Numerical Simulation of the Effect of Rheological Parameters on Shear-Thinning Droplet Formation

2014 ◽  
Author(s):  
Voon-Loong Wong ◽  
Katerina Loizou ◽  
Phei-Li Lau ◽  
Richard S. Graham ◽  
Buddhika N. Hewakandamby
Keyword(s):  
Relaxation Time ◽  
Steady State ◽  
Shear Rate ◽  
Level Set ◽  
Droplet Diameter ◽  
Shear Thinning ◽  
Droplet Formation ◽  
Droplet Breakup ◽  
Rheological Parameters ◽  
Characteristic Relaxation Time

Immiscible non-Newtonian-Newtonian fluid systems in microfluidics constitute an essential study as non-Newtonian fluids consistently met in medical and biological systems. Although a large number of experimental investigations have been reported in this area, attempts to develop predictive models appear to be limited. This paper is an attempt to incorporate a non-Newtonian stress model together with front-tracking scheme used in computational fluid dynamics. A conservative two-phase level set method (LSM) was applied for capturing the droplet breakup dynamics and relevant hydrodynamics of shear-thinning carboxymethylcellulose (CMC) droplets. Our droplets comprise of 0.02wt% to 1.2wt% CMC solutions in a Newtonian continuous fluids system (olive oil) employed in a T-shaped microfluidic cell. A Carreau-Yasuda viscosity model for shear-thinning CMC droplets has been implemented. This shear-dependent constitutive model fitted well to our steady state non-linear shear measurements for polymeric CMC solutions, with asymptotic viscosities at zero and infinite shear rates, and with different degrees of shear thinning (η0/η∞) in steady state. The particular focus of this study was to systematically undergo parametric studies on the influence of rheological parameters of the specified model such as zero (η0) and infinite shear viscosity (η∞), and relaxation time (λ) on the droplet formation processes. The level set simulation predicted that the droplet diameter increases with increasing η0/η∞. The effect of η0/η∞ has been found to have more prominent impact on droplet diameter for higher CMC concentrations. The variation in droplet diameter becomes less significant at the higher degrees of shear-thinning for all concentrations of CMC dispersed solutions. In the limit of zero shear-thinning effect, the droplet diameter increases when the dispersed phase viscosity decreases. Additionally, the effect of λ on the droplet diameter is also discussed. The reciprocal of the characteristic relaxation time (1/λ) corresponds to a critical shear rate that indicates the onset shear rate for shear-thinning. As λ increases, the numerical studies clearly reveal that the droplet diameter is increasing until it reaches a plateau for larger values of λ. The influence of λ leads to a more significant impact on droplet diameter for higher CMC concentration. These findings will ultimately help in understanding the sensitivity of rheological parameters to the microdroplet formation.

Analysis of Flow of Shear Thinning Colloidal and Polymeric Systems Which Exhibit Elastic Recovery or Rigidity

1967 ◽  
Vol 40 (5) ◽  
pp. 1505-1515
Author(s):  
T. Gillespie
Keyword(s):  
Experimental Data ◽  
Relaxation Time ◽  
Shear Rate ◽  
Elastic Recovery ◽  
Relaxation Times ◽  
Shear Thinning ◽  
Structural Theory ◽  
Polymeric Systems ◽  
New Equation

Abstract The hydrodynamic-structural theory of viscosity is extended to take into account the possibility of a distribution of relaxation times. A new equation is presented which is easily applied to experimental data. The effect of a distribution of lifetimes is to extend the range of shear rate over which shear thinning occurs. When the ratio of the largest relaxation time to the smallest relaxation time is greater than 1 but less than 10 the new equation gives results in agreement with the Willamson equation. When this ratio of maximum relaxation time to minimum relaxation time is 300 ± 100 the new equation agrees with an equation recently suggested by Cross. The utility of the new equation is discussed and is illustrated by using it to determine the relaxation time spectra in polystyrene melts.

scholarly journals Non-Newtonian Droplet Generation in a Cross-Junction Microfluidic Channel

Polymers ◽  
2021 ◽  
Vol 13 (12) ◽  
pp. 1915
Author(s):  
Maryam Fatehifar ◽  
Alistair Revell ◽  
Masoud Jabbari
Keyword(s):  
Droplet Size ◽  
Power Law ◽  
Microfluidic Channel ◽  
Shear Thinning ◽  
Droplet Formation ◽  
Considerable Effect ◽  
Droplet Generation ◽  
Rheological Parameters ◽  
Polymeric Solutions ◽  
Detachment Time

A two-dimensional CFD model based on volume-of-fluid (VOF) is introduced to examine droplet generation in a cross-junction microfluidic using an open-source software, OpenFOAM together with an interFoam solver. Non-Newtonian power-law droplets in Newtonian liquid is numerically studied and its effect on droplet size and detachment time in three different regimes, i.e., squeezing, dripping and jetting, are investigated. To understand the droplet formation mechanism, the shear-thinning behaviour was enhanced by increasing the polymer concentrations in the dispersed phase. It is observed that by choosing a shear-dependent fluid, droplet size decreases compared to Newtonian fluids while detachment time increases due to higher apparent viscosity. Moreover, the rheological parameters—n and K in the power-law model—impose a considerable effect on the droplet size and detachment time, especially in the dripping and jetting regimes. Those parameters also have the potential to change the formation regime if the capillary number (Ca) is high enough. This work extends the understanding of non-Newtonian droplet formation in microfluidics to control the droplet characteristics in applications involving shear-thinning polymeric solutions.

scholarly journals Characteristic of selected rheological parameters of stallion ejaculate

2008 ◽  
Vol 51 (1) ◽  
pp. 16-22
Author(s):  
L. Severa ◽  
L. Máchal ◽  
I. Křivánek ◽  
M. Machatková ◽  
O. Mamica
Keyword(s):  
Shear Rate ◽  
Dynamic Viscosity ◽  
Sperm Concentration ◽  
Shear Thinning ◽  
Experimental Series ◽  
Time Dependent ◽  
Rheological Parameters ◽  
Average Value

Abstract. Dynamic viscosity of native (30 minutes after ejaculation) and 24 hours stored (at 4 °C) stallion ejaculate was measured. The ejaculate from 10 breeding stallions was examined in three different experimental series. The average value of dynamic viscosity at shear rate 1.02 s−1 was found to be 416.8 ± 10.1 mPa.s. The correlation between ejaculate volume, sperm concentration and viscosity was tested. The experiments resulted in finding a dependence between increasing viscosity and decreasing sperm concentration (rp = −0.67; P<0.05). Performed experiments with changing shear rate demonstrated non-Newtonian characteristics of stallion ejaculate with a clear shear-thinning behaviour. Stallion ejaculate appeared to be slightly time-dependent liquid.

The Characterization of the Stability of Gel Ink by Rheological Method

2013 ◽  
Vol 816-817 ◽  
pp. 660-664
Author(s):  
Wang Zhao Yao ◽  
Wei Chao Wang ◽  
Ai Ping Chen ◽  
Hui Shen ◽  
Hong Fei Hao ◽  
...  
Keyword(s):  
Steady State ◽  
Shear Rate ◽  
Dynamic Stress ◽  
Experimental Methods ◽  
Rheological Parameters ◽  
Time Scanning ◽  
Rheological Method ◽  
The Stability ◽  
Dynamic Time

The rheological performance of gel ink was investigated by the experimental methods of steady-state shear rate scanning, dynamic stress scanning and dynamic time scanning. The results show that some rheological parameters (such asn,K,τ0, and ect.) can be used to characterize the stability of gel ink.

scholarly journals Numerical studies of shear-thinning droplet formation in a microfluidic T-junction using two-phase level-SET method

2017 ◽  
Vol 174 ◽  
pp. 157-173 ◽  
Author(s):  
Voon-Loong Wong ◽  
Katerina Loizou ◽  
Phei-Li Lau ◽  
Richard S. Graham ◽  
Buddhika N. Hewakandamby
Keyword(s):  
Level Set Method ◽  
Level Set ◽  
Shear Thinning ◽  
Droplet Formation ◽  
Two Phase ◽  
Numerical Studies

scholarly journals Generation and Dynamics of Janus Droplets in Shear-Thinning Fluid Flow in a Double Y-Type Microchannel

Micromachines ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 149
Author(s):  
Fan Bai ◽  
Hongna Zhang ◽  
Xiaobin Li ◽  
Fengchen Li ◽  
Sang Woo Joo
Keyword(s):  
Surface Tension ◽  
Formation Mechanism ◽  
Computational Study ◽  
Shear Thinning ◽  
Droplet Formation ◽  
Continuous Phase ◽  
Viscous Force ◽  
Rheological Parameters ◽  
Janus Droplet ◽  
Shear Thinning Fluid

Droplets composed of two different materials, or Janus droplets, have diverse applications, including microfluidic digital laboratory systems, DNA chips, and self-assembly systems. A three-dimensional computational study of Janus droplet formation in a double Y-type microfluidic device filled with a shear-thinning fluid is performed by using the multiphaseInterDyMFoam solver of the OpenFOAM, based on a finite-volume method. The bi-phase volume-of-fluid method is adopted to track the interface with an adaptive dynamic mesh refinement for moving interfaces. The formation of Janus droplets in the shear-thinning fluid is characterized in five different states of tubbing, jetting, intermediate, dripping and unstable dripping in a multiphase microsystem under various flow conditions. The formation mechanism of Janus droplets is understood by analyzing the influencing factors, including the flow rates of the continuous phase and of the dispersed phase, surface tension, and non-Newtonian rheological parameters. Studies have found that the formation of the Janus droplets and their sizes are related to the flow rate at the inlet under low capillary numbers. The rheological parameters of shear-thinning fluid have a significant impact on the size of Janus droplets and their formation mechanism. As the apparent viscosity increases, the frequency of Janus droplet formation increases, while the droplet volume decreases. Compared with Newtonian fluid, the Janus droplet is more readily generated in shear-thinning fluid due to the interlay of diminishing viscous force, surface tension, and pressure drop.

scholarly journals Droplet breakup driven by shear thinning solutions in a microfluidic T-junction

2017 ◽  
Vol 2 (12) ◽  
Author(s):  
Enrico Chiarello ◽  
Anupam Gupta ◽  
Giampaolo Mistura ◽  
Mauro Sbragaglia ◽  
Matteo Pierno
Keyword(s):  
Shear Thinning ◽  
Droplet Breakup

Investigation on the Rheological Behavior of Polyamide6/Montmorillonite Nanocomposites by Reactive Extrusion

2011 ◽  
Vol 233-235 ◽  
pp. 1998-2001 ◽  
Author(s):  
Ming Zhao ◽  
Xiao Zhong Lu ◽  
Kai Gu ◽  
Xiao Min Sun ◽  
Chang Qing Ji
Keyword(s):  
Activation Energy ◽  
Shear Stress ◽  
Shear Rate ◽  
Rheological Behavior ◽  
Reactive Extrusion ◽  
Shear Thinning ◽  
Experimental Results ◽  
Montmorillonite Nanocomposites

The rheological behavior of PA6/montmorillonite(MMT) by reactive extrusion was investigated using cone-and-plate rheometer. The experimental results indicated that PA6/MMT exhibited shear-thinning behavior. The shear stress of both neat PA6 and PA6/MMT increased with the increase in the shear rate. The reduction of the viscous activation energy with the increase of shear stress reflected PA6/MMT can be processed over a wider temperature.

Induced polarization and pore radius — A discussion

Geophysics ◽  
2016 ◽  
Vol 81 (5) ◽  
pp. D519-D526 ◽  
Author(s):  
Andreas Weller ◽  
Zeyu Zhang ◽  
Lee Slater ◽  
Sabine Kruschwitz ◽  
Matthias Halisch
Keyword(s):  
Diffusion Coefficient ◽  
Relaxation Time ◽  
Diffusion Coefficients ◽  
Pore Radius ◽  
Mercury Porosimetry ◽  
Induced Polarization ◽  
Reliable Estimate ◽  
Characteristic Relaxation Time ◽  
A Value ◽  
Apparent Diffusion

Permeability estimation from induced polarization (IP) measurements is based on a fundamental premise that the characteristic relaxation time [Formula: see text] is related to the effective hydraulic radius [Formula: see text] controlling fluid flow. The approach requires a reliable estimate of the diffusion coefficient of the ions in the electrical double layer. Others have assumed a value for the diffusion coefficient, or postulated different values for clay versus clay-free rocks. We have examined the link between a widely used single estimate of [Formula: see text] and [Formula: see text] for an extensive database of sandstone samples, in which mercury porosimetry data confirm that [Formula: see text] is reliably determined from a modification of the Hagen-Poiseuille equation assuming that the electrical tortuosity is equal to the hydraulic tortuosity. Our database does not support the existence of one or two distinct representative diffusion coefficients but instead demonstrates strong evidence for six orders of magnitude of variation in an apparent diffusion coefficient that is well-correlated with [Formula: see text] and the specific surface area per unit pore volume [Formula: see text]. Two scenarios can explain our findings: (1) the length scale defined by [Formula: see text] is not equal to [Formula: see text] and is likely much longer due to the control of pore-surface roughness or (2) the range of diffusion coefficients is large and likely determined by the relative proportions of the different minerals (e.g., silica and clays) making up the rock. In either case, the estimation of [Formula: see text] (and hence permeability) is inherently uncertain from a single characteristic IP relaxation time as considered in this study.

Enhancement lubricity properties of water-based mud with nanoparticles

2020 ◽  
pp. 70-74
Author(s):  
V.V. Guliyev ◽  
◽  
◽  
Keyword(s):  
Yield Point ◽  
Coefficient Of Friction ◽  
Drilling Fluid ◽  
Research Work ◽  
Shear Thinning ◽  
Rheological Parameters ◽  
Drilling Process ◽  
Drilling Mud ◽  
Pseudoplastic Fluid ◽  
Water Based

Currently, a great number of drilling fluids with different additives are used all over the world. Such additives are applied to control the properties of the drilling mud. The main purpose for controlling is to achieve more effective and safe drilling process. This research work aims to develop Water-Based Mud (WBM) with a Coefficient of Friction (CoF) as low as Oil-Based Mud (OBM) and better rheological properties. As it is known, produced CoF by WBM is higher than OBM, which means high friction between wellbore or casing and drill string. It was the reason for studying the effect of nanosilica on drilling fluid properties such as lubricity, rheological parameters and filtrate loss volume of drilling mud. The procedures were carried out following API RP 13B and API 13I standards. Five concentrations of nanosilica were selected to be tested. According to the results obtained, it was defined that adding nanosilica into the mud decreases CoF of basic WBM by 26 % and justifies nanosilica as a good lubricating agent for drilling fluid. The decreasing trend in coefficient of friction and plastic viscosity for nanosilica was obtained until the concentration of 0.1 %. This reduction is due to the shear thinning or pseudoplastic fluid behavior. After 0.1 %, an increase at PV value trend indicates that it does not follow shear thinning behavior and after reaching a certain amount of dissolved solids in the mud, it acts like normal drilling fluid. The yield point of the mud containing nanoparticles was higher than the basic one. Moreover, a growth in the concentration leads to an increase in yield point value. The improvement of this fluid system cleaning capacity via hydraulics modification and wellhole stability by filter cake endurance increase by adding nanosilica is shown as well. The average well construction data of “Neft Dashlary” field was used for the simulation studies conducted for the investigation of hydraulics parameters of reviewed fluids for all series of experiments. The test results were accepted reliable in case of at least 3 times repeatability.

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