SCALING PROPERTY OF THE DILUTE-DENSE TRANSITION IN 2D GRANULAR FLOWS

2004 ◽  
Vol 18 (17n19) ◽  
pp. 2441-2447 ◽  
Author(s):  
MEIYING HOU ◽  
WEI CHEN ◽  
TONG ZHANG ◽  
KUNQUAN LU ◽  
C. K. CHAN
Keyword(s):  
Experimental Study ◽  
Granular Flow ◽  
Granular Flows ◽  
Critical Value ◽  
Inflow Rate ◽  
Critical Rate ◽  
Jamming Transition ◽  
Variable Λ ◽  
Outflow Rate ◽  
Dense Flow

In this paper we report our experimental study of dilute-dense transition in a 2-dimensional granular flow of particle size d0 and channel width D with confined exit of width d. It is found that a maximum inflow rate Qc exists, above which the outflow changes from dilute to dense and the outflow rate Q(t) drops abruptly from Qc to a dense flow rate Qd. The re-scaled critical rate qc(≡Qc/(D/d0)) is found to be a function of a scaling variable λ only, i.e. qc~F(λ), and [Formula: see text]. The form of this new variable λ suggests that the dilute-to-dense transition is a global property of the flow; unlike the jamming transition, which depends only on [Formula: see text]. It is also found that this transition occurs when the area fraction of particles near the exit reaches a critical value 0.65±0.03.

Factors of the Transition from Dilute Flow to Dense Flow in Two-Dimensional Channel

2003 ◽  
Vol 17 (22n24) ◽  
pp. 4382-4386 ◽  
Author(s):  
Xun-Sheng Zhang ◽  
De-Song Bao ◽  
Guang-Lei Xu ◽  
Guo-Qi Hu ◽  
Zheng-Quan Pan ◽  
...  
Keyword(s):  
Granular Flow ◽  
Channel Width ◽  
Square Root ◽  
Two Dimensional ◽  
Inflow Rate ◽  
Outflow Rate ◽  
Dense Flow ◽  
Flow Case

Granular flow of steel beads from dilute flow to dense flow on an inclined two-dimensional channel is studied. The initial inflow Q0 is always a dilute flow. A transition from dilute to dense is observed when D≤Dc. In the dense flow the outflow rate (Q) depends only on opening (D), given by [Formula: see text]. For different inflow rate Q0 in the dilute flow case, the relation between the transition critical exit width (Dc) and the channel width (W) is given. And in larger inflow, the critical exit width is approximately in proportion to the square root of inflow rate, [Formula: see text].

GRANULAR FLOW IN THE PRESENCE OF AN ELECTRIC FIELD

2002 ◽  
Vol 16 (17n18) ◽  
pp. 2536-2541
Author(s):  
KUNQUAN LU ◽  
WEI CHEN ◽  
MEIYING HOU ◽  
ZEHUI JIAN
Keyword(s):  
Electric Field ◽  
Flow Rate ◽  
Granular Flow ◽  
Applied Field ◽  
Critical Value ◽  
Vertical Pipe ◽  
Initial State ◽  
Dense Flow ◽  
Two Phases ◽  
Controlled Flow

The granular flow in a vertical pipe in the presence of electric field E is studied. Depending upon its initial state and the applied field voltage the controlled flow rate remains in two phases, dilute flow or dense flow. For dilute flow, the electric field has no effect on the flow rate until V reaches a critical value V 1. At V = V 1, the flow rate drops abruptly and a transition of the particulate from dilute to dense flow occurs. For dense flow, the flow rate decreases monotonically with increasing V. A two-dimensional computer simulation has been done and the results agree qualitatively well with the experimental measurements.

Dilute-to-dense flow transition and flow-rate behavior of lateral bifurcated granular flow

2021 ◽  
Vol 383 ◽  
pp. 536-541
Author(s):  
Xiaoyan Zhou ◽  
Shikun Liu ◽  
Zihan Zhao ◽  
Xin Li ◽  
Changhao Li ◽  
...  
Keyword(s):  
Flow Rate ◽  
Granular Flow ◽  
Flow Transition ◽  
Dense Flow ◽  
Rate Behavior

scholarly journals Stress level effect on mobility of dry granular flows of angular rock fragments

Landslides ◽  
2021 ◽  
Author(s):  
B. Cagnoli
Keyword(s):  
Stress Level ◽  
Granular Flow ◽  
High Stress ◽  
Granular Flows ◽  
Flow Dynamics ◽  
Small Scale ◽  
Flow Volume ◽  
Rock Fragments ◽  
Rock Avalanches ◽  
Flow Mobility

AbstractGranular flows of angular rock fragments such as rock avalanches and dense pyroclastic flows are simulated numerically by means of the discrete element method. Since large-scale flows generate stresses that are larger than those generated by small-scale flows, the purpose of these simulations is to understand the effect that the stress level has on flow mobility. The results show that granular flows that slide en mass have a flow mobility that is not influenced by the stress level. On the contrary, the stress level governs flow mobility when granular flow dynamics is affected by clast agitation and collisions. This second case occurs on a relatively rougher subsurface where an increase of the stress level causes an increase of flow mobility. The results show also that as the stress level increases, the effect that an increase of flow volume has on flow mobility switches sign from causing a decrease of mobility at low stress level to causing an increase of mobility at high stress level. This latter volume effect corresponds to the famous Heim’s mobility increase with the increase of the volume of large rock avalanches detected so far only in the field and for this reason considered inexplicable without resorting to extraordinary mechanisms. Granular flow dynamics is described in terms of dimensionless scaling parameters in three different granular flow regimes. This paper illustrates for each regime the functional relationship of flow mobility with stress level, flow volume, grain size, channel width, and basal friction.

A Convex Complementarity Approach for Simulating Large Granular Flows

2010 ◽  
Vol 5 (3) ◽  
Author(s):  
Alessandro Tasora ◽  
Mihai Anitescu
Keyword(s):  
Granular Flow ◽  
Complementarity Problems ◽  
Particle Interaction ◽  
Granular Flows ◽  
Rigid Bodies ◽  
Integration Time ◽  
Frictional Contacts ◽  
Physical Experiments ◽  
Dense Granular Flow ◽  
Number Of Particles

Aiming at the simulation of dense granular flows, we propose and test a numerical method based on successive convex complementarity problems. This approach originates from a multibody description of the granular flow: all the particles are simulated as rigid bodies with arbitrary shapes and frictional contacts. Unlike the discrete element method (DEM), the proposed approach does not require small integration time steps typical of stiff particle interaction; this fact, together with the development of optimized algorithms that can run also on parallel computing architectures, allows an efficient application of the proposed methodology to granular flows with a large number of particles. We present an application to the analysis of the refueling flow in pebble-bed nuclear reactors. Extensive validation of our method against both DEM and physical experiments results indicates that essential collective characteristics of dense granular flow are accurately predicted.

INTRA-LEFT VENTRICULAR FLOW DISTRIBUTIONS IN DIASTOLIC AND SYSTOLIC PHASES, BASED ON ECHO VELOCITY FLOW MAPPING OF NORMAL SUBJECTS AND HEART FAILURE PATIENTS, TO CHARACTERIZE LEFT VENTRICULAR PERFORMANCE OUTCOMES OF HEART FAILURE

2012 ◽  
Vol 12 (05) ◽  
pp. 1240029 ◽  
Author(s):  
THU-THAO LE ◽  
RU-SAN TAN ◽  
FEIQIONG HUANG ◽  
LIANG ZHONG ◽  
SRIDHAR IDAPALAPATI ◽  
...  
Keyword(s):  
Heart Failure ◽  
Velocity Vector ◽  
Normal Subjects ◽  
Performance Outcomes ◽  
Left Ventricular ◽  
Inflow Rate ◽  
Flow Mapping ◽  
Velocity Flow ◽  
Outflow Rate ◽  
Blood Flow Patterns

Heart failure (HF), one of the most common diseases in the world, causes left ventricular dysfunction (LV) and high mortality. HF patients are stratified into two groups based on their LV ejection fraction (EF) — HF with normal EF (HFNEF) and with reduced EF (HFREF). EF is a commonly used measure of LV contractile performance. Despite preserved EF, a complex mixture of systolic and diastolic dysfunction and variable degrees of LV remodelling underlying HFNEF poses challenges to diagnose and provide pharmacological treatment for HFNEF. In recent years, the velocity flow mapping (VFM) technique has been developed to generate flow velocity vector fields by post-processing color Doppler echocardiographic (echo) images. We aim to obtain the intra-LV blood flow patterns for patients with HFNEF, HFREF, and normal subjects, in order to characterize the LV performance outcomes of normal subjects and HF patients. Two subjects from each group of HFNEF, HFREF, and normal underwent echo scans. Velocity vector distributions throughout the cardiac cycle were then analysed using the VFM technique. In each subject, the outflow rate during systole, inflow rate during diastole, as well as wall stress-based pressure-normalized contractility index, dσ*/dt max , were computed and compared among the groups. This study demonstrated the use of VFM to visualize LV blood flow patterns in HF patients and normal subjects. Different patterns of flow distributions were observed in these subjects. In HFREF patients, dσ*/dt max , the peak outflow rate and peak inflow rate during early filling were markedly reduced. In HFNEF patients, peak outflow rates were increased compared to those of normal subjects.

scholarly journals Формирование и деформация капель жидкости в микроканалах

2020 ◽  
Vol 46 (15) ◽  
pp. 18
Author(s):  
Ф.В. Роньшин ◽  
Ю.А. Дементьев ◽  
Е.А. Чиннов
Keyword(s):  
Experimental Study ◽  
Flow Regime ◽  
Cross Section ◽  
Weber Number ◽  
Rectangular Cross Section ◽  
Critical Value ◽  
Drop Formation ◽  
Liquid Bridges ◽  
Liquid Moving ◽  
Side Walls

An experimental study of drop formation in narrow horizontal microchannels with rectangular cross section and a height from 50 to 150 micrometers was performed. It is shown that in these channels there is a new flow regime when drops moving along the microchannel, which are vertical liquid bridges. Three mechanisms of the formation of such drops are distinguished: the formation directly near the liquid nozzle, the separation of droplets from the liquid moving along the side walls of the channel, and due to the destruction of strongly deformed drops and horizontal liquid bridges. It was found that the deformation of drops increases with an increase in the Weber number. It is shown that when the first critical value of the Weber number is reached, the drops begin to deform, and when the second Weber number is reached, they break.

The Granular Lubricated Journal Bearing: Evidence of Lift Formation

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Venkata K. Jasti ◽  
Martin C. Marinack ◽  
Deepak Patil ◽  
C. Fred Higgs
Keyword(s):  
Carrying Capacity ◽  
Granular Flow ◽  
High Speed ◽  
Journal Bearing ◽  
Hydrodynamic Lubrication ◽  
Flow Behavior ◽  
Extreme Environments ◽  
Granular Flows ◽  
Load Carrying Capacity ◽  
Load Carrying

This work demonstrates that granular flows (i.e., macroscale, noncohesive spheres) entrained into an eccentrically converging gap can indeed actually exhibit lubrication behavior as prior models postulated. The physics of hydrodynamic lubrication is quite well understood and liquid lubricants perform well for conventional applications. Unfortunately, in certain cases such as high-speed and high-temperature environments, liquid lubricants break down making it impossible to establish a stable liquid film. Therefore, it has been previously proposed that granular media in sliding convergent interfaces can generate load carrying capacity, and thus, granular flow lubrication. It is a possible alternative lubrication mechanism that researchers have been exploring for extreme environments, or wheel-regolith traction, or for elucidating the spreadability of additive manufacturing materials. While the load carrying capacity of granular flows has been previously demonstrated, this work attempts to more directly uncover the hydrodynamic-like granular flow behavior in an experimental journal bearing configuration. An enlarged granular lubricated journal bearing (GLJB) setup has been developed and demonstrated. The setup was made transparent in order to visualize and video capture the granular collision activity at high resolution. In addition, a computational image processing program has been developed to process the resulting images and to noninvasively track the “lift” generated by granular flow during the journal bearing operation. The results of the lift caused by granular flow as a function of journal rotation rate are presented as well.

scholarly journals Thermal Performance of Solar Collectors with EPDM Absorber Plates

1988 ◽  
Vol 41 (4) ◽  
pp. 623
Author(s):  
MJ O'Keefe ◽  
JLA Francey
Keyword(s):  
Experimental Study ◽  
Thermal Resistance ◽  
Flat Plate ◽  
Heat Loss ◽  
Thermal Performance ◽  
Critical Value ◽  
Solar Collectors ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
High Thermal Resistance

An experimental study of flat-plate solar collectors using ethylene, propylenediene monomer (EPDM) absorber plates is descn"bed. In spite of the high thermal resistance of this material the performance is found to compare well with metal absorbers and to be in agreement with the Hottel-Whillier-Bliss equation. There is, however, an observed increase in the heat loss coefficient for mass flow rates below a critical value.

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