A two-phase model for dry density-varying granular flows

A granular flow is normally comprised of a mixture of grain-particles (such as sand, gravel or rocks) of different sizes. In this study, dry granular flows are modeled utilizing a set of equations akin to a two-phase mixture system, in which the interstitial fluid is air. The resultant system of equations for a two-dimensional configuration includes two continuity and two momentum balance equations for the two respective constituents. The density variation is described considering the phenomenon of air entrainment/extrusion at the flow surface, where the entrainment rate is assumed to be dependent on the divergent or convergent behavior of the solid constituent. The density difference between the two constituents is extremely large, so, as a consequence scaling analysis reveals that the flow behavior is dominated by the solid species, yielding small relative velocities between the two constituents. A non-oscillatory central (NOC) scheme with total variation diminishing (TVD) limiters is implemented. Three numerical examples are investigated: the first being related to the flow behaviors on a horizontal plane with an unstable initial condition; the second example is devoted to simulating a dam-break problem with respect to different initial conditions; and in the third one investigates the behavior of a finite mass of granular material flowing down an inclined plane. The key features and the capability of the equations to model the behavior are illustrated in these numerical examples.     

Identification of a new sildenafil analogue adulterant,desethylcarbodenafil, in a herbal supplement

In a maca-containing herbal supplement claimed to remedy erectile dysfunction, a new sildenafil analogue was found using adulterant screening with TLC, GC-MS and LC-MS/MS. This compound was isolated by column chromatography and HPLC, and identified by extensive 1D- and 2D-NMR and mass spectral analyses. The structure of this new compound was established as 5-[2-ethoxy-5-(piperazine-1-carbonyl) phenyl]-1-methyl-3-propyl-1,6-dihydro-pyrazolo[4,3-d]pyrimidin-7-one, and was named desethylcarbodenafil.     

Segregation to mixing in wet granular matter under vibration

This study intends to investigate the influences of the content and viscosity of small amount of silicone oils added to a binary-mixture on the segregation phenomena in a vibrated shaker. The silicon oils with five different viscosities and six different liquid contents are utilized in this study. The dimensionless average height of the larger particles was measured so as to characterize the so-called “Brazil nut effects.” The experimental results indicate that the dimensionless average height of the larger particles decreases with the increase of the viscosity and liquid content of the added silicone oil. The results show that not only liquid content but also liquid viscosity plays a significant role on the final segregation state. We also find that the liquid bridge force does not have significant effect on the final segregation state if adding very low-viscosity liquid even if the liquid content is increased. Finally, we find that the size segregation could be controlled by the addition of different liquid content and viscosities.     

Influence of the initial volume fill ratio of the granulator on melt agglomeration behavior in a high-shear mixer

The purpose of this study was to investigate the effects of different initial volume fill ratios of the granulator on granular agglomeration in a high-shear mixer. Calcium carbonate powders, with mean granule sizes of 75–150 μm were used as the raw material. Polyethylene glycol 6000 (PEG 6000) was used as the melting binder. The initial liquid to solid weight ratio was fixed at 0.15. Four different initial granulator fill ratios were used 11%, 14.7%, 18.4% and 22%. The results showed that the granules that formed during the nucleation stage were a little larger when the initial fill ratio was lower than higher. In the rapid-growth stage, the agglomeration growth rate increased as the initial fill ratio increased. The range in granule size at the end of agglomeration also increased as initial fill ratio increased. SEM images of the surface structure of the granules during the nucleation and final stages are shown.     

Investigation of the gas inlet velocity distribution in a fixed granular bed filter

Granular bed filter (GBF) technology can be applied for high-temperature gas cleanup in integrated gasification combined-cycle (IGCC) and pressurized fluidized-bed combustion (PFBC) advanced coal-fired power plants. The design of the gas inlet component of the granular bed filter is important to achieve a uniform gas distribution and higher usage rate of the filter media. Previous studies show that the gas velocity at the inlet is not uniformly distributed. This non-uniformity may lead to a lower usage rate of the filter media. In this study a baffle device is introduced to the inlet system in order to achieve a more uniform gas velocity distribution. A more uniform gas inlet distribution can be obtained by adjustment of the lengths and angles of the baffles. The gas velocities along the inlet and filtration surfaces are measured using a pitot tube. The uniformity of the gas velocity distribution can be characterized by looking at the distributions of the standard deviation of the gas velocity and the differences in the mean velocities between the two filtration surfaces.     

The influence of gravity on dynamic properties in sheared granular flows

The influences of gravity on the granular flow behavior and dynamic properties were experimentally studied in a vertical shear cell device where the shear dilation direction of granular materials was perpendicular to the gravity direction. The particle motions were recorded by a high-speed camera from three different observational views. By using image processing technology and the particle tracking method, the average velocities and granular temperatures in the streamwise and the transverse directions were successfully measured and analyzed. The results show that the anisotropic motions exist in sheared granular flows. The dynamic properties in the streamwise direction are larger than those in the transverse direction. Due to the gravity effect and bulk flow of granular materials, the local packing structure is not homogenous in the vertical shear cell. By comparing the three different observational views in the vertical shear cell, we find that the spatial average velocity and self-diffusion coefficient are the greatest but the shear rate and granular temperature are the smallest when the particles are co-flowing with gravity causing the most dilute packing structure due to the gravity effect. Similar experiments were also performed in a horizontal shear cell where the shear dilation direction of granular materials was against the gravity direction. The dynamic properties are smaller in the horizontal shear cell than those in the vertical shear cell. It is because the horizontal shear cell has the smaller shear rate with the shear dilation direction against the gravity direction.     

Experimental study of the gas flow behavior in the inlet of a granular bed filter

The Moving Granular Bed Filter (MGBF) is an important apparatus being developed for filtration of the hot gas. Our research group demonstrated a good solution to diminish stagnant zones in MGBF during the filtration process. However, there still remain some systematic problems that have to be worked out prior to commercializing a whole facility.The design of the gas inlet component of the granular bed filter is important for achieving a uniform gas distribution and higher usage rate of the filter media. Non-uniformity may lead to a lower usage rate. The new gas inlet component design uses baffle devices in order to achieve a more uniform gas velocity distribution. Fixed bed and moving bed conditions were studied. The uniformity of the gas velocity distribution can be characterized by the standard deviation definitions and the differences in the mean velocities between the two filtration surfaces. The baffle lengths and angles affected the uniformity of gas velocity in inlet and filtration surfaces. The optimal experimental parameters were found by using different baffle lengths, angles and mass flow rate of filter media. The uniform gas velocity distributions were obtained by a series experiments. Furthermore, the results give important information about IGCC system that will be helpful for designing better models of moving granular bed filters in the future.     

A New Method for Measuring Cake Thickness by a Powder Pressure—Displacement System

An on-line powder pressure–displacement measurement system was developed based on a static measurement instrument (vernier caliper). This system consists of a pressure sensor and a displacement subsystem, and has the on-line capability to measure the thickness of powder packing with different powder sizes. The design principle employs a pressure sensor to determine the thickness by different signals generated when the pressure sensor contacts the free surface zone of powder packing and when it contacts the other powder zone. The powder materials adopted to validate this newly developed system were glass beads, sand and dust. This measurement technique can be applied under different measurement conditions.     

Flow patterns and velocity fields in two-dimensional thin slice panel with flow-corrective insert

An experimental two-dimensional (2-D) thin slice panel for studying flow patterns of fine silica sand was designed and manufactured. As supplier of sand was not known at that time, flow properties of the silica sand were assessed without shear tests. A preliminary design of plane-flow hopper of the experimental 2-D panel was assumed to be close to the mass flow conditions. Sand was circulated in the experimental panel to study the steady state flow. Tests of flow patterns suggested typical funnel-flow patterns with stagnant zones in the hopper and in the vertical part of the panel. Stagnant zones near the bottom of the hopper indicated insufficient width of the hopper outlet. Shear tests for estimation of flow properties of silica sand were carried out additionally and two methods of how to transform the funnel flow of sand to the mass flow were followed up; (a) existing 2-D panel was retrofitted with flow-corrective element, and (b) the width of outlet in existing experimental panel was widen into the size, calculated according to mass flow conditions. Both modifications were proven to be successful and the last-in first-out funnel flow was transformed into first-in first-out mass flow of sand. Velocities of individual tracer particles were measured during mass flow and velocity field was evaluated. Velocity profile of particles in the vicinity of flow-corrective insert was studied in detail.     

DEM simulation of oblique shocks in gravity-driven granular flows with wedge obstacles

Deflecting wedge obstacles are often built to divert hazardous flows away from residential areas that are in the way of harm. When a rapid avalanche flow is deflected by an obstacle, this usually causes abrupt changes in the flow thickness and velocity and exhibits characteristics like oblique shock waves in the aerodynamic system or oblique hydraulic jumps in the open channel flows. In this study, the Discrete Element Method (DEM) is employed to simulate the motion of granular materials impinging on a wedge obstacle in an adjustable inclination chute. We use chutes with four different inclined angles combined with wedge obstacles having different angles to investigate the overall flow behavior. Both the flow velocity and the flow depth are obtained by averaging the numerical simulation data, and then the granular temperature and the shock angle are calculated. The results of the DEM simulation are compared with that of the classical oblique shock theory. We find that there is good agreement between the classical oblique granular shock theoretical calculations and the DEM simulation results. Moreover, the microdynamic variables related to flow structure such as the packing density and the coordination number are also discussed in the present study.