Some salts have been proven to inhibit bubble coalescence above a certain concentration called the transition concentration. The transition concentration of salts has been investigated and determined ...by using different techniques. Different mechanisms have also been proposed to explain the stabilizing effect of salts on bubble coalescence. However, as yet there is no consensus on a mechanism which can explain the stabilizing effect of all inhibiting salts. This paper critically reviews the experimental techniques and mechanisms for the coalescence of bubbles in saline solutions. The transition concentrations of NaCl, as the most popularly used salt, determined by using different techniques such as bubble swarm, bubble pairs, and thin liquid film micro-interferometry were analyzed and compared. For a consistent comparison, the concept of TC95 was defined as a salt concentration at which the “percentage coalescence” of bubbles reduces by 95% relative to the highest (100% in pure water) and lowest (in high-salt concentration) levels. The results show a linear relationship between the TC95 of NaCl and the reciprocal of the square root of the bubble radius. This relationship holds despite different experimental techniques, salt purities and bubble approach speeds, and highlights the importance of the bubble size in bubble coalescence. The available theoretical models for inhibiting effect of salts have also been reviewed. The failure of these models in predicting the salt transition concentration commands further theoretical development for a better understanding of bubble coalescence in salt solutions.
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•Review of experimental techniques and results of bubble coalescence in salt solutions•“TC95” found consistent for NaCl transition concentrations by different techniques•Linear change of TC95 of NaCl vs. reciprocal of the square root of bubble size•Review of hypotheses for bubble coalescence inhibition in salt solutions•Theoretical models for transition salt concentrations were reviewed and scrutinized.
•Critical review and analysis of 3947 flow regime data points for vertical flows.•Assessment of the available models for prediction of upward flow regime transition.•Generation of a universal flow ...map for upward flows based on Reynolds numbers.
The accurate prediction of two-phase gas and liquid flow regimes is important in the proper design, operation and scale-up of pressure management and fluid handling systems in a wide range of industrial processes. This paper provides a comprehensive review of 3947 published experimental data points for gas-liquid flow maps in vertical pipes and annuli, including a critical analysis of state-of-the-art measurement techniques used to identify bubble, slug, churn and annular flow regimes. We examine the critical factors of pipe geometry (diameters, deviation from vertical), fluid properties and flow conditions that affect the transition from one flow regime to another. The review surveys the theoretical models available to predict flow regime transitions, and we validate the accuracy of these models using the published experimental data. The most reliable flow regime transition models for upward co-current flows are analytically shown to be: (i) Barnea 1987 for dispersed bubble to bubble flow, (ii) Taitel et al. 1980 for bubble to slug flow, (iii) Barnea 1987 for slug to churn flow, and (iv) Mishima and Ishii 1984 for churn to annular flow regime transition.
Moreover, based on the review we provide an outlook on the research needs and important developments in prediction of two-phase flow in vertical pipes including the use of computational fluid dynamics (CFD) techniques to simulate gas-liquid flows in vertical geometries.
This study presents the equilibrium surface tension (ST), critical micelle concentration (CMC) and the dilational viscoelasticity of sodium dodecylbenzene sulfonate (SDBS)-adsorbed layers in the ...presence of NaCl, KCl, LiCl, CaCl2 and MgCl2 at 0.001–0.1 M salt concentration. The ST and surface dilational viscoelasticity were determined using bubble-shape analysis technique. To capture the complete profile of dilational viscoelastic properties of SDBS-adsorbed layers, experiments were conducted within a wide range of SDBS concentrations at a fixed oscillating frequency of 0.01 Hz. Salts were found to lower the ST and induce micellar formation at all concentrations. However, the addition of salts increased dilational viscoelastic modulus only at a certain range of SDBS concentration (below 0.01–0.02 mM SDBS). Above this concentration range, salts decreased dilational viscoelasticity due to the domination of the induced molecular exchange dampening the ST gradient. The dilational viscoelasticity of the salts of interest were in the order CaCl2 > MgCl2 > KCl > NaCl > LiCl. The charge density of ions was found as the corresponding factor for the higher impact of divalent ions compared to monovalent ions, while the impact of monovalent ions was assigned to the degree of matching in water affinities, and thereby the tendency for ion-pairing between SDBS head groups and monovalent ions.
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•Provided a systematic study on dilational viscoelasticity of SDBS with NaCl.•Identified a non-monotonic change of viscoelastic of SDBS with NaCl concentration.•NaCl can increase or ...decrease surface rheology depending on the SDBS concentration.•Salts shift the surfactant transition concentration to smaller SDBS concentrations.•Frumkin model predicts well the dynamic adsorption of SDBS with and without salt.
This study investigates the adsorption mechanisms and the dilational surface rheology of the anionic surfactant sodium dodecylbenzene sulfonate (SDBS) at the air–liquid interface, in the presence and absence of NaCl over a wide range of SDBS concentrations. We also evaluate the Langmuir and Frumkin models in order to predict the dynamic adsorption of SDBS solutions. Our results reveal that the equilibrium surface tension of SDBS solutions is a monotonically decreasing function of NaCl concentration. However, the dilational viscoelastic properties of SDBS solutions are found to be a non-monotonic function of NaCl concentration. NaCl manifests opposing effects on the dilational viscoelastic moduli of the gas–liquid interface, depending on the frequency of surface oscillation and surfactant bulk concentration. Our measured dilational surface elasticity and viscosity data show a shift in the surfactant transition concentration, at which the viscoelastic moduli reach their maximum values, towards smaller surfactant bulk concentrations with increasing salt concentration. It is attributed to suppressing the electrostatic repulsion between the hydrophilic head groups of surfactant molecules in the presence of electrolytes. The maximum viscoelastic moduli at different NaCl concentrations is found to be the reflection of the relative impact of enhanced adsorption and increased diffusion exchange between bulk and interface.
On the stability of thin films of pure water Karakashev, Stoyan I.; Firouzi, Mahshid; Wang, Jianlong ...
Advances in colloid and interface science,
06/2019, Volume:
268
Journal Article
Peer reviewed
The stability of water films has been the focus of many researchers in the recent decades. Unfortunately, there is no consensus on the stability of these foam films or on the mechanisms responsible ...for stabilizing water films. This paper examines the reported results on this matter and scrutinizes them based on speciation analysis of the dissolved species and the recent achievements in the adsorption of inorganic ions on the air/water interface. Our results confirm the key role of surface contamination, interface approach velocity and evaporation in the drainage and lifetime of these water films. It confirms the stabilizing effect of contamination and the destabilizing effect of air-water interface approach velocity. Moreover, the negative sign of the surface/zeta potential of the air/water interface and its dependence on the pH value were explained.
Interferogram of foam film of distilled water. Display omitted
•Speciation analysis of fresh DI and distilled water, and degassed DI water•Experimental data on the negative electrical charge of air bubbles and thin foam films from DI or distilled water•Theoretical proof of the negative charge of the air bubbles and thin foam films•Controversial experimental data on the drainage and stability of foam films from DI and distilled water•Criterion for validity of the experimental data
•Investigated the effect of salt and particles on dynamic behaviour of foam flow.•Characterised regimes of three-phase foam flow using signal analysis of pressure data.•Demonstrated the effect of ...salt and particle on the frictional pressure of foam flow.
Foam flows containing particles are present in many applications including mining, wastewater treatment, environmental remediation of contaminants such as PFAS using foam fractionation, dewatering of gas wells and particle cleanout in pipelines. These applications usually involve dissolved salts and solid particulates, which may have a positive or adverse impact on the foam flow and its performance depending on the application, the system’s constituents (e.g., type and concentration of salt/particles) and the operating condition (e.g., gas and liquid flowrates). This work aims to investigate the effect of salts (primarily NaCl) up to 0.2 M salt and solid particulates (mainly clay) up to 25 g/L particles on the dynamic behaviour of 200 ppm sodium dodecylbenzene sulfonate (SDBS) foam flows, frictional and hydrostatic pressure gradient, foam holdup and flow regimes in a vertical column. Flow regimes are analysed through power spectral density (PSD) and the probability density function of differential pressure data. The results show that salt and particles affect the foaming performance of SDBS solutions, thus influencing the transition of flow regimes. Our static tests show a 1.2-to-2.2-fold increase in the effect of salts and particles on the foamability of the SDBS solutions, whereas the foam flow dynamic data show a strong dependence on the hydrodynamics of the system. For example, the pressure gradient of the foam flow experienced a 16% reduction with the addition of salt and particles at low gas superficial velocity (Vsg of 0.48–2.4 m/s and fixed Vsl of 0.02 m/s) due to the domination of gravitational dP/dz while it increased up to 22% at high Vsg of up to 11.2 m/s due to the domination of frictional forces. Our results demonstrate that the foam static properties such as foamability, foam stability and wetness are useful to understand the stabilising mechanisms of foams. However, they cannot represent and explain the foam behaviour in dynamic systems.
Microhydrodynamics retards the particle approach to the air bubble surface and significantly affects the bubble-particle collision interaction.
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► Micro hydrodynamics (MH) works at ...short inter-surface separation distance. ► MH influences bubble–particle collision interaction in flotation. ► MH decreases collision efficiency for both immobile and mobile bubble surfaces. ► Collision angle first decreases and then increases with increasing particle size and density.
Interactions between particles and bubbles are influenced by hydrodynamic forces of the aqueous medium in which the flotation process takes place. This paper investigates the effect of liquid hydrodynamic forces working at short inter-surface separation distance, referred to as microhydrodynamic forces, on the bubble–particle collision (encounter) interaction. The full equation of particle motion around an air bubble with either a mobile surface (e.g., the potential flow) or an immobile surface (e.g., the Stokes flow) has been solved and analyzed numerically. The effect of particle density, size and film thickness (i.e., inter-surface separation distance) on the bubble–particle collision angle and efficiency has been examined. The new results were compared against the results obtained under the condition that microhydrodynamic effect has been ignored (the conventional theory). The effect of microhydrodynamics on the collision angle and efficiency has been found significant. Generally, the microhydrodynamic effect decreases the collision efficiency due to retarding the particle approach to the rising bubble surface. There also exists a critical set of particle size and density, where the collision angle is minimal, for both the mobile and immobile bubble surfaces. Away from the critical particle size and density the collision angle increases to 90°.
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Understanding the interfacial properties of concentrated salt solutions is critical for various applications in physical, chemical and biological processes. This study aims to ...evaluate the interfacial properties of potassium chloride (KCl) solutions with concentrations ranging from 1 to 4M using the molecular dynamics simulation technique. We used two different water models, TIP4P/2005 and SPC/E to calculate the local density and angle distribution, viscosity, interfacial tension and surface potential of the salt solutions. The surface tension values predicted by the TIP4P/2005 model showed an incremental trend in agreement with experimental data. For viscosity, the predictions of TIP4P/2005 are close to the experimental data, while the predictions of SPC/E are in poor agreement with the measured viscosities. Our results show that the selection of water models significantly affects the structure properties of concentrated KCl solutions. Also, the TIP4P/2005 model compares very closely with the measured interfacial properties of salt solutions.
Pickering foams are available in many applications and have been continually gaining interest in the last two decades. Pickering foams are multifaceted, and their characteristics are highly dependent ...on many factors, such as particle size, charge, hydrophobicity and concentration as well as the charge and concentration of surfactants and salts available in the system. A literature review of these individual studies at first might seem confusing and somewhat contradictory, particularly in multi-component systems with particles and surfactants with different charges in the presence of salts. This paper provides a comprehensive overview of particle-stabilized foams, also known as Pickering foams and froths. Underlying mechanisms of foam stabilization by particles with different morphology, surface chemistry, size and type are reviewed and clarified. This paper also outlines the role of salts and different factors such as pH, temperature and gas type on Pickering foams.
Further, we highlight recent developments in Pickering foams in different applications such as food, mining, oil and gas, and wastewater treatment industries, where Pickering foams are abundant. We conclude this overview by presenting important research avenues based on the gaps identified here. The focus of this review is limited to Pickering foams of surfactants with added salts and does not include studies on polymers, proteins, or other macromolecules.
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•Reviews Pickering foams of surfactants and particles with different charges.•Elucidates underlying mechanisms for the effect of salts on Pickering foams.•Outlines the effect of temperature, pH and gas type on Pickering foams.•Highlights recent development in Pickering foams in different industries.
•A real-time predictive model was developed for prediction of FBHP.•First predictive model for prediction of flowing pressure in unconventional wells.•The model was successfully validated against a ...large volume of industry data.•The proposed model enables continuous accurate and uninterrupted estimation of FBHP.
Prediction of the flowing bottom hole pressure (FBHP) of gas–water two-phase flows is of great importance in optimising the production of gas and reducing down-time in unconventional gas wells. Unlike the case for conventional gas wells, prediction of FBHP for unconventional gas wells, particularly coal seam gas (CSG) wells, has not been studied.
Monitoring of FBHP typically is done using a downhole pressure sensor placed close to the bottom of the well. Replacing a failed pressure sensor or recalibration of a pressure gauge, which is required frequently throughout the life of a well for reliable measurement of FBHP, requires interruption of the gas production at a high cost. A low-cost and reliable model for continuous prediction of FBHP, would enable smooth operation of CSG wells in the event a pressure gauge fails, without interrupting the well production.
This work presents predictive models for real-time and reliable prediction of FBHP using surface and subsurface data, acquired from 91 CSG wells in Australia over 5–19 month production periods. Two sets of models are developed; one for specific wells using data from that individual well and another one for a group of wells. Three different modelling approaches, multiple linear regression, linear mixed-effects and gradient boosting regression tree (XGBoost) are implemented. The XGBoost modelling outcomes show promising results with the best mean absolute percentage error (MAPE) of 10% and 11.7% for specific well models and multiple well models, respectively.
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