Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session H13: Granular Flows II: Applications |
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Chair: Nicholas Pohlman, Northern Illinois University Room: 301 |
Monday, November 25, 2013 10:30AM - 10:43AM |
H13.00001: Erosion and flow of hydrophobic granular materials Brian Utter, Thomas Benns, Joseph Mahler We experimentally investigate submerged granular flows of hydrophobic and hydrophilic grains both in a rotating drum geometry and under erosion by a surface water flow. While slurry and suspension flows are common in nature and industry, effects of surface chemistry on flow behavior have received relatively little attention. In the rotating drum , we use varying concentrations of hydrophobic and hydrophilic grains of sand submerged in water rotated at a constant angular velocity. Sequential images of the resulting avalanches are taken and analyzed. High concentrations of hydrophobic grains result in an effectively cohesive interaction between the grains forming aggregates, with aggregate size and repose angle increasing with hydrophobic concentration. However, the formation and nature of the aggregates depends significantly on the presence of air in the system. We present results from a related experiment on erosion by a surface water flow designed to characterize the effects of heterogeneous granular surfaces on channelization and erosion. [Preview Abstract] |
Monday, November 25, 2013 10:43AM - 10:56AM |
H13.00002: Granular dynamics of the low fill regime in a cylindrical tumbler: particle-wall slip Dennis Ivan W. Diaz, Paul B. Umbanhowar, Julio M. Ottino, Richard M. Lueptow Investigations of granular flow in tumblers generally avoid low fill fractions due to the absence of a well-defined flowing layer and the high amount of slip between particles and the tumbler wall. Motivated by results from spherical and double-cone tumblers that exhibit slow axial drift and shallow layers near the ``poles,'' we explored the low fill fraction regime using video analysis to track the particle motion. Large angular amplitude slip occurred at low fill levels and rotation rates. As fill level was increased, the mean time between slip events decreased as did the slip amplitude until, above a critical fill level, particle-wall slip effectively ceased. The mean time between slip events at fixed fill level was reduced by both increasing the tumbler rotation rate and decreasing the particle diameter. We use our results to evaluate the relationship between particle-wall slip and formation of a flowing layer. [Preview Abstract] |
Monday, November 25, 2013 10:56AM - 11:09AM |
H13.00003: The effects of soft-sphere contact models on heat transfer to particles flowing over a heated surface Aaron Morris, Christine Hrenya, Zhiwen Ma, Sreekanth Pannala, Tom O'Brien DEM simulations are performed for solid particles flowing around a heated surface. For moderately dense granular flows with enduring particle-wall contacts, particles in contact with the surface are warmed by conduction across the mutual contact area. Heat transfer may also occur via conduction through the interstitial fluid within the small gaps between particles and the wall. The conductive heat transfer depends on the specific contact model, i.e. Hertzian or linear spring dashpot (LSD), because such models determine the contact area and duration. In this work, we use MFIX DEM (an open source simulation tool developed at NETL) to simulate particles falling in crossflow around a heated cylinder. Heat transfer models for both contact conduction as well as conduction across the interstitial fluid are included in these simulations. We discuss how different collision models impact the heat transfer to the particles as well as the sensitivity to various model parameters. We also compare the heat transfer predicted by different contact conduction thermal models. [Preview Abstract] |
Monday, November 25, 2013 11:09AM - 11:22AM |
H13.00004: Stagnation, circulation, and erosion of granular materials through belt conveyor sluice gate Nicholas Pohlman, Michael Moralda, Ryan Dunne Control of flow rates in conversion reactors for discrete materials like biomass can be achieved in belt conveyors through a combination of belt speed, hopper size, and aperture opening. As material is extracted from the bottom of the storage hopper, other material cannot achieve plug flow and therefore is restricted from exiting through a sluice-gate type opening. The excess material moves vertically from the opening causing a pile up and recirculation back along the free surface of the hopper. Experimental results obtained through high speed imaging show the position of the stagnation point as well as the rate of circulation is dependent on the mass flow rate achieved and instantaneous fill level. The movement of material into the plug flow along the belt allows verification of deposition models on erodible beds rather than rigid surfaces with artificial roughness of glued particles. Similarly, the pile-up at the exit influences the efficiency of the transport affecting the narrow energy return on investment of biomass resources. The laboratory-scale behavior can therefore be translated into industrial performance metrics for increased operational efficiency. [Preview Abstract] |
Monday, November 25, 2013 11:22AM - 11:35AM |
H13.00005: Incorporation of Interstitial Gas Effects on Granular Flows Christine Hrenya, Vicente Garzo, Sudheer Tenneti, Shankar Subramaniam Numerous examples of granular flows exist in which the role of the interstitial gas cannot be ignored. A range of approaches have been taken to incorporate these effects into continuum descriptions. Early efforts simply added a mean drag law to the momentum balance. This ad hoc approach was followed by more rigorous treatments in which an instantaneous drag was incorporated directly into the kinetic equation. Analytical expressions for the resulting continuum description were obtained in the Stokes limit, but not possible higher Reynolds numbers. In the current effort, DNS-based simulations are used to develop a model for the instantaneous drag force that is applicable to a wide range of Reynolds number. This model, based on the Langevin equation, is incorporated into the Enskog equation in order to derive a continuum description for the gas-solid flow. In the limit of Stokes flow, the additional terms arising in the conservation equation are found to match those of previous analytical treatments. Furthermore, the impact of gas on the solid-phase constitutive relations, which was ignored in analytical treatments, is determined. The parameter space examined is consistent with that found in circulating fluidized beds. For such systems, the results indicate a non-negligible impact of the gas phase on the shear viscosity and the Dufour coefficient. [Preview Abstract] |
Monday, November 25, 2013 11:35AM - 11:48AM |
H13.00006: Experimental and computational investigation on the flow behavior of granular particles through an inclined rotating chute Sushil Shirsath, Johan Padding, Herman Clercx, Hans Kuipers In blast furnaces operated in the steel industry, particles like coke, sinter and pellets enter from a hopper and are distributed on the burden surface by a rotating chute. Such particulate flows suffer occasionally from particle segregation in chute, which hinders efficient throughflow. To obtain a more fundamental insight into these effects, monodisperse particles flowing through a rotating chute inclined at a fixed angle has been studied both with experiments and with a discrete particle model. We observe that the prevailing flow patterns depend strongly on the rotation rate of the chute.With increasing rotation rate the particles are moving increasingly to the side wall.The streamwise particle velocity is slightly reduced in the first half length of the chute due to the Coriolis force, but strongly increased in the second half due to the centrifugal forces.The particle bed height becomes a two-dimensional function of the position inside the chute, with a strong increase in bed height along the sidewall due to the Coriolis forces. It was found that the DPM model was agreed well with the experimental measurements.We will also discuss ongoing work, where we investigate the effects of binary particle mixtures with different particle size or density, different chute geometry. [Preview Abstract] |
Monday, November 25, 2013 11:48AM - 12:01PM |
H13.00007: Collapsing granular beds: The role of interstitial air Devaraj van der Meer, Christa Gjaltema, Tess Homan A pre-fluidized sand bed consisting of fine particles compactifies when it is subjected to a shock. We find that the response depends on both the shock strength and the ambient pressure where, counterintuitively, the bed height decreases less at lower ambient pressures. We investigate what happens to the interstitial air during compaction by measuring the pressure variations above and below the bed: The top pressure is observed to decrease abruptly --on the time scale of the compaction-- whereas that below the bed very slowly rises to a maximum. Subsequently both pressures slowly relax to ambient values. We introduce a one-dimensional diffusion model that uses only the change in bed height and the ambient pressure as an input, and find that it accurately accounts for the measured pressure variations. [Preview Abstract] |
Monday, November 25, 2013 12:01PM - 12:14PM |
H13.00008: Avalanche to Continuous flow transition in wet and cohesive granular media Ashish Orpe, Saprativ Basu, Pankaj Doshi We have studied the flow of wet and cohesive granular media in a partially filled, horizontally rotating cylinder. Very small, amount of viscous liquid is added to dry granular particles and the mixture is rotated in the cylinder at various rotational speeds to determine the angle of repose in the avalanching regime, the continuous regime and at the transition rotational speed separating the two regimes. Every experimental run is carried out afresh at a pre-defined rotational speed using liquids with different free surface tension and added in different amounts. Increasing the liquid surface tension increases the angle of repose as well as shifts the transition rotational speed to increasingly higher values. Similar qualitative behaviour is also observed on increasing the amount liquid added. A linear dependence is observed when the transition angle of repose for all cases is plotted against the corresponding transition rotational speed. The entire flow regime is modeled using momentum and mass balance equations for the flowing layer of particles. The total stress in the flowing mass of particles is assumed to be a linear combination of frictional, collisional and capillary force contributions. The model equations are able to reproduce most of the observed flow behavior. [Preview Abstract] |
Monday, November 25, 2013 12:14PM - 12:27PM |
H13.00009: ABSTRACT WITHDRAWN |
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