Flowing fluid, velocity imaging

The molecular translations are spatially resolved by combining the velocity encoding sequence with the conventional spatial imaging encodings. In this velocity imaging", the phase shift of the spins reflects the information about their displacement as well as the spatial position. In this work, a flow-compensation [25] is implemented in the velocity imaging pulse sequence to eliminate the actifacts due to fluid flow. 

An example of the spin-velocity density function is demonstrated in Figure 4.1.6. A velocity imaging experiment was performed on water flowing through a 6-mm diameter tube. The velocity density function was spatially resolved along the axial direction of the tube, denoted by z in the figure. It is observed that the velocity density function has a steep peak at zero velocity when the fluid is not flowing, but is shifted to a positive velocity when the flow rate was increased to 2.5 mL min-1. 

Velocity images and profiles at several selected heights are shown in Figure 4.3.6, where the noisy points in the images indicate the air space where a liquid signal was not detected. When the fluid is inside the glass pipette, the velocity profile is nearly Poiseuille and a non-slip boundary condition is almost achieved. This is consistent with one of the early tube flow reports that the 0.5% w/v solution of... 

Fig. 4.3.6 Velocity maps and profiles at differ- mark the NMR foldbacks from the stationary ent heights of the Fano column. The dark ring fluid at the inner surface of the fluid reservoir, surrounding the pipe at z= 1.5 mm (larger In the velocity profiles, the solid curves are the white arrow) is due to a layer of stationary fluid calculated Poiseuille profiles in tube flow, adhering to the pipe exterior following the Velocity images are reprinted from Ref. [20], dipping of the pipe into the reservoir at the with permission from Elsevier, start of the experiment. The small white arrows...

Fig. 5.1.5 Quantitative data on the correlation of biofilm and velocity for a slice perpendicular to the flow axis. The images on the left are from top to bottom T2 map, z velocity component, x velocity component and y velocity component. One dimensional profiles through lines A, in bulk fluid, and B, intersecting biofilm fluid interface, are shown on the right. The biofilm signal indicator, dotted grey line, has been normalized so that zero corresponds to no biomass and 1 corresponds to the highest...

Such regions of the bed are associated with high fluid velocities, and inertial effects increasingly influence the flow profile as Reynolds number increases (80). On the basis of these images, it is clear that any theoretical analysis of the flow within such a reactor must account for distinct populations of fast- and slow-moving liquid— channeling does not occur just at the walls of the bed. 

Flow is an important parameter in industrial processes. Magnetic resonance imaging has been used to determine the velocity profile in flowing fluids. In the case of laminar flow... 

The key challenge for the successful use of NMR velocity-imaging techniques to characterize fluid flow properties is the interpretation of the measured parameters. Different experimental strategies provide information about flow processes at different spatial and dynamic scales in porous media. In principle, the flow velocity can be probed either as a local quantity with an image resolution below the pore level,2425 or as a macroscopic flow property corresponding to local volume and temporal averages of fluid molecular displacements.26 One must develop a suitable methodology to correctly determine the parameters that best describe the properties of interest. 

Voidage. Single- and two-phase flows in fixed-bed reactors were visualized by three-dimensional NMR imaging and MRI velocimetry. The fluid velocity vector is determined at a pore-scale resolution of 156 pm. Characteristics of... 

Typically in fluid mechanics, a wealth of information about any given flow system can be fotmd from the velocity field, which is often visualized and quantified through the use of tracer particles. As mentioned above, micro-PIV and micro-PTV are both well-established tools for extracting quantitative information from microscale fluid systems [3], However, special care must be taken in applying these techniques to very nearwall flows with evanescent wave illumination. Both techniques require imaging the instantaneous positimis of tracer particles seeded in the flow at two different instances in time to infer fluid velocities. 

Velocimetry is the measurement of fluid velocity. In the context of microfluidics and nanofluidics, velocimetry involves the determination of the velocity field in small-scale internal flows. Most commonly, velocimetry involves optical tracking of a fluid marker. In such cases, the terms flow visualization and velocimetry are used interchangeably. A variety of velocimetry methods have been developed for small-scale flows. Visualization-based methods can be divided into particle-based techniques such as microparticle image velocimetry and scalar-based techniques such as molecular tagging. Nonvisualization-based velocimetry methods have also been developed such as electrochemical velocimetry, where fluid velocity is determined via generation of a redox species. 

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