NMR imaging of pulp suspension flowing through an abrupt pipe expansion

Arola, Darren F.; Powell, Robert L.; McCarthy, Michael J.; Li, Tie‐Qiang; Ödberg, Lars

doi:10.1002/aic.690441203

Cited by 26 publications

(12 citation statements)

References 26 publications

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“…The core of the jet above the mixing layer closest to the center of the geometry appeared to be more or less constant along the jet and the main increase in width was caused by an increase in the size of the mixing layer. These behaviors have also been discussed by Heat et al and Arola et al…”

Section: Uvp Measurementssupporting

confidence: 67%

“…Floc deformation was analyzed with a high‐speed camera and the findings were used to develop a system for analyzing fiber flocculation. Arola et al studied the fiber reflocculation time in a circular pipe after an 1:1.7 expansion with nuclear magnetic resonance imaging. Images were taken from both upstream and downstream the expansion zone both in water and in a pulp suspension with a concentration of 0.5% at different velocities.…”

Section: Introductionmentioning

confidence: 99%

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Measurement and analysis of flow of concentrated fiber suspensions through a 2‐D sudden expansion using UVP

Claesson¹,

Rasmuson²,

Wiklund

et al. 2012

AIChE Journal

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The ultrasound velocity profiling technique (UVP) was used to study flow structures after a two-dimensional (2-D) 1:11 sudden expansion of pulp fiber suspensions at varied average velocities (1-2.2 m/s) and concentrations (1.8 and 2.8 wt %). One advantage of studying jet geometry is the potential to investigate the main flow structures away from walls. Measurements done at the same percent of the total jet length, at constant concentration, show that an increase in flow rate gave a faster decrease in centerline velocity and a quicker increase in jet width. Increasing the concentration, at the same jet length, the centerline velocity was more stable and the width of the mixing layer increased more rapidly. Comparisons with CFD simulations in the laminar regime, using the Bingham plastic model, show that the main flow structures were captured if the yield stress used in the simulations is approximately 20% of the measured using a rheometer.

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Section: Uvp Measurementssupporting

confidence: 67%

Section: Introductionmentioning

confidence: 99%

Measurement and analysis of flow of concentrated fiber suspensions through a 2‐D sudden expansion using UVP

Claesson¹,

Rasmuson²,

Wiklund

et al. 2012

AIChE Journal

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show abstract

“…With regards to papermaking suspensions, there is evidence of seemingly two different behavious. Arola et al (1998), for example, imaged the axial velocity profile of a 0.5% (wt) wood pulp suspension flowing through a 1:1.7 sudden expansion using NMR. These authors report that the pulp suspension exhibited behavior similar to that of a confined jet.…”

Section: Introductionmentioning

confidence: 99%

Visualization of the flow of a fiber suspension through a sudden expansion using PET

et al. 2007

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in Wiley InterScience (www.interscience.wiley.com).The motion of 18 F radioactively labeled papermaking fibers flowing through an axisymmetric 1:5 sudden expansion has been studied using positron emission tomography (PET). Various length fractions of a mechanical pulp were radioactively labeled and then introduced into a nonradioactive aqueous 0.4 wt. % (consistency) wood pulp suspension. Fully three-dimensional (3-D) images were reconstructed both upstream and downstream of the expansion plane for cases in which the upstream velocity U was set from 0.5 to 0.9 m/s (an approximate Reynolds number range of 7,000 to 13,000). Two distinct flow regimes were clearly identified. With U ; 0.5 m/s we find that the fiber suspension was not fluidized, and the tracer fibers passed through the expansion as a plug. No mixing was observed between the confined central jet and the static outer region. At larger velocities, we observed that the papermaking suspension was fully fluidized. Our results in this regime indicate that albeit fluidized, concentration inhomogeneities were evident. We find that a particle depletion zone was evident between the central jet, and the recirculating zone resulting from the inlet concentration profile formed in the upstream tube. Particle accumulation was observed in the vortices. No significant differences were observed between the different length tracer fibers.

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“…3 However, increased recirculation lengths have been seen in fluids with shear thinning properties as well as dilute concentrations of suspended fibers. 4 Additionally, Moraczewski et al 1 found that recirculation lengths were greater for concentrated suspensions at low Reynolds numbers ͑0.01-3.5 in the downstream tube͒ as compared to Newtonian flows at similar Reynolds numbers. It was suggested that the concentration inhomogeneities leading to the long recirculation regions developed during flow in the long, narrow inlet tube and were convected downstream.…”

Section: Introductionmentioning

confidence: 97%

The effect of inlet conditions on concentrated suspension flows in abrupt expansions

Moraczewski

Shapley

2006

Physics of Fluids

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This work explores the influence of inlet conditions on the particle concentration distribution and flow field of a concentrated suspension undergoing steady flow in an abrupt, axisymmetric 1:4 expansion. Specifically, we consider the impact of inlet conditions in the upstream narrow tube on the resulting downstream profiles. Particle concentration and velocity profiles were measured by using nuclear magnetic resonance imaging. Experiments were conducted with two contrasting inlet tube lengths of 10d 1 and 128d 1 , where d 1 is the diameter of the narrow inlet tube. In the short inlet case, none of the particle concentration fields were fully developed upon entering the expansion, whereas several of the suspensions had fully developed profiles in the long inlet case. Results indicate that concentration differences between the core and annular regions were greater for the cases with a long inlet tube than in cases with a short inlet tube, likely owing to the higher degree of particle migration occurring in the long inlet tube before entry into the expansion. Also, the lengths of recirculating regions were greater for suspensions in the long inlet than in the short inlet geometry, while both systems followed the same trend of increasing recirculation length with bulk particle volume fraction and correlation with the ratio of tube center to wall concentration values.

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NMR imaging of pulp suspension flowing through an abrupt pipe expansion

Cited by 26 publications

References 26 publications

Measurement and analysis of flow of concentrated fiber suspensions through a 2‐D sudden expansion using UVP

Measurement and analysis of flow of concentrated fiber suspensions through a 2‐D sudden expansion using UVP

Visualization of the flow of a fiber suspension through a sudden expansion using PET

The effect of inlet conditions on concentrated suspension flows in abrupt expansions

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