liquid volume fraction, which has motivated many studies on foam drainage in the last decade. Theoretical developments and recent experimental results have suggested that two macroscopic drainage regimes could be expected, in relation with flow transitions occurring at the microscopic level, essentially in the Plateau border channels. We have constructed a setup, the Plateau border apparatus, to study the hydrodynamics of a single Plateau border channel, focusing on the surface properties of the foaming solution. Experimental results have shown that the actual theoretical models only partially predict the dissipation of liquid flow through a Plateau border channel. The major discrepancies can be explained considering additional dissipation processes related to the properties of the interface, and to the liquid flows induced in adjoining films as the liquid flows in the channel. Evidence of the hydrodynamic coupling between the channel and the adjoining films is given in the paper.     

Foam drainage

This review focuses on recent works on foam drainage + including both the advanced theoretical and experimental studies into foam drainage, standard and extended drainage theories with analytical and numerical solutions. Highlights of recent works include the effect of physico-chemical properties of the gas–liquid interface on foam drainage, and the foam-structure related properties governing the channel-and node-dominated drainage regimes. Important results obtained using the foam pressure drop technique which allows a systematic investigation of foam drainage with the constant and varying Plateau border radius are discussed. The free and forced drainage methods have also been the useful experimental techniques for revealing two important drainage regimes by the channels and the nodes. Finally, the influence of the syneresis on the foam stability and destruction is reviewed.     

Pore-Scale Studies on the Stability of Microfoam and the Effect of Parameters on Its Bubble Size

This paper presents a new method to prepare microfoam with excellent stability and high by using a sandpack foam generator. The micromorphology of microfoam were analyzed, and average bubble diameter and uniformity of microfoam were studied by microscope. The stability of xanthan gum-stabilized microfoam and common microfoam at the pore scale was also compared. The results showed that a highly uniform microfoam ranging in size from 10 to 100 µm in diameter with a variable coefficient less than 10% was successfully prepared. The bubble size of the microfoam could be controlled by solution viscosity, gas and liquid flow rate, temperature, and backpressure. The bubble size of microfoam decreased and became uniform with the increase of solution viscosity, total flow rate, and backpressure. The bubble size increased slightly and became non-uniform with the increase of temperature, while the concentration of foaming agent had little effect on the bubble size when above 5000 mg/L. The xanthan gum in the solution increased the viscosity and thickness of liquid membrane, so xanthan gum-stabilized microfoam maintained better stability within microconfined media than common microfoam under condition of 160 g/L salinity, 90°C, and 6 MPa backpressure.     

Bubble motion measurements during foam drainage and coarsening

We have studied bubble motion within a column of foam allowed to undergo free drainage. We have measured bubble motion upward with time and as a function of their initial positions. Depending on the gas used, which sets the coarsening and drainage rates, different bubble upward motion types have been identified (constant speed, acceleration or deceleration) and explained in relation with liquid downward flows. The proofs of the consistency between bubble upward motion and liquid downward flow are obtained both by comparing the bubble motion curves to the liquid drainage ones, and by comparing the time variations of the liquid fraction extracted from bubble motion to direct liquid fraction measurements by electrical conductimetry. The agreement between bubble position tracking and electrical conductivity shows in particular that it is possible to determine the drainage regime from such simple bubble motion measurements. This work also allowed us to demonstrate a special case of foam coarsening and expansion, occurring when the foam gas is less soluble than the outside one, caused by diffusion of this external gas into the foam. All these results allow us to build a picture of drainage and coarsening seen from the bubble point of view.     

Drainage of aqueous film-forming foam stabilized by different foam stabilizers

The present study focuses on the drainage property of aqueous film-forming foam stabilized by different types and concentrations of foam stabilizers. Aqueous film-forming foam (AFFF) formulation concentrates are prepared based on the main components of fluorocarbon surfactant, hydrocarbon surfactant, and organic solvents. Carboxymethylcellulose sodium (CS), xanthan gum (XG), and lauryl alcohol (LA) are selected as foam stabilizers of the AFFF. Surface tension, viscosity, and foamability tests of the AFFF solutions are conducted to evaluate the effect of foam stabilizers on the properties of AFFF solutions. Particularly, an apparatus is established based on the law of connected vessel in order to obtain the instantaneous mass of liquids drained from foams. The drainage features of the AFFFs containing different foam stabilizers are analyzed and compared with each other. The results indicate that AFFF drainage is significantly affected by the type and the concentration of foam stabilizers. The addition of CS and XG to AFFF results in a deceleration of foam drainage, while foam drainage is accelerated by the addition of LA. The variations of surface tension, viscosity, and liquid fraction of foams are the main reasons for the varying foam drainage rate. This study provides a direct connection between chemical components and fundamental properties of AFFF.     

Effect of Xanthan Gum on the Performance of Aqueous Film-Forming Foam

Solution properties of aqueous film-forming foam (AFFF) formulations containing different xanthan gum contents were investigated first by varying the mass fraction of xanthan gum in the range of 0.1–0.5%. Foam properties and fire-extinguishing performance of the AFFF formulations were then evaluated. Results indicated that xanthan gum content slightly affected surface tension of foam solutions. However, xanthan gum significantly affected viscosity of AFFF concentrates. Foaming of the AFFF formulations was hardly affected by xanthan gum, but foam stability of the compounds was obviously enhanced with the addition of xanthan gum. Optimal xanthan gum content was determined as 0.3%, which resulted in the shortest 90% control time and fire extinguishment time. Burnback time of foams increased with the addition of xanthan gum because of the enhanced foam stability.     

Effects of denaturation on soy protein-xanthan interactions: comparison of a whipping-rheological and a bubbling method

The effect of xanthan on foam formation and on physical mechanisms of destabilization involved in the breakdown of foams made from native and denatured soy protein at neutral pH was studied by a bubbling and a whipping-rheological method. Parameters describing foam formation and destabilization by liquid drainage and disproportionation obtained by the two methods showed that the addition of xanthan was accompanied by delayed rates of drainage and disproportionation and reduced foam height decay (collapse). Drainage showed the largest reduction, mainly because of the increased bulk viscosity. In the absence of xanthan, protein denaturation enhanced foam formation and stability against drainage and disproportionation, but increased the collapse of foams. In the presence of xanthan, differences in foam formation and drainage/disproportionation stability between native and denatured soy protein were greatly reduced. However, differences in foam collapse were greatly enhanced. The increased stability of foams in the presence of xanthan could not be explained purely in terms of increased aqueous phase viscosity. More specific interactions of xanthan and soy proteins at the air-water interface influencing the surface rheology, and the protein composition and aggregation, are involved.     

Foam drainage on the microscale I. Modeling flow through single Plateau borders

The drainage of liquid through a foam involves flow in channels, also called Plateau borders, which generally are long and slender. We model this flow by assuming the flow is unidirectional, the shear is transverse to the flow direction, and the liquid/gas interfaces are mobile and characterized by a Newtonian surface viscosity, which does not depend on the shear rate. Numerical finite difference simulations are performed, and analytical approximations for the velocity fields inside the channels and the films that separate the bubbles are given. We compare the liquid flow rates through interior channels, exterior channels (i.e., channels contacting container walls) and films. We find that when the number of exterior channels is comparable to the number of interior channels, i.e., narrow container geometries, the exterior channels can significantly affect the dynamics of the drainage process. Even for highly mobile interfaces, the films do not significantly contribute to the drainage process, unless the amount of liquid in the films is within a factor of ten of the amount of liquid in the channels.     

Effect of time on the interfacial and foaming properties of beta-lactoglobulin/acacia gum electrostatic complexes and coacervates at pH 4.2

The electrostatic complexation between beta-lactoglobulin and acacia gum was investigated at pH 4.2 and 25 degrees C. The binding isotherm revealed a spontaneous exothermic reaction, leading to a DeltaHobs = -2108 kJ mol(-1) and a saturation protein to polysaccharide weight mixing ratio of 2:1. Soluble electrostatic complexes formed in these conditions were characterized by a hydrodynamic diameter of 119 +/- 0.6 nm and a polydispersity index of 0.097. The effect of time on the interfacial and foaming properties of these soluble complexes was investigated at a concentration of 0.1 wt % at two different times after mixing (4 min, referred as t approximately 0 h and t = 24 h). At t approximately 0 h, the mixture is mainly made of aggregating soluble electrostatic complexes, whereas after 24 h these complexes have already insolubilize to form liquid coacervates. The surface elasticity, viscosity and phase angle obtained at low frequency (0.01 Hz) using oscillating bubble tensiometry revealed higher fluidity and less rigidity in the film formed at t approximately 0 h. This observation was confirmed by diminishing bubble experiments coupled with microscopy of the thin film. It was thicker, more homogeneous and contained more water at t approximately 0 h as compared to t = 24 h (thinner film, less water). This led to very different gas permeability's of Kt approximately 0 h = 0.021 cm s(-1) and Kt=24 h) = 0.449 cm s(-1), respectively. Aqueous foams produced with the beta-lactoglobulin/acacia gum electrostatic complexes or coacervates exhibited very different stability. The former (t approximately 0 h) had a stable volume, combining low drainage rate and mainly air bubble disproportionation as the destabilization mechanism. By contrast, using coacervates aged for 24 h, the foam was significantly less stable, combining fast liquid drainage and air bubble destabilization though fast gas diffusion followed by film rupture and bubble coalescence. The strong effect of time on the air/water interfacial properties of the beta-lactoglobulin/acacia gum electrostatic complexes can be understood by their reorganization at the interface to form a coacervate phase that is more fluid/viscous at t approximately 0 h vs rigid/elastic at t = 24 h.     

Gas Holdups of Small and Large Bubbles in a Large-scale Bubble Column with Elevated Pressure

Gas holdups of large bubbles and small bubbles were measured by means of dynamic gas disengagement approach in the pressured bubble column with a diameter of 0. 3 m and a height of 6.6 m. The effects of su-perficial gas velocity, liquid surface tension, liquid viscosity and system pressure on gas holdups of small bub-bles and large bubbles were investigated. The holdup of large bubbles increases and the holdup of small bub-bles decreases with an increase of liquid viscosity. Meanwhile, the holdup of large bubbles decreases with in-creasing the system pressure. A correlation for the holdup of small bubbles was obtained from the experimen-tal data.     

Marangoni effects in aqueous polypropylene glycol foams

The foam behavior of three polypropylene glycols covering the molecular weight range between 192 and 725 g/mol has been examined. Static and dynamic surface tension data, as well as bubble size distribution and retention time in the foam, were incorporated into a simple model of foam stability. The latter clearly indicates that surface tension differences between the plateau border and lamellar region adjacent to the bubble surface are the dominant factor in controlling foamability, causing liquid flow in the direction opposite to liquid drainage, a process termed the Marangoni effect.     

Influence of polymers on dust-related foam properties of sodium dodecyl benzene sulfonate with Foamscan

Foamability, liquid holdup, and foam appearance are key factors that determine dust control efficiencies. As the foam production method of the FoamScan instrument is similar to foaming device used for dust control, and its measurement means can satisfy the requirements of precise measuring, the FoamScan technology is adopted to explore the influence of xanthan gum (XG) and partial hydrolytic polyacrylamide (HPAM) on dust-related foam properties of sodium dodecyl benzene sulfonate (SDBS). It was found that with the increase of the polymer mass fraction, the liquid volume in the foam gradually increased. Additionally, the foaming time t₂₀₀ of the foaming agent decreased at first, then remained almost constant for both polymers, which indicated that the foamability and liquid holdup were enhanced by the addition of polymers into SDBS. In addition, the efficiencies of XG are higher than that of HPAM. The image analysis using the CSA software revealed that the mean radius formed by XG was smaller than that by HPAM and the number of bubbles was larger with XG than with HPAM. Thus, the XG foam has more area to contact with dust and could control dust better. The highly branched molecular structure and hydrogen bonds formed by XG played important roles in dust-related foam properties.     

Mass transfer of volatile organic carbons through aqueous foams

A model is developed to study diffusive mass transfer of hydrocarbon vapor through a flexible foam blanket. The model accounts for the diffusion of hydrocarbon vapor through gas-phase and liquid lamellae, the combined gravity and capillary drainage from the plateau border, the thinning of foam lamellae caused by the forces of capillary suction, London-van der Waals attraction, and electrostatic double-layer repulsion, and foam collapse. Uniform bubble size is assumed, and hence, interbubble gas diffusion arising out of variation in bubble sizes alone is not incorporated into the model. A high-stability aqueous foam formulation that remains stable in the presence of oil (hexane) at foam-oil contact was developed using surfactants, stabilizers, and viscosifiers. Emission of hexane vapor through the foam was measured. The model predicts that the initially taller foam columns collapse faster. Their mass-transfer resistance is higher before the onset of collapse but not very different from that of the shorter foam columns at long times. If the solubility and diffusivity of the hexane gas in the foam liquid are unaffected, the foams with higher viscosities persist longer and provide greater diffusive mass-transfer resistance. Foam bubble size does not significantly impact the mass-transfer resistance of the foam column before the onset of foam collapse. However, the foams with smaller bubbles collapse earlier, and their ability to act as a mass-transfer barrier to the diffusing hydrocarbon vapor diminishes rapidly. The experimental results compared reasonably with the model for varying initial foam heights and bubble sizes.     

Experimental Study on Stability and Improving Sweep Efficiency with Microfoam in Heterogeneous Porous Media

In this paper, we attempted to prepare microfoam by using a sandpack filled with glass beads with co-flowing gas and foaming solution, the microfoam stability and effectiveness in improving profile control capacity at micromodel and pore media were evaluated by micromodel tests and double-core experiments. The results of micromodel tests showed that microfoam stability was increased with increasing xanthan gum concentration due to a higher solution viscosity and viscoelasticity of liquid film. The xanthan gum-stabilized microfoam had a longer propagation distance through the low permeable region of heterogeneous micromodel at time of breakthrough than common microfoam, the optimum performance of microfoam for fluid diversion was multiple bubble trapping and mobilization rather than lamella division. According to the results of double-core experiments, the microfoam could plug the high permeability sandpack and improve the sweep efficiency in the low permeability sandpack, which could improve the water injection profile of porous media effectively. The increase in profile control effects had a good correspondence with the increase of xanthan gum concentration. The presented results were useful in understanding and designing microfoam injection in reservoirs for enhanced oil recovery.     

On the Origin of Foam Stability: Understanding from Viscoelasticity of Foaming Solutions and Liquid Films

The foam stability (drainage half-life) of α-olefin sulfonate (AOS) with partially hydrolyzed polyacrylamide (HPAM) or xanthan gum (XG) solution was evaluated by the Warring Blender method. With the increase of polymer (HPAM or XG) concentration, foam stability of the surfactant–polymer complexes increased, and the drainage half-life of AOS-XG foam was higher than that of AOS-HPAM foam at the same polymer and surfactant concentration. With the addition of polymer (HPAM or XG), the viscoelasticity of bulk solution and the liquid film were enhanced. The viscoelasticity of AOS-XG bulk solution and liquid film were both higher than that of AOS-HPAM counterparts.