• Fire Science and Engineering
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• v.30 no.2
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• pp.62-67
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• 2016

In this study, the optical depth is analyzed with the effects of droplet size distribution of the water curtain nozzle to attenuate the radiative heat transfer. The HELOS/VARIO equipment is used for the measurement of the droplet size distributions. The spray characteristics are quantified by the investigation of Deirmenjian's modified gamma distribution function. The distribution constant of the nozzle can be obtained as ${\alpha}=1$ and ${\gamma}=5.2$. The generalized equation of the optical depth related with the droplet size distribution is introduced. These results will be applicable to the analysis of the design condition of the water curtain nozzle.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.3 s.168
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• pp.187-193
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• 2005

The temperature distribution of the deposited droplet was predicted by using the finite element analysis and it was assumed that the droplet was axisymmetrical model. The analysis of residual stress was performed with the temperature data, which is obtained from the result. Axisymmetric droplet is deposited three times to consider the actual phenomenon of droplet deposition. The analysis of the temperature distribution is respectively performed whenever the axisymmetric droplet is laminated and the residual stresses of the laminated axisymmetric droplet are calculated with the value of the temperature distribution.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.7
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• pp.439-445
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• 2015

We established the emulsion method using membrane filter with precise control of LC droplet distribution in PDLC. PDLC cells with various LC droplet size distributions such as single droplet sizes of $1.0{\mu}m$, $1.9{\mu}m$ and $3.5{\mu}m$, the mixture of two different LC droplet sizes and the mixture of three different LC droplet sizes were fabricated and the electro-optical properties of the emulsion type PDLC cells with various droplet size distribution were investigated. In the appropriate droplet size range, the PDLCs with the single droplet sizes distributions have good electro optical properties than those with the mixture of three different LC droplet sizes. In addition, the PDLC cells with the mixture of two different LC droplet sizes have the better electro optical properties than those with single droplet sizes distribution. The PDLC cell with dual droplet size distribution of $1.0+1.9{\mu}m$ shown the best electro optical properties than the PDLC cells with other size distributions. This method enabled us to find the proper LC droplet size distribution for achieving both high transmittance and contrast ratio.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.7 s.262
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• pp.611-619
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• 2007

In this study, the droplet size distribution of a slit injector at different surrounding conditions, such as air flow and fuel temperature, were investigated. Phase Doppler anemometry (PDA) was utilized to investigate the initial droplet size distribution and the effect of fuel temperature and air flow on droplet size distribution. The entrained air motion was also evaluated by the temporal velocity profile of droplets. When the air flow velocity increased, the small droplets were more entrained to the upper and central parts of the spray and this tendency was confirmed by plotting the temporal velocity profile of droplets. This entrainment of small droplets at high airflow velocities caused relatively small mean droplet size at upper and central parts of the spray and the large mean droplet size at downstream and edge of the spray, compared to that of low airflow velocities. The total mean droplet size, obtained by averaging the size of all droplets measured at all test locations, decreased when the high airflow velocities were applied. The increased fuel temperature, with an airflow velocity of 10m/s, caused reduced droplet size at all test locations. However, the decreased value of mean droplet size at high fuel temperatures was relatively higher at upper parts of the spray, compared to downstream, as a result of enhanced entrainment of small droplets to upper parts of the spray.

• Nuclear Engineering and Technology
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• v.51 no.5
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• pp.1261-1271
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• 2019

Droplet size and distribution are important parameters determining venturi scrubber performance. In this paper, we proposed physical models for a maximum stable droplet size prediction and upper limit log-normal (ULLN) distribution parameters. For the proposed maximum stable droplet size prediction model, a Eulerian-Lagrangian framework and a Reitz-Diwakar breakup model are solved simultaneously using CFD calculations to reflect the effect of multistage breakup and droplet acceleration. Then, two ULLN distribution parameters are suggested through best fitting the previously published experimental data. Results show that the proposed approach provides better predictions of maximum stable droplet diameter and Sauter mean diameter compared to existing simple empirical correlations including Boll, Nukiyama and Tanasawa. For more practical purpose, we developed the simple, one dimensional (1-D) calculation of Sauter mean diameter.

• 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.

• Journal of the Korean Society of Safety
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• v.32 no.4
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• pp.16-21
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• 2017

The sprinkler system is a basic fire extinguishing system that uses water as an extinguishing agent. In order to evaluate the fire extinguishing performance of the sprinkler system, information such as the discharge angle, discharge speed, discharge pressure, flow rate, and water droplet size of the installed head are required. However, there is a lack of research on droplets size compared to other requirements. In this study, to evaluate the extinguishing characteristics of sprinkler system, the droplet size distribution was measured for various types of sprinkler heads actually used. The size of the droplet was measured using laser diffraction method. The 50% cumulative volume distribution ($D_{v50}$) according to discharge coefficient(K factor) was $540{\mu}m{\sim}695{\mu}m$ for K50, $542{\mu}m{\sim}1,192{\mu}m$ for K80, $980{\mu}m{\sim}1,223{\mu}m$ for K115 and $1,188{\mu}m{\sim}1,234{\mu}m$ for K202. Based on the measured results, the vaeiance of the droplet particle distribution and the distribution ($D_{v50}$) according to discharge coefficient(K factor) was $540{\mu}m{\sim}695{\mu}m$ for K50, $542{\mu}m{\sim}1,192{\mu}m$ for K80, $980{\mu}m{\sim}1,223{\mu}m$ for K115 and $1,188{\mu}m{\sim}1,234{\mu}m$ for K202. Based on the measured results, the vaeiance of the droplet particle distribution and the Rosin-Rammler index value are presented. As a result of the fire simulation with FDS, it was confirmed that the performance difference occurs according to the water droplet size distribution even when the same amount of water is used. Therefore, the extinguishing performance of the sprinkler system should be evaluated considering the droplet size distribution according to the sprinkler head type.

• Journal of Hydrogen and New Energy
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• v.15 no.1
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• pp.72-81
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• 2004

Study on the analysis of sodium spray fire using Gaussian drop size distribution, which redistributes a droplet spectrum with given mean diameter if its size classes with critical diameter(D>8mm) occur, was carried out. In this case, the oversized droplets were reduced to a stable diameter. Results calculated by the code using Gaussian drop size distribution were in better agreement with AI experimental results than those of NACOM and SPRAY code. The effect of variance on pressure in the test cell appeared greatly by introducing Gaussian function, which could represent various sodium droplet size distribution. The increase of the variance with mean droplet size resulted had an important effect upon the pressure in the test cell.

• Journal of ILASS-Korea
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• v.20 no.3
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• pp.175-180
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• 2015

A series of sprinkler discharging tests was conducted to measure the droplet size and its distribution of residential fire sprinkler heads. Droplet sizes in sprinkler spray were measured using a laser diffraction method for the flush, circular and pendent type sprinkler head. In this study, the $D_{v,50}$ of the flush type sprinkler heads were ranged between $530{\sim}1040{\mu}m$ and those of circular and pendent type were $988{\mu}m$ and $916{\mu}m$, respectively. The measured cumulative volume distributions were followed by a combination of the log-normal and Rosin-Rammler distribution which is widely used in the computational fire analysis and the parameters of distribution function were obtained from the best fit line through the measured data.

• Journal of ILASS-Korea
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• v.6 no.2
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• pp.16-21
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• 2001

This paper describes the macroscopic behavior and atomization characteristics of the high-pressure gasoline swirl injector in direct-injection gasoline engine. The global spray behavior of fuel injector was visualized by shadowgraph technique. The atomization characteristics of gasoline spray such as mean diameter and mean velocity of droplets were measured by the phase Doppler particle analyzer system. The macroscopic visualization and experiment of particle measurement on the fuel spray were investigated at 7 and 10 MPa of injection pressure under different spray cone angle. The results of this work show that the geometry of injector was more dominant over the macroscopic characteristics of spray than the fuel injection pressure and injection duration. As for the atomization characteristics, the increase of injection pressure resulted in the decrease of fuel droplet diameter and the atomization characteristics differed as to the spray cone angle. The most droplets had under $25{\mu}m$ diameter and for the large droplets(upper $40{\mu}m$) as the spray grew the atomization presses were very slow. Comparison results between the measured droplet distribution and the droplet distribution functions revealed that the measured droplet distribution is very closed to the Normal distribution function and Nukiyama-Tanasawa's function.