• Journal of ILASS-Korea
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• v.6 no.1
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• pp.18-24
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• 2001

Liquid fossil fuel contaminated by water can cause trouble in the combustion processes and affect the endurance of a combustion system. Using an optical sensor to monitor the water content instantaneously in a fuel pipeline is an effective means of controlling the fuel quality in a combustion system. In two component liquid flows of oil and water, the flow pattern and characteristics of water droplets are changed with various flow conditions. Additionally, the light scattering of the optical sensor measuring the water content is also dependent on the flow patterns and droplet characteristics. Therefore, it is important to investigate the detailed behavior of water droplets in the pipeline of the fuel transportation system. In this study, the flow patterns and characteristics of water droplets in the turbulent pipe flow of two component liquids of gasoline and water were investigated using optical measurements. The dispersion of water droplets in the gasoline flow was visualized, and the size and velocity distributions of water droplets were simultaneously measured by the phase Doppler technique. The Reynolds number of the gasoline pipe flow varied in the range of $4{\times}10^{4}\;to\;1{\times}10^{3}$, and the water content varied in the range of 50 ppm to 300 ppm. The water droplets were spherical and dispersed homogeneously in all variables of this experiment. The velocity of water droplets was not dependent on the droplet size and the mean velocity of droplets was equal to that of the gasoline flow. The mean diameter of water droplets decreased and the number density increased with the Reynolds number of the gasoline flow.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.8
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• pp.913-919
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• 2012

This paper presents results for dispensing and measuring micro-particles using a pneumatic dispensing system. Particle-suspended liquid droplets were dispensed and analyzed quantitatively at various particle concentrations and applied pressures. By using a developed experimental setup, the number of particles and the particle volume ratio in sequentially dispensed droplets were measured. Hydrophilic and hydrophobic surfaces were tested to find a suitable surface for counting the number of particle. It was confirmed that the dispensed particles concentrated into the center of the droplet on the smooth CD surface after evaporation of liquid. As the applied positive pressure increased, the number of particles per droplet increased consistently and the volume fraction of particles remained constant.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.214-219
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• 2001

In this study, numerical investigation has been performed on the spreading and solidification of a droplet impacting onto a solid substrate in the thermal spray process. The finite difference method with volume-of-fluid approach is used to analyze the free surface flow and the source-based enthalpy method is employed to model the latent heat release during the solidification. In this work, the numerical model is validated through the comparison of the present numerical result with experimental data available for the flat substrate.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.6
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• pp.1529-1538
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• 1995

In this study, a liquid sheet type co-axial nozzle has been used to investigate the turbulent atomization characteristics which could result in the experimental data to be used in designing a jet nozzle with high performance. Image processing technique and immersion sampling method were employed to measure droplet size. In atomizing characteristics, droplet size distributions and absolute droplet sizes, SMD(Sauter Mean Diameter) have been investigated in the wide ranges of flow field depending upon the air-water mass ratios. And the comparisons between the present data and the semi-empirical curves have been conducted semi-empirical correlation for SMD has been derived in the present analysis.

• Journal of the Korean Applied Science and Technology
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• v.28 no.3
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• pp.313-320
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• 2011

Encapsulation of L-ascorbic acid(AA) into BGsome was attempted to improve its stability. BGsome is a bio-compatible vesicular system prepared by dispersion of hydrated liquid crystalline phase formed through hydration of 1,3-butylene glycol(BG)-dissolved lecithin with an aqueous solution containing hydrophilic component. The characteristics of AA encapsulated BGsome, such as droplet size, surface charge, and solution appearance, was investigated. The concentration of AA solution had considerable effect on droplet size and surface charge of BGsome. Several tens nanometer droplet made by sonication treatment did not showed any change of size with storage time. Stability of AA was improved by encapsulation into BGsome, which was verified through DPPH test and HPLC assay.

• Journal of the Korean Society of Combustion
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• v.3 no.2
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• pp.51-63
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• 1998

Air-assisted atomizer flames are investigated numerically to study spray structures in nonburning and burning conditions based on experimental data. A PDA is used to measure droplet size, velocity, and number density for both nonburning and burning spray. Computations utilize time-averaged gas-phase equations and $k-{\varepsilon}$ turbulence model for simplicity. The major features of the liquid-phase model are that a SSF approach is used to represent the effect of gas-phase turbulence on droplet trajectories and vaporization, an infinite-diffusion model is employed to represent the transient liquid-phase process. Computation and experiment results show that the droplet acceleration and evaporation proceed quickly in near the atomizer, characterizing high number densities and a strong convective effect. The primary combustion zone, however, is dorminated by the gas phase reaction and exhibits a sheath combustion.

• Journal of ILASS-Korea
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• v.15 no.4
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• pp.202-207
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• 2010

Mist cooling is widely employed as a cooling technique of high temperature surfaces, and it has heat transfer characteristics similar to boiling heat transfer which has the convection, nucleate and film boiling regions. In the present study, mist cooling heat transfer was experimentally investigated for the mist flow impacting on the heated surfaces of mico-fins. The mist flow was generated by supersonic vibration. Experiments were conducted under the test conditions of droplet flow rate, $Q=6.02{\times}10^{-9}{\sim}3.47{\times}10^{-8}\;m^3/s$ and liquid temperature, $T_f=30{\sim}35^{\circ}C$. From the experimental results, it is found that an increase in the droplet flow rate improves mist cooling heat transfer in the both case of smooth surface and surfaces of micro-fins. Micro-fins surfaces enhance the mist cooling heat transfer. Besides, the experimental results show that an increase in the droplet flow rate decrease the heat transfer efficiency of mist cooling.

• Nuclear Engineering and Technology
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• v.50 no.3
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• pp.379-388
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• 2018

Models for the rate of atomization and deposition of droplets for stratified and annular flow in horizontal pipes are presented. The entrained fraction is the result of a balance between the rate of atomization of the liquid layer that is in contact with air and the rate of deposition of droplets. The rate of deposition is strongly affected by gravity in horizontal pipes. The gravitational settling of droplets is influenced by droplet size: heavier droplets deposit more rapidly. Model calculation and simulation results are compared with experimental data from various diameter pipes. Validation for the suggested models was performed by comparing the Safety and Performance Analysis Code for Nuclear Power Plants calculation results with the droplet experimental data obtained in various diameter horizontal pipes.

• 한국연소학회:학술대회논문집
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• 2007.05a
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• pp.107-113
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• 2007

The burning characteristics of interacting droplets with internal circulation in a convective flow are numerically investigated at various particle arrangement and size difference. In this simulation some conditions are fixed, surround gas temperature is 1250K, pressure is 10 atm and drolet's initial temperature is 300K. The transient combustion of arranged droplets, the fixed droplet distances of 4 radii to 20 radii horizontally, is studied. And the range of size of droplet is 75${\mu}m$ to 100${\mu}m$. The results obtained from the present numerical analysis reveal that the transient flame configuration and retardation of droplet internal motion with the horizontal spacing substantially influence lifetime of interacting droplets. At a Reynolds number 10, lifetime of the three droplets with decreasing horizontal droplet spacing increases monotonically. But when droplet spacing decreases further to 4radii, Lifetime of interacting droplets are increase. So Lifetime of interacting droplets exhibits a strong dependence on the horizontal droplet spacing and size difference. It can be investigated well with these conditions to that of single burning droplet.

• Journal of ILASS-Korea
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• v.21 no.2
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• pp.78-87
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• 2016

This study experimentally investigated the effects of droplet temperature on the heat transfer characteristics during collision of a single droplet on a heated wall above the Leidenfrost temperature. Experiments were performed by varying temperature from 40 to $100^{\circ}C$ while the collision velocity and wall temperature were maintained constant at 0.7 m/s at $500^{\circ}C$, respectively. Evolution of temperature distribution at the droplet-wall interface as well as collision dynamics of the droplet were simultaneously recorded using synchronized high-speed video and infrared cameras. The local heat flux distribution at the collision surface was deduced using the measured temperature distribution data. Various physical parameters, including residence time, local heat flux distribution, heat transfer rate, heat transfer effectiveness and vapor film thickness, were measured from the visualization data. The results showed that increase in droplet temperature reduces the residence time and increases the vapor film thickness. This ultimately results in reduction in the total heat transfer by conduction through the vapor film during droplet-wall collision.