Dynamic generation of aqueous foams and fiber foams in a mixing tank

Mixing tanks are employed in paper and pulp industries to generate aqueous foams and fiber foams. The aim of the present study was to investigate the effect of impeller geometry on dynamic foam generation in a 60 L mixing tank. Three impeller geometries including two radial—Rushton turbine (RT), Bakker turbine (BT6), one axial high solidity pitched blade turbine (HSPBT), and four dual impeller combinations were investigated. Compressed air, water and sodium dodecyl sulphate were used as gas phase, liquid phase and surfactant, respectively, to generate aqueous foam. 1% mass consistency softwood fiber was used to generate fiber foam. The change in aqueous foam density for any given impeller was limited to ± 40 kg/m3 indicating foam density was dictated by impeller type rather than power input. Single impellers generated bubbly liquids whereas dual impellers generated low-density aqueous foams. Besides, stable foam was produced even at low power input compared to single impellers due to increase in impeller swept volume and blade contact area. Addition of fibers increased the foam density by ~ 100–150 kg/m3 and reduced the half-life time by almost threefold for all impellers due to lower air content and higher bubble size. Placement of high shear impeller (BT6) at bottom and down-pumping axial impeller (HSPBT) on top generated fine bubbles.

Modeling of weak shock waves propagation in aqueous foam layer

Dynamics of low-intensity air shock waves in the shock tube containing an aqueous foam layer is theoretically investigated. Modeling of studied process is carried out using two-phase model of aqueous foam developed by the authors in single-pressure, single-speed and two-temperature approximations. The model takes into account the Ranz-Marshall interphase contact heat transfer, effective Herschel-Bulkley viscosity, which describes foam behavior as a non-Newtonian fluid, and elastic properties of aqueous foam under a weak shock impaction without destruction of foam structure. Properties of air and water as the foam components are described by realistic equations of state. Computer implementation of the aqueous foam model is carried out in the solver, developed by the authors in OpenFOAM software. The influence of aqueous foam viscoelastic properties on the intensity and structure of a shock wave has been investigated. When analyzing the obtained solutions, reliability of the proposed model and method of numerical modeling is estimated by comparative analysis of the found solutions and literature experimental data.

Numerical Modeling of Combustion and Detonation in Aqueous Foams

Combustible aqueous foams and foamed emulsions represent prospective energy carriers. This paper is devoted to the overview of model assumptions required for numerical simulations of combustion and detonation processes in aqueous foams. The basic mathematical model is proposed and used for the analysis of the combustion development in the wet aqueous foam containing bubbles filled with reactive gas. The numerical results agree with the recent experimental data on combustion and detonation in aqueous foams containing premixed hydrogen–oxygen. The obtained results allowed for distinguishing the mechanisms of flame acceleration, transition to detonation, detonation propagation, and decay.

Low Adsorbing CO2 Soluble Surfactants for Commercially Viable Implementation of CO2 Foam EOR Technology

Several gas Enhanced Oil Recovery (EOR) pilots enhanced with aqueous-foam based conformance solutions have been implemented in the last 30 years. While these pilots were technically successful, there were economic challenges limiting their commercial viability. Many of these pilots were implemented with water-soluble foaming surfactants that can get adversely affected by near wellbore gas-water gravity segregation and adsorption loss up to 90% of the injected surfactant. Novel, gas-soluble surfactants can be injected with the gas phase where these surfactants are carried with the gas to thief zones faster and deeper with relatively lower adsorption to the rock surface. However, the conventional foam modeling approach relied only on the surfactant concentration in brine to determine foam strength, which adversely predicted the performance of gas soluble surfactants. With proven laboratory evaluations and multiple successful field implementations, the advantages of low adsorbing and gas soluble surfactants cannot be ignored. In this paper, the advantages of surfactant partitioning to the gas phase are confirmed by correcting the conventional foam modeling approach while simulating 1D transport of CO2-foam displacing brine in porous media. An empirical foam model was developed from the lab scale core flooding work of CO2foam transport through porous media using a novel gas-soluble foaming surfactant. While investigating the performance of gas soluble surfactants, global surfactant concentration was used to determine foam strength as the surfactant can transport to the gas-water interface from both the phases. Lab experiments and simulations with an improved foam modeling approach confirmed that a higher gas phase partitioning surfactant generated robust foam and deeper foam propagation while injecting surfactant with CO2in a water saturated core. In addition, comparing three partition coefficient scenarios around 1 on mass basis, the higher gas phase partitioning surfactant showed the larger delay in gas breakthrough. Overall, the simulation results with our better modeling approach do support the advantages of the higher gas phase surfactant partitioning in deeper foam transport and conformance enhancement for the gas-EOR technology.

Foaming and rheological properties of aqueous solutions: an interfacial study

Although aqueous foam is composed of simple fluids, air and water, it shows a complex rheological behavior. It exhibits solid-like behavior at low shear and fluid-like behavior at high shear rate. Therefore, understanding such behavior is important for many industrial applications in foods, pharmaceuticals, and cosmetics. Additionally, air–water interface of bubble surface plays an important role in the stabilizing mechanism of foams. Therefore, the rheological properties associated with the aqueous foam highly depend on its interfacial properties. In this review, a systematic study of aqueous foam are presented primarily from rheology point of view. Firstly, foaming agents, surfactants and particles are described; then foam structure was explained, followed by change in structure under applied shear. Finally, foam rheology was linked to interfacial rheology for the interface containing particles whose surface properties were altered by surfactants.

Linear, spatio-temporally resolved ultrasound measurement of the liquid fraction distribution in froth

Froth flotation is an important process for separating metal particles from gangue. A single flotation circuit for copper uses approx. 44 billion litres water a year. In situ process monitoring of the foam’s parameters and closed-loop control can reduce the resource use. However, no measurement technique is broadly employed that yields the liquid fraction distribution in the froth. Optical measurements are prevented by the bulk foam’s opacity. Though, ultrasound in the low frequency range is able to penetrate froth. In this paper we investigate the application of ultrasound to measure the local liquid content of aqueous foam in the axis of the ultrasound beam. Assuming a dependency of the backscattering coefficient b on the foam’s liquid fraction ϕ, we developed a model to calculate b from the echo signal. Local backscattering coefficients b n {b_{n}} can be determined for time gated windows and show a trend in the dependency on the foam’s liquid fraction ϕ (for ϕ < 0.8 \phi <0.8 %). The absolute uncertainty of the liquid fraction determined by means of an electrical reference measurement is σ ϕ = 0.079 {\sigma _{\phi }}=0.079 %. We demonstrated the capability of spatio-temporally resolved measurements with a frame rate of 0.33 Hz and an axial resolution of 7.9 mm in an experiment with a time-varying, inhomogeneous liquid fraction. This research work is contributing to a determination of in situ information of the foam’s parameter in a flotation process.