Local Velocity and Concentration of the Single Components in Water/Oil Mixtures Monitored by Means of MRI Flow Experiments in Steady Tube Flow

Abstract

In this paper the spatially resolved determination of velocities in two-phase systems consisting of water and oil by means of nuclear magnetic resonance (NMR) imaging (MRI) techniques is described and applied to steady tube flows with regard to the total flow rate. As MRI offers the possibility to study the flow of multiphase materials spatially resolved with various forms of contrast, even optically opaque water/oil mixtures can be studied in the interior of the material. Besides snapshot images of the actual flow pattern also local velocity and concentration fields of both phases can be obtained separately. The insight into the inner micro flow processes and microstructure allows to characterize fluid mixtures or emulsions. Flow rate and preparation/ mixing method were varied in order to realize changes of the flow pattern and the structure of the mixture during flow. Physical models of the flow behavior and physical stability of these complex systems can be based upon this information.

Wide-gap Couette flows of dense emulsions: Local concentration measurements, and comparison between macroscopic and local constitutive law measurements through magnetic resonance imaging

“…This chemical shift is quite small (about 4-4.5 ppm relative difference, whenever carbon or silicon oils are used). Nevertheless this shift can be accurately observed provided that B o inhomogeneities across the sample have a much smaller amplitude than 4.5ppm of the mean B o value (e.g., see spectrum by Götz and Zick [31]). Indeed, the precession frequency is also proportional to local B o intensity, and one should avoid confusion between the original chemical shift and any spurious one originating from field heterogeneities.…”

“…Quite early results deal with the use of chemical shift imaging (CSI) for a quantitative assessment of oil/fat content in food emulsions [32], or the separation of oil and water components of an emulsion during a filtration process [33]. More recently, Götz and Zick [31] and Hollingsworth and Johns [17] managed to carry out quite well resolved local measurements of water/oil concentrations and/or velocities in model suspensions flowing through a pipe in a laminar regime. Unfortunately, the chemical shift contrast can hardly be transposed in the case of a Couette cell.…”

Some Applications of Magnetic Resonance Imaging in Fluid Mechanics: Complex Flows and Complex Fluids

“…these applications is that the distribution of the phases in the flow has a great impact on the flow properties (for instance, the pressure drop), but the fluid distribution in general is not known. Although in principle MRI is a powerful tool to use to access both velocity and concentration profiles in a flowing system, few MRI experiments on multiphase flow exist (Götz & Zick 2003, Le Gall et al 2001, Muller et al 2007). …”

Recent experimental probes of shear banding

“…Later works combining NMR velocimetry and deuterium NMR spectroscopy have shown that birefringence bands do not necessarily correspond to shear bands [61,62]. Finally, more recently, fast NMR velocimetry allowed the authors to resolve temporal fluctuations of the flow field [83,122,123] Since the early work by Callaghan et al, NMR velocimetry has been used in a growing number of complex fluids to investigate shear banding or shear localization including emulsions [67], colloidal systems [82,196], wet granular materials [91], cement pastes [98], and other soft glassy materials studied by Coussot et al [28,44,168,170].…”