Viscous Flow Mechanism Research Articles

Liquid like behavior of solid metals

Condensed states of matter existing in nature are easily recognizable due to their particular features. One of them is viscosity, which helps to distinguish between liquids and crystalline solids. Metals belong to this second group of materials for which viscosity, measured as resistance to shape change under the influence of load, is very high even at temperatures close to melting point. The presented work attempts to answer the following question: “How to make hardly deformable materials behave like liquids?” The conclusions, drawn from experiments, indicate that extrusion by the KOBO method activates viscous flow mechanism in metals regardless of their temperature.

Characterization of gas transport behaviors in shale gas and tight gas reservoirs by digital rock analysis

Due to the extremely tiny pore size of tight gas and shale gas reservoir, the modified Darcy’s law in which the intrinsic permeability is replaced by the apparent permeability that can be obtained by a function of three transport parameters (intrinsic permeability, porosity and tortuosity), is used to describe the combined mechanisms of viscous flow, Knudsen diffusion, the effect of the adsorbed layer thickness and surface diffusion through the adsorbed layer. A new apparent permeability estimation method based on digital rock was proposed in this paper. The digital rock with nanopores could be constructed by 3D pore structure images obtained from micro/nano CT and FIB-SEM images directly or reconstructed with Markov Chain Monte Carlo (MCMC) method from the 2D SEM images of pore structure; then Lattice Boltzmann method can be applied to calculate the intrinsic permeability, porosity and tortuosity of 3D digital rock. These parameters are used to calculate the apparent permeability under consideration of different combined gas transport mechanisms. This method is applied to samples from the shale gas reservoir in Silurian Longmaxi Formation of Sichuan Basin and from the tight gas reservoir in the Wenchang Formation of Huizhou Sag. The results show that all considered transport mechanisms greatly impact the shale apparent permeability and cannot be ignored in shale samples. In tight gas reservoirs, Knudsen diffusion is an important mechanism at low pressures of less than 1MPa. However, Knudsen diffusion could be ignored when pressure is greater than 1MPa due to its smaller impact.

Apparent gas permeability in an organic-rich shale reservoir

Accurate models of gas transport in shale gas reservoirs must consider complex gas transport mechanisms and phase behavior in nanopores, as well as different pore types. The gas transport mechanisms in shale gas reservoirs include viscous flow, Knudsen diffusion, surface diffusion, adsorption and desorption. In this study, a unified model of nanopore gas transport in shale gas reservoirs is presented. Gas storage patterns are different in organic pores and inorganic pores. Therefore, we develop two fully coupled apparent permeability models to describe gas transport in organic pores and inorganic pores separately. The apparent permeability model of organic pores considers the gas transport mechanisms of viscous flow, Knudsen diffusion, surface diffusion, adsorption and desorption. The apparent permeability model of inorganic pores considers the gas transport mechanisms of viscous flow and Knudsen diffusion. In both models, stress dependence, real gas effects and phase behavior are taken into account. Then, the influences of pore pressure, effective stress, real gas effects, pore radius, phase behaviors and transport properties on apparent gas permeabilities in organic pores and inorganic pores are analyzed based on the proposed models.

Effect of temperature on viscometric properties of aliphatic amino acids glycine/l-alanine/l-valine in aqueous solutions of tetraethylammonium iodide

Viscosities, η, for solutions of glycine, l-alanine and l-valine in (0.03, 0.05, 0.1, 0.15 and 0.2) mol·kg−1 aqueous tetraethylammonium iodide (TEAI) at temperature T=(288.15, 293.15, 298.15, 303.15 and 308.15) K have been measured as a function of molality of amino acids. The viscosity B-coefficients for the amino acids in aqueous TEAI solutions have been calculated at different temperatures employing the Jones–Dole equation. The trends of variation in viscosity values of amino acids with an increase in molal concentration of TEAI solutions and also with an increase in temperature have been ascribed to the solute–solvent interactions operative in the solutions. The contribution of the solute to the activation parameters (Δμ20⁎, ΔH0⁎ and ΔS0⁎) for viscous flow of the solution has been obtained to throw light on the mechanism of viscous flow. The contributions of the charged end group (NH3+,COO−) and (CH2) groups of the amino acids to B-coefficient and Δμ20⁎ have also been estimated using the linear correlations between B-coefficient or Δμ20⁎ and the number of carbon atoms in the alkyl chains of the amino acids. All these parameters have been discussed in terms of the solute–solvent interactions in the ground and transition states.

Processing, phase evaluation and mechanical properties of MoSi2 doped 4TaC–HfC based UHTCs consolidated by spark plasma sintering

In this research, binary 4TaC–HfC based composites were consolidated using carbide materials and addition of 0–15vol.% MoSi2 by means of spark plasma sintering at 2000°C. The nearly full dense and monophase specimens were fabricated with a relative density value higher than 99%. Mechanical tests revealed values of 18–19GPa and 4–4.3MPa·m1/2, for average Vickers hardness and fracture toughness of the composites, respectively. Analysis of linear shrinkage during densification revealed that MoSi2 addition increased densification rate and decreased the time required to reach full density at 2000°C. It is proposed that at the intermediate stage of sintering, mass transfer can be accelerated by formation of a silicide based liquid phase and viscous flow mechanisms. The formation of binary 4TaC–HfC solid solution phase enhanced the densification process at the final stage of sintering.

Relationship between densification behavior and stabilization of quasi-liquid grain boundary layers in CuO-doped 0.7CaTiO3–0.3NdAlO3 microwave ceramics

In a combination with aberration-corrected TEM and water quench treatment, CuO–xCu2O grain boundary quasi-liquid layers in multicomponent 0.7CaTiO3–0.3NdAlO3 perovskite microwave ceramics doped by 0.5wt% CuO are observed. Their structure and chemistry are identified. The relationship between their stabilization and densification behavior during the early sintering stage is clarified by constant-heating-rate/isothermal sintering experiments. It is revealed that the densification of CuO-doped 0.7CaTiO3–0.3NdAlO3 ceramics is dominated by viscous flow mechanism. Additionally, the appearance of quasi-liquid layers during the early sintering stage promotes mass transport by short-circuit diffusion. These results can be used as a guide to control the microstructure and properties of microwave ceramics.

A study of gas diffusion characteristics on a micro porous composite silica ceramic membrane

The purpose of this study is to investigate gas permeation behaviour of five gases (CO2, He, H2, N2 and Ar) across two silica modified ceramic membranes, Membrane Y and Membrane Z. An examination of the variations in their layer thickness and flow rate was determined. Solution-dip coating process was used for the modification process specifically for pore size reduction. This resulted in some level of modifications in the layer thickness after a successive dipping time as well as flow rate in relation to pressure drop. The effect of number of dips generally influenced the layer thickness of both membranes. Membrane Y layer thickness through five successive dipping was in the range of 89.2–36μm while Membrane Z ranges between 150.72 and 43.69μm. Gas permeability as a function of mean pressure for Membrane Z was calculated using data obtained experimentally. The permeation tests confirmed the contribution of both Knudsen and viscous flow mechanism with an estimation and prediction of the membrane pore radius.

Atomic-Force Thermodilatometry of Two-Dimensional Ensembles of Nanoparticles

Atomic-force thermodilatometry is used to investigate the change in the morphology of two-dimensional ensembles of iron metal-oxide nanoparticles obtained by reactive evaporation and subsequent programmable low-temperature (20–160°C) annealing. It is shown that when ensembles of nanoparticles are annealed, thermal shrinkage occurs (up to 25% of the volume) due to dehydration, oxidation and possible coalescence and spreading by a viscous flow mechanism.

Continual model variant of viscous materials Report 2. Experimental proof

Considering the non-uniform character of viscous flow of hard phase, the continual model of hot deformation of porous powder materials has been checked. The procedure of the phenomenological creep parameter identification for the hard phase of powder materials is described. A particular mechanism of viscous flow of hard phase particles is shown to be realized depending on temperature-force strain conditions. Unlike the cast materi- als the powder material creep process, alongside with volume and boundary diffusion, can be controlled by superficial diffusion as well. In case of the same creep mechanism, the offered continual model allows us to use for powder materials directly the phenomenological constants of cast materials.

A Numerical Study on Agglomeration in High Temperature Fluidized beds

Soft-sphere discrete element method (DEM) and Navier-Stokes equations were coupled with equations of energy for gas and solids to investigate the process of agglomeration in fluidized bed of polyethylene particles at high temperature. The Newton’s second law of motion was adapted for translational and rotational motion of particles and agglomerates. The cohesive force for polyethylene particles was calculated based on a time dependent model for solid bridging by the viscous flow mechanism. The motion of agglomerates was described by means of the multi-sphere method. By taking into account the cohesiveness of particles at high temperatures and considering real dynamic agglomerates, the fluidization behavior of a bed of polyethylene particles was successfully simulated in terms of increasing the size of agglomerates. Effect of the inlet gas temperature on mass and size of agglomerates was investigated. A mechanistic study in terms of contact time, cohesive force and repulsive force, which are the key parameters in the formation of agglomerates, were also carried out.

Identification of Molecular Transport Mechanisms in Micro-Porous Hydrotalcite–Silica Membrane

Hydrotalcite (HT) materials have been known to be able to adsorb $$\hbox {CO}_{2}$$ even at high temperature. However, HT has not been made into a micro-porous membrane because of its meso-porous nature. In order to form a micro-porous HT membrane, silica was selected as a host matrix due to its ability to retain its micro-porosity. In this paper, a micro-porous hydrotalcite–silica membrane was formed on a meso-porous $$\upgamma $$ -alumina layer supported by a macro-porous $$\upalpha $$ -alumina substrate. Most of the micro-porosity determined from nitrogen adsorption measurement was found to be either closed or open but not interconnected, whereas most of the meso-porosity (at ca. 11.2 nm) in the micro-porous membrane was open and interconnected, thereby promoting gas flow. Viscous flow mechanism was observed to dominate transport of gases in macro-porous membrane. Knudsen diffusion dominated transport of gases in meso-porous membrane. On the other hand, surface affinity influenced the transport of carbon dioxide through the micro-porous membrane rather significantly. While permeability of pure hydrogen and carbon dioxide were independent of pressure, the permeability of the gases in the binary mixtures decreased with increasing pressure. Both experiment and simulation demonstrated consistent results.

Comprehensive Method of Studying and Predicting the Deformation of Ceramic Products During Sintering

A comprehensive method is proposed for predicting the deformation of ceramic products under their own weight (the force of gravity) during sintering. The method is based on the torsion of thin-walled tubes, finite-element modeling, a calibration process that includes tests of specimens of the material in cantilever bending, and validation of the numerical solution. The method can be used to predict the deformation of thin-walled and solid products made of materials whose rheology is based on the mechanisms of viscous and/or diffusion flow.

Densification behaviour and sintering mechanisms of Cu- or Co-doped SnO2: A comparative study

Compared with the CuO–SnO2 system, there is a lack of experimental evidence of a eutectic liquid phase in the CoO–SnO2 system. It is therefore believed that the densification behaviour and sintering mechanisms of the two systems are completely different. However, our present study clearly demonstrated that the Co- and Cu-doped SnO2 ceramics exhibited a similar densification behaviour. The 1wt.% Cu- or Co-doped SnO2 ceramics could reach over 95% relative density when sintered to 1250°C with a heating rate of 5°Cmin−1. It was found that both CoO4/3- and CuO-doped SnO2 follow the same mass transport mechanism – viscous flow sintering during early-stage sintering. This was verified with the classic isothermal and constant-heating-rate models, as well as Frenkel’s viscous flow theory. The viscous flow mechanism dominated densification up to ∼73 and ∼78% relative density with the apparent activation energies of 362 and 440kJmol−1 for Co and Cu doping cases, respectively.

Numerical simulation of gas transport mechanisms in tight shale gas reservoirs

Due to the nanometer scale pore size and extremely low permeability of a shale matrix, traditional Darcy’s law can not exactly describe the combined gas transport mechanisms of viscous flow and Knudsen diffusion. Three transport models modified by the Darcy equation with apparent permeability are used to describe the combined gas transport mechanisms in ultra-tight porous media, the result shows that Knudsen diffusion has a great impact on the gas transport and Darcy’s law cannot be used in a shale matrix with a pore diameter less than 1 μm. A single porosity model and a double porosity model with consideration of the combined gas transport mechanisms are developed to evaluate the influence of gas transport mechanisms and fracture parameters respectively on shale gas production. The numerical results show that the gas production predicted by Darcy’s law is lower than that predicted with consideration of Knudsen diffusion and the tighter the shale matrix, the greater difference of the gas production estimates. In addition, the numerical simulation results indicate that shale fractures have a great impact on shale gas production. Shale gas cannot be produced economically without fractures.

Transport behavior of l-alanine, l-valine and l-leucine in ampicillin solutions over temperature range (305.15 to 315.15) K

The viscosities, η of l-alanine, l-valine and l-leucine with drug ampicillin (AMP) have been measured as a function of temperature at T=(305.15, 310.15 and 315.15)K. The viscosity data have been utilized to determine viscosity B-coefficients employing the Jones–Dole equation. The trends of variation in viscosity values of amino acids with an increase in molal concentration of AMP solutions and also with an increase in temperature have been ascribed to the solute–solvent interactions operative in the solutions. The activation parameters of viscous flow have been obtained to throw light on the mechanism of viscous flow. These parameters have been discussed in the light of ion–ion and ion–solvent interactions.

Viscometric measurements of l-serine with antibacterial drugs ampicillin and amoxicillin at different temperatures: (305.15 to 315.15) K

The viscosities, η of l-serine with drug ampicillin (AMP) and amoxicillin (AMX) have been measured as a function temperature at T=(305.15, 310.15 and 315.15) K. The viscosity data have been utilized to determine viscosity B-coefficients employing the Jones–Dole equation. The trends of variation in viscosity values of amino acid with an increase in molal concentration of AMP and AMX solutions and also with an increase in temperature have been ascribed to the solute–solvent interactions operative in the solutions. The activation parameters of viscous flow have been obtained to throw light on the mechanism of viscous flow. These parameters have been discussed in the light of ion–ion and ion–solvent interactions.

Reverse osmosis performance of organosilica membranes and comparison with the pervaporation and gas permeation properties

Hybrid organosilica membranes were successfully prepared using bis(triethoxysilyl)ethane (BTESE) and applied to reverse osmosis (RO) desalination. The organosilica membrane calcined at 300°C almost completely rejected salts and neutral solutes with low‐molecular‐weight. Increasing the operating pressure led to an increase in water flux and salt rejection, while the flux and rejection decreased as salt concentration increased. The water permeation mechanism differed from the viscous flow mechanism. Observed activation energies for permeation were larger for membranes with a smaller pore size, and were considerably larger than the activation energy for water viscosity. The organosilica membranes exhibited exceptional hydrothermal stability in temperature cycles up to 90°C. The applicability of the generalized solution‐diffusion (SD) model to RO and pervaporation (PV) desalination processes were examined, and the quantitative differences in water permeance were accurately predicted by the application of generalized transport equations. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1298–1307, 2013

Investigation of the Mechanisms Involved in the Sintering of Chalcogenide Glasses and the Preparation of Glass‐Ceramics by Spark Plasma Sintering

The sintering of the 80GeSe2–20Ga2Se3 chalcogenide glass composition as well as the preparation of the corresponding glass‐ceramics has been investigated using pulsed current electrical sintering also known as spark plasma sintering. Amorphous powder has been synthesized by mechanical alloying. Due to the electrical insulating property of this glass composition, powder is heated mostly through the heating of the graphite die. It was found that densification of glass powder occurs through a viscous flow mechanism prior to devitrification. A model has been successfully applied to determine the viscosity and activation energy of the glass. This model has been confirmed by ball penetration technique to determine the glass sample viscosity.

Preparation and characterization of CaO–Al2O3–SiO2 glass/fused silica composites for LTCC application

A new glass/ceramic system containing low-softening CAS (CaO–Al2O3–SiO2) glass and high-softening fused silica for LTCC (low temperature cofired ceramics) application was studied. The compositions of CAS glass were properly designed from the viewpoint of achieving low thermal expansion. XRD results of both the composites and pure CAS glasses showed that cristobalite phase was significantly reduced by increasing the sintering rate and shortening the soaking time. Sufficient densification was achieved at 900°C, when the glass content increased to 70wt%. In the present study, the mechanism of viscous flow dominated the sintering process. The results of thermal expansion constant (TEC) of the prepared glasses were in the range of (5.18–6.30)×10−6°C−1, close to the designed value (4.5×10−6°C−1). The 70wt% CAS glass/fused silica composites sintered at 900°C with a sintering rate of 5°C/min and a soaking time of 2h exhibited high TECs in the range of (12.32–16.96)×10−6°C−1. However, TEC significantly dropped when the sintering rate was increased to 8°C/min and the soaking time was shortened to 1h. The 70wt% CAS Glass C/fused silica composite exhibited a low TEC of 4.80×10−6°C−1, close to that of silicon (3.1×10−6°C−1), and a low dielectric constant of 4.7. Both the TEC and the dielectric constant of the composite were on the lower side of that reported for commercial products, indicating its suitability for LTCC application.

Fast vapor phase growth of SiO2 nanowires via surface-flow on Ag core/SiO2 shell structure

Uniform, millimeter-long SiO2 nanowires were grown from co-evaporation of Ag2O and SiO powders. The ‘frozen’ growth scenario by cooling enables revelation of the vapor-liquid-solid mechanism here in action, which is generally inaccessible due to the high temperature and high pressure condition. Ag core/SiO2 shell preformed in the vapor and wetting the substrate will expose its liquid Ag-core to catalyze nanowire growth, at a rate over 10 nm/s, via viscous flow of the encasing SiO2 layer which precipitates through a liquid neck zone. This method is characteristic of high-yield of catalytic seeds free from overgrowth or consuming, easy control of wire thickness by vapor pressure adjustment, enhanced rooting ability since catalyst deposition on substrate becomes dispensable, etc. Also spinning growth of nanowires observed in many other circumstances can be explained by the viscous flow mechanism.