Influence of End-Wall Friction on the Flow Rates of Granular Materials in Wedge-Shaped Hoppers

1982 ◽  
Vol 49 (2) ◽  
pp. 451-454
Author(s):  
M. Sayed ◽  
S. B. Savage
Keyword(s):  
Granular Materials ◽  
Wall Friction ◽  
Flow Rates ◽  
End Wall

scholarly journals Powder flow down a vertical pipe: the effect of air flow

2002 ◽  
Vol 459 ◽  
pp. 317-345 ◽  
Author(s):  
Y. BERTHO ◽  
F. GIORGIUTTI-DAUPHINÉ ◽  
T. RAAFAT ◽  
E. J. HINCH ◽  
H. J. HERRMANN ◽  
...  
Keyword(s):  
Small Diameter ◽  
Stationary Flow ◽  
Momentum Conservation ◽  
Wall Friction ◽  
Particle Fraction ◽  
Friction Forces ◽  
Flow Rates ◽  
Lower Flow ◽  
Grain Flow ◽  
Grain Distribution

The dynamics of dry granular flows down a vertical glass pipe of small diameter have been studied experimentally. Simultaneous measurements of pressure profiles, air and grain flow rates and volume fractions of particles have been realized together with spatio-temporal diagrams of the grain distribution down the tube. At large grain flow rates, one observes a stationary flow characterized by high particle velocities, low particle fractions and a downflow of air resulting in an underpressure in the upper part of the pipe. A simple model assuming a free fall of the particles slowed down by air friction and taking into account finite particle fraction effects through Richardson–Zaki's law has been developed: it reproduces pressure and particle fraction variations with distance and estimates friction forces with the wall. At lower flow rates, sequences of high-density plugs separated by low-density bubbles moving down at a constant velocity are observed. The pressure is larger than outside the tube and its gradient reflects closely the weight of the grains. Writing mass and momentum conservation equations for the air and for the grains allows one to estimate the wall friction, which is less than 10% of the weight for grains with a clean smooth surface but up to 30% for grains with a rougher surface. At lower flow rates, oscillating-wave regimes resulting in large pressure fluctuations are observed and their frequency is predicted.

Effects of end wall friction in rotating cylinder granular flow experiments

2005 ◽  
Vol 7 (4) ◽  
pp. 199-202 ◽  
Author(s):  
J. E. Maneval ◽  
K. M. Hill ◽  
B. E. Smith ◽  
A. Caprihan ◽  
E. Fukushima
Keyword(s):  
Granular Flow ◽  
Rotating Cylinder ◽  
Wall Friction ◽  
End Wall ◽  
Flow Experiments

scholarly journals Particle motion in mixed flow dryers

2021 ◽  
Vol 9 (3) ◽  
pp. 114-121
Author(s):  
Tamás Tolnai
Keyword(s):  
Velocity Field ◽  
Moisture Content ◽  
Wall Friction ◽  
Particle Flow ◽  
Mixed Flow ◽  
Efficient Operation ◽  
Flow Rates ◽  
Flow Velocity Field ◽  
Long Time ◽  
Drying Chamber

Differences in flow rates of this nature have a significant effect on the unevenness of the moisture content of the dried material, since the material which remains in the drying chamber for an unnecessarily long time is over-dried and the under-drying is a problem for the material remaining in the dryer for too short a time. In this article, I analyzed the effect of increasing particle-wall friction on the unevenness of the particle flow velocity field. The research has shown that dead zones are formed in the vicinity of the rough walls, which reduce the uniformity of the flow. The results show that the tribological properties of the inner wall surfaces of the dryers can have a very significant effect on the efficient operation of the dryers.

scholarly journals Improved evaluation of granular media flows using an X-ray scanning compatible cone-plate setup

2021 ◽  
Vol 249 ◽  
pp. 03020
Author(s):  
Zohreh Farmani ◽  
Jing Wang ◽  
Ralf Stannarius ◽  
Martina Bieberle ◽  
Frank Barthel ◽  
...  
Keyword(s):  
Granular Materials ◽  
High Speed ◽  
Granular Media ◽  
Flow Behavior ◽  
Three Dimensional ◽  
High Speed Imaging ◽  
Flow Measurements ◽  
Flow Rates ◽  
X Ray ◽  
Wide Range

To understand the typically heterogeneous flowing behavior of granular materials, it is important to combine flow tests with three-dimensional imaging. To probe the flow behavior of granular materials over a wide range of flow rates, it is imperative to be able to impose such flow rates in a well controlled manner while performing imaging tests that are compatible with all imposed flow rates. Achieving both flow control and bulk imaging capacity is challenging for a number of reasons. Here, we describe the design of a setup in which we are able to do imaging while imposing a constant overall shear rate on a granular material. We characterize the setup in which flow tests will be performed, which consists of a bottom-driven cone-plate or double-cone design. We show that the setup can be integrated in x-ray microtomography devices to aid particle tracking based flow measurements. The design is also compatible with typical rheometer setups. We also perform high speed imaging of a granular flow in an ultra-fast x-ray scanner, for which we provide proof-of-principle data in a simplified shear setup. The designed flow geometry is also compatible with said high speed imaging facility, where particle image velocimetry can be employed to extract quantitative flow field data.

Experimental Investigation of Turbine Leakage Flows on the 3D Flow Field and End Wall Heat Transfer

2006 ◽  
Author(s):  
Hans-Ju¨rgen Rehder ◽  
Axel Dannhauer
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Secondary Flow ◽  
Mass Flow ◽  
Flow Behavior ◽  
Leakage Flow ◽  
Wall Heat Transfer ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
End Wall

Within a European research project the tip end wall region of LP turbine guide vanes with leakage ejection was investigated at DLR in Go¨ttingen. For this purpose a new cascade wind tunnel with three large profiles in the test section and a contoured end wall was designed and built up, representing 50% height of a real low pressure turbine (LPT) stator and simulating the casing flow field of shrouded vanes. The effect of tip leakage flow was simulated by blowing air through a small leakage gap in the end wall just upstream of the vane leading edges. Engine relevant turbulence intensities were adjusted by an active turbulence generator mounted in the test section inlet plane. The experiments were performed with tangential and perpendicular leakage ejection and varying leakage mass flow rates up to 2%. Aerodynamic and thermodynamic measurement techniques were employed. Pressure distribution measurements provided information about the end wall and vane surface pressure field and its variation with leakage flow. Additionally streamline pattern (local shear stress directions) on the walls were detected by oil flow visualization. Downstream traverses with 5-hole pyramid type probes allow a survey of the secondary flow behavior in the cascade exit plane. The flow field in the near end wall area downstream of the leakage gap and around the vane leading edges was investigated using a 2D Particle Image Velocimetry (PIV) system. In order to determine end wall heat transfer distributions, the wall temperatures were measured by an infra-red camera system, while heat fluxes at the surfaces were generated with electric operating heating foils. It turned out from the experiments that distinct changes in the secondary flow behavior and end wall heat transfer mainly occur when the leakage mass flow rate is increased from 1% to 2%. Leakage ejection perpendicular to the main flow direction amplifies the secondary flow, in particular the horse-shoe vortex, whereas tangential leakage ejection causes a significant reduction of this vortex system. For high leakage mass flow rates the boundary layer flow at the end wall is strongly affected and seems to be highly turbulent, resulting in entirely different heat transfer distributions.

Gravity flow of cohesionless granular materials in chutes and channels

1979 ◽  
Vol 92 (1) ◽  
pp. 53-96 ◽  
Author(s):  
Stuart B. Savage
Keyword(s):  
Granular Materials ◽  
Constitutive Relations ◽  
Side Wall ◽  
Wall Friction ◽  
Hydraulic Jumps ◽  
Two Dimensional ◽  
High Deformation ◽  
Gravity Flows ◽  
Theoretical Predictions ◽  
Set Up

A constitutive equation appropriate for flow of cohesionless granular materials at high deformation rates and low stress levels is proposed. It consists of an extension and a reinterpretation of the theory of Goodman & Cowin (1972), and accounts for the non-Newtonian nature of the flow as evidenced by Bagnold's (1954) experiments. The theory is applied to analyses of gravity flows in inclined chutes and vertical channels. Experiments were set up in an attempt to generate two-dimensional shear flows corresponding to these analyses. Velocity profiles measured by a technique which makes use of fibre optic probes agree qualitatively with the theoretical predictions, but direct comparison is inappropriate because of unavoidable side-wall friction effects in the experiments. The existing measure of agreement suggests that the most prominent effects have been included in the proposed constitutive relations. Tests in the inclined chute revealed the possible existence of surge waves and granular jumps analogous to hydraulic jumps.

Effect of Boundary Layer Suction on the Corner Separation in a Highly Loaded Axial Compressor Cascade

2020 ◽  
Author(s):  
Tian Liang ◽  
Bo Liu ◽  
Stephen Spence
Keyword(s):  
Boundary Layer ◽  
Axial Compressor ◽  
Compressor Cascade ◽  
Flow Uniformity ◽  
Suction Surface ◽  
Flow Rates ◽  
Corner Separation ◽  
Boundary Layer Suction ◽  
End Wall ◽  
Suction Flow

Abstract Control of corner separation in axial compressor blade rows has attracted much interest due to its potential to improve compressor efficiency and the energy utilization in turbomachinery. This paper investigates the effectiveness and mechanisms of boundary layer suction in controlling the corner separation of a highly loaded axial compressor cascade. Numerical simulations have been carried out to investigate the effect of different suction schemes on the loss downstream of the cascade and the change in incidence characteristics with the variation of the suction flow rate. The results show that the effectiveness of flow suction in controlling the flow separation depends heavily on the proportion of the blade for which it is applied. It was found that suction along part of the blade span on the suction surface could effectively remove the separation at the region of the span influenced by the suction slot. However, this resulted in a deterioration of the flow field at other parts of the span. The full span suction scheme on the suction surface not only eliminated the separation of the boundary layer in the middle of the blade, but also significantly improved the flow uniformity near the end-wall. Despite the improvement in flow uniformity using the full-span suction scheme, a three-dimensional (3D) corner separation still existed due to the strong cross-passage pressure gradient. To improve the flow field uniformity further, two combined suction schemes with one spanwise slot on the suction surface and another slot on the end-wall were designed in order to fully remove both the separated flow on the blade suction surface and the 3D corner separation. It was found that the total pressure loss coefficient was reduced significantly by 63.8% with suction flow rates of 1.88% and 0.82% for the slots on the suction surface and the end-wall respectively. Further work showed that the behavior of the loss coefficient is different as the combination of suction flow rates is changed for different incidence. The cascade loss at high incidence operation can be more effectively reduced with suction control on the end-wall. When implementing combined suction, it is necessary to determine the best combination of suction flow rate according to the incidence level.

scholarly journals ELECTROSTATIC EFFECTS IN PNEUMATIC TRANSPORT OF GRANULAR MATERIALS

2012 ◽  
Vol 19 ◽  
pp. 351-361
Author(s):  
ELDIN WEE CHUAN LIM ◽  
JUN YAO ◽  
YANLIN ZHAO
Keyword(s):  
Granular Materials ◽  
Experimental Studies ◽  
Pneumatic Transport ◽  
Operating Conditions ◽  
Low Flow ◽  
Pneumatic Conveying ◽  
Electrostatic Effects ◽  
Flow Rates ◽  
Drag Forces ◽  
Fluid Drag

The methodology of coupling the Discrete Element Method (DEM) with Computational Fluid Dynamics (CFD) was applied for computational studies of pneumatic transport of granular materials through vertical and horizontal pipes in the presence of electrostatic effects. The simulations showed that a thin layer of particles formed and remained adhered to the pipe walls during the pneumatic conveying process due to the effects of strong electrostatic forces of attraction towards the pipe walls. Particle concentrations were generally higher near the pipe walls than at the pipe centre resulting in the ring flow pattern observed in previous experimental studies. The close correspondence between particle velocity vectors and fluid drag force vectors was indicative of the importance of fluid drag forces in influencing particle behaviors. In contrast, the much weaker particle-particle electrostatic repulsion forces had negligible effects on particle behaviors within the system under all operating conditions considered. The electrostatic field strength developed during pneumatic conveying increased with decreasing flow rate due to increased amount of particle-wall collisions. Based on dynamic analyses of forces acting on individual particles, it may be concluded that electrostatic effects played a dominant role in influencing particle behaviors during pneumatic conveying at low flow rates while drag forces became more important at high flow rates.

scholarly journals Energy dissipation due to breakage during confined compaction of granular materials

2021 ◽  
Vol 249 ◽  
pp. 07006
Author(s):  
Brett Kuwik ◽  
Ryan C. Hurley
Keyword(s):  
Particle Size ◽  
Total Energy ◽  
Granular Materials ◽  
Wall Friction ◽  
Size Distributions ◽  
Input Energy ◽  
Particle Size Distributions ◽  
Ottawa Sand ◽  
Dissipation Of Energy ◽  
Energy Dissipated

The dissipation of energy during the compaction of granular materials was studied by performing confined drop tower experiments on Ottawa sand. Energy dissipated due to breakage was quantified by evaluating the creation of new surfaces at varying drop heights. Post-compaction particle size distributions (PSD) were measured and the amount of breakage was quantified by the position of the current PSD relative to the pre-compaction and ultimate PSD. Our observations revealed that the percentage of input energy dissipated due to breakage accounted for less than 0.5% of the total energy budget and was a constant proportion regardless of the total energy applied to the system. We also evaluated the effects of die wall friction by measuring post-compaction PSD in various positions within the sample.

Heat Transfer for the Film-Cooled Vane of a 1-1/2 Stage High-Pressure Transonic Turbine—Part II: Effect of Cooling Variation on the Vane Airfoil and Inner End Wall

2012 ◽  
Vol 135 (2) ◽  
Author(s):  
Harika S. Kahveci ◽  
Charles W. Haldeman ◽  
Randall M. Mathison ◽  
Michael G. Dunn
Keyword(s):  
Heat Transfer ◽  
High Pressure ◽  
External Heat ◽  
Stanton Number ◽  
Inlet Temperature ◽  
Trailing Edge ◽  
Flow Rates ◽  
Pressure Surface ◽  
End Wall ◽  
The Impact

The impact of film cooling on heat transfer is investigated for the high-pressure vane of a 1-1/2 stage high-pressure turbine operating at design corrected conditions. Cooling is supplied through three independently controllable circuits to holes in the inner and outer end wall, vane leading edge showerhead, and the pressure and suction surfaces of the airfoil, in addition to vane trailing edge slots. Four different overall cooling flow rates are investigated and one cooling circuit is varied independently. All results reported in this part of the paper are for a radial inlet temperature profile, one of the four profiles reported in part I of this paper. Part I describes the experimental setup, data quality, influence of inlet temperature profile, and influence of cooling when compared to a solid vane. This part of the paper shows that the addition of coolant reduces airfoil Stanton number by up to 60%. The largest reductions due to cooling are observed close to the inner end wall because the coolant to the majority of the vane is supplied by a plenum at the inside diameter. While the introduction of cooling has a significant impact on Stanton number, the impact of changing coolant flow rates is only observed for gauges near 5% span and on the inner end wall. This indicates that very little of the increased coolant mass flow reaches all the way to 90% span and the majority of the additional mass flow is injected into the core flow near the plenum. Turning off the vane outer cooling circuit that supplies coolant to the outer end wall holes, vane trailing edge slots, and three rows of holes on the pressure surface of the airfoil, has a local impact on Stanton number. Changes downstream of the holes on the airfoil pressure surface indicate that internal heat transfer from the coolant flowing inside the vane is important to the external heat transfer, suggesting that a conjugate heat-transfer solution may be required to achieve good external heat-transfer predictions in this area. Measurements on the inner end wall show that temperature reduction in the vane wake due to the trailing edge cooling is important to many points downstream of the vane.

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