scholarly journals Measurement of snow particle size and velocity in avalanche powder clouds

2017 ◽  
Vol 63 (238) ◽  
pp. 249-257 ◽  
Author(s):  
YOICHI ITO ◽  
FLORENCE NAAIM-BOUVET ◽  
KOUICHI NISHIMURA ◽  
HERVÉ BELLOT ◽  
EMMANUEL THIBERT ◽  
...  
Keyword(s):  
Particle Size ◽  
Settling Velocity ◽  
Test Site ◽  
The Core ◽  
Large Particles ◽  
Ultrasonic Anemometer ◽  
Particle Speed ◽  
Avalanche Flow ◽  
Surface Particle ◽  
Snow Particle

ABSTRACTParticle size, particle speed and airflow speed have been measured in the powder snow clouds of avalanches to investigate the suspension and transportation processes of snow particles. The avalanches were artificially triggered at the Lautaret full-scale avalanche test-site (French Alps) where an ultrasonic anemometer and a snow particle counter were setup in an avalanche track for measurements. Relatively large particles were observed during passage of the avalanche head and then the size of the particles slightly decreased as the core of the avalanche passed the measurement station. The particle size distribution was well fitted by a gamma distribution function. A condition for suspension of particles within the cloud based on the ratio of vertical velocity fluctuation to particle settling velocity suggests that the large particles near the avalanche head are not lifted up by turbulent diffusion, but rather ejected by a process involving collisions between the avalanche flow and the rough snow surface. Particle speeds were lower than the airflow speed when large particles were present in the powder cloud.

scholarly journals Association of Cryptosporidium with bovine faecal particles and implications for risk reduction by settling within water supply reservoirs

2006 ◽  
Vol 4 (1) ◽  
pp. 87-98 ◽  
Author(s):  
Justin D. Brookes ◽  
Cheryl M. Davies ◽  
Matthew R. Hipsey ◽  
Jason P. Antenucci
Keyword(s):  
Particle Size ◽  
Water Supply ◽  
Risk Reduction ◽  
Settling Velocity ◽  
Three Dimensional ◽  
Three Dimensional Model ◽  
Particle Size Fractions ◽  
Size Classes ◽  
Large Particles ◽  
Water Supply Reservoirs

Artificial cow pats were seeded with Cryptosporidium oocysts and subjected to a simulated rainfall event. The runoff from the faecal pat was collected and different particle size fractions were collected within settling columns by exploiting the size-dependent settling velocities. Particle size and Cryptosporidium concentration distribution at 10 cm below the surface was measured at regular intervals over 24 h. Initially a large proportion of the total volume of particles belonged to the larger size classes (>17 μm). However, throughout the course of the experiment, there was a sequential loss of the larger size classes from the sampling depth and a predominance of smaller particles (<17 μm). The Cryptosporidium concentration at 10 cm depth did not change throughout the experiment. In the second experiment samples were taken from different depths within the settling column. Initially 26% of particles were in the size range 124–492 μm. However, as these large particles settled there was an enrichment at 30 cm after one hour (36.5–49.3%). There was a concomitant enrichment of smaller particles near the surface after 1 h and 24 h. For Pat 1 there was no difference in Cryptosporidium concentration with depth after 1 h and 24 h. In Pat 2 there was a difference in concentration between the surface and 30 cm after 24 h. However, this could be explained by the settling velocity of a single oocyst. The results suggested that oocysts are not associated with large particles, but exist in faecal runoff as single oocysts and hence have a low (0.1 m d−1) settling velocity. The implications of this low settling velocity on Cryptosporidium risk reduction within water supply reservoirs was investigated through the application of a three-dimensional model of oocyst fate and transport to a moderately sized reservoir (26 GL). The model indicated that the role of settling on oocyst concentration reduction within the water column is between one and three orders of magnitude less than that caused by advection and dilution, depending on the strength of hydrodynamic forcing.

Snow particle sizes and their distributions in Dronning Maud Land, Antarctica, at sample, local and regional scales

2016 ◽  
Vol 28 (3) ◽  
pp. 219-231
Author(s):  
Susanne Ingvander ◽  
Peter Jansson ◽  
Ian A. Brown ◽  
Shuji Fujita ◽  
Shin Sugyama ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Particle Size ◽  
Temporal Variations ◽  
Spatial And Temporal Variations ◽  
Coupled Processes ◽  
Sample Type ◽  
Surface Snow ◽  
Dronning Maud Land ◽  
Size Variability ◽  
Snow Particle

AbstractIn this study, snow particle size variability was investigated along a transect in Dronning Maud Land from the coast to the polar plateau. The aim of the study was to better understand the spatial and temporal variations in surface snow properties. Samples were collected twice daily during a traverse in 2007–08 to capture regional variability. Local variability was assessed by sampling in 10×10 m grids (5 m spacing) at selected locations. The particle size and shape distributions for each site were analysed through digital image analysis. Snow particle size variability is complex at different scales, and shows an internal variability of 0.18–3.31 mm depending on the sample type (surface, grid or pit). Relationships were verified between particle size and both elevation and distance to the coast (moisture source). Regional seasonal changes were also identified, particularly on the lower elevations of the polar plateau. This dataset may be used to quantitatively analyse the optical properties of surface snow for remote sensing. The details of the spatial and temporal variations observed in our data provide a basis for further studies of the complex and coupled processes affecting snow particle size and the interpretation of remote sensing of snow covered areas.

Study on the Formula of Settling Velocity of Sediment Particle Cloud in the Water

2012 ◽  
Vol 212-213 ◽  
pp. 225-229
Author(s):  
Jie Gu ◽  
Dan Qing Ma ◽  
Wei Chen ◽  
Xin Qin ◽  
Xiao Li Wang
Keyword(s):  
Experimental Data ◽  
Particle Size ◽  
Settling Velocity ◽  
Sediment Particle ◽  
Particle Cloud ◽  
Characteristic Particle ◽  
Experimental Values ◽  
New Formula ◽  
Sediment Settling

Based on the experimental data of sediment particle cloud during the settlement process in the water and combined with the existed sediment settling velocity formulae, a new formula for calculation of the settling velocity of sediment particle cloud is proposed by the introduction of the characteristic particle size of sediment particle cloud ( D' ). By using experimentally measured settling velocity values of sediment particle cloud to verify the settling velocity values of sediment particle cloud which calculated by using this new formula, the results show that the calculated settling velocity values using this new formula are closer to the experimental values.

scholarly journals Simulation of Volcanic Ash Ingestion Into a Large Aero Engine: Particle–Fan Interactions

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Andreas Vogel ◽  
Adam J. Durant ◽  
Massimo Cassiani ◽  
Rory J. Clarkson ◽  
Michal Slaby ◽  
...  
Keyword(s):  
Particle Size ◽  
Stream Flow ◽  
Mass Concentration ◽  
Volcanic Ash ◽  
Particle Mass ◽  
Core Flow ◽  
Turbine Engine ◽  
The Core ◽  
Core Section ◽  
Particle Mass Concentration

Volcanic ash (VA) clouds in flight corridors present a significant threat to aircraft operations as VA particles can cause damage to gas turbine engine components that lead to a reduction of engine performance and compromise flight safety. In the last decade, research has mainly focused on processes such as erosion of compressor blades and static components caused by impinging ash particles as well as clogging and/or corrosion effects of soft or molten ash particles on hot section turbine airfoils and components. However, there is a lack of information on how the fan separates ingested VA particles from the core stream flow into the bypass flow and therefore influences the mass concentration inside the engine core section, which is most vulnerable and critical for safety. In this numerical simulation study, we investigated the VA particle–fan interactions and resulting reductions in particle mass concentrations entering the engine core section as a function of particle size, fan rotation rate, and for two different flight altitudes. For this, we used a high-bypass gas-turbine engine design, with representative intake, fan, spinner, and splitter geometries for numerical computational fluid dynamics (CFD) simulations including a Lagrangian particle-tracking algorithm. Our results reveal that particle–fan interactions redirect particles from the core stream flow into the bypass stream tube, which leads to a significant particle mass concentration reduction inside the engine core section. The results also show that the particle–fan interactions increase with increasing fan rotation rates and VA particle size. Depending on ingested VA size distributions, the particle mass inside the engine core flow can be up to 30% reduced compared to the incoming particle mass flow. The presented results enable future calculations of effective core flow exposure or dosages based on simulated or observed atmospheric VA particle size distribution, which is required to quantify engine failure mechanisms after exposure to VA. As an example, we applied our methodology to a recent aircraft encounter during the Mt. Kelud 2014 eruption. Based on ambient VA concentrations simulated with an atmospheric particle dispersion model (FLEXPART), we calculated the effective particle mass concentration inside the core stream flow along the actual flight track and compared it with the whole engine exposure.

Investigation on the arc erosion behavior of new silver matrix composites: Part I. Reinforced by particles

2003 ◽  
Vol 18 (4) ◽  
pp. 804-816 ◽  
Author(s):  
Shou-Yi Chang ◽  
Chia-Jung Hsu ◽  
Cher-Hao Hsu ◽  
Su-Jien Lin
Keyword(s):  
Particle Size ◽  
Erosion Resistance ◽  
High Viscosity ◽  
Matrix Composites ◽  
Particle Content ◽  
Arc Erosion ◽  
Erosion Behavior ◽  
Surface Areas ◽  
Large Particles ◽  
Silver Matrix

Static-gap, single-spark tests were used to investigate the arc erosion behavior of newly developed silicon carbide and alumina particle reinforced silver matrix composites (SiCp/Ag, Al2O3p/Ag). Craters and hills exist on the surfaces of eroded silver matrix composites, and their depths and sizes decrease as the particle content increases and the particle size decreases. Obvious melting, flow, severe splash of molten silver, and the segregation of particles are present on the surfaces of eroded composites containing low volume percents of large particles. Easier silver flow results in smooth surfaces and reduces the total surface areas of the eroded composites containing large particles. The flow and splash of silver decreased with increasing particle content and decreasing particle size, exhibiting a better erosion resistance to single-spark tests. The static-gap, single-spark erosion behavior of silver matrix composites is dominated by the flow and splash of molten composites. A high viscosity of the liquids provides the composites a good arc erosion resistance.

Examination of Dust in AVR Pipe Components

2008 ◽  
Author(s):  
Johannes Fachinger ◽  
Heiko Barnert ◽  
Alexander P. Kummer ◽  
Guido Caspary ◽  
Manuel Seubert ◽  
...  
Keyword(s):  
Particle Size ◽  
Optical Microscopy ◽  
Phase 1 ◽  
Median Number ◽  
Primary Circuit ◽  
Pipe Surface ◽  
Dose Rates ◽  
The Core ◽  
Chemical Decontamination ◽  
Dust Surface

Pebble Bed HTGR’s like the AVR in Ju¨lich have the advantage of continuous fuelling. However the multiple passes of the fuel pebbles through the core have the disadvantage that the pebble’s movement through the fuelling system and the core produces graphite dust. This dust is transported from the core to other parts of the primary circuit and deposits on components. Although previous experiments performed during AVR operation have given some insight into the dust particle size and activity, there is little information on the behaviour of the dust that was deposited in the system. The decommissioning of the AVR has provided the opportunity to sample and characterise such dust from a number of components and gauge the adhesion strength. From the side of PBMR Pty Ltd this opportunity is considered important to enhance the knowledge about dust characteristics before the PBMR Demonstration Power Plant (DPP) is operational and able to produce specific plant information through sampling and analysis. AVR GmbH has provided a number of pipes and joints for investigation of loose and bound dust. Phase 1 of the analysis was used to determine the best techniques to be used on larger items. No measurable loose dust could be collected. Thereupon rings were cut from a T-section and subdivided into eight segments. The surface of the untreated segments were photographed and documented by optical microscopy, the dose rates were measured and gamma-spectrometry performed. Following this a mechanical or chemical decontamination was carried out to remove and isolate the bound dust. The average isolated dust amount was about 2 mg/cm2. Both decontamination processes indicates a strong bonding of the dust surface layer. In the case of mechanical decontamination about 60% and by chemical decontamination about 95% of the radionuclide inventory could be removed. The contribution of removed metal needs to be investigated in more detail. The median number related particle size measured by optical microscopy was found to be in the range of 0.2 to 0.7 μm whereas the median weight related size is in the range of 0.8 to 1.5 μm. The initial results indicate that this dust sticks very strongly to the pipe surface. Phase 2 will concentrate on longer pieces of piping where hopefully more loose dust can be obtained and analysed. If the same strong bonding is observed the reason for this phenomenon needs to be explained and perhaps tested with non-active dust.

scholarly journals Carbon-supported Platinum Electrocatalysts probed in a Gas Diffusion Setup with Alkaline Environment: how Particle Size and Mesoscopic Environment influence the Degradation Mechanism

2020 ◽  
Author(s):  
Shima Alinejad ◽  
Jonathan Quinson ◽  
Johanna Schröder ◽  
Jacob J. K. Kirkensgaard ◽  
Matthias Arenz
Keyword(s):  
Particle Size ◽  
Degradation Mechanism ◽  
Active Phase ◽  
Active Surface ◽  
Carbon Support ◽  
Gas Diffusion ◽  
Active Surface Area ◽  
Electrochemical Cells ◽  
Co Stripping ◽  
Large Particles

In this work, we investigate the stability of four different types of Pt/C fuel cell catalysts upon applying accelerated degradation tests (ADTs) in a gas diffusion electrode (GDE) setup equipped with an anion exchange membrane (AEM). In contrast to previous investigations exposing the catalysts to liquid electrolyte, the GDE setup provides a realistic three-phase boundary of the reactant gas, catalyst and ionomer which enables reactant transport rates close to real fuel cells. Therefore, the GDE setup mimics the degradation of the catalyst under more realistic reaction conditions as compared to conventional electrochemical cells. Combining the determination of the loss in electrochemically active surface area (ECSA) of the Pt/C catalysts via CO stripping measurements with the change in particle size distribution determined by small-angle X-ray scattering (SAXS) measurements, we demonstrate that i) the degradation mechanism depends on the investigated Pt/C catalyst and might indeed be different to the one observed in conventional electrochemical cells, ii) degradation is increased in an oxygen gas atmosphere (as compared to an inert atmosphere), and iii) the observed degradation mechanism depends on the mesoscopic environment of the active phase. The measurements indicate an increased particle growth if small and large particles are immobilized next to each other on the same carbon support flakes as compared to a simple mix of two catalysts with small and large particles, respectively.

scholarly journals THE EFFECT OF CAVITATION TREATMENT ON THE EXTINGUISHING OF PARTICLES OF OILS IN FUEL BOILERS

2019 ◽  
Vol 20 (9-10) ◽  
pp. 52-59
Author(s):  
M. A. Taymarov ◽  
R. V. Akhmetova ◽  
S. M. Margulis ◽  
L. I. Kasimova
Keyword(s):  
Particle Size ◽  
Combustion Zone ◽  
Consumption Rate ◽  
Fuel Oil ◽  
Particle Sizes ◽  
Oil Consumption ◽  
Boiler Efficiency ◽  
Large Particles ◽  
Oil Particles

The difficulties of burning the watered fuel oil used at the TPP as a reserve fuel for boilers are associated with its preparation by heating to reduce viscosity and the choice of a method of spraying with nozzles into the combustion zone. The quality of the preparation of fuel oil for combustion affecting the boiler efficiency is estimated by the length of the flame, the presence of burning large particles of fuel oil, the injection of coke and unburned particles onto screen and other heat-receiving surfaces. One of the ways to prepare fuel oil for combustion is cavitation treatment, which results in an emulsion consisting of fine micronsized particles. Heating of fuel oil particles after the nozzle in contact with the combustion zone is due to the flow of radiation from the burning torch. Therefore, in this article, the values of the flux density from the torch during the combustion of fuel oil are experimentally determined. The influence of particle size on the burning rate of the fuel oil M100 with the different density of the thermal radiation of the flame. It is found that the effect of cavitation treatment of fuel oil on the combustion rate is most significantly manifested in particle sizes less than 10 microns. For this purpose, the use of hydrodynamic cavitators are preferred at high fuel oil consumption rate.

scholarly journals Gravitational differentiation in the regimes from stokes settling to Rayleigh–Raylor flows

2019 ◽  
pp. 15-30
Author(s):  
V. P. Trubitsyn
Keyword(s):  
Viscous Fluid ◽  
Interacting Particles ◽  
Small Particles ◽  
Continuous Transition ◽  
New Approach ◽  
Earth's Core ◽  
The Core ◽  
The Earth ◽  
Large Particles ◽  
Two Component

The Earth’s core was formed under gravitational differentiation in the course of the separation of iron and silicates. Most of the iron has gone into the core as early as when the Earth was growing. However, iron continued to precipitate even during the subsequent partial solidification which developed from the bottom upwards. At the different stages and in the different layers of the mantle, iron was deposited in different regimes. In this paper, the mechanisms of the deposition of a cloud of heavy interacting particles (or drops) in a viscous fluid are considered. A new approach suitable for analytical and numerical tracing the changes in the structure of the flows in a two-component suspension under continuous transition from the Stokessettling (for the case of a cloud of large particles) to the Rayleigh–Taylor flows and heavy diapirs (for the case of a cloud of small particles) is suggested. It is numerically and analytically shown that the both regimes are the different limiting cases of the sedimentation convection in suspensions.

scholarly journals Processing parameters optimization of cotton stalk (Gossypium hirsutum L.) particleboards with emulsifiable polymeric isocyanate adhesive

BioResources ◽  
2021 ◽  
Vol 16 (2) ◽  
pp. 4149-4170
Author(s):  
Thanh Tung Nguyen ◽  
Adam Redman ◽  
William Leggate ◽  
Luigi-j Vandi ◽  
Henri Bailleres ◽  
...  
Keyword(s):  
Particle Size ◽  
Internal Bond ◽  
Fine Particles ◽  
Processing Parameters ◽  
Parameters Optimization ◽  
Modulus Of Rupture ◽  
Cotton Stalk ◽  
Thickness Swelling ◽  
Surface Particle ◽  
Polymeric Isocyanate

The compaction behavior of cotton stalk particle mats, temperature profile inside the particle mats, and influence of surface particle size were studied relative to the properties of three-layered cotton stalk particleboards. Modulus of rupture (MOR), modulus of elasticity (MOE), internal bond, and thickness swelling were used as a measure for mechanical and physical performance. Two types of cotton stalk particleboard were manufactured. Results indicated that compression stiffness of the particle mat increased with increasing particle size; however, it decreased with increasing mat moisture content and temperature. At mat moisture contents of 12% and 18%, the plateau temperature at the centerline was not significantly different between boards having coarse and fine particles. However, the plateau time of boards with coarse particles was significantly lower than that of boards with fine particles. Additionally, thickness swelling of boards with a surface particle size of 2 mm was significantly lower than that of boards with surface particle size of 4 mm. Boards with a surface particle size of 2 mm had MOR and MOE values 15% and 10% higher, respectively, than boards with surface particle size of 4 mm. Internal bond decreased 6.5% with decreasing surface particle size from 4 mm to 2 mm.

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