Abstract
We investigate the feasibility of in-laboratory tomographic X-ray particle tracking velocimetry (TXPTV) and consider creeping flows with nearly density matched flow tracers. Specifically, in these proof-of-concept experiments we examined a Poiseuille flow, flow through porous media and a multiphase flow with a Taylor bubble. For a full 360^circ computed tomography (CT) scan we show that the specially selected 60 micron tracer particles could be imaged in less than 3 seconds with a signal-to-noise ratio between the tracers and the fluid of 2.5, sufficient to achieve proper volumetric segmentation at each time step. In the pipe flow, continuous Lagrangian particle trajectories were obtained, after which all the standard techniques used for PTV or PIV (taken at visible wave lengths) could also be employed for TXPTV data. And, with TXPTV we can examine flows inaccessible with visible wave lengths due to opaque media or numerous refractive interfaces. In the case of opaque porous media we were able to observe material accumulation and pore clogging, and for flow with Taylor bubble we can trace the particles and hence obtain velocities in the liquid film between the wall and bubble, with thickness of liquid film itself also simultaneously obtained from the volumetric reconstruction after segmentation. While improvements in scan speed are anticipated due to continuing improvements in CT system components, we show that for the flows examined even the presently available CT systems could yield quantitative flow data with the primary limitation being the quality of available flow tracers.Graphic abstract
Highlights
Multiphase flows are all around us, and inside us
We found that the film between a Taylor bubble and the pipe wall could be resolved in the same experimental setup with the same flow and acquisition parameters as used for Sect. 3.1
For the purposes of tomographic X-ray particle tracking velocimetry (TXPTV) one could define as success a case where particles had sufficient contrast to be detected in the first place while being nominally neutrally buoyant, and particle centroids are localizable in the computed tomography (CT) reconstruction
Summary
From waves breaking and exchanging atmospheric gases with the ocean water, to the blood in our veins with red blood cells in plasma Fundamental discoveries in these flows lead to energy savings, medical advancements and reduced pollution. Only recently, it was discovered that under certain conditions shedding cavitation in an adverse pressure gradient can be dominated by shock waves instead of re-entrant jets (Ganesh et al 2016; Mäkiharju et al 2017). Discoveries such as these are enabled by new “in-the-lab” quantitative measurement techniques, some utilizing X-ray techniques (e.g., Mäkiharju et al (2013)). Some of the information we need to be able to obtain with improved or new experimental techniques include: phase fractions and velocity fields in highly thermally conducting (e.g., metal) foam filled channels and porous media, flow velocities of multiple phases even in annular flows, and flow velocities in cavitating and other opaque flows
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