Increase In Effective Viscosity Research Articles

Adsorption Characteristics and Mechanical Responses of Lubricants Containing Polymer Additives under Fluid Lubrication with a Narrow Gap.

The adsorption behavior of poly(methyl acrylate) (PMA)-based polymer additives and their mechanical response under fluid lubrication in narrow gaps were investigated by using neutron reflectometry, microchannel devices, and the narrow gap viscometer. The surface adsorption layer formed by the polymer additive in a stationary field that was investigated by neutron reflectometry was only about 3 nm thick. On the other hand, when the sample oil containing the polymer additive was flowed into the microchannel device with channels about 500 nm deep, the adsorption layer grew over a long period of time and eventually formed a layer that appeared to be more than 100 nm thick. The mechanical response was measured during one-directional rotation with a constant gap length by using the narrow gap viscometer. The results showed that the effective viscosity increased in the low shear rate range. The same behavior was also observed in the reciprocating rotational tests, where the mechanical response showed a distinctive distortion only when the shear rate was low near 0 rpm. The results of the neutron reflectometer, incorporating the narrow gap viscometer, showed no effect of the rotational speed with regard to the structure of the homogeneous layer over a large area. However, the discrepancy between the reflectivity profile and the fitting curve became progressively more pronounced with time, confirming the formation of inhomogeneous structures with time. It is finally suggested that the inhomogeneous structure is due to the formation of local aggregates by PMA molecules, and it acts as flow resistance only in the low shear rate, resulting in an increase in effective viscosity.

Analysing the Influence of Fibers on Fresh Concrete Rheometry by the Use of Numerical Simulation

Measuring the flow properties of fiber-laden fresh concrete poses a substantial challenge because not only the fraction of fibers but also their orientation process during the measurement influence the measured quantities. Numerical simulations of the flow in a ball probe rheometer are used to determine the fiber orientation process during the measurement of the flow properties and its influence on the measured variables. Through analytical considerations and comparison with measurement results, it can be shown that the constitutive law applied can reproduce the real flow behavior very well, taking the fiber orientation into account. At the same time, it is investigated why no orientation influence on the torque is recognizable in the experimental measurement curves, although the orientation process demonstrably exceeds the duration of the measurement process. The results show that fluid inertia is overcome before the recognizable onset of fiber orientation, and the spatially inhomogeneous flow minimises the impact of the orientation process on torque. The simulation model aligns well with experimental outcomes, indicating a linear increase in effective viscosity with increasing fiber volume fraction. The findings can be used to accurately measure the objective material parameters of the orientation-considering constitutive law using ball probe rheometers, so that an accurate prediction of the flow process of fresh concrete with fibers is made possible, for example for the simulation of formwork fillings.

Investigation on gas/water two-phase flow in quartz nanopores from molecular perspectives

Understanding the gas/water two-phase occurrence, flow patterns, and underlying mechanisms in quartz nanopores is crucial for gas transport and production in shale reservoirs. In this study, we investigated the flow characteristics of methane and water in hydroxylated quartz nanopores employing the grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations and focused on elucidating the effects of water saturation, pressure gradient and ion concentration in various aperture nanopores. Results show that water molecules preferentially adsorb on the hydrophilic quartz surface to form water film, increasing methane flow friction and reducing its slippage velocity significantly. Water bridges are formed to wrap gas bubbles and hinder the gas flow with increased water saturation. The water phase occupies a larger pore space with increasing water saturation resulting in an increase in methane effective viscosity and a decrease in apparent permeability. The water bridge is broken under the joint action of external force and gas driving when the pressure gradient is much larger, leading to a dramatic growth of gas flow, and the high-speed gas will produce a shear driving effect on the thick water layers. Ions will weaken the formation of hydrogen bonds between water molecules, but the flux of the water phase decreases with the increasing ion concentration due to the combined impact of ion spatial structure and electroviscous effects and counteracts the gas phase, thus impeding its flow. This study shed light on the flow phenomena of gas/water phases in hydrophilic nanopores. The results are expected to provide some insight into energy and environmental issues, such as fracturing fluid optimization, enhanced gas recovery (EGR) by water flooding, and the fabrication of microfluidic chips.

An Experimental Model of Unconfined Bubbly Lava Flows: Importance of Localized Bubble Distribution

AbstractMost lava flows carry bubbles and crystals in suspension. From earlier works, it is known that spherical bubbles increase the effective viscosity while bubbles deformed by rapid flow decrease it. Changes in the spatial distribution of bubbles can lead to variable rheology and flow localization and thus modify the resulting lava flow structure and morphology. To understand the roles of bubble and solid phase crystal distributions, we conducted a series of analog experiments of high bubble fraction suspensions. We poured the analog lava on an inclined slope, observed its shape, calculated the velocity field, and monitored its local thickness. A region of localized rapid flow and low vesicularity, whose thickness is thinner than the surrounding area, develops at the center of the bubbly flows. These features suggest that the locally higher liquid fraction decreases the effective viscosity, increases the fluid density, and accelerates the flow. We also found that a halted particle‐bearing bubbly flow can resume flowing. We interpret this to result from the upward vertical separation of bubbles, which generates a liquid‐rich layer at the bottom of the flow. In our experiment, bubbles are basically spherical and decrease the flow velocity, while our estimate suggests that bubbles in natural lava flows could increase or decrease flow velocity. Downstream decreases in flow velocity stops the bubble deformation and can cause a sudden increase of effective viscosity. The vertical segregation of the liquid phase at the slowed flow front may be a way to generate a cavernous shelly paho’eho’e.

Розробка технології та дослідження показників якості йогурту із натуральним наповнювачем у процесі зберігання

The subject of research – yogurt and pumpkin powder. The purpose of the study – to develop the technology of making yogurt with filler – pumpkin powder. Methods. Standard and practical research methods of dairy products were used. The qualitative indicators of the developed yogurt (sensorial indicators, viscosity, microbiological and toxicological indicators) during storage (15 days) were studied. The results of the study. Modern technologies of yogurt production include the use of various additives to improve the technological properties, as well as quality and texture characteristics. In this work, new technological solutions were developed in the formulations of yogurts without stabilizer with dietary fiber contained in pumpkin meal powder, the acceptability of new types of yogurts was evaluated. The dependence of a rheological indicator - the viscosity of the product depending on the amount of filler - in the storage process is analyzed. It was found that the largest increase in effective viscosity was observed in the sample with the introduction of pumpkin meal powder in the amount of 10 %, and the smallest – in the sample with the introduction of pumpkin meal powder in the amount of 5 %. This is due to the quantitative introduction of pumpkin meal powder into the formulation, which is a good sorbent that promotes a more even distribution of moisture between the particles of crushed plant material, which contributes to the formation of a denser clot. The influence of the filler – pumpkin meal powder on the microbiological parameters of yogurt during storage was determined. Studies of microbiological parameters of the control sample of yogurt classic and experimental samples with pumpkin meal powder during storage (15 days) indicate that the opportunistic and pathogenic microflora are within acceptable values. Toxicological studies have shown that safety indicators developed samples of yogurt with filler – pumpkin meal powder – meet the toxicological requirements for the type of product. Based on research, it is proven that yogurt with a natural filler – pumpkin meal powder retains high quality throughout the storage period. Scope of research results. The results of the research will be used to improve the technology of yogurt production at dairy plants.

STRUCTURAL AND MECHANICAL PROPERTIES OF THE DEVELOPED FRUIT AND BERRY SEMI-FINISHED PRODUCT

One of progress directions of the modern food industry is the development and introduction of innovative technologies and assortment of functional food products, allowing to decrease risks of disease progression and favoring the population health.
 Such products include multicomponent fruit and berry pastes and dried powder fractions. They are natural vitamin carriers, may be used as a supplement or a base for creating a wide spectrum of food products with healthy properties.
 A production way for fruit and berry semi-finished product using non-traditional raw materials has been created. For creating paste or dried faction, raw materials with a high content of pectins for better structuring and with correspondent healing-prophylactic properties were selected. Apple was taken as a base of the paste with adding non-traditional raw materials – ziziphus and black aronia. The way differs by the process of dehydration by concentrating up to 44…46 % of dry substances in a rotor evaporator, then, if necessary, additional drying in a thermoradiative one-drum rolling dryer up to 5..8 % of dry substances.
 Structural-mechanical parameters of experimental samples of the paste after concentrating up to 45 % content of dry substances have been determined. An effective viscosity increase for all three experimental samples as 33…59 % comparing with apple paste has been established. It is explained by higher content of pectin substances in ziziphus. The most effective viscosity index is 584 Pa∙s belongs to a sample with the components content: apple – 50 %, ziziphus – 45 %, black aronia – 5 %.
 The developed semi-product may be used as a vitamin supplement, filler or thickener at producing functional food products in confectionary, milk, bakery industry and also for preparing dishes and drinks at restaurant economies and under home conditions

Modeling, simulation and machine learning for rapid process control of multiphase flowing foods

Across many modern industries, as technologies have matured, the use of more complex processes involving multiphase materials has increased. In the food industry, multiphase fluids are now relatively wide-spread, in particular, because of the desire to have faster throughput for large-scale food production. In many cases involving transport, such materials consist of a fluidized binder material with embedded particles. As one increases the volume fraction of particles, a corresponding increase in effective overall viscosity occurs. Often, during the process, the material must be heated, for example, to ensure food safety, induce pasteurization, sterilization, etc. For real-time control, this requires rapidly computable models to guide thermal processing, for example by applied electrical induction. In the present analysis, models are developed for the required heating field (electrically induced) and pressure gradient needed in a pipe to heat a multiphase material to a target temperature and to transport the material with a prescribed flow rate.

Interaction with Cartilage Increases the Viscosity of Hyaluronic Acid Solutions.

Injection of hyaluronic acid (HA) viscosupplements is a prevalent treatment for patients suffering from mild to moderate osteoarthritis. The efficacy of these supplements is attributed to increased synovial fluid viscosity, which leads to improved lubrication and reduced pain. Therefore, viscosity is a key parameter to consider in the development of HA supplements. HA localizes near the cartilage surface, resulting in a viscosity gradient with heightened viscosity near the surface. Traditional rheological measurements confine HA between metal fixtures and therefore do not capture the effect of HA localization that occurs on cartilage. In these experiments, we investigate the effect of modifying rheometer fixtures with cartilage surface coatings on the effective viscosity of HA solutions. Our results demonstrate up to a 20-fold increase in effective viscosity when HA was confined between cartilage surfaces compared to steel surfaces. For low-molecular-weight HA, the effective viscosity was dependent on the gap height between the rheometer plates, which is consistent with the formation of a viscous boundary film. Together, these results indicate that this method for assessing HA viscosity may be more relevant to lubrication than traditional methods and may provide a more accurate method for predicting the viscosity of HA viscosupplements in vivo where HA is able to interact with the cartilage surface.

A microfluidic platform for simultaneous quantification of oxygen-dependent viscosity and shear thinning in sickle cell blood.

The pathology of sickle cell disease begins with the polymerization of intracellular hemoglobin under low oxygen tension, which leads to increased blood effective viscosity and vaso-occlusion. However, it has remained unclear how single-cell changes propagate up to the scale of bulk blood effective viscosity. Here, we use a custom microfluidic system to investigate how the increase in the stiffness of individual cells leads to an increase in the shear stress required for the same fluid strain in a suspension of softer cells. We characterize both the shear-rate dependence and the oxygen-tension dependence of the effective viscosity of sickle cell blood, and we assess the effect of the addition of increasing fractions of normal cells whose material properties are independent of oxygen tension, a scenario relevant to the treatment of sickle patients with blood transfusion. For untransfused sickle cell blood, we find an overall increase in effective viscosity at all oxygen tensions and shear rates along with an attenuation in the degree of shear-thinning achieved at the lowest oxygen tensions. We also find that in some cases, even a small fraction of transfused blood cells restores the shape of the shear-thinning relationship, though not the overall baseline effective viscosity. These results suggest that untransfused sickle cell blood will show the most extreme relative rheologic impairment in regions of high shear and that introducing even small fractions of normal blood cells may help retain some shear-thinning capability though without addressing a baseline relative increase in effective viscosity independent of shear.

Рrospects of research development and new applications of concentrated artificial latexes

The phenomenon of strong stabilization of concentrated aqueous dispersions (emulsions) of polymers by colloidal particles of organic nature (microparticles of synthetic latexes), not accompanied by a significant increase in effective viscosity, opened, firstly, the possibility of carrying out the processes of pigmenting them at low energy costs with a maximum yield (dynamic state, meets the conditions of intensification of heterogeneous chemical-technological processes) and, secondly, determined the directions of further research in this area. So, in contrast to the classical method of emulsion stabilization by mineral microparticles adsorbed directly on the surface of their droplets, microparticles of organic origin interact with them through an interlayer of the dispersion medium, localizing in the immediate vicinity of the dispersed phase and thus maintaining a high mobility of the interphase boundaries. In this regard, the proposed method for predicting the type of emulsions of polymers, taking into account the contact wetting angle and the wetting area of the surface of solid particles of a stabilizer with water and a polymer, requires further verification on various systems. The obtained data of fundamental importance also allowed us to propose new applications of stabilized concentrated artificial latexes for solving applied problems.

Influence of Water on Structure, Dynamics, and Electrostatics of Hydrophilic and Hydrophobic Ionic Liquids in Charged and Hydrophilic Confinement between Mica Surfaces.

Water is ubiquitous in the environment and is the origin for operational constraints in ionic-liquid based electrolytes for supercapacitors. In this study, the influence of water on the interfacial behavior of hydrophilic (1-ethyl-3-methylimidazolium ethylsulfate, abbr. [EMIM][EtSO4]) and hydrophobic (1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, abbr. [EMIM][FAP] and [EMIM][TFSI], respectively) ionic liquids (ILs) confined between mica surfaces was investigated at separations precisely modulated by a surface force apparatus and at controlled relative humidity between 0% and 50% RH. Diffusion experiments revealed that water spontaneously invades the nanoconfined ILs above a certain humidity threshold and that the confined hydrophobic IL is completely replaced by water at sufficiently high environmental humidity (∼45% here) as a result of surface-induced phase separation. This behavior is expected to be universal for other ILs that are not fully miscible with water when they are confined in hydrophilic nanopores of a few nanometers in width. The effect of environmental humidity on interfacial structure, dynamics, and electrostatics was studied via dynamic force measurements. In the dry state, several layers of ions are immobilized on the mica surface, and the effective viscosity increases by up to 2 orders of magnitude with a decrease in film thickness from ∼10 to ∼3 nm. Based on recent work, it is proposed that nanoconfinement enhances the anion-cation association in highly concentrated electrolytes, thereby justifying the loss of fluidity of the ILs. When phase separation is excluded, water is intercalated in the layered structure of the three ILs, and it leads to a change of the layer thickness compared to the dry state. Furthermore, our results reveal that interfacial water prevents ions from being immobilized on the surface and facilitates the outflow of both hydrophilic and hydrophobic ILs by reducing their effective viscosity in the order [EMIM][FAP] < [EMIM][TFSI] < [EMIM][EtSO4]. The underlying mechanisms are evaluated by considering the roles of water in enhancing ion dissociation through screening of electrostatic interactions and solvation of the selected ILs to different extents. The discussed experimental observations support the recent discoveries made by molecular dynamic simulations and neutron scattering studies that using hydrophilic ILs coupled with water as cosolvent could lead to the enhanced power density of IL-based supercapacitors, and therefore, that water-in-(hydrophilic) ILs is a direction worth exploring as electrolytes for supercapacitors.

Solid Nano-Composite Electrolytes (nano-SCE) with Ion Conductivity Promotion at an Interfacial Ice Layer on the Mesoporous Silica Matrix

The transition to solid-state Li-ion batteries requires solid electrolytes with Li-ion conductivity exceeding 1 mS/cm. Solid composite electrolytes or SCEs consisting of an ionic conductor and a dielectric matrix offers an elegant strategy to enhance the ionic conductivity of electrolytes by engineering the interface conduction. Composite electrolyte materials with inorganic oxide matrixes such as silica, alumina or titania with, for example, inorganic or polymer electrolytes have indeed shown enhancements in ion conductivity, however, the total ion conductivity was still well below 1mS/cm due to the low conductivity of the starting individual electrolytes used. Also composites of mesoporous oxide matrix filled with non-volatile ionic liquid electrolyte (ILE) fillers have been explored as solid electrolyte option. The advantage is that ILE can already have quite high ionic conductivity as individual electrolyte component. However, simple confinement of an electrolyte solution in nanometer size pores results in lower conductivity as its effective viscosity increases. The decrease in ion conductivity is expected the worse for mesoporous channels (~10nm in diameter) where the ionic liquid can even turn solid. To achieve higher ion conductivity, interface enhancement has to exceed the decrease in conductivity by confinement. Monolithic nanoporous silica with ILE confined in the porous structures, also named “ionogels” have shown ion conductivities approaching that of the ILE bulk conductivity, indeed, indicating the presence of interface enhancement in these materials. However, so far, the ionic conductivity of the confined ILE in the nanoporous oxide has never exceeded that of the ILE conductivity itself. These ionogels are fabricated by a sol-gel process e.g. by hydrolysis-condensation reaction with tetra-ethylorthosilicate (TEOS) precursor and typically formic acid where the ILE is added in the solution as the template for the silica to grow around. In this paper we demonstrate that the Li-ion conductivity of nano-composites consisting of a mesoporous silica monolith with an ionic liquid electrolyte as filler can be several times higher than that of the pure ionic liquid electrolyte itself when the silica surface is appropriately hydroxylated. Interfacial ice layers induce strong adsorption and ordering of the ionic liquid molecules through H-bonding rendering it immobile and solid-like as for the interfacial ice layer itself. The dipole over the adsorbate results in solvation of the Li+ ions for enhanced conduction. The existence of an interfacial mesophase layer is proven by Infrared and Raman spectroscopy. Higher Li-ion diffusion coefficients for the nanocomposite compared to the pure ionic liquid electrolyte reference is shown by Pulsed-Field-Gradient NMR. The principle of ion conduction enhancement is generic and could be applied to different ion systems. The concept also allows for further (nano)engineering towards specific properties of ion conduction, transport number, electrochemical window, safety and cost for future battery cell generations. The nano-SCE was fabricated in a similar way as the ionogels: a single-step sol-gel process with a TEOS precursor and with the ionic liquid electrolyte in the homogeneous precursor solution, except we did not use formic acid but water. We will focus on systematic study of our nano-SCE model system with (N-butyl- N-methyl pyrrolidinium bis(trifluoromethanesulfonyl) imide ([BMP]TFSI) and bis(trifluoromethanesulfonyl)imide lithium salt (LiTFSI). Comparison with ILE-based composite electrolytes with solid and mesoporous oxide particles will be made, showing that enhancement exist only in the monolith structures and not in the particle systems where percolation limits the conductivity.

Solid Nano-Composite Electrolytes (nano-SCE) with Ion Conductivity Promotion at an Interfacial Ice Layer on the Mesoporous Silica Matrix

The transition to solid-state Li-ion batteries requires solid electrolytes with Li-ion conductivity exceeding 1 mS/cm. Solid composite electrolytes or SCEs consisting of an ionic conductor and a dielectric matrix offers an elegant strategy to enhance the ionic conductivity of electrolytes by engineering the interface conduction. Composite electrolyte materials with inorganic oxide matrixes such as silica, alumina or titania with, for example, inorganic or polymer electrolytes have indeed shown enhancements in ion conductivity, however, the total ion conductivity was still well below 1mS/cm due to the low conductivity of the starting individual electrolytes used. Also composites of mesoporous oxide matrix filled with non-volatile ionic liquid electrolyte (ILE) fillers have been explored as solid electrolyte option. The advantage is that ILE can already have quite high ionic conductivity as individual electrolyte component. However, simple confinement of an electrolyte solution in nanometer size pores results in lower conductivity as its effective viscosity increases. The decrease in ion conductivity is expected the worse for mesoporous channels (~10nm in diameter) where the ionic liquid can even turn solid. To achieve higher ion conductivity, interface enhancement has to exceed the decrease in conductivity by confinement. Monolithic nanoporous silica with ILE confined in the porous structures, also named “ionogels” have shown ion conductivities approaching that of the ILE bulk conductivity, indeed, indicating the presence of interface enhancement in these materials. However, so far, the ionic conductivity of the confined ILE in the nanoporous oxide has never exceeded that of the ILE conductivity itself. These ionogels are fabricated by a sol-gel process e.g. by hydrolysis-condensation reaction with tetra-ethylorthosilicate (TEOS) precursor and typically formic acid where the ILE is added in the solution as the template for the silica to grow around. In this paper we demonstrate that the Li-ion conductivity of nano-composites consisting of a mesoporous silica monolith with an ionic liquid electrolyte as filler can be several times higher than that of the pure ionic liquid electrolyte itself when the silica surface is appropriately hydroxylated. Interfacial ice layers induce strong adsorption and ordering of the ionic liquid molecules through H-bonding rendering it immobile and solid-like as for the interfacial ice layer itself. The dipole over the adsorbate results in solvation of the Li+ ions for enhanced conduction. The existence of an interfacial mesophase layer is proven by Infrared and Raman spectroscopy. Higher Li-ion diffusion coefficients for the nanocomposite compared to the pure ionic liquid electrolyte reference is shown by Pulsed-Field-Gradient NMR. The principle of ion conduction enhancement is generic and could be applied to different ion systems. The concept also allows for further (nano)engineering towards specific properties of ion conduction, transport number, electrochemical window, safety and cost for future battery cell generations. The nano-SCE was fabricated in a similar way as the ionogels: a single-step sol-gel process with a TEOS precursor and with the ionic liquid electrolyte in the homogeneous precursor solution, except we did not use formic acid but water. We will focus on systematic study of our nano-SCE model system with (N-butyl- N-methyl pyrrolidinium bis(trifluoromethanesulfonyl) imide ([BMP]TFSI) and bis(trifluoromethanesulfonyl)imide lithium salt (LiTFSI). Figure caption: Ball-and-stick model for the adsorbed mesophase layer on silica with an interfacial ice water layer. The strong H-bonding between TFSI anions and OH surface groups result in polarization of the adsorbed ILE layer and the dissociation of Li+ from TFSI- anion. The free Li-ions can move faster through the liquid-like layer just above the adsorbed mesophase layer resulting in enhanced ion conductivity. Figure 1

Pore Network Investigation of Trapped Gas and Foam Generation Mechanisms

The mobility of gas is greatly reduced when the injected gas is foamed. The reduction in gas mobility is attributed to the reduction in gas relative permeability and the increase in gas effective viscosity. The reduction in the gas relative permeability is a consequence of the larger amount of gas trapped when foam is present while the increase in gas effective viscosity is explicitly a function of foam texture. Therefore, understanding how foam is generated and subsequent trapped foam behavior is of paramount importance to modeling of gas mobility. In this paper, we push the envelope to enlighten our decisions of which descriptions are most physical to foam flow in porous media regarding both the flowing foam fraction and the rate of generation. We use a statistical pore network interwoven with the invasion percolation with memory algorithm to model foam flow as a drainage process and investigate the dependence of the flowing foam fraction on the pressure gradient and to shed light on foam generation mechanisms. A critical snap-off probability is required for strong foam to emerge in our network. The pressure gradient and, hence, the gas mobility reduction are very low below this critical snap-off probability. Above this snap-off probability threshold, we find that the steady-state flowing lamellae fraction scales as $$(\nabla \tilde{p})^{0.19}$$ in 2D lattices and as $$(\nabla \tilde{p})^{0.32}$$ in 3D lattices. Results obtained from our network were convolved with percolation network scaling ideas to compare the probabilities of snap-off and lamella division mechanisms in the network during the initial gas displacement at the leading edge of the gas front. At this front, during strong foam flow, lamella division is practically nonexistent in 2D lattices. In 3D lattices, lamella division occurs, but the probability of snap-off is always greater than the probability of lamella division.

Rheology of Hydrate-Forming Emulsions Stabilized by Surfactant and Hydrophobic Silica Nanoparticles

Observed effects of hydrophobic fumed silica nanoparticles (of average primary particle size 7 nm) on the rheological behavior of hydrate-forming emulsions are presented. Liquid cyclopentane (CP) is the hydrate former. The hydrate slurry is prepared in a Couette geometry at atmospheric pressure from a water-in-oil emulsion with the phases density matched to avoid segregation. Hydrates are formed upon quenching to a low temperature at a fixed shear rate. Dispersed water droplets convert to hydrate particles, leading to an effective viscosity increase by orders of magnitude. The hydrate inhibition by silica nanoparticles at the water–oil interface, forming a Pickering type of emulsion, is characterized using the onset time of steep viscosity rise after seeding with small hydrate particles; this is termed the critical time. Seeding eliminates stochasticity associated with nucleation of the hydrate. The critical time is increased when the interface is covered with silica nanoparticles. For a particle concentr...

Degassing vs. eruptive styles at Mt. Etna volcano (Sicily, Italy). Part I: Volatile stocking, gas fluxing, and the shift from low-energy to highly explosive basaltic eruptions

Abstract Basaltic magmas can transport and release large amounts of volatiles into the atmosphere, especially in subduction zones, where slab-derived fluids enrich the mantle wedge. Depending on magma volatile content, basaltic volcanoes thus display a wide spectrum of eruptive styles, from common Strombolian-type activity to Plinian events. Mt. Etna, in Sicily, is a typical basaltic volcano where the volatile control on such a variable activity can be investigated. Based on a melt inclusion study in products from Strombolian or lava-fountain activity to Plinian eruptions, here we show that for the same initial volatile content, different eruptive styles reflect variable degassing paths throughout the composite Etnean plumbing system. The combined influence of i) crystallization, ii) deep degassing and iii) CO2 gas fluxing can explain the evolution of H2O, CO2, S and Cl in products from such a spectrum of activity. Deep crystallization produces the CO2-rich gas fluxing the upward magma portions, which will become buoyant and easily mobilized in small gas-rich batches stored within the plumbing system. When reaching gas-dominated conditions (i.e., a gas/melt mass ratio of ~ 0.3 and CO2,gas/H2Ogas molar ratio ~ 5), magma batches will erupt effusively or mildly explosively. In case of the 122 BC Plinian eruption, open-system degassing conditions took place within the plumbing system, such that earlier CO2-fluxing determined gas accumulation on top of the magmatic system, likely followed by H2O-fluxing further hydrating the shallow magma. The emission of such a cap in the early eruptive phase triggered the arrival of deep H2O-rich magma whose fast decompression and bubble nucleation led to the highly explosive character, enhanced by abundant microlite crystallization and consequent increase of magma effective viscosity. This could explain why open system basaltic systems like Etna may experience highly explosive or even Plinian episodes during eruptions that start with effusive to mildly explosive phases. The proposed mechanism also determines a depression of chlorine contents in CO2-fluxed (and less explosive) magmas with respect to those feeding Plinian events like 122 BC. The opposite is seen for sulfur: low to mild-explosive fluxed magmas are S-enriched, whereas the 122 BC Plinian products are relatively S-poor, likely because of early sulfide separation accompanying magma crystallization. The proposed mechanism involving CO2 separation and fluxing may suggest a subordinate role for variable mixing of different sources having different degrees of K-enrichment. However, such a mechanism requires further experimental studies about the effects on S and Cl dissolution and does not exclude self-mixing between degassed and undegassed parcels within the Etna plumbing system. Finally, our findings may represent a new interpretative tool for the geochemical and petrologic monitoring of plume gas discharges and melt inclusions, and allow tracking the switch from mild-explosive to highly explosive or even Plinian events at Etna.

The Effect of Polymer Rheology and Induced Fracturing on Injectivity and Pressure-Transient Behavior

Summary Polymer transport and fluid rheology were implemented in a fully implicit hydraulic-fracturing and reservoir simulator. For flow in the matrix, a fluid-rheology function was used with shear thickening at high shear rates and shear thinning at medium and low shear rates. For flow in fractures, a shear-thinning constitutive law with a zero shear-rate plateau was used. The average viscosity in each fracture element was calculated by assuming smooth and parallel fracture walls and numerically solving for the velocity, shear rate, and viscosity distribution across the aperture. The simulator was used to investigate the effect on injectivity of shear thickening at high shear rates near the wellbore. For comparison, simulations were performed by use of the full shear-thickening and shear-thinning rheology function and by use of a shear-thinning-only rheology function. In the former case, the shear thickening caused rapid buildup of fluid pressure and the creation of a hydraulic fracture at the wellbore. Once the fracture formed, shear thickening no longer occurred because there was lower Darcy velocity in the matrix caused by lower concentration of flow at the wellbore. As a result, after the formation of the hydraulic fracture, injectivity in the simulation with shear thickening and thinning was nearly identical to that in the simulation with only shear thinning. The simulations were repeated with the constraint that a hydraulic fracture was not permitted to form. In this case, the simulation with shear thickening had a significantly lower injectivity than the simulation with shear thinning only. This result shows that formation of an induced fracture is a plausible explanation for unexpectedly high injectivity during polymer injection because it prevents shear thickening caused by high flow rate because of concentration of flow at the wellbore. Simulations were performed to investigate the effect of polymer rheology on the pressure transients occurring after shut-in of an injection well. Shear thickening affected the shut-in transient only at very-early time. Shear thinning affected the entire duration of the transient, causing an increase in effective fluid viscosity as the Darcy velocity gradually decreased over time. Despite fluid-rheology effects, linear flow was clearly identifiable after shut-in in the simulations with hydraulic fractures. This result shows that hydraulic fractures around polymer-injection wells can be diagnosed in field data from the linear-flow regime in the shut-in transient, regardless of fluid-rheology effects.

Phase split characteristics of slug and annular flow in a dividing micro-T-junction

The characteristics of slug and annular gas–liquid two-phase flow when moving through a rectangular micro-channel dividing T-junction were investigated with experiments focusing on the relationships between the phase split and the two-phase superficial velocity, liquid surface tension, and liquid effective viscosity. The effects of the pipe sizes and pipe cross section shapes on phase split were compared and analyzed. Phase split was tested using a 100×800μm rectangular dividing micro-T-junction. Air was used as the gas medium and the liquid mediums were water, 0.01% SDS solution, 0.5% SDS solution, 0.1wt% PAAm, 0.25wt% PAAm, and 0.5wt% PAAm. Results showed that whether the inlet flow pattern was slug or annular flow, the liquid taken off from side branch at the dividing T-junction decreases with an increase in liquid superficial velocity and that there is little effect of inlet gas flow rate on the liquid taken off. It was also found that the liquid taken off from side branch decreases with a decrease in liquid surface tension and increases with an increase in liquid effective viscosity. When results were compared to those from studies using channels of other diameters, it was seen that the phase split of the slug flow was similar at different sized dividing T-junction, while the phase split of annular flow varied at different pipe sizes. It was also seen that the phase split characteristics of a dividing micro-T-junction are dependent on the aspect ratios of the channel’s cross section. A predictive model of phase split characteristics studied in this investigation was formulated with the regression analysis of the experimental data and verified by calculations showing little error.

Field and experimental constraints on the rheology of arc basaltic lavas: the January 2014 Eruption of Pacaya (Guatemala)

We estimated the rheology of an active basaltic lava flow in the field, and compared it with experimental measurements carried out in the laboratory. In the field we mapped, sampled, and recorded videos of the 2014 flow on the southern flank of Pacaya, Guatemala. Velocimetry data extracted from videos allowed us to determine that lava traveled at ∼2.8 m/s on the steep ∼45° slope 50 m from the vent, while 550 m further downflow it was moving at only ∼0.3 m/s on a ∼4° slope. Estimates of effective viscosity based on Jeffreys’ equation increased from ∼7600 Pa s near the vent to ∼28,000 Pa s downflow. In the laboratory, we measured the viscosity of a representative lava composition using a concentric cylinder viscometer, at five different temperatures between 1234 and 1199 °C, with crystallinity increasing from 0.1 to 40 vol%. The rheological data were best fit by power law equations, with the flow index decreasing as crystal fraction increased, and no detectable yield strength. Although field-based estimates are based on lava characterized by a lower temperature, higher crystal and bubble fraction, and with a more complex petrographic texture, field estimates and laboratory measurements are mutually consistent and both indicate shear-thinning behavior. The complementary field and laboratory data sets allowed us to isolate the effects of different factors in determining the rheological evolution of the 2014 Pacaya flows. We assess the contributions of cooling, crystallization, and changing ground slope to the 3.7-fold increase in effective viscosity observed in the field over 550 m, and conclude that decreasing slope is the single most important factor over that distance. It follows that the complex relations between slope, flow velocity, and non-Newtonian lava rheology need to be incorporated into models of lava flow emplacement.

Characterization of mechanical properties of hybrid contrast agents by combining atomic force microscopy with acoustic/optic assessments

Multi-parameter fitting algorithms, which are currently used for the characterization of coated-bubbles, inevitably introduce uncertainty into the results. Therefore, a better technique that can accurately determine the microbubbles׳ mechanical properties is urgently needed. A comprehensive technology combining atomic force microscopy, optical, and acoustic measurements with simulations of coated-bubble dynamics was developed. Using this technique, the mechanical parameters (size distribution, shell thickness, elasticity, and viscosity) of hybrid (ultrasound/magnetic-resonance-imaging) contrast microbubbles and their structure–property relationship were determined. The measurements indicate that when more superparamagnetic iron oxide nanoparticles are embedded in the microbubbles׳ shells, their mean diameter and effective viscosity increase, and their elastic modulus decreases. This reduces the microbubbles׳ resonance frequency and thus enhances acoustic scattering and attenuation effects.