• Korea-Australia Rheology Journal
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• v.21 no.4
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• pp.269-280
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• 2009

The drop formation dynamics of a shear thinning, elastic, yield stress ($\tau_o$) fluid (Carbopol 980 (poly(acrylic acid)) dispersions) in silicone oil has been investigated in a flow-focusing microfluidic channel. The rheological character of each solution investigated varied from Netwonian-like through to highly non-Newtonian and was varied by changing the degree of neutralization along the poly (acrylic acid) backbone. We have observed that the drop size of these non-Newtonian fluids (regardless of the degree of neutralisation) showed bimodal behaviour. At first we observed increases in drop size with increasing viscosity ratio (viscosity ratio=viscosity of dispersed phase (DP)/viscosity of continuous phase (CP)) at low flowrates of the continuous phases, and thereafter, decreasing drop sizes as the flow rate of the CP increases past a critical value. Only at the onset of pinching and during the high extensional deformation during pinch-off of a drop are any differences in the non-Newtonian characteristics of these fluids, that is extents of shear thinning, elasticity and yield stress ($\tau_o$), apparent. Changes in these break-off dynamics resulted in the observed differences in the number and size distribution of secondary drops during pinch-off for both fluid classes, Newtonian-like and non-Newtonian fluids. In the case of the Newtonian-like drops, a secondary drop was generated by the onset of necking and breakup at both ends of the filament, akin to end-pinching behavior. This pinch-off behavior was observed to be unaffected by changes in viscosity ratio, over the range explored. Meanwhile, in the case of the non-Newtonian solutions, discrete differences in behaviour were observed, believed to be attributable to each of the non-Newtonian properties of shear thinning, elasticity and yield stress. The presence of a yield stress ($\tau_o$), when coupled with slow flow rates or low viscosities of the CP, reduced the drop size compared to the Newtonian-like Carbopol dispersions of much lower viscosity. The presence of shear thinning resulted in a rapid necking event post onset, a decrease in primary droplet size and, in some cases, an increase in the rate of drop production. The presence of elasticity during the extensional flow imposed by the necking event allowed for the extended maintenance of the filament, as observed previously for dilute solutions of linear polymers during drop break-up.

• Korea-Australia Rheology Journal
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• v.21 no.4
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• pp.225-233
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• 2009

In various attempts to relate the behaviour of highly-elastic liquids in complex flows to their rheometrical behaviour, obvious candidates for study have been the variation of shear viscosity with shear rate, the two normal stress differences $N_1$ and $N_2$, especially $N_1$, and the extensional viscosity $\eta_E$. In this paper, we shall be mainly interested in 'constant-viscosity' Boger fluids, and, accordingly, we shall limit attention to $N_1$ and $\eta_E$. We shall concentrate on two important flows - axisymmetric contraction flow and "splashing" (particularly that which arises when a liquid drop falls onto the tree surface of the same liquid). Modern numerical techniques are employed to provide the theoretical predictions. It is shown that the two obvious manifestations of viscoelastic rheometrical behaviour can sometimes be opposing influences in determining flow characteristics. Specifically, in an axisymmetric contraction flow, high $\eta_E$ can retard the flow, whereas high $N_1$ can have the opposite effect. In the splashing experiment, high $\eta_E$ can certainly reduce the height of the so-called Worthington jet, thus confirming some early suggestions, but, again, other rheometrical influences can also have a role to play and the overall picture may not be as clear as it was once envisaged.

• Smart Structures and Systems
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• v.16 no.5
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• pp.961-980
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• 2015

Magnetorheological (MR) fluids are capable of changing their rheological properties under the application of external fields. When MR fluids operate in the so-called squeeze mode, in which displacement levels are limited to a few millimetres but there are large forces, they have many potential applications in vibration isolation. This paper presents an experimental and a numerical investigation of the performance of an MR fluid under tensile and compressive loads and oscillatory squeeze-flow. The performance of the fluid was found to depend dramatically on the strain direction. The shape of the stress-strain hysteresis loops was affected by the strength of the applied field, particularly when the fluid was under tensile loading. In addition, the yield force of the fluid under the oscillatory squeeze-flow mode changed almost linearly with the applied electric or magnetic field. Finally, in order to shed further light on the mechanism of the MR fluid under squeeze operation, computational fluid dynamics analyses of non-Newtonian fluid behaviour using the Bingham-plastic model were carried out. The results confirmed superior fluid performance under compressive inputs.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.196-201
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• 2001

In this paper, we have described the microchannel fluid behavior in a slot between rotating curvilinear surfaces of revolution using micropolar fluid theory. ]n order to solve this problem, we have used boundary layer equations and applied non-zero values of the microrotation vector on the wall. The results are compared with the corresponding flow problems for Newtonian fluid. Results show that both the velocity distribution and the microrotation component distribution for a micropolar fluid are lower than that of a Newtonian fluid.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.465-470
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• 2006

An experimental investigation is carried out to study 2-phase vertically upward hydraulic transport of solid particles by water and non-Newtonian fluids in a slim hole concentric annulus with rotation of the inner cylinder. Rheology of particulate suspensions in viscoelastic fluids is of importance in many applications such as particle removal from surfaces, transport of proppants in fractured reservoir and cleaning of drilling holes, etc. In this study a clear acrylic pipe was used in order to observe the movement of solid particles. Annular fluid velocities varied from 0.2 m/s to 3.0 m/s. Pressure drops and average flow rate and particle rising velocity are measured. For both water and 0.2% CMC solutions, the higher the concentration of the solid particles is, the larger the pressure gradients become.

• Korea-Australia Rheology Journal
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• v.12 no.1
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• pp.27-38
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• 2000

• 한국전산유체공학회:학술대회논문집
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• 1999.05a
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• pp.192-198
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• 1999

The present study proposes modified temperature-dependent non-Newtonian viscosity model and investigates flow characters and heat transfer enhancement of the viscoelastic non-Newtonian fluid in a 2:1 rectangular duct. The proposed modified temperature dependent viscosity model has non-zero value near the high temperature and high shear rate region while on the existing viscosity models have zero value. Two versions of thermal boundary conditions involving difference combination of heated walls and adiabatic walls are analyzed in this study. The combined effect of temperature dependent viscosity, buoyancy, and secondary flow caused by second normal stress difference are ail considered. The Reiner-Rivlin model is adopted as a viscoelastic fluid model to simulate the secondary flow caused by second normal stress difference. Calculated Nusselt numbers by the modified temperature-dependent viscosity model gives under prediction than the existing temperature-dependent viscosity model in the regions of thermally developed with same secondary normal stress difference coefficients with experimental results in the regions of thermally developed. The heat transfer enhancement of the viscoelastic fluid in a 2:1 rectangular duct is highly dependent on the secondary flow caused by the magnitude of second normal stress difference.

• 제어로봇시스템학회:학술대회논문집
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• 1997.10a
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• pp.1754-1757
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• 1997

Three-dimensional optimum design of coat-hanger die is performed using power-law and Carreau models. It is found that the three-dimensional optimum design algorithm shows good convergence with the non-Newtonian fludis. the nore realistic optimum design is accomplished by employing Carreau model with the three-dimensional design method. The effect of vixcosity modles is investigated by comparing the optimum manifold profiles and flow rate distributions of power-law and Carreau modles. Through the accurated viscosity representation of Carreau model, the effect of total flow rate on the optimum manifold profile is investigated.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.5
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• pp.1717-1724
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• 1996

The present study investigates the effect of the shear rate-dependent thermal conductivity of non-Newtonian fluids on the heat transfer enhancement in a pipe flow. An axially-constant heat flux boundary condition was adopted in the thermal fully developed region. The present analytical results of Nusselt numbers for various non-Newtonian fluids show heat transfer enhancement over those of a shear rate-independent thermal conductivity fluids. The present analytical results showed good agreement with the previous experiments which excluded the temperature-dependent viscosity effect on heat transfer. This study also proposes the use of a shear rate-dependent thermal conductivity fluids in the design of a heat exchanger for heat transfer enhancement as well as reduction of fouling.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.16 no.3
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• pp.181-192
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• 2012

Here in this paper, the steady paint film flow on a vertical wall of a non-Newtonian pseudo plastic fluid for drainage problem has been investigated. The exact solution of the nonlinear problem is obtained for the velocity profile. Also the average velocity, volume flux, shear stress on the wall, force to hold the wall in position and normal stress difference have been derived. We retrieve Newtonian case, when material constant ${\mu}_1$ and relaxation time ${\lambda}_1$ equal zero. The results for co-rotational Maxwell fluid is also obtained by taking material constant ${\mu}_1$ = 0. The effect of the zero shear viscosity ${\eta}_0$, the material constant ${\mu}_1$, the relaxation time ${\lambda}_1$ and gravitational force on the velocity profile for drainage problem are discussed and plotted.