scholarly journals Evaluation of the Constant Head and the Constant Flow-Rate Permeability Tests for Low-Permeability Geomaterials.

1999 ◽  
pp. 427-435 ◽  
Author(s):  
Tetsuro ESAKI ◽  
Ming ZHANG ◽  
Mikio TAKEDA ◽  
Manabu TAKAHASHI ◽  
Kentarou SAKAI
Keyword(s):  
Flow Rate ◽  
Low Permeability ◽  
Constant Flow ◽  
Constant Flow Rate ◽  
Constant Head

Theoretical Evaluation of the Transient Response of Constant Head and Constant Flow-Rate Permeability Tests

1998 ◽  
Vol 21 (1) ◽  
pp. 52 ◽  
Author(s):  
RC Chaney ◽  
KR Demars ◽  
M Zhang ◽  
M Takahashi ◽  
RH Morin ◽  
...  
Keyword(s):  
Transient Response ◽  
Flow Rate ◽  
Constant Flow ◽  
Theoretical Evaluation ◽  
Constant Flow Rate ◽  
Constant Head

Physical clogging of soil filters under constant flow rate versus constant head

2005 ◽  
Vol 42 (3) ◽  
pp. 804-811 ◽  
Author(s):  
Lakshmi N Reddi ◽  
Ming Xiao ◽  
Malay G Hajra ◽  
In Mo Lee
Keyword(s):  
Flow Rate ◽  
Operating Conditions ◽  
Permeability Reduction ◽  
Constant Flow ◽  
Earth Dams ◽  
Good Qualitative Agreement ◽  
Constant Flow Rate ◽  
Rate Versus ◽  
Constant Head ◽  
Filter Clogging

In this study, the differences in soil filter clogging are evaluated under two operating conditions: constant head and constant flow rate. Whereas filters placed around well screens and leachate collection systems are subjected to a constant flow rate, filters in earth dams and pavement drainage systems operate under constant or slightly varying heads. In this study, the experiments revealed similar permeability reductions with respect to time in both cases; however, the permeability reduction under the condition of constant head occurred in much fewer pore volumes than under the condition of constant flow rate. Self-filtration appeared to be greater under the condition of constant head. The physical clogging model developed for the conditions of constant flow rate and constant head showed good qualitative agreement with experimental observations.Key words: particle, clogging, filter, constant, head, flow.

Pumpless Fuel Supply Using Pressurized Fuel Regulated by Autonomous Flow-Rate Regulation Valves

2012 ◽  
Vol 9 (3) ◽  
Author(s):  
Il Doh ◽  
Young-Ho Cho
Keyword(s):  
Fuel Cells ◽  
Flow Rate ◽  
Electrical Power ◽  
Initial Pressure ◽  
Flow Regulation ◽  
Present System ◽  
Constant Flow ◽  
Constant Flow Rate ◽  
Fuel Supply ◽  
Fuel Flow

A pumpless fuel supply using pressurized fuel with autonomous flow regulation valves is presented. Since micropumps and their control circuitry consume a portion of the electrical power generated in fuel cells, fuel supply without micropumps makes it possible to provide more efficient and inexpensive fuel cells than conventional ones. The flow regulation valves in the present system maintain the constant fuel flow rate from the pressurized fuel chamber even though the fuel pressure decreases. They autonomously adjust fluidic resistance of the channel according to fuel pressure so as to maintain constant flow rate. Compared to previous pumpless fuel supply methods, the present method offers more uniform fuel flow without any fluctuation using a simple structure. The prototypes were fabricated by a polymer micromolding process. In the experimental study using the pressurized deionized water, prototypes with pressure regulation valves showed constant flow rate of 5.38 ± 0.52 μl/s over 80 min and 5.89 ± 0.62 μl/s over 134 min, for the initial pressure in the fuel chamber of 50 and 100 kPa, respectively, while the other prototypes having the same fluidic geometry without flow regulation valves showed higher and gradually decreasing flow rate. The present pumpless fuel supply method providing constant flow rate with autonomous valve operation will be beneficial for the development of next-generation fuel cells.

scholarly journals Axisymmetric three-dimensional gravity currents generated by lock exchange

2018 ◽  
Vol 851 ◽  
pp. 507-544 ◽  
Author(s):  
Roberto Inghilesi ◽  
Claudia Adduce ◽  
Valentina Lombardi ◽  
Federico Roman ◽  
Vincenzo Armenio
Keyword(s):  
Froude Number ◽  
Flow Rate ◽  
Rapid Development ◽  
Three Dimensional ◽  
Gravity Currents ◽  
Constant Flow ◽  
Axially Symmetric ◽  
Grashof Number ◽  
Constant Flow Rate ◽  
Dimensional Gravity

Unconfined three-dimensional gravity currents generated by lock exchange using a small dividing gate in a sufficiently large tank are investigated by means of large eddy simulations under the Boussinesq approximation, with Grashof numbers varying over five orders of magnitudes. The study shows that, after an initial transient, the flow can be separated into an axisymmetric expansion and a globally translating motion. In particular, the circular frontline spreads like a constant-flow-rate, axially symmetric gravity current about a virtual source translating along the symmetry axis. The flow is characterised by the presence of lobe and cleft instabilities and hydrodynamic shocks. Depending on the Grashof number, the shocks can either be isolated or produced continuously. In the latter case a typical ring structure is visible in the density and velocity fields. The analysis of the frontal spreading of the axisymmetric part of the current indicates the presence of three regimes, namely, a slumping phase, an inertial–buoyancy equilibrium regime and a viscous–buoyancy equilibrium regime. The viscous–buoyancy phase is in good agreement with the model of Huppert (J. Fluid Mech., vol. 121, 1982, pp. 43–58), while the inertial phase is consistent with the experiments of Britter (Atmos. Environ., vol. 13, 1979, pp. 1241–1247), conducted for purely axially symmetric, constant inflow, gravity currents. The adoption of the slumping model of Huppert & Simpson (J. Fluid Mech., vol. 99 (04), 1980, pp. 785–799), which is here extended to the case of constant-flow-rate cylindrical currents, allows reconciling of the different theories about the initial radial spreading in the context of different asymptotic regimes. As expected, the slumping phase is governed by the Froude number at the lock’s gate, whereas the transition to the viscous phase depends on both the Froude number at the gate and the Grashof number. The identification of the inertial–buoyancy regime in the presence of hydrodynamic shocks for this class of flows is important, due to the lack of analytical solutions for the similarity problem in the framework of shallow water theory. This fact has considerably slowed the research on variable-flow-rate axisymmetric gravity currents, as opposed to the rapid development of the knowledge about cylindrical constant-volume and planar gravity currents, despite their own environmental relevance.

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