With a sharp reduction in conventional oil and gas resources, tight oil and gas resources have attracted great interest in the petroleum industry. Relative permeability plays an important role in ...modeling fluid flow in tight reservoirs. Here, considering the nanoconfinement effects (abnormal viscosity effect (AVE) and slip effect) and dynamic contact angle (DCA) effect, a relative permeability model for tight reservoirs is proposed. The results show that the proposed model can accurately describe the relative permeability in tight reservoirs. As the AVE of water or oil increases, the relative permeability of water decreases, while the relative permeability of oil hardly changes for rocks with an average pore radius of 298 nm and decreases for the ones with an average pore radius of 49 nm. As the slip length of oil increases, the relative permeabilities of both water and oil decrease. As the DCA effect increases, the relative permeability of water increases, while the relative permeability of oil is unchanged. With a decrease in the pore size, the nanoconfinement effects on relative permeability become more notable, while the DCA effect on relative permeability becomes smaller. This work is of great significance to the development of tight reservoirs.
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•A relative permeability model for tight reservoirs is proposed.•The effects of slip and abnormal viscosity are considered.•The effect of dynamic contact angle on relative permeability is revealed.•The effect of capillary pressure on relative permeability is identified.
Benefiting from the cost-performance advantage, large-tow carbon fiber (LCF) is under the rapid development and shows great application potential in various products like wind turbine blade and ...hydrogen storage cylinder. However, the numerous and densely stacked monofilaments of LCF require further researches on wetting behavior, laying the foundation for improving the mechanical strength of composite. Here, the established strategy for optimizing the wettability of LCF at dual-scale reveals the microscopic wetting mechanism driven by surface energy and capillary wicking. Firstly, at microscale, the relationship between surface energy and dynamic wetting behavior of single fiber is accurately established by dynamic contact angle and molecular kinetic theory (MKT), and the positive correlation between wettability and interfacial strength is verified. At macroscale, the quantification of fiber bundle wettability is achieved by infiltration rate constant. Meanwhile, the overall wettability of fiber bundle is evaluated and improved through the capillary wicking theory and tension-driven optimization mechanism. Such mechanism is further validated by an increase in infiltration rate constant of 144.7% and composites tensile strength of 16.4%, demonstrating that tension-driven optimization mechanism opened viable opportunities and inspirations for the enhancement of mechanical properties in LCF reinforced polymers.
Dynamic contact angle (DCA) is of crucial importance in the numerical investigation of water management problems in proton exchange membrane fuel cells (PEMFCs). In order to well predict the ...gas-liquid two-phase flow in the complex flow field in PEMFCs, first, it is very critical to build a robust DCA model that is capable of simulating droplet behaviors on a single surface under various conditions. In our previous research work, an advancing-receding DCA (AR-DCA) model is developed and has been successfully validated against a series of experiments from the available literature for droplet impact on surfaces. In this study, the AR-DCA model is further applied to simulate droplet behaviors on inclined surfaces with different droplet impact velocities, impact angles and viscosities. It is found that the droplet spreading and deformation from the simulations have excellent agreement with those captured in the corresponding experiments. The results also indicate that higher impact velocity and impact angle can facilitate the spreading trend at the droplet trailing edge and have no notable effects on the leading edge. In addition, the increase of droplet viscosity leads to a transition from droplet deposition phenomenon to partial rebound on the surface.
•Droplet behaviors on inclined surfaces are simulated based on AR-DCA model.•Effects of impact velocity, impact angle and viscosity are investigated.•The numerical results have excellent agreement with the experiments.•AR-DCA model is capable of predicting droplet behaviors under various conditions.
•A new apparatus was designed to exam dynamic capillary pressure at different capillary numbers.•The second critical capillary number for chemical flooding is proposed and verified.•Sensitivity ...analysis by numerical production simulations on a real formation were carried out.•The dynamic interface properties were investigated to reveal the fluid transport behavior.
High capillary numbers are often adopted for chemical flooding in reservoirs to achieve the highest oil recovery. A high capillary number may be disadvantageous for high and medium permeability formations, while no experimental or field data are available for low permeability formations. In this work, through the use of a newly designed experimental apparatus for the measurement of the dynamic capillary pressure in low permeability formations, chemical flooding experiments on sandstone core samples (1–10 mD) were conducted to investigate the effects of high capillary numbers (0.001–2). In addition, these effects were examined through numerical production simulations on a real low permeability reservoir. The dynamic capillary pressure and relative permeability were measured to reveal the dynamic fluid flow characteristics. The dynamic contact angle was investigated to explore the dynamic interface properties. The results show that there is a second critical capillary number (higher than 0.02) that can be used to optimize the chemical flooding performance in low permeability reservoirs. Moreover, the oil relative permeability reaches its highest value at the second critical capillary number, while the water relative permeability always increases with the increase in the capillary number. The dynamic contact angle will reach approximately 180° at a high capillary number, causing an oil film to remain. An optimized capillary number range is proposed for chemical flooding in low permeability reservoirs.
•Comprehensive numerical method on supercooled droplet impingement pertinent to aircraft icing.•Time-dependent solidification proportion and final frozen shape of droplets.•Concept of activity ...duration to investigate the effect of LWC.•Logarithmic correlation for predicting transient heat transfer through the wall.
In-flight icing usually occurs when supercooled droplets impact on the cold surface of an aircraft, which should be concerned for its adverse effects on aerodynamic performance. To fundamentally elucidate the detailed mechanism of aircraft icing, a mathematical model on the impingement dynamics and solidification of a supercooled water droplet was developed and further validated with previous experimental results. Considering the effects of surface tension, wall adhesion and contact line dynamics, the coupled volume of fluid and level-set method was used to track the air–water interface, with the solidification issue solved by the enthalpy-porosity method. The temporal evolutions of the water phase, flow velocity, temperature and heat flux distributions were tracked and analyzed after the phase transition of supercooled water occurred. High impact velocities and millimeter-sized droplets were considered in this study to make the results more applicable to in-flight icing. As concluded, the spreading ratios of the droplets mainly distribute in the range of 0.8 ± 0.1 corresponding to LWC = 1.0 g/m3. Besides, the transient heat transfer between the solid surface and droplets could be fitted by a logarithmic function after appropriate dimensionless processing, which was proportional to the 1.5th power of the liquid fraction. Contributions of this work could be an effort to understand the microphysical phenomenon in the aerodynamic icing process.
•Parameters' effects on the accuracy of phase-field simulations are discussed for Liquid-Liquid microcapillary imbibition.•The impacts of contact angle and viscosity ratio on precursor film are ...discussed.•Viscosity ratios are considered in the Cox-Voinov model as the contact angle between 0o and 30o.•Precursor films cause the dynamic contact angle smaller than predictions of the Cox-Voinov model.•Precursor films reduce 10% to 20% of the theoretical total imbibition time.
Precursor film flow has been extensively studied on flat surfaces in Liquid-Gas systems. However, its effects in capillary imbibition processes, especially in Liquid-Liquid systems, are lack investigation. Using the phase-field method, this work simulates microcapillary imbibition processes in strong imbibition regimes with the viscosity ratio magnitude from 10−1 to 10. The numerical model is first tuned with a prescribed contact angle of 30o under which the precursor film is less likely occurs. The model validation results indicate that simulation accuracy of microcapillary imbibition is more sensitive to the Cn number and the model length than the mobility tuning parameter and viscosity ratio. After that, we discussed the effects of contact angle and viscosity ratio on imbibition processes considering precursor film. 25o is the critical contact angle for occurring the precursor film in the capillary filling. Compared with the contact angle, the effects of the viscosity ratio on film flow is limited. Though the viscosity ratio effects are considered in the Cox-Voinov model by solving the power-law approximations of the integrand, the simulated dynamic contact angle is still observed lower than the theoretical values because of the precursor film. Moreover, it also found that the simulated dynamic contact angle could reach a value lower than the static contact angle in tested unfavorable viscosity ratios. The significant effects of precursor film make the simulated total imbibition time roughly 10% to 20% less than the theoretical imbibition time without considering precursor film flow.
In surfactant solutions, the bulk hydrodynamic flow couples to extensional/compressional surface flows due to Marangoni stresses induced at the interface. With the increasing surfactant ...concentration, these Marangoni stresses can suppress the surface flows and lead to non-moving, retarded, surfaces. We review this phenomenon with special focus on the dynamic dewetting of a substrate pulled out of a pool of surfactant solution. In this case, the dewetting meniscus surface can be retarded (fully or partially) because of the appearance of surface tension gradients opposing the flow in the adjacent liquid. With an increasing flow velocity, the non-uniformity of the meniscus surface becomes stronger resulting in its separation on a mobile and an immobile part with a sharp transition between them. The presence of a non-uniform adsorption layer at the meniscus surface strongly complicates the dewetting dynamics which becomes dependent on the surfactant balance at the surface.
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We adopt a thermodynamically consistent multi-phase, multi-component phase-field model to investigate the morphological evolution of peritectic transition in carbon steel though 2-D ...and 3-D simulations. By using phase-field method, we rationalize the peritectic solidification in both 2-D and 3-D simulations under different liquid supersaturations as well as on the δ particle with distinct microstructures. Through the comparison between 2-D and 3-D simulation results, we clarify the reason for the different growth rate of γ phase in two and three dimensions. In 3-D simulation, we observe the unequal growth rate of γ phase in radial and axis directions. In addition, a novel measurement method is proposed to determine the dynamic contact angle. We anticipate that the simulation results can be applied to interpret the isothermal peritectic transition with a liquid supersaturation in alloys.
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•Systematic measurements of the apparent dynamic contact angle of dilute polymer solution drops are presented.•Polymer concentrations cover almost entirely the dilute regime.•Drop ...impacts onto commercial PTFE surfaces are investigated at different Weber numbers.
The dynamic contact angle of dilute polymer solution drops impacting on a hydrophobic PTFE surface is studied experimentally by high-speed imaging, for polymer concentrations ranging between 0ppm and 400ppm, and impact Weber numbers between 15 and 115. Images with spatial resolution of 16.4μm/pixel were captured at 8000fps to resolve the short time-scale dynamics. Results show that the receding contact angle of dilute polymer solution drops is significantly smaller than in case of drops of pure water, suggesting that the receding contact line encounter a higher resistance to its displacement. The minimum contact angle decreases with respect to both increasing polymer concentration and increasing Weber number. At lower Weber numbers, contact angle oscillations were observed, which can be related to the liquid flow to and from the rim during drop retraction.
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Wilhelmy plate method does not consider viscous force in the force balance equation to measure the dynamic contact angle and this results in a significant error in the measurement. ...Differences between the results obtained by optical method and Wilhelmy plate method indicate the importance of viscous force in the force balance equation. A theoretical viscous model is proposed, which must be considered in the force balance equation in Wilhelmy plate method to increase the accuracy of the dynamic contact angle measurement, especially for the case of highly viscous liquids and for experiments at large speeds of the plate, which can lead to large shear rate along the surface of the plate.
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