Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session G28: Particle-laden Flows: Experimental Techniques |
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Chair: Sarah Hormozi, Ohio University Room: F149 |
Monday, November 21, 2016 8:00AM - 8:13AM |
G28.00001: X-ray Mapping of Dynamic Suspensions Mohammad Gholami, Nicolas Lenoir, Guillaume Ovarlez, Sarah Hormozi Dense non-colloidal suspensions are materials with broad application both in industrial processes and natural phenomena. In most of these applications, the suspensions are either far from equilibrium or strongly non-Newtonian (i.e., non-colloidal particles are suspended in non-Newtonian fluid) meaning that the flow kinetics are not only strain-dependent but also strain-rate dependent. Therefore, experimental techniques must be developed to analyze the flows of these complex suspensions over a wide range of steady and transient shear rates. Techniques such as Nuclear Magnetic Resonance/Imaging (NMR/I) are inapplicable due to low sampling frequency and low image resolution[1] (typically 10 minutes per averaged NMR image of 1x1cm). We introduce a new technique using an X-ray/CT-scan system to study dynamic suspensions. We show our recent results on the application of this technique for the study of shear induced migration of particles in a yield stress matrix fluid in a wide-gap cylindrical Couette cell. This work opens new avenues to study dynamic non-colloidal suspensions and the suspensions with other types of nonlinear suspending fluids such as viscoelastic and shear thickening fluids. [1] Ovarlez,G., et al.,Journal of Rheology, Vol 50, 2006, pp. 259-292. [Preview Abstract] |
Monday, November 21, 2016 8:13AM - 8:26AM |
G28.00002: Size segregated ring pattern formation in particle impactors J. R. Saylor, S. A. Fredericks Typical particle impactors consist of a nozzle that directs a particle laden flow onto a plate, and is designed to capture particles greater than a cutoff diameter. Connected in series as a cascade, with each impactor designed to have a progressively smaller cutoff diameter, the particle size distribution can be measured. Typical impactors utilize a nozzle-to-plate distance $S$ that is on the order of one nozzle diameter $W$, $S/W \sim 1$, and give a nominally Gaussian particle deposition pattern on the plate. We explored conditions where $S/W << 1$ and observed deposition patterns consisting of very fine rings. Moreover, we found that the ring diameter increased with decreasing particle diameter and the ring thickness increased with particle diameter. These results suggest a potential method for sizing particles by using the mature technology of impactors in a different way. Potential mechanisms for how these ring patterns are formed will be discussed. We note that prior studies have observed conditions where particle deposition patterns exhibited ``halos". These halos appear less distinct than the rings we have observed, and it is unclear whether they are related. [Preview Abstract] |
Monday, November 21, 2016 8:26AM - 8:39AM |
G28.00003: Development of a Magnetic Resonance Imaging-Based Method for Particle Concentration Measurement Daniel D. Borup, Christopher J. Elkins, John K. Eaton Magnetic Resonance Imaging (MRI) is well suited for the study of fluid mechanics in complex flows where optical access is not possible. Current MRI-based techniques allow for the measurement of 3D, 3-component velocity and scalar concentration fields. The current work aims to develop and validate a technique for measuring the concentration of a dispersed phase of solid microspheres in a turbulent water flow. Such a diagnostic would allow for the study of the transport of small particles in arbitrarily complicated biological, engineering, or natural flows. In the presence of paramagnetic particles, MRI signal decays more rapidly than it does for pure water due to small disturbances in the magnetic field. We predicted the spatial extent and magnitude of this disturbance using a standard theoretical framework for MRI and obtained reasonable agreement with experimental results. Using the linear relationship between particle volume fraction and signal decay rate, we also obtained 3D concentration data for a particle streak injected into a ribbed serpentine channel flow. These data were used to validate the new method, and the transport of solid particles was compared to the transport of a passive scalar in the same flow. Daniel Borup is supported by NSF Grant No. DGE-114747. [Preview Abstract] |
Monday, November 21, 2016 8:39AM - 8:52AM |
G28.00004: Multi-camera PIV of two-phase oscillating sheet flow Chang Liu, Ken Kiger We present a multi-camera thin light sheet imaging method to accurately measure dispersed phase concentration and velocity up to optical densities of close to O[1]. The work is an extension of prior single camera methods that utilize particle image characteristics to identify the dispersed phase and infer the effective measurement volume thickness. By introducing multiple camera perspectives, stereo photogrammetry can be combined with the redundancy of information available in the images to provide 1) increased accuracy in determining individual particle locations, and 2) increased reliability in identifying all of the dispersed phase objects. As a byproduct, the velocity of all three components is also available. As an example, this new method is directly applied to oscillating sheet flow conditions. From a single image pair, individual particles are identified and tracked, giving the instantaneous volume concentration and dispersed phase velocity. A median filter method is used to isolate an image composed only of the much smaller tracer particles, and processed to generate a 3-component continuous phase velocity field. Given the concentration and velocities of the two phases, two-phase flow properties such as the sedimentation rate and momentum coupling will be reported. [Preview Abstract] |
Monday, November 21, 2016 8:52AM - 9:05AM |
G28.00005: A simultaneous charge and size measurement method for individual airborne particles using digital holographic particle imaging Adam Hammond, Zhongwang Dou, Zach Liang, Hui Meng Recently, significant inquiry to understand the effects of particle charge on particle laden flow have been made, particularly in the study of Lagrangian particle-pair statistics. Quantification of individual particle charge allows relation of inter-particle electric forces and turbulence-induced forces. Here we offer a simultaneous, individual particle charge and size measurement technique utilizing in-line digital holographic Particle Tracking Velocimetry (hPTV). The method measures particle electric mobility through its velocity response within a uniform electric field using a sequence of holograms, next the particle diameter is measured with the same holograms using a matched-filter developed by Lu et al. (2012) as an input for calculation of charge. Consequently, a benefit of this method is that particle charge is calculated on the individual level, versus a mean charge calculated from a group of particles, offering improved estimations of charge distributions for studies of particle laden flow. [Preview Abstract] |
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