Large Viscosity Difference Research Articles

Application of biopolysaccharide green foam fluid to enhance CO2 sequestration in high-temperature and high-salinity saline aquifer

Saline aquifer, a geological body, is widely distributed in the world and has high CO2 sequestration potential. Due to the large differences in viscosity and density between the CO2 and brine and the micro-heterogeneity of the saline aquifer, CO2 override, and viscous fingering may occur in strata, resulting in low CO2 sequestration efficiency. Following the concept of green chemistry, this study formulated CO2 foam using biopolysaccharides and a green surfactant alkyl polyglycosides (APG), to enhance the CO2 sequestration efficiency in saline aquifers. The ability of three biopolysaccharides (diutan gum, welan gum and xanthan gum) to stabilize CO2 foam was explored. According to the foam drainage activation energy and the Ostwald ripening rate, the CO2 foam with diutan gum as the stabilizer and APG as the foaming agent exhibited the favorable performance. The mechanism of diutan gum stabilizing CO2 foam was analyzed through studies on intermolecular interactions, interfacial properties, rheology, and micromorphology studies. We then investigated the effects of foam quality and flow rate on the CO2 foam rheology in sandstone cores by analyzing the changes in CO2 saturation, the matching relationship between bubble diameters under different conditions and sandstone core pore size, and the variation in foam rheology was explained. Furthermore, the ability of CO2 foam to enhance CO2 sequestration was explored in saline aquifers using core-nuclear magnetic resonance techniques. CO2 foam largely reduces the water saturation of macropores and establishes high-seepage resistance to facilitate CO2 foam diversion to the meso- and micropores. This fully leverages the space in these pores to store CO2 and greatly improves CO2 sequestration in saline aquifers.

Microstructure effects on mechanical properties of network-forming polymer systems: An atomistic simulation study

The coupling mechanism of chain entanglement and crosslinking remains unelucidated at the atomic scale. The network-forming dynamics and mechanical properties of pure-entangled matrix (PEM) and crosslinked & entangled matrix (CEM) were explored using all-atomic molecular dynamics simulations. The generation of side chains and local networks significantly affects the mechanical properties. For the PEM, as the reaction degree (r) increased, the dominant factor affecting the mechanical properties of materials changed from the movement of the main chain to entanglement. For the CEM, as r increased, the system first produced a local cross-linked structure and then formed a complete matrix. At extremely large strain, the CEM directly ruptured; the PEM showed a strain-hardening behavior before the final rupture because of the re-distribution of chain entanglements. The PEM and CEM exhibited almost the same elasticity but demonstrated a large difference in viscosity owing to the presence of long side chains in the CEM.

Narrow, Fast, and “Cool” Mantle Plumes Caused by Strain‐Weakening Rheology in Earth's Lower Mantle

AbstractThe rheological properties of Earth's lower mantle are key for mantle dynamics and planetary evolution. The main rock‐forming minerals in the lower mantle are bridgmanite (Br) and smaller amounts of ferropericlase (Fp). Previous work has suggested that the large differences in viscosity between these minerals greatly affect the bulk rock rheology. The resulting effective rheology becomes highly strain‐dependent as weaker Fp minerals become elongated and eventually interconnected. This implies that strain localization may occur in Earth's lower mantle. So far, there have been no studies on global‐scale mantle convection in the presence of such strain‐weakening (SW) rheology. Here, we present 2D numerical models of thermo‐chemical convection in spherical annulus geometry including a new strain‐dependent rheology formulation for lower mantle materials, combining rheological weakening and healing terms. We find that SW rheology has several direct and indirect effects on mantle convection. The most notable direct effect is the changing dynamics of weakened plume channels as well as the formation of larger thermochemical piles at the base of the mantle. The weakened plume conduits act as lubrication channels in the mantle and exhibit a lower thermal anomaly. SW rheology also reduces the overall viscosity, notable in terms of increasing convective vigor and core‐mantle boundary heat flux. Finally, we put our results into context with existing hypotheses on the style of mantle convection and mixing. Most importantly, we suggest that the new kind of plume dynamics may explain the discrepancy between expected and observed thermal anomalies of deep‐seated mantle plumes on Earth.

Improved well-balanced free-energy lattice Boltzmann model for two-phase flow with high Reynolds number and large viscosity ratio

Spurious velocities and inaccurate density properties arising from the imbalance of discretized forces at discrete level are frequently observed in numerical simulation of multiphase flows based on lattice Boltzmann equation (LBE) models. In this paper, an improved well-balanced free-energy LBE model is proposed for two phase flows with high Reynolds numbers and large viscosity differences based on the well-balanced LBE [Guo et al., Phys. Fluids 33, 031709 (2021)]. To this end, a free parameter associated with the shear rate is introduced into the equilibrium distribution function. This results in a fluid viscosity that is dependent not only on the relaxation time but also on the introduced parameter. The relaxation time can be chosen to improve the numerical stability and accuracy, while the viscosity is mainly determined by the new parameter. To test the capability of the present model in capturing discrete equilibrium states, both one-dimensional flat interface and two-dimensional stationary droplet are simulated. Numerical results show that the present model is capable of eliminating spurious velocities and maintaining a constant chemical potential when the system reaches an equilibrium state. To further validate the performance of the present LBE for dynamic problems, both binary droplet collision and single bubble rising are performed, which demonstrates that the present model has the capability to deal with two phase flows with high Reynolds number and large viscosity ratio.

Oscillatory dynamics of two liquids interface in straight narrow gap

Oscillatory dynamics of the liquid-liquid interface in a straight slot channel is studied experimentally. We use fluids with a large difference in viscosity and similar densities. The experimental conditions are chosen in such a way that the oscillating motion of a low-viscosity liquid is inviscid, and the oscillating motion of viscous liquid obeys Darcy’s law. At the beginning of the experiment, the interface is oriented perpendicular to the channel axis. It is found that the interface takes a shape of a symmetric hill curved towards a viscous liquid under liquid oscillations. The equilibrium interface shape (the hill height) is determined by the amplitude of the interface oscillations.

From droplets to waves: periodic instability patterns in highly viscous microfluidic flows

We experimentally study the transition from droplet to wave regimes in microfluidic liquid–liquid multiphase flows having large differences in viscosity. A unified approach based on periodic pattern analysis is employed to study relationships between dispersed and separated flow regimes, including dripping, jetting, capillary waves, inertial waves and core–annular flows over a wide range of flow rates and viscosity contrasts. We examine the morphology and dynamics of each flow regime based on wavelength, frequency and velocity of repeating unit cells to elucidate their connections and to develop predictive capabilities based on dimensionless control parameters. We demonstrate in particular that pattern selection is contingent upon the propagation velocity of droplets and waves at the transition. We also investigate microfluidic wave breaking phenomena with the formation of ligaments and droplets from wave crests in both capillary and inertial wave regimes. This work expands conventional multiphase flow regimes observed in microchannels and shows new routes to disperse highly viscous materials using interfacial waves dynamics in confined microsystems.

Short‐time fabrication of well‐mixed high‐density polyethylene/ultrahigh‐molecular‐weight polyethylene blends under elongational flow: morphology, mechanical properties and mechanism

AbstractAs linear polyethylenes, ultrahigh‐molecular‐weight polyethylene (UHMWPE) and high‐density polyethylene (HDPE) have the same molecular structure, but the large difference in viscosity between them makes it difficult to obtain well‐mixed blends. An innovative eccentric rotor extruder (ERE) generating an elongational flow was used to prepare HDPE/UHMWPE blends within short processing times. Compared with the obvious two‐phase morphology of a sample from a twin‐screw extruder observed with a scanning electron microscope, few small UHMWPE particles were observed in the HDPE matrix for a sample from the ERE, indicating the good mixing on a molecular level of HDPE/UHMWPE blends achieved by the ERE during short processing times. The morphological changes of blends prepared using the ERE evidenced the good integration of HDPE and UHMWPE even though the UHMWPE content is up to 50 wt% in the blends. Moreover, all blends retained most of the intrinsic molecular weight. The good mixing was further confirmed from the thermal, crystallization and rheological behaviors determined using differential scanning calorimetry and dynamic rheological measurements. Importantly, the 50/50 blend presented improved mechanical properties, especially super‐impact strength of 151.9 kJ m−2 with incomplete‐break fracture state. The strengthening and great toughening effects of UHMWPE on the blends were attributed to the addition of unwrapped UHMWPE long molecular chains. The effective disentanglement mechanism of UHMWPE chains under elongational flow was explained schematically by a non‐parallel three‐plate model. © 2019 Society of Chemical Industry

A Level Set method for capturing interface deformation in immiscible stratified fluids

The interface behavior between two stratified fluids showing a large difference in viscosity was investigated numerically. A three-dimensional numerical method for the simulation of the deformation of the interface in a stirred vessel is presented. In such a systems, the interface is distorted by hydrodynamic stresses and pressure changes. Different regimens of agitation were employed to explore the response of the interface, where the boundary between them is preserved and break up is avoided. The numerical scheme presented explicitly solves the Navier–Stokes equations for an incompressible fluid whilst the convection-diffusion part is treated through a Level-Set method along a moving and deforming interface. The spatial discretization was carried out by implementing a Runge–Kutta method in a second order scheme, along as a Weighted Essentially Non-Oscillatory approach. In addition, surface tension effects were included to observe its influence on the interface response. It was found that due the effect of inertia the interface is reshaped towards the vertical direction, in this process the interface experiences high-pressure gradients, which drag the interface in the upward direction. The numerical methodology was validated by comparison of simulations and experimental measurements of an interface deforming at two low Reynolds number. The results shown that the algorithm is able to resolve accurately the detailed features of the distorted fluid interfaces.

Viscous Wave Breaking and Ligament Formation in Microfluidic Systems.

Rapid layering of viscous materials in microsystems encompasses a range of hydrodynamic instabilities that facilitate mixing and emulsification processes of fluids having large differences in viscosity. We experimentally study the stability of high-viscosity stratifications made of miscible and immiscible fluid pairs in square microchannels and characterize the propagation dynamics of interfacial waves, including breaking and viscous ligament entrainment from wave crests at moderate Reynolds numbers. For large viscosity contrasts, parallel fluid streams adopt widely different velocities and provide a simple model system to probe the role of inflectional instabilities of stratified microflows in relation with classic inviscid-stability theory. We reveal novel viscous wave regimes and unravel dispersion relationships in the presence and absence of interfacial tension. Detailed examination of wave celerity shows the existence of optimal operation conditions for passively disturbing miscible fluid flows and continuously dispersing low-and high-viscosity fluids at the small scale.

Investigations of mechanical, thermal and morphological properties of FDM fabricated parts for friction welding applications

Friction welding is one of the solid state welding techniques, for which the two pieces of thermoplastic materials must be compatible to each other. Friction welding of the two similar thermoplastic is an easy exercise but joining two dissimilar thermoplastic is difficult because of large differences in viscosity, specific density, molecular weight, melting point, crystalline vs. amorphous nature, surface behavior and dynamic-mechanical properties. In last three decades, studies have been reported to perform the friction and friction stir welding of thermoplastics but still the reason for compatibility of thermoplastic is not understood properly. In the present study attempts have been made to perform the compatibility analysis of two dissimilar polymers namely; acrylonitrile butadiene styrene (ABS) and polyamide 6 (PA6) by establishing their melt flow properties after Aluminum (Al) metal powder reinforcement. Twin screw extrusion (TSE) and fused deposition modeling (FDM) technologies were used to fabricate the welding specimen for potential application in maintenance engineering.

Glycerol Hydrogen-Bonding Network Dominates Structure and Collective Dynamics in a Deep Eutectic Solvent.

The deep eutectic solvent glyceline formed by choline chloride and glycerol in 1:2 molar ratio is much less viscous compared to glycerol, which facilitates its use in many applications where high viscosity is undesirable. Despite the large difference in viscosity, we have found that the structural network of glyceline is completely defined by its glycerol constituent, which exhibits complex microscopic dynamic behavior, as expected from a highly correlated hydrogen-bonding network. Choline ions occupy interstitial voids in the glycerol network and show little structural or dynamic correlations with glycerol molecules. Despite the known higher long-range diffusivity of the smaller glycerol species in glyceline, in applications where localized dynamics is essential (e.g., in microporous media), the local transport and dynamic properties must be dominated by the relatively loosely bound choline ions.

Thermal Convection in Binary Mixture with Large Viscosity Difference

Thermal Convection in Binary Mixture with Large Viscosity Difference

Study of the Growth Rate of Polystyrene Nanotube Prepared by Melt Wetting an Anodic Aluminum Oxide Template

Polystyrene nanotubes have been successfully prepared by melt wetting an anodic aluminum oxide (AAO) template at 190, 210, 230 °C. A rapid freezing method with ice was used to control the growth process, and the different heights of the polymer nanotubes for different growth times were investigated by SEM. The average growth rate was calculated to be in the range of 10–7–10–6 m/s, which is about 5–6 orders of magnitude lower than the macroscopic capillary flow rate of water infiltrating a glass tube. This indicates that the size advantage of a nanoscale pore is offset by the very large viscosity difference between the polymer melt and the small molecules. For a specified template, and specified polymer, the main factor influencing the growth rate of polymer nanotubes prepared by melt wetting an AAO template is the viscosity of the polymer melt.

Ubiquitous transient stagnant domain formation during thermal convection in a well-mixed two component fluid with large viscosity difference

The formation of a transient stagnant domain in the presence of thermal convection was previously reported near the sol-gel transition temperature of a gelatin solution. The transient stagnant domain is observed near a critical Rayleigh number where a "roll" pattern is usually stable. It is important to understand the origin of the transient stagnant domain formation since it induces a large deformation of convection patterns; the nature of the formation of the transient stagnant domain remains unclear. Here, we observe thermal convection using several different fluids and find that stagnant domain formation is ubiquitous in two component mixtures. In addition, we find that difference in viscosity between the two components is crucial for transient stagnant domain formation, more so than the concentration gradient induced by the temperature gradient.

Application of the lattice Boltzmann method for simulation of the mold filling process in the casting industry

The aim of this work is the development of the lattice Boltzmann model for simulation of the mold filling process. The authors present a simplified approach to the modeling of liquid metal-gas flows with particular emphasis on the interactions between these phases. The boundary condition for momentum transfer of the moving free surface to the gaseous phase is shown. Simultaneously, the method for modeling influence of gas back pressure on a position and shape of the interfacial boundary is explained in details. The problem of the lattice Boltzmann method (LBM) stability is also analyzed. Since large differences in viscosity of both fluids are a source of the model instability, the so-called fractional step (FS) method allowing to improve the computation stability is applied. The presented solution is verified on the bases of the available reference data and the results of experiments. It is shown that the model describes properly such effects as: gas bubbles formation and air back pressure, accompanying liquid-gas flows in the casting mold. At the same time the proposed approach is easy to be implemented and characterized by a lower demand of operating memory as compared to typical LBM models of two-phase flows.

Instability of the interface in two-layer flows with large viscosity contrast at small Reynolds numbers

The Kelvin–Helmholtz instability is believed to be the dominant instability mechanism for free shear flows at large Reynolds numbers. At small Reynolds numbers, a new instability mode is identified when the temporal instability of parallel viscous two fluid mixing layers is extended to current-fluid mud systems by considering a composite error function velocity profile. The new mode is caused by the large viscosity difference between the two fluids. This interfacial mode exists when the fluid mud boundary layer is sufficiently thin. Its performance is different from that of the Kelvin–Helmholtz mode. This mode has not yet been reported for interface instability problems with large viscosity contrasts. These results are essential for further stability analysis of flows relevant to the breaking up of this type of interface.

Visualization Study on Plugging Characteristics of Temperature-Resistant Gel during Steam Flooding

Steam channeling is a serious problem during steam flooding in heavy oil reservoir. In this paper, an improvement measure was introduced to enhance oil recovery by injecting temperature-resistant gel during steam flooding in heavy oil reservoirs. A two-dimensional (2D) visualization physical model was designed to study the characteristics of viscous fingering and steam channeling during steam flooding. After steam channeling, temperature-resistant gel was injected into the 2D model. Then, the macro- and microscopic mechanisms of improving the development effect were analyzed after gel injection during steam flooding. The experimental results showed that steam channeling was easily formed between the injection well and the production well, resulting from a large viscosity difference of oil–steam or serious heterogeneity of formation, which led to a lower sweep efficiency. Gel first flowed into channeling paths and occupied large pores between the particles to make injected steam bypass mainstream channels ...

Modeling Oilfield Emulsions: Comparison of Cyclopentane Hydrate and Ice

A comparison of cyclopentane hydrate- and ice-forming emulsions is reported. Density-matched 40% (v/v) water emulsions are studied at various salt concentrations, using experimental tools of rheometry and direct visualization of the morphology under formation of hydrate or ice from the liquid water. Viscosity and yield stress were measured at similar subcoolings (temperature differential between dissociation or melting temperature and the system temperature, with the latter lower) and water conversions, which was controlled by the initial salt concentration in the aqueous phase of the emulsions at a fixed temperature. Large differences in viscosity and yield stress of the final structure were observed between the hydrate- and ice-forming emulsions. At water conversions of Xw = 58%–81%, the ratio of final relative viscosity (final slurry viscosity, relative to the continuous phase viscosity) of hydrate- to ice-forming emulsions is given as ηrel-hyd/ηrel-ice = O(102); at complete water conversion (Xw = 100%...

Lattice Boltzmann modeling of contact angle and its hysteresis in two-phase flow with large viscosity difference.

Contact angle hysteresis is an important physical phenomenon omnipresent in nature and various industrial processes, but its effects are not considered in many existing multiphase flow simulations due to modeling complexity. In this work, a multiphase lattice Boltzmann method (LBM) is developed to simulate the contact-line dynamics with consideration of the contact angle hysteresis for a broad range of kinematic viscosity ratios. In this method, the immiscible two-phase flow is described by a color-fluid model, in which the multiple-relaxation-time collision operator is adopted to increase numerical stability and suppress unphysical spurious currents at the contact line. The contact angle hysteresis is introduced using the strategy proposed by Ding and Spelt [Ding and Spelt, J. Fluid Mech. 599, 341 (2008)JFLSA70022-112010.1017/S0022112008000190], and the geometrical wetting boundary condition is enforced to obtain the desired contact angle. This method is first validated by simulations of static contact angle and dynamic capillary intrusion process on ideal (smooth) surfaces. It is then used to simulate the dynamic behavior of a droplet on a nonideal (inhomogeneous) surface subject to a simple shear flow. When the droplet remains pinned on the surface due to hysteresis, the steady interface shapes of the droplet quantitatively agree well with the previous numerical results. Four typical motion modes of contact points, as observed in a recent study, are qualitatively reproduced with varying advancing and receding contact angles. The viscosity ratio is found to have a notable impact on the droplet deformation, breakup, and hysteresis behavior. Finally, this method is extended to simulate the droplet breakup in a microfluidic T junction, with one half of the wall surface ideal and the other half nonideal. Due to the contact angle hysteresis, the droplet asymmetrically breaks up into two daughter droplets with the smaller one in the nonideal branch channel, and the behavior of daughter droplets is significantly different in both branch channels. Also, it is found that the contact angle hysteresis is strengthened with decreasing the viscosity ratio, leading to an earlier droplet breakup and a decrease in the maximum length that the droplet can reach before the breakup. These simulation results manifest that the present multiphase LBM can be a useful substitute to Ba etal. [Phys. Rev. E 88, 043306 (2013)PLEEE81539-375510.1103/PhysRevE.88.043306] for modeling the contact angle hysteresis, and it can be easily implemented with higher computational efficiency.

Numerical Investigation of the Free‐Surface Flow within an Annulus

AbstractThis study describes the free‐surface flow of a highly viscous liquid between two concentric cylinders. In the process the morphology of the phase boundary is determined using a straight volume of fluid approach. Due to large differences in viscosity the gaseous phase is considered as vacuum. The numerical results of free‐surface flow measures are compared to previous calculations and experimental values. The investigation shows that the used two‐phase method is well‐suited to predict the location and shape of the interface. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)