Drag of Tandem Spheroids in Power-Law Fluids at Moderate Reynolds Numbers

2013 ◽  
Vol 52 (33) ◽  
pp. 11773-11778 ◽  
Author(s):  
A. S. Rathore ◽  
P. Chaitanya ◽  
Nanda Kishore
Keyword(s):  
Power Law ◽  
Reynolds Numbers ◽  
Power Law Fluids

Friction Coefficients for Bingham and Power-Law Fluids in Abrupt Contractions and Expansions

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Sergio L. D. Kfuri ◽  
Edson J. Soares ◽  
Roney L. Thompson ◽  
Renato N. Siqueira
Keyword(s):  
Reynolds Number ◽  
Yield Stress ◽  
Power Law ◽  
Reynolds Numbers ◽  
Newtonian Fluids ◽  
Rheological Parameters ◽  
Friction Coefficients ◽  
K Value ◽  
Power Law Fluids ◽  
Pipeline Systems

Industrial processes with non-Newtonian fluids are common in many segments such as petroleum, cosmetic, and food industries. Slurries, emulsions, and gas–liquid dispersions are some examples with industrial relevance. When a fluid flows in a pipe system, pressure losses are always present. For Newtonian fluids, a quite reasonable understanding of this phenomenon was already achieved and is available in the literature. The same cannot be stated for non-Newtonian fluids owing to their complex characteristics, such as pseudoplasticity, viscoplasticity, elasticity, and thixotropy. The understanding of the influence of these characteristics on flow behavior is very important in order to design efficient pipeline systems. The design of such systems requires the estimation of the pressure drop due to friction effects. However, there are few works regarding friction losses for non-Newtonian fluids in pipeline systems, making this task a difficult one. In this study, two classes of fluids are investigated and compared with the Newtonian results. The first category of fluids are the ones that exhibits pseudoplastic behavior and can be modeled as a power-law fluid, and the second category are the ones that possesses a yield stress and can be modeled as a Bingham fluid. Polyflow was used to compute the friction losses in both abrupt contractions and expansions laminar flow conditions. It shows that for the expansion cases, the aspect ratio affects more the local friction coefficients than for the contraction cases. The influence of the power index n on local friction losses is similar for both cases, abrupt contractions and abrupt expansions. At low Reynolds numbers, dilatant fluids present the lowest values of the friction coefficient, K, independent of geometry. At high Reynolds numbers, a reversal of the curves occurs, and the dilatant fluid presents larger values of K coefficient. For the cases investigated, there is also a Reynolds number in which all the curves exhibit the same value of K for any value of the power-law index. The effect of τy′ shows a different behavior between contractions and expansions. In the case of contractions, the material with the highest dimensionless yield stress has the highest K value. In the case of the expansions, the behavior is the opposite, i.e., the higher the yield stress, the lower is the values of the K coefficient. Equations for each accessory as a function of the rheological parameters of the fluid and the Reynolds number of the flow are also proposed. The data were adjusted according to two main equations: the two Ks method proposed by Hooper (1981, “The Two-K Method Predicts Head Losses in Pipe Fittings,” Chem. Eng., 81, pp. 96–100.) is used for all the contractions cases, and the equation proposed by Oliveira et al. (1997, “A General Correlation for the Local Coefficient in Newtonian Axisymmetric Sudden Expansions,” Int. J. Heat Fluid Flow, 19(6), pp. 655–660.) is used for all the expansions cases. The equations found were compared with the numerical results and showed satisfactory precision and thus can be used for engineering applications.

Drag of a Spherical Bubble Rising in Power Law Fluids at Intermediate Reynolds Numbers

2007 ◽  
Vol 46 (3) ◽  
pp. 939-946 ◽  
Author(s):  
Sunil D. Dhole ◽  
Rajendra P. Chhabra ◽  
Vinayak Eswaran
Keyword(s):  
Power Law ◽  
Reynolds Numbers ◽  
Spherical Bubble ◽  
Power Law Fluids ◽  
Bubble Rising

Flow of Power-Law Fluids Past a Sphere at Intermediate Reynolds Numbers

2006 ◽  
Vol 45 (13) ◽  
pp. 4773-4781 ◽  
Author(s):  
Sunil D. Dhole ◽  
Raj P. Chhabra ◽  
Vinayak Eswaran
Keyword(s):  
Power Law ◽  
Reynolds Numbers ◽  
Power Law Fluids

scholarly journals High mixing performances of shear-thinning fluids in two-layer crossing channels micromixer at very low Reynolds numbers

2019 ◽  
Vol 13 (4) ◽  
pp. 5938-5960
Author(s):  
A. Kouadri ◽  
Y. Lasbet ◽  
M. Makhlouf
Keyword(s):  
Reynolds Number ◽  
Power Law ◽  
Transport Model ◽  
Tangential Velocity ◽  
Reynolds Numbers ◽  
Mixing Efficiency ◽  
Species Transport ◽  
Industrial Sectors ◽  
Power Law Fluids ◽  
Power Law Index

In a recent study, the Two-Layer Crossing Channels Micromixer (TLCCM) exhibited good mixing capacities in the case of the Newtonian fluids (close to 100%) for all considered Reynolds number values. However, since the majority of the used fluids in the industrial sectors are non-Newtonians, this work details the mixing evolution of power-law fluids in the considered geometry. In this paper, the power-law index ranges from 0.73 to 1 and the generalized Reynolds number is bounded between 0.1 and 50. The conservation equations of momentum, mass and species transport are numerically solved using a CFD code, considering the species transport model. The flow structure at the cross-sectional planes of our micromixer was studied using the dynamic systems theory. The evolutions of the intensity, also the axial, radial and tangential velocity profiles were examined for different values of the Reynolds number and the power-law index. Besides, the pressure drop of the power-law fluids under different Reynolds number was calculated and represented. Furthermore, the mixing efficiency is evaluated by the computation of the mixing index (MI), based on the standard deviation of the mass fraction in different cross-sections. In such geometry, a perfect mixing is achieved with MI closed to 99.47 %, at very small Reynolds number (from the value 0.1) whatever the power-law index and generalized Reynolds numbers taken in this investigation. Consequently, the targeted channel presents a useful tool for pertinent mass transfer improvements, it is highly recommended to include it in various microfluidic systems.

Two Dimensional Unsteady Laminar Flow of Power Law Fluids Past a Square Cylinder: A Numerical Study

2008 ◽  
Author(s):  
Akhilesh K. Sahu ◽  
Raj P. Chhabra ◽  
V. Eswaran
Keyword(s):  
Reynolds Number ◽  
Power Law ◽  
Shear Thickening ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Shear Thinning ◽  
Shear Thinning Fluids ◽  
Power Law Fluids ◽  
Shear Thickening Fluids ◽  
Edge Separation

The two-dimensional and unsteady flow of power-law fluids past a long square cylinder has been investigated numerically in the range of conditions 60 ≤ Re ≤ 160 and 0.5 ≤ n ≤ 2.0. Over this range of Reynolds numbers, the flow is periodic in time for Newtonian fluids. However, no such information is available for power law fluids. A semi-explicit finite volume method has been used on a non-uniform collocated grid arrangement to solve the governing equations. The macroscopic quantities such as drag coefficients, Strouhal number, lift coefficient as well as the detailed kinematic variables like stream function, vorticity and so on, have been calculated as functions of the pertinent dimension-less groups. In particular, the effects of Reynolds number and of the power-law index have been investigated in the unsteady laminar flow regime. The leading edge separation in shear-thinning fluids produces an increase in drag values with the increasing Reynolds number, while shear-thickening behaviour delays the leading edge separation. So, the drag coefficient in the above-mentioned range of Reynolds number, Re, in shear-thinning fluids (n < 1) initially decreases but at high values of the Reynolds number, it increases. As expected, on the other hand, in case of shear-thickening fluids (n > 1) drag coefficient reduces with Reynolds number, Re. Furthermore, the present results also suggest the transition from steady to unsteady flow conditions to occur at lower Reynolds numbers in shear-thickening fluids than that in Newtonian fluids. Also, the spectra of lift signal for shear-thickening fluids show that the flow is truly periodic in nature with a single dominant frequency in the above range of Reynolds number. In shear-thinning fluids at higher Re, quasi-periodicity sets in with additional frequencies, which indicate the transition from the 2-D to 3-D flows.

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