On the role and the origin of the gas pressure gradient in the discharge of fine solids from hoppers

2003 ◽  
Vol 58 (23-24) ◽  
pp. 5269-5278 ◽  
Author(s):  
Diego Barletta ◽  
Giorgio Donsı̀ ◽  
Giovanna Ferrari ◽  
Massimo Poletto
Keyword(s):  
Pressure Gradient ◽  
Gas Pressure

scholarly journals The effects of magnetic field strength on the properties of wind generated from hot accretion flow

2018 ◽  
Vol 615 ◽  
pp. A35 ◽  
Author(s):  
De-Fu Bu ◽  
Amin Mosallanezhad
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Pressure Gradient ◽  
Magnetic Field Strength ◽  
Magnetic Pressure ◽  
Gas Pressure ◽  
Accretion Flow ◽  
Accretion Flows ◽  
Black Hole Accretion ◽  
The Magnetic Field

Context. Observations indicate that wind can be generated in hot accretion flow. Wind generated from weakly magnetized accretion flow has been studied. However, the properties of wind generated from strongly magnetized hot accretion flow have not been studied. Aims. In this paper, we study the properties of wind generated from both weakly and strongly magnetized accretion flow. We focus on how the magnetic field strength affects the wind properties. Methods. We solve steady-state two-dimensional magnetohydrodynamic equations of black hole accretion in the presence of a largescale magnetic field. We assume self-similarity in radial direction. The magnetic field is assumed to be evenly symmetric with the equatorial plane. Results. We find that wind exists in both weakly and strongly magnetized accretion flows. When the magnetic field is weak (magnetic pressure is more than two orders of magnitude smaller than gas pressure), wind is driven by gas pressure gradient and centrifugal forces. When the magnetic field is strong (magnetic pressure is slightly smaller than gas pressure), wind is driven by gas pressure gradient and magnetic pressure gradient forces. The power of wind in the strongly magnetized case is just slightly larger than that in the weakly magnetized case. The power of wind lies in a range PW ~ 10−4–10−3 Ṁinc2, with Ṁin and c being mass inflow rate and speed of light, respectively. The possible role of wind in active galactic nuclei feedback is briefly discussed.

scholarly journals The Mass and Size Distribution of Planetesimals Formed by the Streaming Instability. II. The Effect of the Radial Gas Pressure Gradient

2019 ◽  
Vol 883 (2) ◽  
pp. 192 ◽  
Author(s):  
Charles P. Abod ◽  
Jacob B. Simon ◽  
Rixin Li ◽  
Philip J. Armitage ◽  
Andrew N. Youdin ◽  
...  
Keyword(s):  
Pressure Gradient ◽  
Size Distribution ◽  
Gas Pressure ◽  
Streaming Instability

scholarly journals Dynamic Characterization during Gas Initial Desorption of Coal Particles and Its Influence on the Initiation of Coal and Gas Outbursts

Processes ◽  
2021 ◽  
Vol 9 (7) ◽  
pp. 1101
Author(s):  
Chaojie Wang ◽  
Xiaowei Li ◽  
Changhang Xu ◽  
Yujia Chen ◽  
Zexiang Tang ◽  
...  
Keyword(s):  
Pressure Gradient ◽  
Dynamic Effect ◽  
Coal Mass ◽  
Gas Pressure ◽  
Coal Surface ◽  
Dynamic Characterization ◽  
Coal Particles ◽  
Expansion Energy ◽  
Gas Expansion ◽  
Two Peaks

The law of gas initial desorption from coals is greatly important for understanding the occurrence mechanism and predicting coal and gas outburst (hereinafter referred to as ‘outburst’). However, dynamic characterization of gas initial desorption remains to be investigated. In this study, by monitoring the gas pressure and temperature of tectonically deformed (TD) coal and primary-undeformed (PU) coal, we established the evolution laws of gas key parameters during the initial desorption. The results indicate that the gas pressure drop rate, mass flow rate, initial desorption rate, and gas velocity increase with increasing gas pressure, with stronger gas dynamic effect, generating a high pressure gradient on the coal surface. Under the same gas pressure, the pressure gradient formed on the TD coal surface is greater than that formed on the surface of the PU coal, resulting in easily initiating an outburst in the TD coal. Moreover, the increased gas pressure increases temperature change rates (falling rate and rising rate) of coal mass. The minimum and final stable temperatures in the TD coal are generally lower compared to the PU coal. The releasing process of gas expansion energy can be divided into two stages exhibiting two peaks which increase as gas pressure increases. The two peak values for the TD coal both are about 2–3 times of those of the PU coal. In addition, the total gas expansion energy released by TD coal is far greater than that released by PU coal. The two peaks and the total values of gas expansion energy also prove that the damage of gas pressure to coal mass increases with the increased pressure, more likely producing pulverized coals and more prone to initiate an outburst.

scholarly journals Creation of new guest accessible space under gas pressure in a flexible MOF: multidimensional insight through combination of in situ techniques

2016 ◽  
Vol 52 (76) ◽  
pp. 11374-11377 ◽  
Author(s):  
Prashant M. Bhatt ◽  
Eustina Batisai ◽  
Vincent J. Smith ◽  
Leonard J. Barbour
Keyword(s):  
Pressure Gradient ◽  
Single Crystal ◽  
Gas Pressure ◽  
Single Crystal Diffraction ◽  
In Situ Techniques

Creation of a new guest accessible space under gas pressure in a flexible MOF studied by in situ single crystal diffraction and Pressure Gradient DSC.

Numerical Experiments on Planetesimal Aggregation during the Formation of the Solar System

1977 ◽  
Vol 3 (2) ◽  
pp. 169-171 ◽  
Author(s):  
K. Hourigan
Keyword(s):  
Solar System ◽  
Pressure Gradient ◽  
Numerical Experiments ◽  
Central Body ◽  
Planetary System ◽  
Gas Pressure ◽  
The Sun ◽  
Major Area ◽  
The Common ◽  
Gaseous Disc

A major area of difficulty in the cosmogony of the solar system is understanding how a large number of small planetesimals, which have condensed from the primordial gas, can aggregate into the ordered planetary system present today. Theories involving aggregation within a gaseous disc [e.g. Cameron (1973)] suffer the common difficulty that the particles, once condensed, are no longer supported by the radial gas pressure gradient and spiral rapidly in towards the Sun. Most of the planetesimals are dragged in to the central body in times several orders of magnitude less than would be required for larger bodies to accrete (Goldreich & Ward 1973).

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.

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