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Author index ►Samer Alokaily, Kathleen Feigl, Franz X. Tanner, Erich J. Windhab

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Numerical Simulations of the Transport of Newtonian and Non-Newtonian Fluids via Peristaltic Motion

Appl. Rheol.28:3 (2018) 32832 (15 pages) ►

Two geometrical models are developed to simulate fluid transport via peristaltic motion in tubes of uniform or linearly decreasing radius: A 2-D axisymmetric tubular model and a 2-D axisymmetric conical model. In both models, peristaltic motion is induced by a traveling wave along the wall of the computational domain which deforms the wall and the computational mesh. These geometrical models are coupled with a finite volume solver from the open source software package OpenFOAM which is used to simulate the peristaltic flow for different Newtonian and non-Newtonian fluids in the laboratory (or Eulerian) frame of reference. After validation of the solver with experimental data, simulations are performed in each geometrical model to determine the influence of a given set of parameters on peristaltic flow behavior and transport efficiency. The parameters that are varied include the wave speed, relative occlusion, Newtonian viscosity, and power-law index for shear-thinning non- Newtonian fluids. For both computational models, the transport efficiency is found to increase strongly with relative occlusion, to decrease as the amount of shear-thinning increases, and to be independent of wave speed. In the tubular model, transport efficiency is found to be independent of Newtonian viscosity, while in the conical model, it decreases as viscosity decreases for Reynolds numbers greater than one.► Cite this publication as follows:

Alokaily S, Feigl K, Tanner FX, Windhab EJ: Numerical Simulations of the Transport of Newtonian and Non-Newtonian Fluids via Peristaltic Motion, Appl. Rheol. 28 (2018) 32832.

Simulations are performed to investigate the flow of a shear-thinning, non-Newtonian fluid in a collapsed elastic tube and comparisons are made with experimental data. The fluid is modeled by means of the Bird- Carreau viscosity law. The computational domain of the deformed tube is constructed from data obtained via computer tomography imaging. Comparison of the computed velocity fields with the ultrasound Doppler velocity profile measurements show good agreement, as does the adjusted pressure drop along the tube.s axis. Analysis of the shear rates show that the shear-thinning effect of the fluid becomes relevant in the crosssections with the biggest deformation. In fact, the maximum shear rate is about a factor of thirty larger than its corresponding maximum value in the undeformed tube, and the viscosity is reduced by a factor of two. The effect of the shear-thinning behavior has also been compared with identical simulations carried out for a Newtonian fluid.► Cite this publication as follows:

Tanner FX, Al-Habahbeh AA, Feigl KA, Nahar S, Jeelani SJA, Case WR, Windhab EJ: Numerical and Experimental Investigation of a Non-Newtonian Flow in a Collapsed Elastic Tube, Appl. Rheol. 22 (2012) 63910.

In-vitro small intestinal flow characteristics of a shear thinning fluid are investigated by transient '2-wave'-squeezing of an elastic tube under different speeds of peristalsis. Such peristaltic flow is the essential physiological transport mechanism in the gastro-intestinal tract. The peristalsis involves both expansion and contraction type of flow (crest and trough of a wavelength). We met the challenge of implementing the UVP technique for monitoring the velocity fields during appropriate peristaltic propulsion of a shear thinning fluid through an elastic tube (in vitro modeled small intestine). The higher wave speed of peristalsis results in higher magnitude of back flow velocity (negative) both in the wave crest and trough regions with positive value being adjacent to the tube wall. In addition, the approximated wall shear rates at the wave trough are also found to be higher than those in the wave crest. The higher value of back flow is expected to be responsible for the improved mixing and convection leading to higher mass transport through the intestinal wall. The measured pressure difference between crest and trough of a peristaltic wave increased, as the wave speed got faster. However, the crest region showed a higher pressure compared to the trough region since the magnitude of back flow velocity in the wave trough is found to be much higher compared to that in the wave crest.► Cite this publication as follows:

Nahar S, Jeelani SAK, Windhab EJ: Peristaltic flow characterization of a shear thinning fluid through an elastic tube by UVP, Appl. Rheol. 22 (2012) 43941.

The in-line rheometer concept based on the combination of the ultrasonic velocity profiling (UVP) technique and pressure difference (PD) measurements was utilized for investigating the influence of particle concentration and size distribution on the rheology of particulate suspensions in pipe flow under realistic industrial process conditions. Well defined model suspensions were used, consisting of 11 mm and 90 mm diameter polyamide particles suspended in rapeseed oil at concentrations ranging from 1 to 25 % by volume. The variation of concentration and particle size distribution had the expected effects on the shear viscositiy of the investigated unimodal and bimodal suspensions. The in-line results showed that the investigated suspensions exhibit Sisko flow behavior and demonstrated that the UVP+PD method can be used to determine the flow behavior of complex fluids and suspensions, even at high solid concentrations, under industrial conditions in-line. The obtained inline results were in good agreement with measurement data obtained using a conventional rotational controlled- stress rheometer. Limitations of commercially available transducer technology were identified and other possible sources of inaccuracy of the UVP+PD method were investigated. Several improvements of the UVP+PD measurement method were proposed.► Cite this publication as follows:

Wiklund J, Birkhofer B, Jeelani S, Stading M, Windhab EJ: In-line rheometry of particulate suspensions by pulsed ultrasound velocimetry combined with pressure difference method, Appl. Rheol. 22 (2012) 42232.

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Eischen JC, Windhab EJ: Viscosity of Cocoa and Chocolate Products, Appl. Rheol. 12 (2002) 32.

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Windhab EJ: Fluid immobilization - a structure-related key mechanism for the viscous flow behavior of concentrated suspension systems, Appl. Rheol. 10 (2000) 134.

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Hugelshofer D, Windhab EJ, Wang J: Rheological and Structural Changes During The Mixing of Suspensions and Emulsions, Appl. Rheol. 10 (2000) 22.W Hanselmann, EJ Windhab

Foam Flow in Pipes

Appl. Rheol.6:6 (1996) 253 ►

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Hanselmann W, Windhab EJ: Foam Flow in Pipes, Appl. Rheol. 6 (1996) 253.

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Wolf B, Windhab EJ: Interfacial Rheology of Deformable Droplets in Viscometric Flows, Appl. Rheol. 5 (1995) 182.

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Windhab EJ: Behaviour of Shear-Induced Structures in Multi-Phase Systems, Appl. Rheol. 2 (1992) 102.

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Windhab EJ, Wolf B: Investigation of the Rheological Behaviour of Small Droplets in Emulsions, Appl. Rheol. 1 (1991) 17.

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