Research on Transient Flow Regulation With the Effect of Quadratic Pressure Gradient

2013 ◽  
Vol 31 (4) ◽  
pp. 408-417 ◽  
Author(s):  
M. Dewei ◽  
J. Ailin ◽  
J. Chengye ◽  
Z. Qian ◽  
H. Dongbo
Keyword(s):  
Pressure Gradient ◽  
Transient Flow ◽  
Flow Regulation

scholarly journals FLOW BEHAVIOUR OF OIL BLOB THROUGH A CAPILLARY TUBE CONSTRICTION DURING PULSED INJECTION

2018 ◽  
Vol 81 (1) ◽  
Author(s):  
Shiferaw Regassa Jufar ◽  
Tareq M Al-Shami ◽  
Ulugbek Djuraev ◽  
Berihun Mamo Negash ◽  
Mohammed Mahbubur Rahman
Keyword(s):  
Pressure Gradient ◽  
Transient Flow ◽  
Capillary Tube ◽  
Reverse Flow ◽  
Flow Behavior ◽  
Adverse Pressure Gradient ◽  
Gradient Zone ◽  
Pulsed Injection ◽  
Time Required ◽  
Continuous Injection

A numerical simulation of flow of oil blob through a capillary tube constriction is presented. The simulation was run in a 2D axisymmetric model. Water is injected at the inlet to mobilize oil blob placed near the capillary tube constriction. Transient flow images were used to understand the flow evolution process. Results from the study show that pulsed injection effectively assisted to squeeze out the oil blob through the capillary tube constriction with shorter time compared to continuous injection.  Pulsed injection reduced the time required for the first droplet to cross the capillary tube constriction by about 3 folds compared to continuous injection. In addition, the droplet that crossed the constriction is larger when the flow was pulsed. In both cases, there is a reverse flow in the opposite direction of the injection. However, the severity of the reverse flow is stronger in the case of continuous injection. Immediately downstream the constriction, there is an adverse pressure gradient zone during continuous injection which limits the mobility of droplet that crossed the constriction. However, in the case of pulsed injection, there is a favorable pressure gradient zone immediately downstream the constriction. This zone expedites mobility of droplets that cross the constriction by transporting them further downstream through suction effect. Apparently, pulsed injection eases off the adverse pressure gradient and allowed more volume of oil to pass through the constriction. Within about two periods of pulsation, 84% of original oil placed at the beginning crossed the constriction compared to only 35% in the case of continuous injection. Even though the same amount of water was injected in both cases, pulsed injection clearly altered the flow behavior. The observation from this study may be extended to more complex flows in order to tailor the method for certain specific applications, such as flow of residual oil through a reservoir.

Plastic Flow Establishment in Tubes: A Comparison of Pressure Gradient and Yield Stress Change Effects

2013 ◽  
Author(s):  
Mario F. Letelier ◽  
Dennis A. Siginer ◽  
Gonzalo A. Uribe ◽  
Juan Stockle
Keyword(s):  
Pressure Gradient ◽  
Steady Flow ◽  
Yield Stress ◽  
Analytical Method ◽  
Transient Flow ◽  
Step Change ◽  
Stress Change ◽  
Mr Fluids ◽  
Time Required ◽  
Exact Analytical Method

The transient flow that follows an instantaneous change of yield stress of a magnetorheological (MR) fluid in round tubes is analyzed by an exact analytical method. The time required to establish steady flow of MR fluids after a sudden yield stress change as well as for combinations of step-change in the pressure gradient and yield stress is determined.

Analysis of transient flow and starting pressure gradient of power-law fluid in fractal porous media

2015 ◽  
Vol 26 (04) ◽  
pp. 1550045 ◽  
Author(s):  
Xiao-Hua Tan ◽  
Xiao-Ping Li ◽  
Lie-Hui Zhang ◽  
Jian-Yi Liu ◽  
Jianchao Cai
Keyword(s):  
Porous Media ◽  
Fractal Dimension ◽  
Pressure Gradient ◽  
Power Law ◽  
Transient Flow ◽  
Power Law Fluid ◽  
Fractal Properties ◽  
Pressure Changes ◽  
Power Law Index ◽  
Starting Pressure Gradient

A transient flow model for power-law fluid in fractal porous media is derived by combining transient flow theory with the fractal properties of tortuous capillaries. Pressure changes of transient flow for power-law fluid in fractal porous media are related to pore fractal dimension, tortuosity fractal dimension and the power-law index. Additionally, the starting pressure gradient model of power-law fluid in fractal porous media is established. Good agreement between the predictions of the present model and that of the traditional empirical model is obtained, the sensitive parameters that influence the starting pressure gradient are specified and their effects on the starting pressure gradient are discussed.

Influence of ramped pressure gradient on transient flow formation in a horizontal porous channel

Heat Transfer ◽  
2021 ◽  
Author(s):  
Basant K. Jha ◽  
Zainab Sa'id Yunus
Keyword(s):  
Pressure Gradient ◽  
Transient Flow ◽  
Porous Channel ◽  
Flow Formation

scholarly journals Transient Flows of Newtonian Fluid through a Rectangular Microchannel with Slip Boundary

2014 ◽  
Vol 2014 ◽  
pp. 1-13 ◽  
Author(s):  
Benchawan Wiwatanapataphee ◽  
Yong Hong Wu ◽  
Suharsono Suharsono
Keyword(s):  
Pressure Gradient ◽  
Newtonian Fluid ◽  
Flow Rate ◽  
Transient Flow ◽  
Flow Behavior ◽  
Separation Of Variables ◽  
Fourier Series Expansion ◽  
Slip Parameter ◽  
Boundary Slip ◽  
Rectangular Microchannel

We study the transient flow of a Newtonian fluid in rectangular microchannels taking into account boundary slip. An exact solution is derived by using the separation of variables in space and Fourier series expansion in time. It is found that, for different forms of driving pressure field, the effect of boundary slip on the flow behavior is qualitatively different. If the pressure gradient is constant, the flow rate is almost linearly proportional to the slip parameterlwhenlis large; if the pressure gradient is in a waveform, as the slip parameterlincreases, the amplitude of the flow rate increases until approaching a constant value whenlbecomes sufficiently large.

Oscillatory Transient Flow Experiments and Analysis in Circular Microchannels

2006 ◽  
Author(s):  
A. Javadi ◽  
K. Javadi ◽  
J. Kra¨gel ◽  
R. Miller ◽  
V. I. Kovalchuk ◽  
...  
Keyword(s):  
Experimental Data ◽  
Velocity Profile ◽  
Pressure Gradient ◽  
Oscillatory Flow ◽  
Transient Flow ◽  
Pure Water ◽  
Experimental Results ◽  
Maximum Speed ◽  
Frequency Range ◽  
Flow Through

In this research purely oscillation fluid flow in two microtubes 150 and 250 μm (3.5 mm length) is studied using computational fluid dynamic (CFD) approach and utilizing a new experimental setup developed for dynamic interfacial tension measurement (capillary pressure technique) in the frequency range between 0.2 and 80 Hz. The experiments are done with pure water at a mean temperature of about 25 °C. The results of oscillatory conditions for microtubes of 0.5 mm in diameter have been compared with experimental results for several frequencies. The computational approach was validated by comparison with experimental data of the continuous constant flow through microtubes and also with experimental results of an oscillatory flow through the same tubes at up to 25 Hz. For evaluation of the effects of hydrodynamic relaxation time th = R2 / ν on the amplitude of the pressure gradient, CFD simulation of the oscillatory flow through microtubes of 0.3 and 0.5 mm (diameter) with th =0.0225 s and 0.0625 s have been provided to compare with own corresponding maximum continuous flow (CMCF) experimental data for each frequency which occurs at maximum speed of sinusoidal motion of the piezo. The comparison demonstrates that for a microtube of 0.5 mm and th=0.0625 s for frequencies F〈(1/th) ≤ 16 Hz the computational results for amplitude of pressure gradient is in relatively good agreement with own CMCF experimental data, while for microtubes of 0.3 mm in diameter this agreement is observed for frequencies lower than F〈(1/th) ≤ 44 Hz. CFD simulations of the velocity profile of oscillatory flow through these microtube support these findings and show a parabolic velocity profile (like Poiseuille flow) for frequencies ≤ 10 Hz for microtube of 0.5 mm diameter while this situation is observed below 40 Hz for microtubes of 0.3 mm diameter. Although for a smaller microtube size a relatively developed flow occurs in a higher frequency range, turbulence effects can appear sooner due to the higher flow rates and consequently higher Reynolds numbers. The combination of these two opposite effects would have to be considered when comparing the flow field through microtubes of different size.

Activated Prominences; Mechanisms for Activation and Eruption

1979 ◽  
Vol 44 ◽  
pp. 307-313
Author(s):  
D.S. Spicer
Keyword(s):  
Pressure Gradient ◽  
Density Gradient ◽  
Current Density ◽  
Convective Instability ◽  
Tearing Mode ◽  
Magnetic Shear ◽  
Long Wavelength ◽  
Ideal Mhd ◽  
Gradient Change ◽  
Accelerated Particles

A possible relationship between the hot prominence transition sheath, increased internal turbulent and/or helical motion prior to prominence eruption and the prominence eruption (“disparition brusque”) is discussed. The associated darkening of the filament or brightening of the prominence is interpreted as a change in the prominence’s internal pressure gradient which, if of the correct sign, can lead to short wavelength turbulent convection within the prominence. Associated with such a pressure gradient change may be the alteration of the current density gradient within the prominence. Such a change in the current density gradient may also be due to the relative motion of the neighbouring plages thereby increasing the magnetic shear within the prominence, i.e., steepening the current density gradient. Depending on the magnitude of the current density gradient, i.e., magnetic shear, disruption of the prominence can occur by either a long wavelength ideal MHD helical (“kink”) convective instability and/or a long wavelength resistive helical (“kink”) convective instability (tearing mode). The long wavelength ideal MHD helical instability will lead to helical rotation and thus unwinding due to diamagnetic effects and plasma ejections due to convection. The long wavelength resistive helical instability will lead to both unwinding and plasma ejections, but also to accelerated plasma flow, long wavelength magnetic field filamentation, accelerated particles and long wavelength heating internal to the prominence.

An Attack on the Contamination Problem in the Electron Microscope

1967 ◽  
Vol 25 ◽  
pp. 368-368
Author(s):  
J. J. Kelsch ◽  
A. Holtz
Keyword(s):  
Electron Microscope ◽  
Pressure Gradient ◽  
Ionization Potential ◽  
Simple Solution ◽  
Specimen Surface ◽  
Contamination Rate ◽  
Local Pressure ◽  
High Ionization ◽  
Hydrocarbon Molecules ◽  
Contamination Problem

A simple solution to the serious problem of specimen contamination in the electron microscope is presented. This is accomplished by the introduction of clean helium into the vacuum exactly at the specimen position. The local pressure gradient thus established inhibits the migration of hydrocarbon molecules to the specimen surface. The high ionization potential of He permits the use of relatively large volumes of the gas, without interfering with gun stability. The contamination rate is reduced on metal samples by a factor of 10.

Hydration Chamber for Jeolco 200 Kv Microscope

1970 ◽  
Vol 28 ◽  
pp. 542-543
Author(s):  
V. R. Matricardi ◽  
G. G. Hausner ◽  
D. F. Parsons
Keyword(s):  
Electron Microscope ◽  
Water Vapor ◽  
Vapor Pressure ◽  
Pressure Gradient ◽  
Room Temperature ◽  
List Type ◽  
Type Number ◽  
Equilibrium Vapor Pressure

In order to observe room temperature hydrated specimens in an electron microscope, the following conditions should be satisfied: The specimen should be surrounded by water vapor as close as possible to the equilibrium vapor pressure corresponding to the temperature of the specimen.The specimen grid should be inserted, focused and photo graphed in the shortest possible time in order to minimize dehydration.The full area of the specimen grid should be visible in order to minimize the number of changes of specimen required.There should be no pressure gradient across the grid so that specimens can be straddled across holes.Leakage of water vapor to the column should be minimized.

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