A pressure gradient facilitates mass flow in the oomycete Achlya bisexualis

The aim of this paper was to develop a model that can characterize the actual micropore structures in coal and gain an in-depth insight into water’s seepage rules in coal pores under different pressure gradients from a microscopic perspective. To achieve this goal, long-flame coals were first scanned by an X-ray 3D microscope; then, through a representative elementary volume (REV) analysis, the optimal side length was determined to be 60 μm; subsequently, by using Avizo software, the coal’s micropore structures were acquired. Considering that the porosity varies in the same coal sample, this study selected four regions in the sample for an in-depth analysis. Moreover, numerical simulations on water’s seepage behaviors in coal under 30 different pressure gradients were performed. The results show that (1) the variation of the simulated seepage velocity and pressure gradient accorded with Forchheimer’s high-velocity nonlinear seepage rules; (2) the permeability did not necessarily increase with the increase of the effective porosity; (3) in the same model, under different pressure gradients, the average seepage pressure decreased gradually, while the average seepage velocity and average mass flow varied greatly with the increase of the seepage length; and (4) under the same pressure gradient, the increase of the average mass flow from the inlet to the outlet became more significant under a higher inlet pressure.

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Numerical Investigation of Condensation Heat Transfer Characteristics of R134A in Rectangular Minichannel

ASME 2019 6th International Conference on Micro/Nanoscale Heat and Mass Transfer ◽

10.1115/mnhmt2019-3950 ◽

2019 ◽

Author(s):

Di Lv ◽

Wei Li ◽

Jingzhi Zhang

Keyword(s):

Heat Transfer ◽

Pressure Gradient ◽

Liquid Film ◽

Mass Flow ◽

Mass Flux ◽

Condensation Heat Transfer ◽

Condensation Process ◽

Vapor Quality ◽

Vof Model ◽

Friction Pressure

Abstract This study numerically investigated the condensation heat transfer and flow characteristics of refrigerants R134a in rectangular minichannels. Three-dimensional simulations were carried out at different mass flux values, vapor qualities and gravity conditions through using the VOF model, the turbulence model and the phase transition model. The effects of various parameters on the surface heat transfer coefficient and the friction pressure gradient is clarified. The condensation process is found to be enhanced due to the increase of vapor quality and mass flow, while the friction pressure gradient decreases with the decrease of vapor quality and mass flow. According to the data obtained from the simulation, the liquid film tends to accumulate along the corner of the cross section in retangular minichannel. And the thickness of liquid film increased with the decrease of mass flux and vapor quality.

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The mechanism of water absorption by roots I. Preliminary studies on the effects of hydrostatic pressure gradients

Proceedings of the Royal Society of London Series B Biological Sciences ◽

10.1098/rspb.1957.0056 ◽

1957 ◽

Vol 147 (928) ◽

pp. 367-380 ◽

Cited By ~ 33

Keyword(s):

Hydrostatic Pressure ◽

Pressure Gradient ◽

Mass Flow ◽

Osmotic Potential ◽

Permeability Coefficient ◽

External Medium ◽

External Pressure ◽

Pressure Gradients ◽

Unit Change ◽

Direct Technique

During transpiration the hydrostatic tension which develops in the xylem conducting elements of the root draws water from the soil through the intervening tissues of the cortex, etc. It is uncertain whether this movement is entirely diffusional or in part a mass flow. To detect any such mass flow tomato plants grown in water culture were decapitated and placed in a canister through the lid of which the cut stem protruded and in which the pressure on the culture medium could be raised. The resulting rate of exudation (flux) was measured, and compared with the flux caused by an equivalent difference in osmotic potential obtained by measuring the ∆ f. p. of the medium and sap exuded. If these values of flux were equal, movement was by diffusion alone, but if pressure caused a greater flux, an additional mass flow was indicated. Preliminary experiments indicated a much greater flux in response to differences of pressure than osmotic potential, but accurate assessment of the effect was precluded by difficulties inherent in this straightforward approach. A less direct technique was therefore devised; the change in flux caused by changing the osmotic potential of the external medium (the hydrostatic pressure being maintained constant) was compared with the change in flux caused by changing the external pressure (the osmotic potential of the external medium being kept constant). The changes in flux were measured in such a way as to minimize changes in the osmotic potential in the xylem and in resistances to diffusion or mass flow respectively. In this way the change in flux per unit change in osmotic potential difference across the cortex (osmotic permeability coefficient, k 0 ) and the change in flux per unit change in pressure difference across the cortex (pressure permeability coefficient, k p ) could be compared under the same pressure gradient and in addition the effects of pressure gradients on k 0 could be studied. Thus, the effects of a pressure gradient on the diffusional movement of water could be assessed, as well as any mass flow component of the flux detected and measured.

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Using computational fluid dynamics to evaluate a novel venous cannula (Smart canula ®) for use in cardiopulmonary bypass operating procedures

Perfusion ◽

10.1177/0267659107083657 ◽

2007 ◽

Vol 22 (4) ◽

pp. 257-265 ◽

Cited By ~ 7

Author(s):

D. Jegger ◽

S. Sundaram ◽

K. Shah ◽

I. Mallabiabarrena ◽

G. Mucciolo ◽

...

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Cardiopulmonary Bypass ◽

Pressure Gradient ◽

Surface Area ◽

Mass Flow ◽

Stokes Equations ◽

Venous Drainage ◽

Dimensional System ◽

Flow Rates

Peripheral access cardiopulmonary bypass (CPB) is initiated with percutaneous cannulae (CTRL) and venous drainage is often impeded due to smaller vessel and cannula size. A new cannula (Smartcanula ®, SC) was developed which can change shape in situ and, therefore, may improve venous drainage. Its performance was evaluated using a 2-D computational fluid dynamics (CFD) model. The Navier-Stokes equations could be simplified due to the fact that we use a steady state and a 2-dimensional system while the equation of continuity (ρ constant) was also simplified. We compared the results of the SC to the CTRL using CFDRC® (Version 6.6, CFDRC research corporation, Huntsville, USA) at two preloads (300 and 700 Pa). The SC's mass flow rate outperformed the CTRL by 12.1% and 12.2% at a pressures of 300 and 700 Pa, respectively. At 700 Pa, a pressure gradient of 50% was measured for the CTRL and 11% for the SC. The mean velocity at the 700 Pa for the CTRL was 1.0 m.s-1 at exit while the SC showed an exit velocity of 1.3 m.s-1. Shear rates inside the cannulae were similar between the two cannulae. In conclusion, the prototype shows greater mass flow rates compared to the classic cannula; thus, it is more efficient. This is also advocated by a better pressure gradient and higher average velocities. By reducing cannula-tip surface area or increasing hole surface area, greater flow rates are achieved. Perfusion (2007) 22, 257—265.

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Coanda Effect on the Impact of Distribution Characteristics of Oil-Air Annular Flow

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.620.166 ◽

2014 ◽

Vol 620 ◽

pp. 166-170

Author(s):

Qi Guo Sun ◽

Dong Xu Chen ◽

Xiong Shi Wang ◽

Zheng Hui Zhou

Keyword(s):

Pressure Gradient ◽

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Annular Flow ◽

Branch Pipe ◽

Coanda Effect ◽

Distribution Characteristics ◽

Coandǎ Effect ◽

The Impact

The T-junction model is simulated in Fluent by changing the curvature of branch pipe, and then the distribution characteristics of the annular flow was studied in T-junction distributor. The mass flow and pressure of the annular flow in this T-junction are studied, and the impact of Coanda Effect on the annular flow distribution characteristic is analyzed in oil-air two phases flow. The results show that, Coanda Effect affects the distribution of oil-air annular flow unevenly. The mass flow rate of air phase and the air velocity of outlet increase with decreasing the curvature, while the mass flow rate of liquid decrease with decreasing the curvature of the branch pipe connection; T-shaped junction inlet pressure is high, but the pressure gradient is small, the pressure gradient in the small curvature manifold is larger than that in the large curvature manifold.

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Condensation Heat Transfer and Flow Properties of R134a Refrigerant in Rectangular Minichannel: A Numerical Study

Journal of Thermal Science and Engineering Applications ◽

10.1115/1.4044168 ◽

2019 ◽

Vol 12 (2) ◽

Author(s):

Wei Li ◽

Di Lyu ◽

Jingzhi Zhang ◽

S. A. Sherif

Keyword(s):

Heat Transfer ◽

Pressure Gradient ◽

Liquid Film ◽

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Numerical Study ◽

Condensation Heat Transfer ◽

Vapor Quality ◽

Vof Model

Abstract This study numerically investigated the condensation heat transfer and flow characteristics of refrigerant R134a in a rectangular minichannel. Three-dimensional simulations were carried out at different mass fluxes, vapor qualities, and gravity conditions using the volume-of-fluid (VOF) model, a turbulence model, and a phase transition model. The effects of various parameters on the surface heat transfer coefficient and the frictional pressure gradient are investigated. The condensation process was found to be enhanced due to the increase of vapor quality and mass flow rate, while the frictional pressure gradient was found to decrease with the decrease of vapor quality and mass flow rate. Simulation results revealed that the liquid film tends to accumulate along the corner of the cross section of the minichannel. Furthermore, the thickness of the liquid film was found to increase with the decrease of mass flux and vapor quality.

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Mechanism of Circumferential Static Pressure Oscillation in a Centrifugal Compressor With Volute

10.1115/gt2021-59051 ◽

2021 ◽

Author(s):

Ce Yang ◽

Botai Su ◽

Xin Shi ◽

Hanzhi Zhang ◽

Wenli Wang ◽

...

Keyword(s):

Boundary Conditions ◽

Pressure Gradient ◽

Mass Flow ◽

Centrifugal Compressor ◽

Static Pressure ◽

Oscillation Amplitude ◽

Circumferential Direction ◽

Pressure Amplitude ◽

High Static Pressure ◽

Circumferential Pressure

Abstract Under the action of an asymmetric volute structure, a non-uniform flow field is formed in the circumferential direction of the centrifugal compressor. During the throttling process of the compressor at different rotational speeds, the static pressure presents a double-peak distribution of two high static pressure strips, one of which is induced by the volute tongue. However, the formation mechanism of the other high static pressure strip remains unclear. In this regard, computations of the steady and unsteady flows in a centrifugal compressor with and without a volute are performed. The purpose of removing the volute is to simplify the boundary conditions at the diffuser exit, eliminate the circumferential pressure gradient distribution in the volute, and retain the circumferential local high static pressure region induced by the VT; thereafter, the circumferential static pressure distributions in the diffuser and impeller are observed. The results indicate that after eliminating the pressure gradient at the diffuser exit along the rotation direction, only local high static pressure boundary conditions can result in the formation of two high static pressure strips in the diffuser and impeller. The local high static pressure at the exit redistributes the mass flow rate at the impeller outlet, forming two regions with high airflow velocity in the diffuser; this leads to the appearance of two high static pressure strips in the circumferential direction. With the increase in the pressure amplitude of the high static pressure at the diffuser exit, the oscillation amplitude of the circumferential pressure is intensified, and the pressure peaks of the two high static pressure strips increase. However, the circumferential positions of the two static pressure peaks practically remain constant. At large mass flow rates, the pressure reduction along the circumferential direction at the diffuser exit preclude the formation of two circumferential high static pressure strips in the diffuser and impeller.

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Film Cooling of an Adiabatic Flat Plate in Zero Pressure Gradient in the Presence of a Hot Mainstream and Cold Tangential Secondary Injection

Journal of Heat Transfer ◽

10.1115/1.3689124 ◽

1965 ◽

Vol 87 (3) ◽

pp. 409-418 ◽

Cited By ~ 11

Author(s):

A. E. Samuel ◽

P. N. Joubert

Keyword(s):

Pressure Gradient ◽

Flat Plate ◽

Mass Flow ◽

Film Cooling ◽

Experimental Investigations ◽

Flow Ratio ◽

Experimental Conditions ◽

Temperature Distributions ◽

Secondary Injection ◽

Mass Flow Ratio

Experimental investigations were conducted in order to clarify some of the problems of film cooling of an adiabatic flat plate in zero pressure gradient downstream of a tangential injection slot. The experimental conditions were a hot mainstream and cold secondary injection. Results are presented for wall temperature distributions at varying injected-to-mainstream mass flow ratios. Results are also presented of boundary layer temperature and velocity profiles in film cooling, for an injected-to-mainstream mass flow ratio of 0.88. The existing literature available in film cooling is reviewed.

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Activated Prominences; Mechanisms for Activation and Eruption

International Astronomical Union Colloquium ◽

10.1017/s0252921100065714 ◽

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.

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An Attack on the Contamination Problem in the Electron Microscope

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100061859 ◽

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.

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