• Journal of ILASS-Korea
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• v.26 no.4
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• pp.189-196
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• 2021

Spray drift of agricultural nozzles has become a big issue because it causes low precision targeting and environmental pollution. In order to reduce the spray drift, study spray characteristics of agricultural nozzles is virtually important. In this study, shadowgraph and Mie-scattering visualization techniques were used to study the macroscopic spray and atomization characteristics of an agricultural nozzle. PDPA was used to measure the atomization characteristics of spray. The injection pressure is set to 1 bar, 3 bar and 5 bar, which covers the working range of the nozzle. For the PDPA experiment, 75 points were measured in an area of 160 mm × 120 mm at 10 mm intervals directly below the nozzle to grasp the overall atomization characteristics of the spray. It was found that the spray width and sheet width showed a linear correlation. As the injection pressure increased, the sheet expansion in the 0-degree direction and the sheet swing in the 90-degree direction jointly promoted the breakup of the sheet. In addition, the area close to the central axis had a large droplet velocity, and since a large droplet velocity promoted atomization of spray, the area close to the central axis had a smaller spray droplet diameter than the left and right regions.

• Journal of computational fluids engineering
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• v.14 no.1
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• pp.1-8
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• 2009

To control the coating thickness of zinc in the process of continuous hot-dip galvanizing, it is known from early days that the gas wiping through an air knife system is the most effective because of the obtainable of uniformity of coating thickness, possibility of thin coating, working ability in high speed and simplicity of control. But, the gas wiping using in the galvanizing process brings about a problem of splashing from the strip edge for a certain high speed of coating. Also, it is known that the problem of splashing directly depends upon the galvanizing speed and nozzle stagnation pressure. In theses connections, in the present study, we proposed two kinds of air knife systems having the same expansion rate of nozzle, and the jet structures and coating thicknesses from a conventional and new proposed nozzles are compared. In numerical analysis, the governing equations consisted of two-dimensional time dependent Navier-Stokes equations, standard k-e turbulence model to solve turbulence stress and so on are employed. As a result, it is found that it had better to use the constant rate nozzle from the point view of the energy saving to obtain the same coating thickness. Also, to enhance the cutting ability at the strip, it is advisable to use an air knife with the constant expansion rate nozzle.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.159-159
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• 2011

Among the semiconductor ternary compounds in the I-III-$VI_2$ series, $CulnS_2$ ($CulnSe_2$) are one of the promising materials for photovoltaic applications because of the suitability of their electrical and optical properties. The $CuInS_2$ thin film is one of I-III-$VI_2$ type semiconductors, which crystallizes in the chalcopyrite structure. Its direct band gap of 1.5 eV, high absorption coefficient and environmental viewpoint that $CuInS_2$ does not contain any toxic constituents make it suitable for terrestrial photovoltaic applications. A variety of techniques have been applied to deposit $CuInS_2$ thin films, such as single/double source evaporation, coevaporation, rf sputtering, chemical vapor deposition and chemical spray pyrolysis. This is the first report that $CuInS_2$ thin films have been prepared by Aerosol Jet Deposition (AJD) technique which is a novel and attractive method because thin films with high deposition rate can be grown at very low cost. In this study, $CuInS_2$ thin films have been prepared by Aerosol Jet Deposition (AJD) method which employs a nozzle expansion. The mixed fluid is expanded through the nozzle into the chamber evacuated in a lower pressure to deposit $CuInS_2$ films on Mo coated glass substrate. In this AJD system, the characteristics of $CuInS_2$ films are dependent on various deposition parameters, such as compositional ratio of precursor solution, flow rate of carrier gas, stagnation pressure, substrate temperature, nozzle shape, nozzle size and chamber pressure, etc. In this report, $CuInS_2$ thin films are deposited using the deposition parameters such as the compositional ratio of the precursor solution and the substrate temperature. The deposited $CuInS_2$ thin films will be analyzed in terms of deposition rate, crystal structure, and optical properties.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.1
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• pp.85-96
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• 2003

For a design of rocket engine nozzle, chemical equilibrium analysis which shares the same numerical characteristics with frozen flow analysis can be used as an efficient design tool for predicting maximum thermodynamic performance of the nozzle. 10 this study, a chemical equilibrium flow analysis code was developed for the design of hydrocarbon fueled rocket engines. 10 oder to understand the thermochemical characteristics occurring in a nozzle through the expansion process, such as recombination of chemical components and the accompanying energy recovery, chemical equilibrium flow analysis was carried out for the KSR-III rocket engine nozzles together with frozen flow and non-equilibrium flow analyses. The performance evaluation based on the present KSR-III nozzle flow analyses has provided an understanding of the thermochemical process in the nozzle and additionally, it has confirmed that the newly designed nozzle shape modified to have a reduced exit area ratio is an adequate design for obtaining an increased ground thrust.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.162.1-162.1
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• 2010

Cavitation phenomenon has long been a difficult problem that regarded as negative event to fluid machines or industrial facilities. In the latest, however, some engineers became to understand the power of cavitation and use it to cleaning wall after developing cavitation nozzle. In this paper, we introduce new concept for power-generation system using cavitation jet flow maid by nozzle and impulse turbine in vacuum condition. The vacuum needed to make cavitation is generated naturally by Torricelli's vacuum, 10.23m effective head drop without additional power. We analyzed water's boiling and the steam's mean free path according to vacuum purity levels for nozzles and turbine blades. The nozzles make water accelerate in the neck and boil in expansion section of the nozzles. The shape of the impulse turbine is designed for absorption of the molecule's kinetic energy of the steam.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.12 s.243
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• pp.1329-1334
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• 2005

Synthesis of silver nanoparticles by the supersonic nozzle expansion method with corona discharge ions was investigated. Corona discharge ions functioned as seeds for heterogeneous nucleation in the silver nanoparticles formation process and provided silver nanoparticles with electronic repulsive force that prevents aggregation of the particles. For ion ejecting, we used sonic-jet corona discharger. Upon application of the corona discharge ions, the mean diameter of the produced particles was decreased from 12.54 to 6.22nm and the standard deviation was decreased from 5.02 to 3.34nm. In addition, the agglomeration of silver nanoparticles was reduced.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.335-340
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• 2000

A 3 valve-type pulse tube refrigerator optains its cooling effect from pressure drop by releasing the part of the charged gas through hot end nozzle. The objective of this study is to analyze the performance and to find an optimal expansion pressure of the 3 valve-type pulse tube refrigerator. It is assumed that gas lumps are not mixed and periodically repeat the adiabatic compression and expansion processes. And the nodal model is applied for the analysis of the regenerator. As the result of analysis, the optimum pressure at the end of expansion process was about 80-90% of the maximum pressure.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.4
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• pp.304-310
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• 2015

Pintle thrusters use pintle stroke to change nozzle throat area, and this controls thrust. Using MATLAB, one-dimensional simulation has been investigated and the results are compared to those of cold flow tests and computational fluid dynamics for the pintle thruster of Chungnam National University. The prediction based on one-dimensional flow theory shows good agreement with measurements for chamber pressure, but deviates for thrust, partly because of nozzle wall separation. Computational results show that nozzle wall separation occurs at an early stage of nozzle expansion, near the design nozzle throat, for the course of pintle strokes. Empirical thrust prediction incorporates nozzle wall separation, and thus 1-D simulation using empirical thrust prediction showed good results for an early stage of pintle stroke.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.3
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• pp.28-34
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• 2019

The thrust control calculation according to the operation of plug nozzle for cold air test and the analysis of the flow characteristics of the pintle shape and operation pressure are performed. The numerical computation was verified by comparing the flow structure and the coefficient of thrust with the experimental data. It was confirmed that the nozzle throat was formed at the design position on each pintle shape, and thrust control up to 1:8 was achieved only by the stroke change. Finally, although the aerospike nozzle is autonomous, it is unfavorable in the under_expansion condition, if it is designed for a very low nozzle pressure ratio.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.3
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• pp.97-103
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• 2012

The combustion chamber and nozzle of a liquid rocket engine should be protected from the high temperature combustion gas generated by the chamber. An upper-stage nozzle extension has a large expansion ratio, therefore, The light-weight refractory materials have been used since the weight impact on the launcher performance is crucial. Gas film cooling method was used before, but was not applicable nowadays. Ablative cooling method and radiative cooling method with niobium alloy, Ni-based superalloy and ceramic based composite have been used to this day.