•Effects of the dynamics contact angle (DCA) on the interfacial area in a packed column.•Effects of the initial wetting of sheets on the interfacial area of a packed column.•Initial wetting and DCA ...has marginal impact on the interfacial area for a highly viscous solvent.
Computational countercurrent flow investigation in the structured packed column is a multiscale problem. Multiphase flow studies using the volume of fluid (VOF) method in the representative elementary unit (REU) of the packed column can provide insight into the local hydrodynamics such as interfacial area, film thickness, etc. The interfacial area dictates the mass transfer in the absorption process and hence the overall efficiency of the column. The impacts of a solvent’s physical properties, liquid loads, and static contact angle (SCA) on the interfacial area have been examined previously. In the present study, the dynamic contact angle (DCA) was used to explore the impact of contact angle hysteresis on the interfacial area. The DCA has pronounced impact on the interfacial area (≈10% relative change) for the aqueous solvent of 0.10 M sodium hydroxide (NaOH). The interfacial area shows undulation and does not achieve the pseudo-steady state. In contrast, the interfacial area gets a net pseudo-steady value for aqueous solvent that contains 40% monoethanolamine (MEA) by weight. Wetting hysteresis was also explored via simulations conducted with initially dry and wetted sheets. For the 0.10 M NaOH aqueous solvent, the use of initially wetted sheets led to a slightly higher value of the interfacial area (≈10%) than the use of initially dry sheets at the same liquid load and DCA. As expected, wetting hysteresis reduces with increasing liquid loads, but wetting hysteresis is not significant for 40% MEA aqueous solvent, which might feature lower surface tension and higher viscosity. Overall, the effect of the DCA on interfacial area is not as pronounced as it is found on a flat surface.
Underground Hydrogen Storage (UHS) is an attractive technology for large-scale (TWh) renewable energy storage. To ensure the safety and efficiency of the UHS, it is crucial to quantify the H2 ...interactions with the reservoir fluids and rocks across scales, including the micro scale. This paper reports the experimental measurements of advancing and receding contact angles for different channel widths for a H2/water system at P = 10 bar and T = 20 °C using a microfluidic chip. To analyse the characteristics of the H2 flow in straight pore throats, the network is designed such that it holds several straight channels. More specifically, the width of the microchannels range between 50 μm and 130 μm. For the drainage experiments, H2 is injected into a fully water saturated system, while for the imbibition tests, water is injected into a fully H2-saturated system. For both scenarios, high-resolution images are captured starting the introduction of the new phase into the system, allowing for fully-dynamic transport analyses. For better insights, N2/water and CO2/water flows were also analysed and compared with H2/water. Results indicate strong water-wet conditions with H2/water advancing and receding contact angles of, respectively, 13°–39°, and 6°–23°. It was found that the contact angles decrease with increasing channel widths. The receding contact angle measured in the 50 μm channel agrees well with the results presented in the literature by conducting a core-flood test for a sandstone rock. Furthermore, the N2/water and CO2/water systems showed similar characteristics as the H2/water system. In addition to the important characterization of the dynamic wettability, the results are also crucially important for accurate construction of pore-scale simulators.
Display omitted
•Dynamic contact angles for H2/water/glass system were measured using a microchip.•H2 dynamic contact angles decreased with increasing channel width.•H2 advancing and receding contact angles were found, respectively, 13–39° and 6–23°.•Similar contact angles were found for H2, N2 and gaseous CO2.
Display omitted
•CFD simulation of droplet formation in a microfluidic T-junction.•Dynamic and constant contact angle models are quantitatively compared.•Using Kistler’s dynamic contact angle model ...significantly improves the prediction of droplet formation.•The value of the advancing contact angle significantly affects the droplet size.
Due to the dominance of interfacial forces, microreactors are commonly applied to multiphase processes where control over the dispersed phase volume is critical. For the design of such microfluidic devices, it is therefore important to accurately predict droplet breakup and the resulting two-phase flow pattern using computational tools. In this work, we show that integrating a dynamic contact angle model into a volume-of-fluid (VOF) solver significantly increases the prediction accuracy of droplet formation in a microfluidic T-junction compared to earlier studies with a constant contact angle model. Furthermore, it was found that the droplet formation is more sensitive to the chosen value of the advancing contact angle, while the receding contact angle showed only a minor influence. The present findings confirm that using a dynamic contact angle model with a VOF approach to simulate droplet formation in microchannels will provide more accurate predictions.
Display omitted
•Express suction head in Green-Ampt model with dynamic contact angle formulas.•Even the simplest linear formula notably improved the infiltration modeling.•Link similarity between ...dynamic capillary-saturation relationship and suction head.
The Green-Ampt model, which is a widely used infiltration model, assumes a constant effective suction head during infiltration; however, the capillary pressure is dynamic and related to the saturation rate. One factor affecting the dynamic suction head is the dynamic contact angle, which is parameterized using different formulas. Previous studies applied a power-law formula to parameterize the effective suction head, which substantially improved the ability to describe the velocity-dependent suction head. However, other dynamic contact angle formulas have not been tested. In this study, we performed a series of 1-D downward infiltration experiments with 60-cm sand columns and constructed modified Green-Ampt models (MGAMs) based on four formulas of dynamic contact angle (power-law, Jiang’s law, Hoffman’s law, and Cox-Voinov law) and a linear approximation. These modified Green-Ampt models were named MGAM-PW, MGAM-Jiang, MGAM-Hoff, MGAM-CV, and MGAM-LN. After parameter optimization, all modified Green-Ampt models resulted in similar root-mean-square errors, which were lower than those of the classical Green-Ampt model. The modified Green-Ampt models yielded similar values for the equilibrium suction head, which were larger than those of the classical Green-Ampt model. Among the modified Green-Ampt models, MGAM-CV has an intrinsic limitation in the range of parameter values. MGAM-Hoff typically requires more fitting parameters than do the other methods. MGAM-LN can be solved more efficiently than other modified Green-Ampt models because of its analytical solution and small number of fitting parameters. We demonstrated that the data length and slight time delay of the measurement affected optimization of the equilibrium suction head. Moreover, the relationship between the capillary pressure and saturation rate based on MGAM-PW was similar to the findings in the literature.
Display omitted
Wetting phenomena play a significant role in oil recovery from complex carbonate reservoirs under harsh conditions. The potential to being able to alter the rock wettability from ...oil-wet to water- or neutral-wet is often considered the pre-requisite to a successful Enhanced Oil Recovery (EOR) process. Hence, there arises the importance of understanding the (static) wetting and (dynamic) wettability alteration of the reservoir rock when the rock comes in contact with injected modified brines, oilfield chemicals, and/or nanofluids. In this study, we investigate the effect of three Carbon nanodots in high salinity brines with and without surfactant on static wetting and dynamic wettability alteration of carbonate reservoirs. Outcrop Indiana limestone and reservoir crude oil samples were used in these tests. The contact angle of the rock-oil-brine system is measured as a function of the nanodot concentration, saturating fluid in the rock matrix and aging, surfactant concentration, temperature, pressure, and brine salinity. The upper limits for the values for temperature, pressure, and salinity are set to be representative of the Saudi Arabian harsh reservoir conditions. The use of Carbon nanofluids demonstrated a clear shift in both static and dynamic measurements towards a more favorable water-wet condition for EOR. Statically, the contact angle of an oil-saturated carbonate rock exhibited a change from a strongly oil-wet condition to slightly water wet (with more than 50 % drop in the contact angle value) in 200 ppm (0.02 wt/v%) solution of carbon nanodot (CND) in seawater (SW) over 24 hours. Dynamically, a smaller but still remarkable change (a shift in the order of 20 %) in the contact angle is noted for a sister rock sample over the same period when a solution at the same concentration of CND in SW is introduced to replace the SW base fluid. Nanofluid spreading experiments on oil-coated glass slides supported our dynamic wettability studies. The spreading efficiency of the Carbon nanofluid was analyzed using optical and confocal microscopy with a clear and remarkable oil dislodging effect. Zeta potential measurements of the different systems were made to aid in the interpretations. The combined mechanistic actions of the various factors, including reservoir environment, disjoining pressure, interfacial tension, capillary pressure alterations and nanodots interactions with the oil/water interface, contributed to this change in wettability. Our study supports a strong and favorable EOR impact of CND as an effective and economically viable additive to waterflood operations in carbonate reservoirs.
Display omitted
Achieving rapid capillary wetting is highly desirable in nature and industries. Previous endeavors have primarily concentrated on passive wetting strategies through surface ...engineering. However, these approaches are inadequate for high-viscosity fluids due to the significant viscous resistance, especially for non-Newtonian fluids. In contrast, forced wetting emerges as a promising method to address the challenges associated with achieving rapid wetting of non-Newtonian fluids in capillaries.
To investigate the forced wetting behavior of viscoelastic fluids in capillaries, we employ Xanthan Gum (XG) aqueous solutions as target fluids with the storage modulus significantly exceeding the loss modulus. We utilize smooth glass capillaries connected to a syringe pump to achieve high moving speeds of up to 1 m/s.
Our experiments reveal a significant distinction in the power-law exponent that governs the scaling relationship between the dynamic contact angle and velocity for viscoelastic fluids compared to Newtonian fluids. This exponent is considerably smaller and varies based on the concentration of viscoelastic fluids and the diameter of the capillaries. We suggest that the viscosity dominates the wetting dynamics of viscoelastic fluids, manifested by the contact line morphology-dependent behavior. This insight has significant implications for microfluidics and drug injectability.
Water migration in the gel pore of the calcium silicate hydrate (C-S-H) influences the durability of cement-based material. The water transport in nanoscale gel pore is dramatically different from ...transport in capillary pore that is governed by the Lucas-Washburn (L-W) function. Coarse grained molecular dynamics (CGMD) is first utilized to model the capillary transport process of water in the 8 nm channel of C-S-H gel. A new capillary transport model is proposed by modifying the classic L-W function, taking into consideration the effects of dynamic contact angle and inertia force, slip length next to interior walls of gel pore and viscosity variation for liquid ultra-confined in nanopores. Theoretical modification reaches reasonable agreement with CGMD results. The effect of pore size on capillary transport is then simulated to confirm the model's transferability. The new model is helpful to understand the transport behavior of liquid in the gel pore of cement-based material.
•Impact dynamics of shear-thinning droplets on spherical particle surface is studied.•The droplet collision process can be divided into three phases.•The shear-thinning feature increases the energy ...dissipation during impact.•Evolutions of spread factor, film thickness and dynamic contact angle are revealed.•An empirical formula is proposed to predict maximum spread factor.
Non-Newtonian droplet impact is common in nature and industry. The viscosity of non-Newtonian liquids changes with shear stress, leading to different impact behaviors compared to Newtonian liquids. This study prepared shear-thinning solutions by adding HPMC polymer into deionized water and investigated its impact dynamics on hydrophobic spherical surface. The evolution patterns of droplet spreading factor, film thickness, and dynamic contact angle are investigated under different impact conditions. The results show that addition of polymers increases the energy dissipation during impact and suppresses droplet rebound from spherical surface compared to Newtonian droplet with similar viscosity. The droplet-impacting process is distinguished into three phases: (I) initial deformation, (II) inertia-dominated, and (III) viscosity-dominated phases. The temporal evolution of film thickness in Phases I and II is fitted by simple equations. In addition, an empirical formula that integrates Weber and Reynold numbers is proposed to predict the maximum spreading factor of HPMC droplets.
Display omitted
Droplet impact on a hydrophobic surface can be controlled by varying the wettability of the surface. In the present work, the wettability of the surface is varied by applying alternating current ...electrowetting on a dielectric (AC EWOD), and the electrowetting-integrated droplet impact characteristics are analyzed for different frequencies, waveforms of applied voltages, and different sizes of droplets. A numerical technique with a dynamic contact model is developed to track the movement of the three-phase contact line in the electrowetting-integrated droplet impact process. The maximum spreading diameter of the droplet increases, and the recoiling of the droplet decreases with the increase in applied frequency at the first oscillation cycle of the droplet. Droplet spreading is more for the sinusoidal waveform than the triangular waveform. The impact of voltage frequency on the droplet spreading is more significant than the voltage waveform. The effect of electrowetting on the droplet impact is less for small-size droplets than the larger droplets. The electrowetting effect increases the dynamic wetting characteristics of the surface, resulting in enhanced spreading and reduced recoiling of the impacting droplet.
Display omitted
Liquid water transport and removal is one of the critical issues in the proton exchange membrane fuel cell (PEMFC) for achieving good performance and durability. In this study, two novel channels ...with different blocks are designed to study their effects on water removal using the volume of fluid (VOF) model considering the dynamic contact angle effect. It is found that compared with the conventional straight channel, both the one-block and two-block channels can promote liquid water removal. The one-block channel leads to faster water movement and removal on the gas diffusion layer (GDL) surface, but results in a much higher pressure drop. The separated two-block channel directly drags water away from the GDL surface by the capillary wicking effect of the block surface, achieving both faster water removal and smaller pressure drop. Effects of the droplet size, air velocity and static contact angle of GDL surface on water removal are investigated comprehensively in both the novel channels, as well as the conventional straight channel, with particular attention on the variations of water removal time, water coverage ratio and pressure drop.
•Two novel fuel cell channels with baffle blocks are designed for fast water removal.•One-block channel promotes water transport and removal by the narrowing effect.•Two-block channel promotes water removal by direct block drag effect.•Two-block channel achieves both faster water removal and smaller pressure drop.•Two-block channel is effective to remove large droplet on more hydrophobic surface.
PDF
