Drop Profile Research Articles

Sandstone acidizing using a new retarded acid system based on gemini surfactants

Sandstone acidizing treatments are conducted to remove the damage in the near-wellbore area and restore the well productivity. Clays and feldspars are abundant in sandstone formations and they have very large surface area compared to quartz and this will deplete the injected HF acid and prevent its deep penetration to remove the damage. There are several environmental and formation damage concerns with the existing retarders such as aluminum chloride, boric acid, and phosphonic acids. In this study, a newly synthesized cationic gemini surfactant was investigated as a new retarder during sandstone acidizing using HF/HCl mud acid system. The new surfactant adsorbed on clays and feldspars surfaces and prevent their reaction with the HF/HCl mud acid. This will allow for more reaction with silicate and the acid can penetrate deeper and remove the damage. Coreflooding experiments were conducted using 12-inch long Scioto sandstone cores with very high clay contents. This work also included a numerical modeling study of the mud acid reactive transport in sandstone. The calibrated model was then implemented to predict the new surfactant impacts on the mud acid penetration and permeability enhancement at field-scale. Numerical simulation was done on the core and field scales. Coreflooding experiments showed that, flushing the rock sample with a 0.5 wt% solution of the new surfactant before the acid treatment minimized the interactions between both HCl and HF with clays and feldspars. This was confirmed by the pressure drop profile during the treatment, ICP cation analysis, and HF concentration collected from the coreflooding effluent. The numerical study showed that the new surfactant could reduce the minerals' surface area exposed to the mud acid by five times. The field-scale simulations showed that the new system would result in an important increase in the acid penetration length and permeability improvement.

Bond Number Revisited: Axisymmetric Macroscopic Pendant Drop.

The numbers Rbθ and Rbr introduced recently (Berim, G.O.; Ruckenstein, E. J. Phys. Chem. 2019, 123, 10294-10300) to characterize the cylindrical pendant drops hanging from the solid surface are modified for characterization of axisymmetric pendant drops which are more common in experiment. Similar to the case of cylindrical drops, Rbθ and Rbr are defined on the basis of rigorous solution of Young-Laplace equation for the drop profile. As a consequence, they contain only the input parameters of the drop-solid system such as the volume of the drop, gravitational acceleration, fluid densities, surface tension, and contact angle. This constitutes the main difference between Rb numbers and traditional Bond and Bond-like numbers which involve the dimensions of the drop unknown prior to the experiment (e.g., height of the drop or radius of curvature at the drop apex). It is shown, that the new numbers can be used, for example, for predicting the breakup conditions of the drop, determining the surface tension, and estimating the deviation of drop shape from the circular one. A good agreement between theoretical predictions and experimental results known from the literature was demonstrated.

A numerical study on two-phase core-annular flows of waxy crude oil/water in inclined pipes

In the present work, a 3D numerical study has been performed to investigate the core-annular flow of waxy crude oil/water in inclined pipes with a gradual expansion. Waxy crudes are highly viscous crude oils that exhibit non-Newtonian flow behavior, and their efficient transportation is still a technical challenge. In the current work, the use of the core-annular method for the transportation of waxy crudes, which are modeled as viscoplastic fluids, is examined comprehensively where the core oil flows in the laminar flow regime, and the water flow field is turbulent. The volume of fluid (VOF) multiphase flow model is used to capture the oil/water interface, and the SST k-ω turbulence model has been employed to predict the turbulent features of the water flow field. The governing equations are discretized and solved using the finite volume method on a structured numerical grid. The effects of several parameters, such as the wax content of the crude oil, inlet velocities, the expansion angle, and the inclination angle of the pipe have been investigated on the non-Newtonian core-annular flow comprehensively. The results revealed that as the wax content of the crude oil increased, the use of the core-annular flow became more economically lucrative for the transportation of waxy crude oils in comparison to the conventional single-phase oil transportation. Moreover, The simulation results indicated that increasing the expansion angle in the core-annular regime from 3.7° to 45° elevated the overall pressure drop more than fourfold. Finally, it is shown that for downward flows, by increasing the inclination angle, the overall pressure drop monotonically decreased. However, in upward flows, the overall pressure drop profile as a function of the inclination angle had a local maximum around 45°.

Partial oxidation of o-xylene to phthalic anhydride in a fixed bed reactor with axial thermowells

The present study analyses the thermowell system for monitoring temperatures in a fixed bed catalytic reactor for the highly exothermic partial oxidation of o-xylene to phthalic anhydride. Particle-resolved computational fluid dynamics (CFD) simulations are presented for the cases of randomly-packed spheres inside cylindrical tubes with tube-to-particle diameter ratios (N) of 3.96, 5.96 and 7.99. Results are obtained for each N value for cases with inner thermowell radius to outer tube radius ratios of 0.0 (no thermowell), 0.05, 0.1 and 0.2. Comparisons of radial void fraction and axial velocity profiles, axial pressure drop and axial temperature profiles under reaction conditions are presented. The presence of the thermowell did change the mass and heat transfer and reaction inside and around the particles, especially at the bed center. The configurations of catalyst particles were rearranged, leading to changes in voidage, flow and temperature profile. The axial temperature profiles from the thermowells differed from the profiles in the undisturbed beds.

Interfacial Properties of Tridecyl Dimethyl Phosphine Oxide Adsorbed at the Surface of a Solution Drop in Hexane Saturated Air

The surface tension of C13DMPO aqueous solution drops in hexane vapor is studied using the drop profile method. The hexane was injected into the measuring cell at three different conditions: before the formation of the solution drop, at a certain moment during the adsorption process, and after reaching the equilibrium of surfactant adsorption. The surface tension values for all experiments at the same concentration and different injection situations ultimately coincide with each other after attaining the final equilibration stage. The equilibrium surface tension isotherms of C13DMPO solutions, and the adsorption of both components—surfactant and hexane—were calculated. It was shown that the presence of surfactant leads to an increased hexane adsorption.

Gas/water foams stabilized with a newly developed anionic surfactant for gas mobility control applications

Carbon dioxide (CO2) flooding is one of the most globally used EOR processes to enhance oil recovery. However, the low gas viscosity and density result in gas channeling and gravity override which lead to poor sweep efficiency. Foam application for mobility control is a promising technology to increase the gas viscosity, lower the mobility and improve the sweep efficiency in the reservoir. Foam is generated in the reservoir by co-injection of surfactant solutions and gas. Although there are many surfactants that can be used for such purpose, their performance with supercritical CO2 (ScCO2) is weak causing poor or loss of mobility control. This experimental study evaluates a newly developed surfactant (CNF) that was introduced for ScCO2 mobility control in comparison with a common foaming agent, anionic alpha olefin sulfonate (AOS) surfactant. Experimental work was divided into three stages: foam static tests, interfacial tension measurements, and foam dynamic tests. Both surfactants were investigated at different conditions. In general, results show that both surfactants are good foaming agents to reduce the mobility of ScCO2 with better performance of CNF surfactant. Shaking tests in the presence of crude oil show that the foam life for CNF extends to more than 24 h but less than that for AOS. Moreover, CNF features lower critical micelle concentration (CMC), higher adsorption, and smaller area/molecule at the liquid–air interface. Furthermore, entering, spreading, and bridging coefficients indicate that CNF surfactant produces very stable foam with light crude oil in both deionized and saline water, whereas AOS was stable only in deionized water. At all conditions for mobility reduction evaluation, CNF exhibits stronger flow resistance, higher foam viscosity, and higher mobility reduction factor than that of AOS surfactant. In addition, CNF and ScCO2 simultaneous injection produced 8.83% higher oil recovery than that of the baseline experiment and 7.87% higher than that of AOS. Pressure drop profiles for foam flooding using CNF was slightly higher than that of AOS indicating that CNF is better in terms of foam–oil tolerance which resulted in higher oil recovery.

Adsorption process for phospholipids of different chain lengths at a fluorocarbon/water interface studied by Du No\xfcy ring and spinning drop

Fluorocarbons are novel systems in the fast-growing fields of diverse biomedical applications and fluorocarbon-water emulsions. However, characterization of these systems with modern measuring techniques such as drop profile analysis tensiometry is almost impossible because of practically identical refractive indexes and high-density differences. Due to the material properties of the fluorocarbon-water system, the invasive Du Noüy ring is the most appropriate method to measure interfacial tensions over long times. However, the influence of the ring on a fluorocarbon/water interface packed with phospholipids needs careful analysis. For the proof of methodology, the spinning drop tensiometry was used for comparison as a non-invasive technique to measure interfacial tension between water and perfluoroperhydrophenanthrene (PFPH) covered by 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) proving almost identical results. This demonstrates the validity of the invasive measurement technique for the studied system. The Du Noüy ring method was applied for further measurements of phospholipids with different chain lengths (1,2-dmyristoyl-sn-glycero-3-phostphatidylcholine, DMPC; 1,2-distearoyl-sn-glycero-3-phosphatidylcholine, DSPC) which revealed a difference in interfacial adsorption kinetics and equilibrium tensions. The Du Noüy ring tensiometry is appropriate to examine the slow adsorption kinetics of phospholipids emulsifying fluorocarbons. The results enable functional optimization of fluorocarbon emulsions regarding physical emulsification parameters and the selection of lipids.

Macroscale modelling of pressure drop for a moulded cylindrical filter within a vacuum pump to predict aerosol loading

AbstractComputational fluid dynamics is used as a tool to predict the oil aerosol loading on filters moulded through ARTm® and are used in an oil‐injected vacuum pump. These filters are essential for reducing exhaust emissions, which, when suspended can cause great harm to the environment, climate, equipment life, and public health. However, flow characteristics in a coalescing filter are quite complex to solve using limited computational power. Therefore, an economically viable model is developed in ANSYS FLUENT with a customised algorithm to determine pressure drop and loading profile across a filter. Oil droplets entering the filter are treated as Rosin–Rammler distribution and are solved through Euler–Lagrangian approach. The developed algorithm is capable of predicting pressure drop with a lower discrepancy of 15% when compared with experimental data for two different flow rates. This model is then used to understand effect of flow characteristics on aerosol loading with resulting velocity ratio of 0.2 that will lead to even aerosol loading on filter media. © 2020 Curtin University and John Wiley & Sons, Ltd.

Unified framework for mapping shape and stability of pendant drops including the effect of contact angle hysteresis

Solution of the Young-Laplace equation for fluid-fluid interface shapes is crucial in several applications related to colloids, capillarity, and surfaces. Despite significant progress in analysis and computation, the solution framework in literature is quite sparse with different norms for non-dimensionalisation and often limited to simplistic boundary conditions. These problems can be overcome and a unified solution framework can be developed if the relevant parameters are non-dimensionalised with respect to the capillary length, and collapsed onto a single graphical chart in the form of axes and contours. Here we use vector parameterized cubic splines to represent axisymmetric droplet profiles, which are then evolved quasi-statically to get to the equilibrium shapes using a novel thermodynamic free energy minimization-based algorithm. The generated dataset for a wide range of geometric and surface parameters is validated and then compiled in the form of a graphical chart. The chart traces the complete profile of axisymmetric pendant drops, predicts their evolution and stability on any surface, all without running any computer simulation. Most importantly, the contact angle contours on this chart offer the capability to incorporate the effect of contact angle hysteresis, a situation which is practically relevant, but has yet not been modelled.

Hydrodynamic Characterization of a Shallow Rectangular Spouted Bed Using Bed Pressure Signals and Image Processing Methods

To support the design of spouted bed reactors, experiments are performed in a rectangular spouted bed to measure the peak pressure drop (ΔPmax) and the internal and external spouting velocities (Uis and Ues). Four particle types spanning under Geldart D and B are used. Uis and Ues are measured from bed pressure drop and expansion ratio profiles, respectively, with the Ues/Uis ratio of each particle type obtained. Correlations predicting the ΔPmax of Geldart D and B particles are developed by reviewing published correlations and investigating the nozzle effect. Good prediction is achieved with a slope of 0.997 and an adjusted R2 of 0.998 in a 95% confidence interval. Ues is predicted through correlations developed by adding effects of dp/Di and H0 in the Mathur–Gishler equation. The calculated Ues agrees well with the experimental data, achieving a slope of 0.998 and an adjusted R2 of 0.998 in a 95% confidence interval.

Effect of particle shape on methanol partial oxidation in a fixed bed using CFD reactor modeling

AbstractParticle shape is one of the most important parameters in the design and optimization of fixed‐bed processes. To address the impact of particle shape on methanol partial oxidation to formaldehyde over molybdate catalyst, packings of spheres, cylinders, rings, and trilobes are numerically generated. The generated packings are used to carry out resolved particle Computational Fluid Dynamics (CFD) simulations under industrial conditions. Pressure drop, voidage and velocity profiles, radial heat transfer, and local and overall conversion and selectivity results are presented. Despite their lower particle surface area, lower particle effectiveness and more uneven flow distribution than trilobes, and lower overall heat transfer coefficient than cylinders, rings had the best conversion and selectivity due to their balance between the factors. Three longer tubes of rings, rings and cylinders, and rings and trilobes are simulated and show a small gain in selectivity for the rings and trilobes.

A laminar-jet-discharging method for measuring the interfacial tension of deformable surfaces

We propose a laminar-jet-discharging method to measure the interfacial tension of deformable surfaces such as soap bubbles. This method avoids the need to measure the small pressure difference inside and outside a soap bubble in a static state. By allowing the air in a soap bubble to discharge in a laminar flow state through a long tube, we show that the surface tension of the soap bubble is proportional to the rate of change of the fourth power of the bubble radius. Experimentally, we verify that this linear relationship is valid over a long period and thus can be measured with cameras at slow recording rates. Our method offers a straightforward and accurate way to measure the surface tension of soap bubbles using easy-to-obtain devices. In addition, we propose a new development of the pendant drop method based on the silhouette of the drop, which does not require any pressure transducer or computation of the second-order derivatives of the drop profile and hence is easier to implement and less sensitive to the accuracy of the drop profile determination. For pure liquids, results from the new pendant drop method compare well with standard values. This method is thus used to verify the laminar-jet-discharging measurements.

Experimental investigation on convective heat transfer of Shear-thinning fluids by elastic turbulence in a serpentine channel

Elastic turbulence has shown great potential to enhance heat transfer performance at the microscale. Most of the studies, however, have only considered global convective heat transfer performance along curvilinear channels, despite that the intensity of the chaotic flow varies along the streamline, leading to different local heat transfer characteristics. This work systematically investigated the local convective heat transfer performance by elastic turbulence of a shear-thinning fluid in a serpentine channel. The flow visualization along the serpentine channel was obtained and analyzed to show the existence of elastic instability and elastic turbulence. Significantenhancement of mixing was observed with the increase of polymer concentration and bulk flowrate. The variations of pressure drop, heat transfer coefficients and Nusselt numbers along the serpentine channel were analyzed to reveal local characteristics of elastic turbulence. A three-stage pressure drop profile was identified due to the variations of viscosity and elastic turbulence intensity at different flowrates and Reynolds numbers. A non-linear heat transfer performance, which increased with the increase of polymer concentrations, was observed. These are mainly attributed to the increasing intensity of elastic instability, resulting from the balance between normal stresses and streamline curvatures. A large increase of Nusselt number versus Weissenberg number was also revealed due to the coupling of shear-thinning behavior and elastic instability effects.

A study on the uniqueness of advancing contact angle for a sessile drop of surfactant solutions

Abstract This study investigated the uniqueness of advancing contact angle (CA) by examining the evaporation process of a sessile drop of surfactant solution [sodium dodecyl sulfate (SDS), hexaethylene glycol monododecyl ether (C12E6) and Triton X-100 (TX-100)] on parafilm. The sessile drop was formed from a pendant drop that had reached its equilibrium surface tension in an atmosphere with ∼100% humidity. The relaxation of the drop profile and wetting diameter were recorded from the moment the drop touched the parafilm, and the data were then analyzed to determine the advancing CA. The results showed that for SDS solution drops, only one advancing CA was observed at each SDS concentration. However, the experimental data of TX-100 and C12E6 solution drops indicated the presence of two distinct regions that showed a near-constant CA with a quasi-equilibrium advance of the triple line; hence matching the definition of an advancing CA. The possibility of the existence of two advancing CA was further explored and the presence of two advancing CA for the sessile drops of TX-100 and C12E6 solution was verified by closely examining the advance of the triple line.

Robust Contact Angle Determination for Needle-in-Drop Type Measurements.

One of the main approaches for contact angle determination using sessile drops with a missing apex (e.g., because of the presence of the needle tip) is the polynomial drop-profile fitting method. The major disadvantage of this fitting procedure is that the derived contact angle is highly sensitive to the polynomial order and the number of pixels involved in the actual fit. In the present work, an easily implementable method is introduced to effectively tackle these drawbacks. Instead of fitting the drop-profile itself, the polynomial fitting is applied to the difference between the drop profile and the circumcircle, independently for both sides of the drop. The derivative value of this difference at the contact point is used to correct the slope obtained analytically from the circumcircle. It is shown that this approach allows the robust determination of the contact angle with high (≤0.6°) accuracy in a straightforward manner, and the results are not affected by the actual contact angle, drop volume, or the resolution of the captured image. Validation of this new approach is also given in the contact angle range of 20°–150° by comparing the results to the values calculated by the Young–Laplace fit.

Modeling Steady-State Foam Flow: Hysteresis and Backward Front Movement

Foaming gaseous injectants is an attractive option because of the much lower gas mobility achieved in porous media. This paper reports an experimental and numerical investigation to improve our understanding of aqueous foam flow in heterogeneous sandstone. Our experimental program reveals two interesting behaviors: hysteresis in the steady-state pressure gradient and movement of a foam front opposite the direction of flow. Steady-state pressure gradient measurements across a sandstone core demonstrate the absence of a critical velocity requirement for foam generation, support the possibility of foam propagation away from the injection well, and exhibit hysteresis in the pressure gradient upon decreasing the injection gas velocity. Quasi-steady pressure drop profiles show that the pressure gradient increases against the direction of flow in what we coin the ”backward front movement”. This paper models experimental observations of steady-state pressure-drop hysteresis as well as quasi-steady backward front movement. Specifically, a steady-state population balance model that is based on pore-scale observations is developed. The model is verified against experimental data to confirm the steady-state predictions of the pressure, the flowing bubble density, and the flowing foam fraction (Tang and Kovscek, Transport in Porous Media 2006, 65, 287–307; Chen et al. SPE J. 2010, 15, 171–183). The model is then used to predict the experimental behavior. The flowing foam fraction (i.e., the fraction of the gas saturation that flows) is a key parameter in interpreting both hysteresis and backward propagation of the pressure gradient. Our findings highlight the importance of the flowing foam fraction to predicting various foam behavior.

Effect of interparticle force on gas dynamics in a bubbling gas–solid fluidized bed: A CFD-DEM study

The influence of cohesive interparticle force (IPF) on gas dynamics in a bubbling gas–solid fluidized bed was numerically investigated while the bed hydrodynamics was described with the help of computational fluid dynamics and discrete element method (CFD-DEM). The model was validated by experimental results in terms of total bed pressure drop profile, probability density distribution of instantaneous local bed voidage signals, and Eulerian solid velocity field. The results showed that the model can satisfactorily predict the hydrodynamics of a bubbling gas–solid fluidized bed that is impacted by the presence of cohesive IPF. The validated CFD-DEM model was adopted to delineate the effects of IPF on the distribution of fluidizing gas between the bubble and emulsion phases and bubble characteristics, such as bubble stability and rise path, which could hardly be explored experimentally. Simulation results revealed that the presence of IPF in the bubbling bed alters the distribution of the fluidizing gas between the bubble and emulsion phases in favor of an increase in the propensity of gas to pass through the bed in the emulsion phase. The results also indicated that the bubble stability increases and the straight rise path of bubbles changes to a tortuous path when enhancing IPF.

A novel energy-efficient kapok filter paper with high DHC for solid-oil mixed aerosol: Performance and loading behavior evolution mechanism

Although typical high efficiency filter media for gas turbine exhibit short lifespan under harsh conditions with excessive oily aerosol, rare literatures are available concerning fundamental reason or introducing filter media for addressing aforementioned conditions. Herein, we developed a novel kapok filter paper with high energy-efficiency and dust holding capacity (DHC) against solid-oil mixed aerosol. Loading behavior of filter media was characterized in terms of both macroscopic loading behavior (pressure drop and DHC evolution over oil content) and micro-scale particle deposition behavior. Owing to hollow lumen and waxy surface of kapok fiber, the novel filter paper was fluffy and oleophilic, which made it outperform typical commercial filter media (F01 and F02) in energy saving and DHC. Under harshest conditions where F01 and F02 manifested low DHC of 8.0 g/m2, 13.3 g/m2 and 29.1 g/m2, 34.7 g/m2 at the oil content of 50%, 75%, respectively, the kapok filter paper owned notably excellent DHC of 160.5 g/m2, 240.8 g/m2, respectively. Moreover, it was revealed that loading behavior evolution (resulted from the increase of oil content) was subject to deposition behavior. Once oil content was above 25%, pressure drop profiles transitioned from that of solid particles loading to that of liquid particles loading. Depositions structure varied from well-defined particles to particles-in-oil with films covered. Due to formation of a porous structure, a critical maximum DHC occurred for mixed aerosol with 25% oil content. Finally, a particle deposition mechanism was proposed, for the first time, to explain the loading behavior evolution over oil content.

Analytical approximation to the flow of a sPTT fluid through a planar hyperbolic contraction

The flow of a viscoelastic model fluid through a planar hyperbolic contraction is studied in the present work. Due to the non-constant flow area, pressure drop and velocity profiles for such a flow are obtained using the appropriate criteria based on the lubrication approximation theory. In this context, the non-Newtonian behavior is represented by the simplified Phan–Thien/Tanner model. As the main result from this work, a generalized solution for the flow field is determined, which is tested here for a hyperbolic contraction, but it can be applied for a variety of geometries by replacing the corresponding function giving the flow area. The resulting profiles are compared with a finite differences numerical scheme, showing a good agreement. In addition, the apparent extensional rate for a hyperbolic contraction device is also approximated by the solution presented here and, a generalization of the analytic solution in terms of Taylor series which allows representing non-linear versions of the Phan–Thien/Tanner model is included.

A study on the determination of the critical micelle concentration of surfactant solutions using contact angle data

The critical micelle concentration (cmc) is an important parameter in colloidal and surface chemistry and a wide range of techniques have been devised for cmc determination. In this study, the determination of the cmc of surfactant solutions from the unique advancing and receding contact angle (CA) data was investigated. The sessile drop was formed from a pendant drop which had reached its equilibrium surface tension (ST) in a saturated atmosphere (~100% humidity). The CA was determined from the best-fit between the edge locations of drop and the Young-Laplace theoretical profile. The advancing and receding CAs were determined from the CA relaxation profiles of the sessile drops. It was observed that the breakpoints of the advancing and receding CAs of SDS solution drop coincided with the cmc determined from the ST data. However, the comparatively slower adsorption and bulk diffusion rates of TX-100 and C12E6 made the CA breakpoints deviate from that of ST. Thus, it was concluded that the approach of using the unique CA data for the determination of cmc could be applied only to those surfactants with a relatively high mass transport rate, such as SDS.