• Journal of ILASS-Korea
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• v.9 no.2
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• pp.41-49
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• 2004

Liquid breakup under the variation of AC frequency has been studied experimentally in the electrohydrodynamic atomization. The effect of parameters such as charging voltage, flow rate, nozzle tip inner diameter and power frequency have been considered. This work was performed to investigate the experimental analysis for the effect of AC frequency on breakup process, the mapping of occurrence of disintegration region, and the relationship between the applied power and the droplet radius. The experimental results show that the increase of applied voltage in a certain frequency band leads to a reduction in the droplet size within the limits from 50Hz to 400Hz. The transition phenomena from dripping mode to spindle mode were observed under the band of sudden fall of droplet radius changing ratio, and the synchronous region were produced within the range of applied voltage from 5kV to 6kV.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.5
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• pp.1330-1337
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• 1994

This study is to predict the lateral dispersion of the particles with time in a vertical pipe. Particle is released downward and located in the center of a pipe through which stationary, homogeneous turbulent air is flowing. We assume that gas turbulence velocities have a Gaussian probability density distribution and the presence of particle is not to alter turbulent structures. Particle trajectory is computed by numerically integrating the particle Lagrangian equation of motion, with a random sampling to determine the fluctuating air velocity experienced by each particle, which considered inertia effect and crossing-trajectories effect. The result shows characterestics of particle dispersion according to flow field condition and droplet size by using the parameters and scales, which expressed characterestics of flow field and particle. Predictions agree reasonably with experimental data.

• Journal of Ocean Engineering and Technology
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• v.14 no.2
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• pp.44-52
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• 2000

The dispersion of surface oil is generally described as a break-up of oil slick into small oil droplets. These small droplets are subjected to turbulence and vertical circulation so that it can be entrained into subsurface. Sometimes they tend to be submerged into sea bottom permanently. The diameter of oil droplets is a critical parameter to determine their behavioral characteristics under water surface. At the same time the variations of droplet stability depends on the weathering of it. That is why the weathered oil has different mechanism from the unweathered one. The variability of physical properties of oil including viscosity and density contribute to interfere with effective separation of oil and emulsion droplets in water. Also in the presence of interactions among the droplets there are coalescing or coagulating effects on the dispersion process of droplets.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.6
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• pp.2147-2159
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• 1991

The effects of principal dimensions of internal mixing twin-fluid atomized and operating conditions on the atomizing characteristics are experimentally investigated. The tests are conducted over the wide range of air/liquid ratio to predict influences of the diameter and length of nozzle, contacting angle between air and liquid in the mixing chamber, and air orifice diameter on the mean drop size(SMD), spray angle, distribution of drop size, and spray dispersion, And also, initial distribution of liquid column by air stream within the mixing chamber are observed through the transparent nozzles. A He-Ne laser particle sizer(MALVERN Model 2604) was used to measure the Sauter.s mean diameter( $D_{321}$) and droplet sizes distribution. In this experiment the air/liquid ratio, mixing length and nozzle diameter have a great influence on SMD, spray angle, droplet sizes distribution and spray dispersion.

• Particle and aerosol research
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• v.13 no.3
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• pp.133-139
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• 2017

In this paper, we proposed an emulsification method without using an emulsifier and investigated the effects of particle size distribution in fluids on dispersion stability. Surfactant-free oil in water emulsion was prepared with 1 % (w/w) of olive oil by using high speed agitation, high pressure and ultrasonic dispersion methods. The particle size, microscopic observation, and dispersion stability of each sample were evaluated and dispersion stability according to various dispersion methods was compared. As a result, the emulsion dispersed by the ultrasonic dispersion method showed the smallest particle size and uniform distribution of $0.07{\sim} 0.3{\mu}m$ and was the most stable in a 7 days stability evaluation. In the above experiment, four olive oil emulsions having different particle sizes were prepared using ultrasonic dispersion technology that was capable of producing stable emulsions. The dispersion stability of each samples with oil droplet sizes of (A) 0.1 to $0.5{\mu}m$, (B) 0.3 to $4{\mu}m$, (C) 1 to $10.5{\mu}m$ and (D) 2 to $120{\mu}m$, was observed for 7 days, and the relationship between the stability and performance was studied. Emulsion (A) with particle size less than $0.5{\mu}m$ displayed the dispersion stability showing below 5 % change in a 7 days stability evaluation. In the case of (B), (C), and (D) that had larger particle than $0.5{\mu}m$, the changes of dispersion stability were 10 %, 13 % and 35 % respectively. From these results, it was proved that dispersion stability of emulsion with uniform particle size of $0.5{\mu}m$ or less was confirmed to be very stable.

• Smart Media Journal
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• v.8 no.4
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• pp.38-45
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• 2019

When there is a spray flow such as from a pesticide nozzle, winds affect the droplet flow of a rotary-wing drone accompanied by a strong wake, with a severe oscillation. Especially, during forwarding flights or when winds come from the side, compare to a simple hovering flight as the droplet is in the effect of aerodynamic drag force, the effect of spraying region becomes even larger. For this reason, the spraying of pesticides using drones may cause a greater risk of scattering or a difference in droplet dispersion between locations, resulting in a decrease in efficiency. Therefore, through proper numerical modeling and its applied simulation, an indication tool is required applicable for the various flight and atmospheric conditions. In this research, we completed both experiment and numerical analysis for the strong downwash from the rotor and flight velocity of the drone by comparing the probability density function of droplet distribution to build a spraying system that can improve the efficiency when spraying droplets in the pesticide spray drone.

• Journal of Mechanical Science and Technology
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• v.14 no.2
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• pp.236-250
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• 2000

Compression ignition direct injection diesel engines employed a high pressure injection system have been developed as a measure to improve a fuel efficiency and reduce harmful emissions. In order to understand the effects of the pressure variation, many experimental works have been done, however there are many difficulties to get data in engine condition. This work gives numerical results for the high pressure effects on spray characteristics in wide or limited space with near walls. The gas phase is modelled by Eulerian continuum conservation equations of mass, momentum, energy and fuel vapour fraction. The liquid phase is modelled using the discrete droplet model approach in Lagrangian form and the drop behavior on a wall is calculated with a new droplet-wall interaction model based on the experiments observing individual drops. The droplet distributions, vapour fractions and gas flows are shown in various injection pressure cases. In free spray case which the injection spray has no wall impaction, the spray dispersion and vapour fraction increase and drop sizes decrease with increasing injection pressure. The same phenomena appears more clearly in wall impaction cases.

• Particle and aerosol research
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• v.9 no.1
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• pp.23-29
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• 2013

Inertial impaction type mist eliminators are the most effective instruments to separate mist from the gas. In this work, the effect of the horizontal chevron type mist eliminators is characterized experimentally. Droplet size distribution and evaluation of removal efficiency of the chevron type mist eliminators at different gas flows were investigated using an aerosol particle size analyzer and a portable aerosol spectrometer, respectively. The experimental investigations showed that the mist removal efficiency in these instruments is dependent in the droplet size, and the pressure drop is nil.

• Journal of Mechanical Science and Technology
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• v.19 no.12
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• pp.2312-2320
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• 2005

The aerodynamic effects of leading-edge accretion can raise important safety concerns since the formulation of ice causes severe degradation in aerodynamic performance as compared with the clean airfoil. The objective of this study is to develop a numerical simulation strategy for predicting the particle trajectory around an MS-0317 airfoil in the test section of the NASA Glenn Icing Research Tunnel and to investigate the impingement characteristics of droplets on the airfoil surface. In particular, predictions of the mean velocity and turbulence diffusion using turbulent flow solver and Continuous Random Walk method were desired throughout this flow domain in order to investigate droplet dispersion. The collection efficiency distributions over the airfoil surface in simulations with different numbers of droplets, various integration time-steps and particle sizes were compared with experimental data. The large droplet impingement data indicated the trends in impingement characteristics with respect to particle size ; the maximum collection efficiency located at the upper surface near the leading edge, and the maximum value and total collection efficiency were increased as the particle size was increased. The extent of the area impinged on by particles also increased with the increment of the particle size, which is similar as compared with experimental data.

• Particle and aerosol research
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• v.12 no.4
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• pp.135-143
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• 2016

Removal of water contents in a gas is needed in industrial field of gas processing related on energy production/conversion, and environmental treatment. Inertial separators are economic devices for separating droplets from the gas stream. For accurate understanding of removal process in a curved vane mist eliminator, a numerical model including turbulent dispersion, evaporation and condensation of water vapor at surface of droplets is required. A two-stage curved vane mist eliminator has been modeled, and fluid flow of mixture of air and water vapor and droplet trajectories were solved simultaneously with taking into account two-way coupling. Removal efficiency of droplets with various inlet condition of relative humidities (RH, 40%, 90%, and 100%) were compared. As RH increased, the effect of evaporation decreased and inertial separation efficiencies of droplets obtained increased especially for droplets of diameter below 10 micrometers.