Rheological Properties Of Liquid Research Articles

Convection velocities in droplets before and after their collisions

High-speed video recording was used together with particle image velocimetry with tracer particles of titanium dioxide to study the characteristics of shifting and mixing of liquid layers in the coalescence, disruption, and separation of droplets. Convection velocities (Uc) were determined in droplets before and after their collisions. Vortex contours of different sizes and in different cross sections of droplets were derived. The average values of Uc were calculated. The effect of a group of factors on Uc was investigated. These factors include the relative velocity before the collision Urel, the ratio of droplet sizes Δ, the Weber number, the impact angle, and the rheological properties of liquid. Uc changed most significantly (more than threefold) from variations in Δ, Urel, and We. When varying the dimensionless linear interaction parameter B, Uc changed by 20%–40%. In disruption, Uc increased more than eightfold. In separation and coalescence, they increased by a factor of 10 and 11, respectively. The convection velocity was maximum after the collision. Then, 0.29–0.37 s after the collision, it fell to the values corresponding to a free-falling droplet. An increase in the convection velocity was compared for different droplet sizes and velocities before and after their interaction. Mathematical equations were obtained to predict the convection velocities affected by several investigated factors, taken separately or in combination. For the first time, the ranges of Uc were found, and the effect of a wide group of parameters (geometric sizes and velocities of droplets, rheological characteristics) on the velocities of convective flows was identified.

Fluid–structure model for disks vibrating at ultra-high frequency in a compressible viscous fluid

Radial mechanical modes of miniature disk-shaped resonators are promising candidates for probing the ultra-high-frequency rheological properties of liquids. However, the lack of an analytical fluid–structure model hinders the inference of liquid properties from the experimental measurement of such radial vibrations. Here, we develop analytical models for the case of a disk vibrating in a compressible viscous liquid. Closed-form expressions for the mechanical quality factor and resonant frequency shift upon immersion are obtained and compared with the results of numerical modeling for a few significant cases. At frequencies above 1 GHz, our model points out the significance of compressibility effects.

The role of liquid rheological properties on the injection process of a spring-driven autoinjector

Accurate injection time prediction is essential in developing spring-driven autoinjector devices since the drug delivery is expected to finish within seconds to bring convenience, reduce the risk for early lift-off, and provide a consistent experience to users. The Carreau model captures the liquid’s shear-dependent viscosity measured in our experiments. Thus, a quasi-steady model, which uses the Carreau model to describe the liquid’s viscosity, is developed to predict the injection time of spring-driven autoinjectors. Analytical relations between the flow rate and the pressure drop in the needle are also obtained. The Carreau number in the spring-driven autoinjector is greater than one and smaller than a critical value; in this region, using the power-law model to describe the liquid viscosity accurately predicts the injection time, which agrees with the current literature findings. Additionally, a force threshold is identified for the friction force between the plunger and the syringe barrel, beyond which the injection time is infinite. Appreciation of this force threshold can help avoid device stalling and reduce the risk of underdosing. Moreover, the role of liquid’s shear-thinning index on the injection time of spring-driven autoinjectors is quantified. Understanding the shear-thinning index allows formulators to experiment with excipients and pH to enhance confidence in drug/device combination product design and integration. Our experimental and theoretical results can help drug product and device developers with integrated product design and improve the patient experience.

Probing the Rheological Properties of Liquids Under Conditions of Elastohydrodynamic Lubrication Using Simulations and Machine Learning

In elastohydrodynamic lubrication (EHL), the lubricant experiences pressures in excess of 500 MPa and strain rates larger than 10^5 text{s}^{-1}. The high pressures lead to a dramatic rise in the Newtonian viscosity and the high rates lead to large shear stresses and pronounced shear thinning. The extraction of accurate rheological properties using non-equilibrium molecular dynamics simulations (NEMD) has played a key role in improving our understanding of lubricant flow in EHL conditions. However, the high dimensionality of the output data generated by NEMD simulations often makes a deeper interrogation of the link between molecular-scale features and rheological properties challenging. In this paper, we explore the use of machine learning to analyze and visualize the high-dimensional output data generated in typical NEMD simulations. We show that dimension reduction of NEMD simulation data describing the shear flow of squalane enables a clear visualization of the transition from Newtonian to non-Newtonian shear thinning with increasing shear rate and provides a reliable assessment of the correlation between shear thinning and the evolution in molecular alignment. The end-to-end atom pairs dominate the largest variations in pair orientation tensor components for low-pressure systems (0.1, 100 MPa) and provide the clearest separation of the orientation tensors with rate. On the other hand, the side atom pairs dominate the largest variation in the tensor components for the high-pressure systems (Pge 400 MPa) which exhibit an overall limited evolution in orientation tensors as a function of rate. Dimension reduction using all the six components of the orientation tensors of all 435 pairs associated with a squalane molecule shows that the decrease in viscosity with rate for low pressures is strongly correlated with changes in molecular alignment. However, for high pressures, shear thinning occurs at saturated orientational order.

Green and facile procedure for the preparation of liquid and gel-like polyurethanes based on castor oil and lignin: Effect of processing conditions on the rheological properties

This work presents a comprehensive study on the influence of processing variables (temperature, agitation speed) and type of diisocyanate crosslinker on the rheological properties of liquid and gel-like polyurethane formulations based on lignin and castor oil. With this aim, a green and facile one-step preparation protocol which avoids the use of any harmful catalyst or solvent was proposed. Different processing temperatures (25, 45, 70 °C), stirring speeds (23, 70, 140 rpm) and kinds of diisocyanates (hexamethylene diisocyanate, and toluene diisocyanate) were selected to process the different bio-sourced polyurethane samples. These processing variables have proven to be crucial to modulate and control the rheological (viscous and viscoelastic) properties, and curing kinetics after processing, due to the different chemical structures achieved that were elucidated by means of Fourier-transform infrared spectroscopy and differential scanning calorimetry. In general, a low processing temperature and low stirring speed favour the achievement of gel-like characteristics and/or the formation of highly viscous polyurethanes, as a consequence of a higher number of total hydrogen-bonded carbonyl groups, urethane/urea ratio and ratio of hydrogen-bonded/non-bonded urethane and urea linkages. Besides, the selected one-step process, in comparison with the reported two-step process, provides polyurethanes with similar rheological characteristics by significantly reducing the isocyanate content. Finally, lignin was demonstrated to act as an effective filler agent increasing the values of the viscoelastic moduli.

Coating and Drying of Thin Liquid Films: Effect of Rheological Properties of Liquids on Defect Formation

Coating and Drying of Thin Liquid Films: Effect of Rheological Properties of Liquids on Defect Formation

Numerical Investigation of Degassing Behavior of Highly Viscous Non‐Newtonian Fluids under Stirring

AbstractA method for accelerating bubble removal in non‐Newtonian liquids by forced stirring is proposed. Numerical simulations based on an Eulerian‐Eulerian multiphase model are performed to test its feasibility for various liquids including shear‐thickening, shear‐thinning, and Newtonian ones. Effects of the rotating speed of the stirrer and rheological properties of liquids on the degassing efficiency are evaluated, and the influencing mechanisms are analyzed in detail. The feasible regions of degassing in shear‐thinning liquids covering a certain range of viscosities are determined, from which one can easily decide the optimal rotating speed given the viscosity of liquids. The results provide a new idea of efficient degassing in shear‐thinning liquids for researchers and engineers.

Fluidization using pseudoplastic liquids – Elutriation and ANN modeling

Experimental work on elutriation of irregularly shaped sand particles (0.538–2.03 mm diameter) was carried out in three different Perspex columns (47 mm, 72 mm and 92.3 mm) using different non-Newtonian pseudoplastic liquids (0.4–0.8 kg/m3 SCMC solution). The effects of operating parameters, column diameter, bed weight, particle diameter, particle sphericity, liquid rheological properties on the minimum elutriation velocity were examined. The statistically accepted empirical correlation was developed. ANN model could predict the experimental data of minimum elutriation velocity with a correlation coefficient of 0.9951.

Rheological Properties of Liquids Under Conditions of Elastohydrodynamic Lubrication

There is an ongoing debate concerning the best rheological model for liquid flows in elastohydrodynamic lubrication (EHL). Due to the small contact area and high relative velocities of bounding solids, the lubricant experiences pressures in excess of 500 MPa and strain rates that are typically $$10^5{-}10^7\,\text {s}^{-1}$$ . The high pressures lead to a dramatic rise in Newtonian viscosity $$\eta _{N}$$ and the high rates lead to large shear stresses and pronounced shear thinning. This paper presents detailed simulations of a model EHL fluid, squalane, using nonequilibrium molecular dynamics methods to extract the scaling of its viscosity with shear rate ( $$10^5{-}10^{10}\,\text {s}^{-1}$$ ) over a wide range of pressure P (0.1 MPa to 1.2 GPa), and temperature T ( $$150{-}373$$ K). Simulation results are consistent with a broad range of equilibrium and nonequilibrium experiments. At high T and low P, where $$\eta _{N}$$ is low, the response can be fit to a power law, as in the common Carreau model. Shear thinning becomes steeper as $$\eta _{N}$$ increases, and for $$\eta _{N}\gtrsim 1$$ Pa s, shear thinning is consistent with the thermally activated flow assumed by another common model, Eyring theory. Simulations for a bi-disperse Lennard–Jones (LJ) system show that the transition from Carreau to Eyring is generic. For both squalane and the LJ system, the viscosity decreases by only about a decade in the Carreau regime, but may fall by many orders of magnitude in the Eyring regime. Shear thinning is often assumed to reflect changing molecular alignment, but the alignment of squalane molecules saturates after the viscosity has dropped by only about a factor of three. In contrast, thermal activation describes shear thinning by six or more decades in viscosity. Changes in the diagonal elements of the stress tensor with rate and shear stress are also studied.

Numerical Models for Viscoelastic Liquid Atomization Spray

Atomization spray of non-Newtonian liquid plays a pivotal role in various engineering applications, especially for the energy utilization. To operate spray systems efficiently and well understand the effects of liquid rheological properties on the whole spray process, a comprehensive model using Euler-Lagrangian approaches was established to simulate the evolution of the atomization spray for viscoelastic liquid. Based on the Oldroyd model, the viscoelastic linear dispersion relation was introduced into the primary atomization; an extended viscoelastic version of Taylor analogy breakup (TAB) model was proposed; and the coalescence criteria was modified by rheological parameters, such as the relaxation time, the retardation time and the zero shear viscosity. The predicted results are validated with experimental data varying air-liquid mass flow ratio (ALR). Then, numerical calculations are conducted to investigate the characteristics of viscoelastic liquid atomization process. Results showed that the evolutionary trend of droplet mean diameter, Weber number and Ohnesorge number of viscoelastic liquids along with axial direction were qualitatively similar to that of Newtonian liquid. However, the mean size of polymer solution increased more gently than that of water at the downstream of the spray, which was beneficial to stable control of the desirable size in the applications. As concerned the effects of liquid physical properties, the surface tension played an important role in the primary atomization, which indicated the benefit of selecting the solvents with lower surface tension for finer atomization effects, while, for the evolution of atomization spray, larger relaxation time and zero shear viscosity increased droplet Sauter mean diameter (SMD) significantly. The zero shear viscosity was effective throughout the jet region, while the effect of relaxation time became weaken at the downstream of the spray field.

Investigation of mass transfer intensification under power ultrasound irradiation using 3D computational simulation: A comparative analysis

This paper aims at investigating the influence of acoustic streaming induced by low-frequency (24kHz) ultrasound irradiation on mass transfer in a two-phase system. The main objective is to discuss the possible mass transfer improvements under ultrasound irradiation. Three analyses were conducted: i) experimental analysis of mass transfer under ultrasound irradiation; ii) comparative analysis between the results of the ultrasound assisted mass transfer with that obtained from mechanically stirring; and iii) computational analysis of the systems using 3D CFD simulation. In the experimental part, the interactive effects of liquid rheological properties, ultrasound power and superficial gas velocity on mass transfer were investigated in two different sonicators. The results were then compared with that of mechanical stirring. In the computational part, the results were illustrated as a function of acoustic streaming behaviour, fluid flow pattern, gas/liquid volume fraction and turbulence in the two-phase system and finally the mass transfer coefficient was specified. It was found that additional turbulence created by ultrasound played the most important role on intensifying the mass transfer phenomena compared to that in stirred vessel. Furthermore, long residence time which depends on geometrical parameters is another key for mass transfer. The results obtained in the present study would help researchers understand the role of ultrasound as an energy source and acoustic streaming as one of the most important of ultrasound waves on intensifying gas-liquid mass transfer in a two-phase system and can be a breakthrough in the design procedure as no similar studies were found in the existing literature.

Gaseous bubble oscillations in anisotropic non-Newtonian fluids under influence of high-frequency acoustic field

Progress of technology and medicine dictates the ever-increasing requirements (heat resistance, corrosion resistance, strength properties, impregnating ability, etc.) for non-Newtonian fluids and materials produced on their basis (epoxy resin, coating materials, liquid crystals, etc.). Materials with improved properties obtaining is possible by modification of their physicochemical structure. One of the most promising approaches to the restructuring of non-Newtonian fluids is cavitation generated by high-frequency acoustic vibrations. The efficiency of cavitation in non-Newtonian fluid is determined by dynamics of gaseous bubble. Today, bubble dynamics in isotropic non-Newtonian fluids, in which cavitation bubble shape remains spherical, is most full investigated, because the problem reduces to ordinary differential equation for spherical bubble radius. However, gaseous bubble in anisotropic fluids which are most wide kind of non-Newtonian fluids (due to orientation of macromolecules) deviates from spherical shape due to viscosity dependence on shear rate direction. Therefore, the paper presents the mathematical model of gaseous bubble dynamics in anisotropic non-Newtonian fluids. The model is based on general equations for anisotropic non-Newtonian fluid flow. The equations are solved by asymptotic decomposition of fluid flow parameters. It allowed evaluating bubble size and shape evolution depending on rheological properties of liquid and acoustic field characteristics.

Tribological properties of rice starch in liquid and semi-solid food model systems

This study investigated the tribological and rheological properties of liquid and semi-solid food model systems containing micro-granular rice starch. Native (uncooked) and gelatinized rice starch dispersions, o/w emulsions and emulsion-filled gelatin gels were studied as food model systems. Native rice starch particles behaved as active fillers and increased the gel modulus with increasing concentration. At low concentration, soft gelatinized rice starch particles decreased gel modulus. At high concentration, gelatinized rice starch increased the gel modulus due to dense packing of particles. Native and gelatinized rice starch increased friction coefficients with increasing concentration due to different mechanisms. Native rice starch particles increase friction probably due to their irregular shape and particle agglomerations (at high concentration) that indirectly increase surface roughness and asperity contacts. Gelatinized rice starch particles increase friction probably due to the stickiness of leached-out starch polymers. The presence of oil droplets in rice starch-o/w emulsions could reduce the friction caused by stickiness of gelatinized rice starch. The tribological behaviors of rice starch-emulsion-filled gels are more complex than liquids due to the bulk and breakdown properties of the gel matrix. We conclude that morphology and surface properties of the rice starch particles together with bulk and breakdown properties of matrices are the main factors determining the tribological properties of food model systems containing rice starch particles.

Registration of rheological properties of liquids by electromagnetic levitation

The presented paper is focused on possibilities of research of rheological properties of liquids with use of the device based on the principle of electromagnetic levitation. The device works on the principle of damping of the levitated body vibrations by the liquid. Levitation is ensured by feedback control of the magnetic field using an optical barrier. Vibrations are excited by controlled interruptions of electromagnetic field. Thanks to this principle it is possible to investigate the liquid of non-Newtonian character, as well as liquids susceptible to clinging on spindles of rotational viscometers. The equipment was calibrated using silicate oil standards and its performance was compared with commercially used models of viscometers Anton Paar FRS1600 (viscosity range 3 mPa s–20 Pa s, precision 0.5%, temperature range 300–1600°C) and Brookfield DV-III Ultra (viscosity range 1.4 mPa s–20 Pa s, precision 1%, temperature range 100–1600°C).

Rheological Properties of Liquid and Particle Stabilized Foam

In Earth-Pressure-Balance (EPB) tunnelling the excavated ground is used as face support medium to prevent surface settlements. In general, the excavated ground (e.g. for cohesionless soils) does not exhibit suitable conditions to support the tunnelling face. This technical challenge can be solved by adding conditioning agents that are mainly foams. In order to physically understand the rheological properties of the (added) liquid foam and the foam-soil (foam-particle) mixture and to comprehend its influence on the soil, advanced rheological investigations are necessary. Therefore, rheological experiments such as flow curve tests have been performed to determine the effective yield stress. Since the morphology, i.e. the microstructure of the foam accounts for effective rheological properties, size, shape and distribution of the cells of the foam and particle-laden foam were characterized in detail applying imaging techniques. In order to perform the above mentioned experiments, polymer- stabilised shaving foam seems to be a good replacement of tunnelling foam and suitable for laboratory tests due to its time stability, characteristic length scales of the microstructure and accessibility. Glass beads (of different diameter and volume fractions, i.e. specific surface areas) are used to investigate the effective material behaviour of foam-particle mixtures. The experimental results are compared with yield stress models of modified Herschel-Bulkley- Papanastasiou type.

Analysis of the Rheological Behaviour of Selected Semi-Solid Slag Systems in Blast Furnace Flow Conditions

Abstract The rheological properties of liquid and semi-solid systems of slag and hot metal in a blast furnace are extremely important from the perspective of their dripping in the unit. The rheological nature and the values of the dynamic viscosity coefficient of liquid and semi-solid phases - slag and hot metal - determine the permeability of the zones in which those systems exist. The modelling of dripping processes and e.g. static and dynamic holding/retention of liquid in the bed, requires an accurate description of the rheological behaviour of slag and iron systems. Determining the liquid flow through the lump bed of the blast furnace is based on the assumption that liquids in the unit in the whole range of their occurrence are similar to a Newtonian ideal liquid. This study presents an analysis of the findings of high-temperature rheometric measurements of CaO-SiO2-Al2O3-MgO systems, liquid, semi-solid slags of the blast furnace type doped with TiO2 and solids in the form of TiN. The tests were performed within a temperature range of 1310-1490°C. Also measurement results for glycerol solutions with concentrations of 86% and 100% at the ambient temperature, simulating blast furnace slags with various contents of solids - PC, anthracite - are presented.

Driving modes and material stability of a double membrane rheometer and density sensor

Abstract. This contribution presents the analysis of an earlier proposed double membrane sensor for measuring mass density and rheological properties of liquids with respect to different driving modes. Concerning practical implementation the sensor mounting and the stability of the polyethylene foil, currently used as membrane material, are investigated. The sensor is based on two opposed membranes vibrating in parallel where a sample liquid is enclosed between the membranes. The excitation and read-out mechanisms of the membrane vibration are based on Lorentz forces induced in a static magnetic field. Each membrane carries three conductive paths for excitation, which can be separately connected to the excitation currents. This allows the excitation of the first and second modes of vibration and enables prestressing the second mode of oscillation. Analyzing the material-stability of the used polyethylene foil shows a strong long-term drift of the modulus of elasticity and an increase of internal damping with increasing temperature. Comparing the resonance frequency of the fundamental mode with earlier measurements achieved with the second mode of resonance indicates an increased sensitivity to density featuring a reasonably sustained quality factor for high viscosities. Thereby, the sensitivity can be adjusted by varying the distance between the membranes.

The effect of extensional viscosity on the effervescent atomization of polyacrylamide solutions

The paper contains the results of experimental investigation of the rheological characteristics and atomization process of solutions of polymer. The solutions had the polyacrylamide (PAA) mass fraction in the range from 0.0025 to 0.001. The solutions of polymer have non-Newtonian characteristics. It has been shown that shear viscosity increases with polymer concentration in the solutions. Extensional viscosity increases with increasing extensional rates. The Trouton ratio for glycerol solution is about 5.4. The Trouton ratios observed for the polymer solutions increase with increasing shear (extensional) rate and polymer concentration in solution.This paper draws a link between the extensional viscosity and the effervescent atomization. The polymer addition to cause the solution viscosity to increase, thereby different disintegration of liquid could be obtained. During two-phase atomization process of polymer solutions the characteristic stages in spray development have been observed. The phenomenon of the formation of “beads on a string” for solutions with low concentrations of polymer has been observed. The thin filament between droplets and/or bubbles was observed for all polymer solutions studied. Analysis of photos on forming the droplets showed that droplets diameter increases with increasing of polymer concentration. In all two-phase systems studied the Sauter mean diameter decreases with increase of gas to liquid flow rates ratio value. Sauter mean diameter is dependent on gas and liquid flow rates and the liquid properties. It is particularly important in processes in which the value of the average droplet diameter plays a key role.High molecular polymers added to a solvent involve the changes in the rheological properties of liquid and the disintegration of liquid jets and/or sheets. The effect of extensional viscosity on the droplets formation has been shown. The data obtained in the present study have shown that the decreasing of the extensional viscosity of the solution will reduce the spray's Sauter mean diameter. The results may be used, for example, to verify numerical models or in comparison with similar atomization processes.

The Experimental Analysis of the Polyacrylamide Solutions Effervescent Atomization

Abstract The paper contains the results of experimental investigation of the rheological characteristics and atomization process of polymer solutions. The solutions had the polyacrylamide mass fraction in the range from 0.0025 to 0.001. The solutions of polymer have non-Newtonian characteristics. It has been shown that viscosity increases with increasing of polymer concentration in the solutions. Extensional viscosity increases with increasing of extensional rates. The Trouton ratios observed for the polymer solutions increase with increasing shear (extensional) rate and polymer concentration in solution. High molecular polymers added to a solvent involve the changes in the rheological properties of liquid and the disintegration of liquid jets and/or sheets. The effect of extensional viscosity on the droplets formation has been shown. The data obtained in the present study have shown that the decreasing of the extensional viscosity of the solution will reduce the spray's droplets sizes. The results may be used for example to verify numerical models or comparisons with respect to similar atomization processes.

Studies on Minimum Fluidization Velocity and Liquid Hold in an Internal Loop Airlift Fluidized Bed Reactor

The influence of superficial gas and liquid velocities, particle diameter and sphericity, physical and rheological properties of liquids on minimum fluidization velocity and liquid holdup were studied in an internal loop airlift fluidized bed reactor. Spheres, Bearl saddles and Raschig rings were used as solid phases. Water, n-Butanol, two concentrations of Glycerol (60 and 80%) were used as Newtonian liquids and three concentrations (0.25%, 0.6% and 1.0%) of Carboxy Methyl Cellulose (CMC) solutions were used as non-Newtonian liquids. Superficial gas velocity was varied from 0.142 x 10-3 m/s to 5.662 x 10-3 m/s and superficial liquid velocity was varied from 0.001 to 0.12 m/s. The experimental results showed that increase in particle size and sphericity increased minimum fluidization velocity whereas increase in superficial gas velocity decreased minimum fluidization velocity. The liquid holdup increased with increase in particle size and superficial liquid velocity. An increase in superficial gas velocity decreased the liquid holdup for Newtonian and non-Newtonian systems. Based on the experimental results separate correlations were developed for the prediction of minimum fluidization velocity and liquid holdup for both Newtonian and non-Newtonian liquids for a wide range of operating conditions.