1,720,961 research outputs found
Experimental investigation and CFD modeling of interstitial fluid effect in fluid -particle flow with particle -particle collisions
No full textA new two-fluid model, which employs kinetic theory of dense gas concepts to describe momentum and kinetic energy transfer between colliding particles, has been developed to simulate dilute turbulent fluid-particle flows with particle-particle collisions. The present model incorporates the influence of the interstitial fluid on the random motion of the particles by introducing two distinct particle coefficients of restitutions ef and es to characterize the inelasticity of particles colliding in a fluid and in a vacuum, respectively. Unlike other existing two-fluid flow models, which are restricted to applications in gas-particle flows, the present model is capable of simulating the dynamics of both turbulent gas-particle and liquid-particle flows. The model predictions have been compared with several dilute turbulent fluid-particle experimental data found in the literature. Although a large body of experimental works exists for turbulent fluid-particle flows in the literature, a majority of those works exhibits either no interstitial fluid effect (ef ≈ es) or very significant interstitial fluid effect (e f \u3c\u3c es). In order to thoroughly assess the predictive capability of the present model, detailed gas-particle flow data having intermediate ef values have been obtained by conducting Laser Doppler Velocimetry (LDV) experiments of a downward gas-particle flow in a vertical pipe. The ef values are modified in the experiments by varying either the particle loading or the Reynolds number. In general, good agreement is found between the model predictions and the experimental data for both the fluid and particle phase at the level of the mean and fluctuating velocity. Lastly, Reynolds number (Re) dependence of gas-phase turbulence in gas-particle flow has been investigated experimentally using two particle sizes and two particle densities. The experimental results at a dilute particle loading suggest that the Re dependence of the gas-phase mean and fluctuating velocities vary depending on the particle density, but not on the particle size. In addition, the gas turbulence, which is dampened at low Re compared to the single-phase flow, is enhanced at high Re due to the change in the segregation pattern of the particles at high Re
An experimental study on effects of fluid aerodynamics and particle size distribution in particle-laden jet flows
No full textThe present study focused on performing experimental investigations of turbulent gas solid flows by means of laser Doppler velocimetry (LDV) and flow visualization. Glass bead particles with mean diameter of 25 and 70 microns were used in this study. The first goal of this dissertation was to investigate the effect of fluid aerodynamics on particle motion in the near field region of coaxial particle-laden jets. The fluid aerodynamics was modified by varying the inlet velocity ratio of the annular to central jet velocity at 0, 1.0, and 1.5. The solid loading of the particles was set at 0.5. Flow visualization showed that as the velocity ratio increased, the instantaneous spatial distribution of the particles became less symmetric with respect to the axial axis and wavier. LDV measurement indicated that the dispersion of particles was enhanced with decreasing particle size and with increasing the velocity ratio greater than 1.0. The present study also recognized the particle-phase radial velocity fluctuation as an important parameter to characterize the particle-turbulence interaction and the spatial distribution of particles in coaxial laden jets. The second goal of this dissertation was to explore the effect of particle size distribution (PSD) in a turbulent pipe flow with Re of 8,400. Binary mixtures of the 25 μm and 70 μm particles were investigated, and the PSD of the binary mixtures was varied by modifying the mass fraction of the fine particles, while the total solid loading was maintained at 1.0. LDV measurements showed that the addition of the fine particles enhanced the axial mean velocity of the coarse particles near the pipe center. In contrast, the motion of the fine particles was not influenced by the presence of the coarse particles. Based on this finding, it was hypothesized that the fine particles did not engage direct collision with the coarse particles, but the fine particles increased the resistance for the coarse particles to move as if the effective gas viscosity was increased. Moreover, the investigation of PSD effect was extended to a particle-laden jet flow. The radial spreading of the coarse particles was reduced by the presence of the fine particles
LDV Measurements and Analysis of Gas and Particulate Phase Velocity Profiles in a Verticle Jet Plume in a 2D Bubbling Fluidized Bed.
Full text linkFluidized beds are commonly used as chemical reactors and solid fuel combustors, where high-speed gas jets are employed to introduce reactants to the system. Quantitative gas and particulate phase velocity measurements are needed to characterize the transport phenomena of these jet plumes into the particulate emulsion. Two component Laser Doppler velocimetry (LDV) was used to investigate the gas and particulate phase velocities and resulting transport of a vertically injected gas jet plume in a two-dimensional bubbling bed.
LDV measurements of this optically dense multiphase flow are challenging due to laser intensity fluctuations, which mix with the recorded burst frequencies. This problem was resolved by optimizing the Bragg Cell configuration and burst signal processing. The jet gas was seeded with ice crystals, and bursts from the bed particles and gas tracers were simultaneously acquired. These bursts were differentiated based on their intensity and coincidence to determine the gas and particulate phase velocities.
The behavior of the single-phase gas jet in the empty bed was examined. The self-similar velocity profile growth was consistent the development of a free two-dimensional turbulent jet. The bed was filled with high-density polyethylene microspheres. The gas and particulate phase velocity profiles of the jet were measured. Similarity profiles are presented and the resulting void fraction, mass flow and momentum transport calculations are analyzed. The effect of fluidization velocity on the jet dynamics was examined and was shown to influence the rate of mass entrainment into the jet plume and the momentum exchange between the phases.
The ratio of the maximum gas and particulate phase velocities appeared to follow a similar trend for all test conditions. Hence, the ratio of the drag force coupling to the particulate or gas phase momentum is constant at a given axial location from the jet inlet. Additionally, the mass-averaged velocity ratio for the two phases, which is equivalent to the ratio of the centerline velocities, develops in a similar fashion. This phenomenon is observed for high-speed gas jets in bubbling beds with spherical particle entrainment when Rep > 1,000 so that CD ~ 0.4.PhDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/77768/1/almych_1.pd
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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