• Fire Science and Engineering
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• v.23 no.1
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• pp.48-54
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• 2009

The present study has been performed to investigate the effect of statistical number of droplets on the simulation of the sprinkler spray using fire field model. In order to simulate the sprinkler spray characteristics, the present study uses NIST Fire Dynamics Simulator version 5.2. A group of Lagrangian particles with similar droplet characteristics, such as diameter, velocity, temperature and so on, is represented by parcel concept to decrease the total number of droplets tracked in the simulation. The present study introduces a new parameter to represent the ratio between real number of droplets and computational parcels. The dependency of the number of parcels on the fire suppression characteristics and spray patterns is quantitatively examined for different ratio between the real number of droplets and computational parcels.

• Journal of ILASS-Korea
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• v.26 no.3
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• pp.127-134
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• 2021

Fire sprinkler initial spray was analyzed by Large eddy simulation (LES) and Volume of Fluid (VoF) integrated method. The IsoAdvector geometric VoF was used to identify the liquid-gas interface clearly even with the large Courant-Friedrichs-Lewy number. To reduce the computational costs, sector meshes and Adaptive Mesh Refinement up to level 3 were used. Base mesh size was 1 mm, which is roughly equivalent to the initial sprinkler droplet. Top surface radius of boss and deflector size were modified to investigate the effects of sprinkler head design on primary breakup process. When top surface radius of boss was increased, vertical liquid sheet was formed. This phenomenon reduced the sheet breakup radius, sheet thickness and velocity. Due to reduced liquid sheet thickness, a large amount of ligaments was created from the liquid sheet. As a result, there was a dramatic decrease in volume per surface area, indicating an increase in breakup process. Spray pattern viewed in radial direction also changed when top surface radius of boss increased. When top surface radius of boss was increased, a T-shaped pattern was observed while a V-shaped pattern was observed in all other cases. When the deflector size increases, the spray pattern remains V-shaped, even if the top surface radius of boss increased. Further studies on promoting atomization of the water supplied to the lower part of the sprinkler head in the T-shape pattern should be conducted.

• 한국연소학회:학술대회논문집
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• 2004.06a
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• pp.192-198
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• 2004

A numerical study was conducted to determine the effects of high temperature air, including equivalent ratio on flow field, temperature, evaporation, and overall temperature distribution in gas turbine combustor. A sector model of a typical wall jet can combustor, featuring introduction of primary air and dilution air via wall jet, was used in calculations. Flow field and temperature distribution were analyzed. Operating conditions such as inlet temperature and overall equivalent ratio were varied from 373 to 1300 K, and from 0.3 to 0.6, respectively, while any other operating conditions were fixed. The RNG ${\kappa}-{\varepsilon}$ model and eddy breakup model were used for turbulence and combustion model respectively. It was found that the increase with the inlet air temperature, velocity in the combustor is accelerated and evaporation of liquid fuel is not affected in primary zone, high temperature inlet air enhances the evaporation and improves overall temperature distribution factor.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.6
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• pp.1-7
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• 2017

The atomization of a liquid into multiple droplets has many important industrial applications, including the atomization of fuels in combustion processes and coating of surfaces and particles. Ultrasonic atomizing nozzle has a transducer that receives electrical input in the form of a high frequency signal from a power generator and converts that into mechanical energy at the same frequency. Liquid is atomized into a fine mist spray using high frequency sound vibrations. In coating applications, the unpressurized, low-velocity spray reduces the amount of overspray significantly because the droplets tend to settle on the substrate, rather than bouncing off it. The spray can be controlled and shaped precisely by entraining the slow-moving spray in an ancillary air stream using specialized types of spray-shaping equipment. The desired patterns of spray can be obtained using an air stream. To simulate the water mist behavior of an ultrasonic atomizing nozzle using an air stream, the Lagrangian dispersed phase model was employed using the commercial code FLUENT. The effects of the nozzle contraction shape, water droplet size and the pneumatic pressure drop on the spray characteristics were investigated to obtain the optimal condition for coating applications.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.385-388
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• 2002

The researches of a two-phase atomizers have been carried out in the field of automotive and aerospace industries in order to improve the atomization performance of the liquid droplets ejecting from these nozzles. The smaller droplets have the advantages of the reduction of environmental pollution matter and effective use of energy through the improvement of heat and mass transfer efficiency. Thus, to propose the basic information of two-phase flow, an internal mixing atomizer was designed, its shape factor was 0.6 and the liquid feeding hole was positioned at the center of the mixing tube which was used to mix the air and liquid. The experimental work was performed in the field after the nozzle exit orifice. The measurement of the liquid droplets was made by PDPA system. This system can measure the velocity and size of the droplets simultaneously. The number of the droplets used in this calculation was set to 10,000. The flow patterns were regulated by ALR (Air to Liquid mass Ratio). ALR was varied from 0.1024 to 0.3238 depending on the mass flow rate of the air. The analysis of sampling data was mainly focused on the spray characteristics such as flow characteristics distributions, half-width of spray, RMS, and turbulent kinetic energy with ALR.

• Transactions of the Korean hydrogen and new energy society
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• v.28 no.3
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• pp.300-307
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• 2017

This study is to investigate particle size and velocity profile of gasoline port injector using Phase Doppler Particle Analyzer (PDPA). In this experiment, a GV 250 Delphi port injector used for motorcycles was used for liquid injection. The injector consists of four holes and has a static flow rate of 2.13 g/s. The fuel used in the injection was N-heptane, which is similar to gasoline, as an alternative fuel. The test fuel was injected at an atmospheric temperature of $20^{\circ}C$ and an open atmosphere of 1 atm. The injection time was 10 ms and the injection pressure was 3.5 bar in PDPA experiment. The experimental target position was fiexd at 30, 50 and 75 mm from the nozzle tip and data were collected for a total of 10,000 samples. The experimental results show that the length diameter (D10), the Sauter mean diameter ($D_{32}$), and the mean droplet velocity (MDV) are $45-54{\mu}m$, $99-115{\mu}m$ and 15-21 m/s, respectively.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.5
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• pp.72-79
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• 2003

Spray characteristics were investigated by impinging F-O-O-F type injector with varying the impingement angle through 15, 20 and 30 degree and the mixture ratio(O/F ratio) from 1.5 to 3.0. Experimental results show that the correlation between dispersion and impingement angle is not influenced of the mixture ratio variation, but which has influence on number density, and there is a linear correlation between dispersion and impingement angle. Velocity distribution, standard deviation and SMD of droplets are decreased as the impingement angle increases. Also, it was confirmed that the distribution of droplet size are in accordance with Rosin-Rammler and Upper-limit distribution.

• Smart Media Journal
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• v.9 no.4
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• pp.176-186
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• 2020

The size and shape of crops are diverse, and the growing environment is also different. Therefore, when one uses a drone to spray pesticides, the characteristics of each crop must be considered, and flight conditions such as the flight height and forwarding velocity of the drone should be changed. The droplet flow of pesticides is affected by various flight conditions, and a large change occurs in the sprayed area. As a result, an uneven distribution of liquid may be formed at the wake, and the transport efficiency will be decreased as well as there would be a risk of toxic scatter. Therefore, this paper analyzes the degree of distribution of pesticides to the crops through numerical analysis when pesticide is sprayed onto the selected three crops with different characteristics by using agricultural drones with different flight conditions. On the purpose of establishing a guideline for spraying pesticides using a drone in accordance with the characteristics of crops, this paper compares the amount of pesticides distributed in the crops at the wake of nozzle flow using the figure of merit, and the sum of transported liquid rate divided by the root mean square of the probability density function.