scholarly journals Estimation of Liquid Fraction of Wet Snow by Using 2-D Video Disdrometer and S-Band Weather Radar

2021 ◽  
Vol 13 (10) ◽  
pp. 1901
Author(s):  
Sung-Ho Suh ◽  
Hong-Il Kim ◽  
Eun-Ho Choi ◽  
Cheol-Hwan You
Keyword(s):  
Particle Density ◽  
Liquid Fraction ◽  
Particle Diameter ◽  
Weather Radar ◽  
Terminal Velocity ◽  
Significant Damage ◽  
Wet Snow ◽  
Shape Irregularity ◽  
Physical Variables ◽  
Highly Correlated

Wet snow may cause significant damage to humans and property, and thus, it is necessary to estimate the corresponding liquid fraction (FL). Consequently, the FL of wet snow was estimated using a novel technique; specifically, the particle shape irregularity (Ir) was estimated through the particle coordinate information obtained using 2-D video disdrometer (2DVD) measurements. Moreover, the possibility of quantitively estimating FL via Ir, based on the temperature (T), was examined. Eight snowfall cases from 2014 to 2016 were observed through a 2DVD installed in Jincheon, South Korea, to analyze the dominant properties of physical variables of snowflakes (i.e., the terminal velocity (VT), particle density (ρs), Ir, and FL) and the corresponding relationships according to the T ranges (−4.5 < T (°C) < 2.5) in which wet snow can occur. It was clarified that the volume-equivalent particle diameter (D)–FL and D–Ir relationships depended on T, and a relationship existed between Ir and FL. The analysis results were verified using the Yong-In Testbed (YIT) S-band weather radar and T-matrix scattering simulation. The D–FL relationship was implemented in the scattering simulation, and the results indicated that the simulated reflectivity (ZS) was highly correlated with the observed reflectivity (ZO) under all T classes. These features can provide a basis for radar analysis and quantitative snowfall estimation for wet snow with various FL values.

scholarly journals Tephra4D: A Python-Based Model for High-Resolution Tephra Transport and Deposition Simulations—Applications at Sakurajima Volcano, Japan

Atmosphere ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 331
Author(s):  
Kosei Takishita ◽  
Alexandros P. Poulidis ◽  
Masato Iguchi
Keyword(s):  
Scale Effects ◽  
Three Dimensional ◽  
Particle Diameter ◽  
Terminal Velocity ◽  
Diameter Distribution ◽  
Velocity Variation ◽  
Small Scale ◽  
Modified Model ◽  
Sakurajima Volcano ◽  
Ash Transport

Vulcanian eruptions (short-lived explosions consisting of a rising thermal) occur daily in volcanoes around the world. Such small-scale eruptions represent a challenge in numerical modeling due to local-scale effects, such as the volcano’s topography impact on atmospheric circulation and near-vent plume dynamics, that need to be accounted for. In an effort to improve the applicability of Tephra2, a commonly-used advection-diffusion model, in the case of vulcanian eruptions, a number of key modifications were carried out: (i) the ability to solve the equations over bending plume, (ii) temporally-evolving three-dimensional meteorological fields, (iii) the replacement of the particle diameter distribution with observed particle terminal velocity distribution which provides a simple way to account for the settling velocity variation due to particle shape and density. We verified the advantage of our modified model (Tephra4D) in the tephra dispersion from vulcanian eruptions by comparing the calculations and disdrometer observations of tephra sedimentation from four eruptions at Sakurajima volcano, Japan. The simulations of the eruptions show that Tephra4D is useful for eruptions in which small-scale movement contributes significantly to ash transport mainly due to the consideration for orographic winds in advection.

Settling Behavior of Particles in Bubble Containing Newtonian Fluids: Experimental Study and Model Development

2021 ◽  
Author(s):  
Silin Jing ◽  
Xianzhi Song ◽  
Zhaopeng Zhu ◽  
Buwen Yu ◽  
Shiming Duan
Keyword(s):  
Reynolds Number ◽  
Drag Coefficient ◽  
Volume Concentration ◽  
Settling Velocity ◽  
Particle Density ◽  
Particle Diameter ◽  
Newtonian Fluids ◽  
Spherical Particles ◽  
Bubble Volume ◽  
Particle Reynolds Number

Abstract Accurate description of cuttings slippage in the gas-liquid phase is of great significance for wellbore cleaning and the control accuracy of bottom hole pressure during MPD. In this study, the wellbore bubble flow environment was simulated by a constant pressure air pump and the transparent wellbore, and the settling characteristics of spherical particles under different gas volume concentrations were recorded and analyzed by highspeed photography. A total of 225 tests were conducted to analyze the influence of particle diameter (1–12mm), particle density (2700–7860kg/m^3), liquid viscosity and bubble volume concentration on particle settling velocity. Gas drag force is defined to quantitatively evaluate the bubble’s resistance to particle slippage. The relationship between bubble drag coefficient and particle Reynolds number is obtained by fitting the experimental results. An explicit settling velocity equation is established by introducing Archimedes number. This explicit equation with an average relative error of only 8.09% can directly predict the terminal settling velocity of the sphere in bubble containing Newtonian fluids. The models for predicting bubble drag coefficient and the terminal settling velocity are valid with particle Reynolds number ranging from 0.05 to 167 and bubble volume concentration ranging from 3.0% to 20.0%. Besides, a trial-and-error procedure and an illustrative example are presented to show how to calculate bubble drag coefficient and settling velocity in bubble containing fluids. The results of this study will provide the theoretical basis for wellbore cleaning and accurate downhole pressure to further improve the performance of MPD in treating gas influx.

Gastric emptying of nondigestible solids in dogs: a hydrodynamic correlation

1990 ◽  
Vol 258 (1) ◽  
pp. G65-G72 ◽  
Author(s):  
P. J. Sirois ◽  
G. L. Amidon ◽  
J. H. Meyer ◽  
J. Doty ◽  
J. B. Dressman
Keyword(s):  
Particle Size ◽  
Gastric Emptying ◽  
Gravitational Constant ◽  
Particle Density ◽  
Particle Diameter ◽  
High Viscosity ◽  
Fluid Viscosity ◽  
Fluid Flow Rate ◽  
Hydrodynamic Correlation ◽  
Viscosity Polymer

The influence of particle size, particle density, fluid viscosity, and fluid flow rate on the gastric emptying of nondigestible solids was investigated in five dogs with chronically placed fistulas. Six hundred and fifty particles of 13 different size and density combinations were administered simultaneously with 500 ml of either normal saline or low-, medium-, or high-viscosity polymer solutions. The canine stomach was found to discriminate between these solids on the basis of size and density at all levels of viscosity above saline. The observed patterns of emptying are consistent with the hypothesis that gastric emptying of nondigestible solids is governed in part by hydrodynamics and correlate well with the gastric-emptying coefficient (GEC), a dimensionless grouping of variables that takes the form GEC = (Dpy/Dp) [g(rho f - rho p)Dp2]/[eta (nu)] where [g(rho f - rho p)] is particle buoyancy consisting of fluid (rho f) and particle (rho p) densities and g, the gravitational constant; (Dp) is the particle diameter, (Dpy) the estimated pyloric diameter, eta the fluid viscosity, and (nu) the average linear velocity of fluid exiting the stomach.

Visualizing Test on the Distribution Rule of Coarse Particles in a Double Blade Pump

2019 ◽  
Author(s):  
Xianfang Wu ◽  
Xiao Tian ◽  
Minggao Tan ◽  
Houlin Liu
Keyword(s):  
Particle Concentration ◽  
Two Phase Flow ◽  
Particle Density ◽  
Particle Diameter ◽  
Phase Flow ◽  
Coarse Particles ◽  
Two Phase ◽  
Solid Liquid ◽  
Blade Pump ◽  
Flow Pump

Abstract As a typical fluid mechanics problem, pump blockage has always been a hot research topic. The obtaining of the distribution of coarse particles in the solid-liquid two-phase flow pump is the basis of improving its non-blocking performance. High-speed photography technique is applied to do visualizing test and research on the distribution of coarse particles in a double blade pump. The effects of particle concentration, particle density and particle diameter on the distribution of coarse particles in the solid-liquid two-phase flow pump at different phases are studied. Besides, the variation of hydraulic performance of the double blade pump under different parameters is also analyzed. The results show that the particles in the impeller mainly located in the vicinity of the blade pressure surface, and the distribution of the particles in each section of the volute is quite different. The great difference in particle density can result in obviously uneven distribution of particles. With the increase of particle diameter, particle density and particle concentration, the pump head and efficiency both decrease while the shaft power increase on the contrary. This research results can also provide a basis for the optimization design of solid-liquid two-phase flow pumps.

The Magnitude of Basset Forces in Unsteady Multiphase Flow Computations

1992 ◽  
Vol 114 (3) ◽  
pp. 417-419 ◽  
Author(s):  
Li Liang ◽  
Efstathios E. Michaelides
Keyword(s):  
Particle Density ◽  
Density Ratio ◽  
Particle Diameter ◽  
Equation Of Motion ◽  
Total Force ◽  
Basset Force ◽  
Flow Reynolds Number ◽  
Order Of Magnitude ◽  
Small Spherical Particle ◽  
Very High

The equation of motion of a small spherical particle moving in a fluid is solved numerically with the radius of the sphere and the ratio of fluid to particle densities being parameters. The Basset force term is computed and compared to the total force on the particle for the case of turbulent flow in a duct. It is found that the Basset force may be neglected in the equation of motion of the particle only when the fluid to particle density ratio is very high and the particle diameter is greater than 1 μm. A dimensional analysis is also performed for the case when the particle size and the characteristic flow dimension are of the same order of magnitude. In the latter case, it is deduced that the Basset force is significant whenever the flow Reynolds number is greater than one.

scholarly journals Transition from fractional to classical Stokes–Einstein behaviour in simple fluids

2017 ◽  
Vol 4 (12) ◽  
pp. 170507 ◽  
Author(s):  
Diego Coglitore ◽  
Stuart P. Edwardson ◽  
Peter Macko ◽  
Eann A. Patterson ◽  
Maurice Whelan
Keyword(s):  
Particle Size ◽  
Molecular Dynamic ◽  
Particle Density ◽  
Particle Diameter ◽  
Molecular Dynamic Simulations ◽  
Optical Technique ◽  
Single Particles ◽  
Dynamic Simulations ◽  
Simple Fluids ◽  
Particle Behaviour

An optical technique for tracking single particles has been used to evaluate the particle diameter at which diffusion transitions from molecular behaviour described by the fractional Stokes–Einstein relationship to particle behaviour described by the classical Stokes–Einstein relationship. The results confirm a prior prediction from molecular dynamic simulations that there is a particle size at which transition occurs and show it is inversely dependent on concentration and viscosity but independent of particle density. For concentrations in the range 5 × 10 −3 to 5 × 10 −6  mg ml −1 and viscosities from 0.8 to 150 mPa s, the transition was found to occur in the diameter range 150–300 nm.

scholarly journals The cyclonic activity and frequency of dangerous weather phenomena over the territory of Belarus

2019 ◽  
pp. 79-93
Author(s):  
Katsiaryna M. Sumak ◽  
Inna G. Semenova
Keyword(s):  
Heavy Rain ◽  
Weather Conditions ◽  
Summer Period ◽  
Severe Convection ◽  
Weather Events ◽  
Atmospheric Fronts ◽  
Significant Damage ◽  
Wet Snow ◽  
The Republic ◽  
The Impact

In recent decades in the world, and in the Republic of Belarus in particular, the question of the impact of weather conditions on the development of sectors of the economy and life of the population has become acute. The sudden changes in weather conditions can lead to adverse and dangerous weather phenomena that cause significant damage to the country’s economy. This paper examines the frequency of dangerous weather phenomena in cyclones of different trajectories that moved through the territory of the Republic of Belarus during the period of 1995–2015. It is identified that southern and western cyclones caused dangerous weather events over the territory of Belarus. The interannual and seasonal frequency of cyclones causing dangerous weather phenomena in Belarus was analyzed. It is shown that the largest number of southern and western cyclones was characteristic mainly for the summer period, as well as the transitional seasons of the year, therefore the dangerous weather phenomena were associated mainly with the development of severe convection on atmospheric fronts. Such phenomena as very heavy rain, snowfall and wind had the highest frequency in cyclones, as in southern as western trajectories. The share of strong sticking of wet snow and large hail were isolated cases and these phenomena were recorded locally over the territory of country.

scholarly journals Parameterization of the Bulk Liquid Fraction on Mixed-Phase Particles in the Predicted Particle Properties (P3) Scheme: Description and Idealized Simulations

2019 ◽  
Vol 76 (2) ◽  
pp. 561-582 ◽  
Author(s):  
Mélissa Cholette ◽  
Hugh Morrison ◽  
Jason A. Milbrandt ◽  
Julie M. Thériault
Keyword(s):  
Solid Phase ◽  
Liquid Fraction ◽  
Phase Changes ◽  
Mixed Phase ◽  
Bulk Liquid ◽  
Microphysics Scheme ◽  
Liquid Component ◽  
Particle Properties ◽  
Wet Snow ◽  
Snow And Ice

Abstract Bulk microphysics parameterizations that are used to represent clouds and precipitation usually allow only solid and liquid hydrometeors. Predicting the bulk liquid fraction on ice allows an explicit representation of mixed-phase particles and various precipitation types, such as wet snow and ice pellets. In this paper, an approach for the representation of the bulk liquid fraction into the predicted particle properties (P3) microphysics scheme is proposed and described. Solid-phase microphysical processes, such as melting and sublimation, have been modified to account for the liquid component. New processes, such as refreezing and condensation of the liquid portion of mixed-phase particles, have been added to the parameterization. Idealized simulations using a one-dimensional framework illustrate the overall behavior of the modified scheme. The proposed approach compares well to a Lagrangian benchmark model. Temperatures required for populations of ice crystals to melt completely also agree well with previous studies. The new processes of refreezing and condensation impact both the surface precipitation type and feedback between the temperature and the phase changes. Overall, prediction of the bulk liquid fraction allows an explicit description of new precipitation types, such as wet snow and ice pellets, and improves the representation of hydrometeor properties when the temperature is near 0°C.

A Parameterization of the Microphysical Processes Forming Many Types of Winter Precipitation

2010 ◽  
Vol 67 (5) ◽  
pp. 1492-1508 ◽  
Author(s):  
Julie M. Thériault ◽  
Ronald E. Stewart
Keyword(s):  
Liquid Fraction ◽  
Winter Precipitation ◽  
The Other ◽  
Mass Content ◽  
Microphysics Scheme ◽  
Winter Storms ◽  
Precipitation Characteristics ◽  
Wet Snow ◽  
Precipitation Type ◽  
Microphysical Processes

Abstract Several types of precipitation, such as freezing rain, ice pellets, and wet snow, are commonly observed during winter storms. The objective of this study is to better understand the formation of these winter precipitation types. To address this issue, detailed melting and refreezing of precipitation was added onto an existing bulk microphysics scheme. These modifications allow the formation of mixed-phase particles and these particles in turn lead to, or affect, the formation of many of the other types of precipitation. The precipitation type characteristics, such as the mass content, liquid fraction, and threshold diameters formed during a storm over St John’s, Newfoundland, Canada, are studied and compared with observations. Many of these features were reproduced by the model. Sensitivity experiments with the model were carried out to examine the dependence of precipitation characteristics in this event on thresholds of particle evolution in the new parameterization.

Operation Performance of a Small Air-Lift Pump for Conveying Solid Particles

2003 ◽  
Vol 125 (1) ◽  
pp. 17-25 ◽  
Author(s):  
Hitoshi Fujimoto ◽  
Satoshi Ogawa ◽  
Hirohiko Takuda ◽  
Natsuo Hatta
Keyword(s):  
Particle Density ◽  
Gas Injection ◽  
Particle Diameter ◽  
Solid Particles ◽  
Operation Performance ◽  
Two Phase ◽  
Experimental Conditions ◽  
Injection Point ◽  
Pump Performance ◽  
Air Lift

The pump performance of a small air-lift system for conveying solid particles is investigated experimentally. The total length of the vertical lifting pipe is 3200 mm, and the inner diameter of the pipe is 18 mm. The gas injector is set at a certain point of the pipe. The flows in the lifting pipe are water/solid two-phase mixtures below the gas injection point, and air/water/solid three-phase mixtures above it. The time-averaged characteristics of the flows are examined for various experimental conditions. The effects of particle diameter, particle density, the gas-injection point, and the volume flux of air on the pump performance are studied systematically. The critical boundary at which the particles can be lifted is discussed in detail based upon one-dimensional mixture model.

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