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The Diffusion of Passive Tracers in Laminar Shear Flow
Published on: May 1, 2018
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Velocity distributions in confined flows of some complex fluids: sequence, sample and hardware issues
T Chevalier1, P F Faure1, C Chevalier2
1Université Paris-Est, Laboratoire Navier (UMR 8205), CNRS, ENPC, IFSTTAR, F-77420 Marne-la-Vallée, France(1).
Journal of Magnetic Resonance (San Diego, Calif. : 1997)
|June 18, 2014
Summary
Pulsed Field Gradient (PFG) experiments can now measure fluid velocity in restricted flows. Optimized parameters and graphical methods enable accurate measurements of complex fluids like emulsions and gels, overcoming diffusion blurring.
Area of Science:
- Physics
- Rheology
- Materials Science
Background:
- Pulsed Field Gradient (PFG) experiments are crucial for studying molecular motion.
- Measuring velocity in complex fluids within restricted geometries is challenging due to molecular diffusion.
- Yield-stress fluids like colloidal suspensions, polymeric gels, and concentrated emulsions present unique measurement difficulties.
Purpose of the Study:
- To develop a method for measuring velocity probability density functions in restricted flows using PFG experiments.
- To overcome the blurring effects caused by diffusive molecular motions in complex fluids.
- To identify optimal experimental conditions for accurate velocity measurements in various complex fluids.
Main Methods:
- Utilized Pulsed Field Gradient (PFG) Nuclear Magnetic Resonance (NMR) techniques.
- Developed graphical methods to determine suitable and optimized sequence parameters.
- Employed asymptotic expressions to approximate the Murday and Cotts formula for diffusion in emulsions.
- Identified different tuning regimes based on fluid properties, flow rate, hardware, and pore size.
Main Results:
- Established a method to create quantitative diagrams for pore size and flow rate selection.
- Demonstrated that low flow rates are constrained by fluid self-diffusivity and microstructure.
- Showed that high flow rates are constrained by hardware characteristics.
- Found that low gradient systems, with optimized tuning, are suitable for many situations and offer wider experimental conditions.
Conclusions:
- Optimized PFG sequence parameters enable accurate velocity measurements in restricted flows of complex fluids.
- Quantitative diagrams guide the selection of experimental parameters for pure velocity assessment.
- Both fluid properties and hardware capabilities play critical roles in measurement feasibility.
- Low gradient NMR systems offer versatile experimental conditions for studying fluid dynamics in porous media.
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