Droplet–turbulence interaction in a confined polydispersed spray: effect of droplet size and flow length scales on spatial droplet–gas velocity correlations

2014 ◽  
Vol 741 ◽  
pp. 98-138 ◽  
Author(s):  
S. Sahu ◽  
Y. Hardalupas ◽  
A. M. K. P. Taylor
Keyword(s):  
Droplet Size ◽  
Gas Flow ◽  
Dynamic Range ◽  
Energy Content ◽  
Effective Length ◽  
Flow Structures ◽  
Stream Velocity ◽  
Gas Velocity ◽  
Length Scales ◽  
Velocity Fluctuations

AbstractThis paper discusses the interaction between droplets and entrained turbulent air flow in the far-downstream locations of a confined polydispersed isothermal spray. Simultaneous and planar measurements of droplet and gas velocities in the spray along with droplet size are obtained with the application of a novel experimental technique, developed by Hardalupaset al. (Exp. Fluids, vol. 49, 2010, pp. 417–434), which combines interferometric laser imaging for droplet sizing (ILIDS) with particle image velocimetry (PIV). These measurements quantified the spatial correlation coefficients of droplet–gas velocity fluctuations ($R_{dg}$) and droplet–droplet velocity fluctuations ($R_{dd}$) conditional on droplet size classes, for various separation distances, and for axial and cross-stream velocity components. At the measurement location close to the spray edge, with increasing droplet size,$R_{dg}$was found to increase in axial direction and decrease in cross-stream direction. This suggests that as the gas-phase turbulence becomes more anisotropic away from the spray axis, the gravitational influence on droplet–gas correlated motion tends to increase. The effective length scales of the correlated droplet–gas motion were evaluated and compared with that for gas and droplet motion. The role of different turbulent eddies of the gas flow on the droplet–gas interaction was examined. The flow structures were extracted using proper orthogonal decomposition (POD) of the instantaneous gas velocity data, and their contribution on the spatial droplet–gas velocity correlation was evaluated, which quantified the momentum transfer between the two phases at different length scales of the gas flow. The droplets were observed to augment turbulence for the first three POD modes (larger scales) and attenuate it for the rest of the modes (smaller scales). It has been realized that apart from droplet Stokes number and mass loading, the dynamic range of length scales of the gas flow and the relative turbulent kinetic energy content of the flow structures (POD modes) must be considered in order to conclude if the droplets enhance or reduce the carrier-phase turbulence especially at the lower wavenumbers.

Film Fraction and Droplet Size inside of a Rectangular Venturi Scrubber

2010 ◽  
Vol 660-661 ◽  
pp. 549-554
Author(s):  
Vádila Giovana Guerra ◽  
M.A.F. Daher ◽  
José Antônio Silveira Gonçalves ◽  
José Renato Coury
Keyword(s):  
Droplet Size ◽  
High Speed ◽  
Gas Flow ◽  
Liquid Flow Rate ◽  
Dimensionless Number ◽  
Gas Velocity ◽  
Flow Rates ◽  
Venturi Scrubber ◽  
Liquid Injection ◽  
Gas Drag

The Venturi scrubber, equipment frequently used in the removal of particles from gases, is constituted basically by a duct with a convergent section followed by a constriction, or throat, and a divergent section. A liquid, usually injected in the throat, is atomized by the flowing air at high speed. The formed droplets act as collectors of particles from the gas. The process of droplet formation from an injected liquid can be described as follows: the liquid enters the gas stream in the form of a jet, perpendicular to the gas flow. As the jet penetrates the gas stream, it is bent by the gas drag. After a given penetration distance, a burst occurs, and the remaining jet is disintegrated as a droplet cloud. Depending on the liquid and gas flow rates, the penetration on the jet into the gas stream may reach the walls of the equipment, and a fraction of liquid deposits in the form of a film. This film contributes little for the removal of particles from the dust laden gas. Few studies have analyzed the formation of film at the scrubber walls and its influence in the droplet size inside the Venturi scrubber. For this reason, the present study is focused on the experimental measurement of the deposition of the liquid film on the walls of a rectangular Venturi scrubber and, simultaneously, the estimation of the droplet size measured in the Venturi throat. The experiments were carried out varying the liquid flow rate, the gas velocity and the number of orifices of liquid injection. A correlation, using a dimensionless number, was proposed to quantify the influence of each experimental condition. The results indicate that film fraction has a significant influence in the droplet size measured inside of Venturi scrubber.

scholarly journals Influence of center gas supply device on gas–solid flow in COREX shaft furnace through DEM–CFD model

2020 ◽  
Vol 18 (5-6) ◽  
Author(s):  
Heng Zhou ◽  
Shuyu Wang ◽  
Binbin Du ◽  
Mingyin Kou ◽  
Zhiyong Tang ◽  
...  
Keyword(s):  
Gas Flow ◽  
Shaft Furnace ◽  
Middle Zone ◽  
Cfd Model ◽  
Gas Velocity ◽  
Gas Distribution ◽  
Particle Segregation ◽  
Solid Flow ◽  
Corex Shaft Furnace ◽  
Gas Supply

AbstractIn order to develop the central gas flow in COREX shaft furnace, a new installment of center gas supply device (CGD) is designed. In this work, a coupled DEM–CFD model was employed to study the influence of CGD on gas–solid flow in COREX shaft furnace. The particle descending velocity, particle segregation behaviour, void distribution and gas distribution were investigated. The results show that the CGD affects the particles descending velocity remarkably as the burden falling down to the slot. Particle segregation can be observed under the inverse ‘V’ burden profile, and the influence of CGD on the particle segregation is unobvious on the whole, which causes the result that the voidage is slightly changed. Although the effect of CGD on solid flow is not significant, the gas flow in shaft furnace has an obvious change. Compared with the condition without CGD, in the case with CGD, the gas velocity is improved significantly, especially in the middle zone of the furnace, which further promotes the center gas distribution. Meanwhile, the pressure drop in the furnace with the installation of CGD is increased partly.

scholarly journals Fluid flow structures in an evaporating sessile droplet depending on the droplet size and properties of liquid and substrate

2021 ◽  
Vol 1730 (1) ◽  
pp. 012029
Author(s):  
M.N. Turchaninova ◽  
E.S. Melnikova ◽  
A.A. Gavrilina ◽  
L.Yu. Barash
Keyword(s):  
Fluid Flow ◽  
Droplet Size ◽  
Flow Structures ◽  
Sessile Droplet

Analyzing Droplet Size Distributions Inside a Self-Priming Venturi Scrubber for Filtered Containment Venting Systems

2018 ◽  
Author(s):  
P. Papadopoulos ◽  
T. Lind ◽  
H.-M. Prasser
Keyword(s):  
Droplet Size ◽  
High Speed ◽  
Nuclear Power ◽  
Power Plants ◽  
Gas Flow ◽  
Tube Bundle ◽  
Droplet Size Distribution ◽  
Severe Accident ◽  
Design Element ◽  
Venturi Scrubber

After the accident in the Fukushima Daiichi nuclear power plant, the interest of adding Filtered Containment Venting Systems (FCVS) on existing nuclear power plants to prevent radioactive releases to the environment during a severe accident has increased. Wet scrubbers are one possible design element which can be part of an FCVS system. The efficiency of this scrubber type is thereby depending, among others, on the thermal-hydraulic characteristics inside the scrubber. The flow structure is mainly established by the design of the gas inlet nozzle. The venturi geometry is one of the nozzle types that can be found in nowadays FCVS. It acts in two different steps on the removal process of the contaminants in the gas stream. Downstream the suction opening in the throat of the venturi, droplets are formed by atomization of the liquid film. The droplets are contributing to the capture of aerosols and volatile gases from the mixture coming from the containment. Studies state that the majority of the contaminants is scrubbed within this misty flow regime. At the top of the venturi, the gas stream is injected into the pool. The pressure drop at the nozzle exit leads to the formation of smaller bubbles, thus increasing the interfacial area concentration in the pool. In this work, the flow inside a full-scale venturi scrubber has been optically analyzed using shadowgraphy with a high-speed camera. The venturi nozzle was installed in the TRISTAN facility at PSI which was originally designed to investigate the flow dynamics of a tube rupture inside a full-length scale steam generator tube bundle. The data analysis was focused on evaluating the droplet size distribution and the Sauter mean diameter under different gas flow rates and operation modes. The scrubber was operated in two different ways, submerged and unsubmerged. The aim was to include the effect on the droplet sizes of using the nozzle in a submerged operation mode.

Plasma Spraying Using Ar-He-H2 Gas Mixtures

1998 ◽  
Author(s):  
S. Janisson ◽  
A. Vardelle ◽  
J.F. Coudert ◽  
B. Pateyron ◽  
P. Fauchais ◽  
...  
Keyword(s):  
Plasma Spraying ◽  
Gas Flow ◽  
Plasma Jet ◽  
Gas Mixtures ◽  
Gas Velocity ◽  
Gas Flow Rate ◽  
Static Behavior ◽  
Operating Variables ◽  
Arc Current ◽  
Plasma Guns

Abstract In D.C. plasma guns used for plasma spraying, the properties of the plasma forming-gas control, to a great extent, the characteristics of the plasma jet and the momentum, heat and mass transfer to the particles injected in the flow. This paper deals with mixtures of argon, helium and hydrogen and the effect of the volume composition of these mixtures on the dynamic and static behavior of the plasma jet. Both were investigated from the measurements of arc voltage and gas velocity. Correlations between these parameters and the operating variables (arc current, gas flow rate, gas mixture composition) were established from a dimensional analysis. The results were supported by the calculation of the thermodynamic and transport properties of the ternary gas mixtures used in this study.

Dynamically tunable ultralong photonic nanojet by a curved surface truncated dielectric microcylinder

2021 ◽  
Author(s):  
yi xing ◽  
fengfeng shu ◽  
huaming xing ◽  
yihui wu
Keyword(s):  
Finite Element Method ◽  
Electric Field Intensity ◽  
Dynamic Range ◽  
Effective Length ◽  
Full Width ◽  
Micro Particles ◽  
Photonic Nanojet ◽  
Half Height ◽  
Working Distance ◽  
Peak Electric Field

Abstract As for micro-particles (microspheres or microcylinders) that form Photonic nanojet (PNJ) in near fied,a curved truncated dielectric microcylinder structure (CSTDM) is investigated by finite element method(FEM) which can form ultralong PNJ with the longest effective length:209.49λ. We found that changing parameter h of structure can realize long dynamic range tuning of the effective length of PNJ. The effective length varies quasi-periodically with h; the law of the variation of main indicators of microcylinder are further discussed, such as the effective length,the working distance, peak electric field intensity and full width half height

Flow transitions and length scales of a channel-confined active nematic

Soft Matter ◽  
2021 ◽  
Author(s):  
Abhik Samui ◽  
Julia M. Yeomans ◽  
Sumesh P. Thampi
Keyword(s):  
Characteristic Length ◽  
Flow Regimes ◽  
Channel Width ◽  
Flow Structures ◽  
Length Scale ◽  
Length Scales ◽  
Turbulence Regime ◽  
Active Turbulence ◽  
Intrinsic Length ◽  
Flow Transitions

Different flow regimes realised by a channel-confined active nematic have a characteristic length same as channel width. Flow structures exhibit the intrinsic length scale of the fluid only in the fully developed active turbulence regime.

scholarly journals The effect of the liquid layer thickness on the evaporation intensity

2018 ◽  
Vol 194 ◽  
pp. 01030
Author(s):  
Aleksei Kreta ◽  
Vyacheslav Maksimov
Keyword(s):  
Experimental Study ◽  
Layer Thickness ◽  
Liquid Layer ◽  
Flow Rate ◽  
Gas Flow ◽  
Shear Stresses ◽  
Gas Velocity ◽  
Evaporation Intensity ◽  
Liquid Layer Thickness ◽  
Thermocapillary Forces

An experimental study of the influence of thermo-capillary forces and shear stresses with the side of the gas flow to the evaporation flow rate has been made. The experiments were carried out at various thicknesses of the liquid layer and constant gas velocity. The influence of the thickness of the liquid layer on the evaporation flow rate (the intensity of evaporation) has been analyzed. It is shown that the thermocapillary forces have a direct effect on the evaporation flow rate of the liquid layer.

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