scholarly journals Dust Eruptions

2021 ◽  
Author(s):  
◽  
Harpreet Singh
Keyword(s):  
Shock Tube ◽  
Pressure Difference ◽  
Momentum Conservation ◽  
Expansion Wave ◽  
Wall Friction ◽  
Good Match ◽  
New Model ◽  
Bead Diameter ◽  
Pressure Changes

<p>We present a new model for the fragmentation of dust beds in laboratory shock tube experiments. The model successfully explains the formation of layers in the bed using mass and momentum conservation. Our model includes the effect of wall friction, inherent cohesion, and gravitational overburden. We find that the pressure changes caused by the expansion wave take time to penetrate into the bed, while simultaneously increasing in magnitude. By the time the pressure difference is large enough to overcome wall friction, the overburden and the intrinsic cohesion of the bed, it has penetrated ~8-15 bead diameters into the bed, thus causing a layer of dust to be lifted off. We have found the dependence of layer size upon bead diameter and found a good match to experiment. We have also predicted the dependence of layer size and fragmentation time on bead density.</p>

scholarly journals Dust Eruptions

2021 ◽  
Author(s):  
◽  
Harpreet Singh
Keyword(s):  
Shock Tube ◽  
Pressure Difference ◽  
Momentum Conservation ◽  
Expansion Wave ◽  
Wall Friction ◽  
Good Match ◽  
New Model ◽  
Bead Diameter ◽  
Pressure Changes

<p>We present a new model for the fragmentation of dust beds in laboratory shock tube experiments. The model successfully explains the formation of layers in the bed using mass and momentum conservation. Our model includes the effect of wall friction, inherent cohesion, and gravitational overburden. We find that the pressure changes caused by the expansion wave take time to penetrate into the bed, while simultaneously increasing in magnitude. By the time the pressure difference is large enough to overcome wall friction, the overburden and the intrinsic cohesion of the bed, it has penetrated ~8-15 bead diameters into the bed, thus causing a layer of dust to be lifted off. We have found the dependence of layer size upon bead diameter and found a good match to experiment. We have also predicted the dependence of layer size and fragmentation time on bead density.</p>

scholarly journals Powder flow down a vertical pipe: the effect of air flow

2002 ◽  
Vol 459 ◽  
pp. 317-345 ◽  
Author(s):  
Y. BERTHO ◽  
F. GIORGIUTTI-DAUPHINÉ ◽  
T. RAAFAT ◽  
E. J. HINCH ◽  
H. J. HERRMANN ◽  
...  
Keyword(s):  
Small Diameter ◽  
Stationary Flow ◽  
Momentum Conservation ◽  
Wall Friction ◽  
Particle Fraction ◽  
Friction Forces ◽  
Flow Rates ◽  
Lower Flow ◽  
Grain Flow ◽  
Grain Distribution

The dynamics of dry granular flows down a vertical glass pipe of small diameter have been studied experimentally. Simultaneous measurements of pressure profiles, air and grain flow rates and volume fractions of particles have been realized together with spatio-temporal diagrams of the grain distribution down the tube. At large grain flow rates, one observes a stationary flow characterized by high particle velocities, low particle fractions and a downflow of air resulting in an underpressure in the upper part of the pipe. A simple model assuming a free fall of the particles slowed down by air friction and taking into account finite particle fraction effects through Richardson–Zaki's law has been developed: it reproduces pressure and particle fraction variations with distance and estimates friction forces with the wall. At lower flow rates, sequences of high-density plugs separated by low-density bubbles moving down at a constant velocity are observed. The pressure is larger than outside the tube and its gradient reflects closely the weight of the grains. Writing mass and momentum conservation equations for the air and for the grains allows one to estimate the wall friction, which is less than 10% of the weight for grains with a clean smooth surface but up to 30% for grains with a rougher surface. At lower flow rates, oscillating-wave regimes resulting in large pressure fluctuations are observed and their frequency is predicted.

Steam Dryer Acoustic Load Predictions in the Main Steam Line Break Event

2008 ◽  
Author(s):  
Jin Yan ◽  
Francis Bolger ◽  
Guangjun Li ◽  
Weimin Dai ◽  
Lev Klebanov
Keyword(s):  
Pressure Difference ◽  
Acoustic Pressure ◽  
Steam Line ◽  
Expansion Wave ◽  
Distribution Area ◽  
Ambient Environment ◽  
Design Basis ◽  
Acoustic Load ◽  
Main Steam Line ◽  
Main Steam

In nuclear reactor design, significant acoustic pressure loads impact the steam dryer hood as a result of the main steam line break outside containment (MSLB) event. When a main steam line breaks, it is assumed that the pipe instantaneously breaks completely open to the ambient environment (double-ended guillotine break). Due to the huge pressure difference between the inside of the reactor pressure vessel (RPV) and surrounding ambient environment, a shock wave will form at the break point and burst into the surrounding environment. At the same time, an expansion wave will travel upstream through the main steam line to the RPV, which results in a pressure reduction on the outside of the steam dryer hood. This expansion wave will create a substantial pressure difference between the two sides of the steam dryer hood with a resultant high stress on the hood. This differential pressure load is the acoustic load used in the structure design evaluations for this event. A key design basis requirement for the steam dryer is to maintain structural integrity during transient, and accident conditions. Demonstration that the steam dryers meet this design basis requires a calculation of the magnitude of the acoustic load on the steam dryer during a MSLB. In this study, Computational Fluid Dynamics (CFD) is used as an alternate calculation method to investigate the phenomenon of MSLB. Transient simulations with fine time steps were carried out. The results show that CFD is a useful tool to provide additional information on the acoustic load as compared to the traditional methods. From the CFD results, the minimum pressure value and its distribution area at different flow times was identified. Through the modeling, an understanding of the detailed transient flow field, particular the acoustic pressure field near the dryer hood during the MSLB was achieved.

Determination of the Efficacy of Sterile Barrier Systems Against Microbial Challenges During Transport and Storage

2009 ◽  
Vol 30 (2) ◽  
pp. 179-183 ◽  
Author(s):  
Hartmut Dunkelberg ◽  
Ulrich Schmelz
Keyword(s):  
Atmospheric Pressure ◽  
Pressure Difference ◽  
Film Material ◽  
Plastic Film ◽  
Exposure Test ◽  
Bacterial Aerosol ◽  
Logarithmic Reduction ◽  
Pressure Changes ◽  
And Storage ◽  
Microbial Challenge

Objective.The sterility assurance level of 10−6 is an established standard that defines the quality of sterile products. The aim of the present study was to develop a method that correlated the results from microbial-barrier testing of flexible sterile barrier systems with the estimated microbial challenge that the package encounters during storage and transport.Methods.The effectiveness of microbial-barrier packaging was determined by the use of an exposure chamber test with 20 periodic atmospheric pressure changes of 50 and 70 hPa. Flexible peel pouches were used as sterile barrier systems. The logarithmic reduction value of a sterile barrier system was calculated on the basis of the experimental results and compared with the logarithmic reduction value required for the microbial challenges to maintain sterility during transport and storage.Results.For pouches made of paper and plastic-film material, a logarithmic reduction value of 5.4 was obtained on the basis of 30 of 99 plates becoming nonsterile after being exposed to a 50 hPa difference in periodic atmospheric pressure changes. For pouches made of paper and plastic-film material, a logarithmic reduction value of 5.2 was obtained on the basis of 48 of 100 plates becoming nonsterile after being exposed to a 70 hPa difference in atmospheric pressure. For pouches made of nonwoven and plastic-film material, logarithmic reduction values of 6.38 (ie, 3 of 99 plates became nonsterile after being exposed to a 50 hPa pressure difference) and 6.07 (ie, 3 of the 99 plates became nonsterile after being exposed to a 70 hPa pressure difference) were obtained. Calculating an expected microbial challenge during transport and storage that requires barrier properties corresponding to a logarithmic reduction value of 5.83 and taking the sterility assurance level into account, we found that only the nonwoven pouches fulfilled the European standard EN 556-1.Conclusions.Using the data obtained in a microbial exposure test with a specified flow rate of a bacterial aerosol, we found that the effectiveness of the sterile barrier system against the actual microbial challenge can be examined and evaluated at the sterility assurance level of 10−6.

A New Model to Predict Average Pressure Difference of Liquid Droplet in Gas Well

2013 ◽  
Author(s):  
Zhong Hai-Quan ◽  
Liu Zhong-Neng ◽  
Liu Tong ◽  
Liang Kai ◽  
Ren Yong
Keyword(s):  
Pressure Difference ◽  
Liquid Droplet ◽  
Average Pressure ◽  
Gas Well ◽  
New Model

scholarly journals Blood pressure changes PVAT function and transcriptome: use of the mid-thoracic aorta coarcted rat

2020 ◽  
Vol 319 (6) ◽  
pp. H1313-H1324
Author(s):  
G. Andres Contreras ◽  
Yongliang Yang ◽  
Emma D Flood ◽  
Hannah Garver ◽  
Sudin Bhattacharya ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Stress Relaxation ◽  
Thoracic Aorta ◽  
Pressure Difference ◽  
Gene Network ◽  
Potential Versus ◽  
Pressure Changes

A mid-thoracic aorta coarcted rat was created to generate a stable pressure difference above versus below the coarctation ligature. This study determined that the PVAT around the thoracic aorta exposed to a higher pressure has a significantly reduced ability to assist stress relaxation versus that below the ligature and appears to retain the ability to be anticontractile. At the same time, the PVAT around the thoracic aorta exposed to higher pressure had a reduced adipogenic potential versus that below the ligature. Transcriptomics analyses indicated that PVAT below the coarctation showed the greatest number of DEGs with an increased profile of the synaptic neurotransmitter gene network.

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