• 한국분무공학회지
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• 제25권4호
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• pp.196-203
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• 2020

Nowadays, urea SCR technology is considered as the most effective NOx reduction technology of diesel engine. However, low NOx conversion efficiency under low temperature conditions is one of its problems to be solved. This is because injection of UWS (Urea Water Solution) is impossible under such a low temperature condition due to the problem of insufficient of urea decomposition and urea deposits. In several previous studies, it has been reported that appropriate control of the amount of ammonia adsorbed on SCR catalyst can improve the NOx conversion efficiency under low temperature conditions. In this study, we tried to find out how much the NOx conversion efficiency increases with respect to the amount of ammonia adsorbed on the catalyst, and what the temperature conditions that the ammonia slip occurs. This study shows the results of 8 times repeated WHTC test with a diesel engine, in which UWS was injected with NH3/NOx mole ratio of '1'. Through this study, it was found that 13% of the NOx conversion efficiency of WHTC increased while the θ (ammonia adsorption rate) increased from "0%" to "22%". In addition, it is found that in cases of high θ value, the significant improvement of NOx conversion efficiency at low temperatures presented during the beginning period of WHTC and at high temperature and transient conditions presented during last part of WHTC test. The NH3 slip occurring condition was 250℃ of catalyst temperature and 10% of θ, and the amount of NH3 slip increased as the temperature and θ are increased.

• Nuclear Engineering and Technology
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• 제50권5호
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• pp.665-672
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• 2018

A venturi scrubber is an important element of Filtered Containment Venting System (FCVS) for the removal of aerosols in contaminated air. The present work involves computational fluid dynamics (CFD) study of dust particle removal efficiency of a venturi scrubber operating in self-priming mode using ANSYS CFX. Titanium oxide ($TiO_2$) particles having sizes of 1 micron have been taken as dust particles. CFD methodology to simulate the venturi scrubber has been first developed. The cascade atomization and breakup (CAB) model has been used to predict deformation of water droplets, whereas the Eulerian-Lagrangian approach has been used to handle multiphase flow involving air, dust, and water. The developed methodology has been applied to simulate venturi scrubber geometry taken from the literature. Dust particle removal efficiency has been calculated for forced feed operation of venturi scrubber and found to be in good agreement with the results available in the literature. In the second part, venturi scrubber along with a tank has been modeled in CFX, and transient simulations have been performed to study self-priming phenomenon. Self-priming has been observed by plotting the velocity vector fields of water. Suction of water in the venturi scrubber occurred due to the difference between static pressure in the venturi scrubber and the hydrostatic pressure of water inside the tank. Dust particle removal efficiency has been calculated for inlet air velocities of 1 m/s and 3 m/s. It has been observed that removal efficiency is higher in case of higher inlet air velocity.

• 한국추진공학회지
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• 제16권5호
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• pp.1-9
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• 2012

동축형 다공성재 분사기에서는 중심 액체제트 주위를 둘러싼 원통형 다공성재의 내부 표면에서 반경방향으로 분사된 기체가 중심액체제트와 상호작용을 하게 된다. 표면분사된 기체제트는 반경방향에서 축방향으로 발달하며, 그 과정에서 액체분무의 중심부까지 운동량을 효과적으로 전달하여 미립화 및 혼합 성능을 향상시킨다. 본 연구에서는 기체분사 면적 및 기체분사 질량유량을 변화시켜 각각 운동량 비 및 웨버수의 크기를 조절하였으며, 이에 따른 물-공기 모사추진제 수류시험에서의 분무특성에 대한 고찰을 수행하고 동일 스케일의 전단 동축형 분사기와의 비교 분석이 이루어졌으며, 동축형 다공성재 분사기에서 반경방향으로의 기체분사가 2상유체의 미립화/혼합에 긍정적인 영향을 주는 것으로 판단된다.

• 대한기계학회논문집
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• 제15권2호
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• pp.618-629
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• 1991

The purpose of this experiment is to understand the distribution of coal particles inside CWM droplet which is believed to be a very important factor controlling the flame stability. CWM slurry is atomized by an air assisted twin fluid nozzle. An experimental rig is designed and fabricated. The mean size of coal particle distribution in CWM slurry, atomizing air pressure, coal particle loading in slurry and sampling position inside spray are main experimental variables. The atomized CWM droplets are sampled on the thin white layer of magnesium oxide by the emergency sampling shutter. The sampled coal particles on magnesium oxide layers are collected into test tubes and dispersed completely by Ultra-Sonicator. The size distribution of coal particles inside droplets are measured by Coulter Counter. The presence of coal particle inside the impressions of droplets on magnesium oxide layer are investigated by photo technique. There are quite many droplets which do not have any coal particles. Those are just water droplets, not CWM droplets. The population ratio of droplets without coal particles to toal number of droplets is strongly affected by the mean size of coal particle distribution in slurry and this ration becomes bigger number as the mean size of coal particles be larger. The size distribution of coal particles inside CWM droplets is not even and depends on the size of droplet. Experimental results show that the larger CWM droplets has droplets has bigger mean value of particle size distribution. This trend becomes more evident as the atomizing air pressure is raised and the mean size of coal particles in CWM slurry is bigger. That is, the distribution of coal particles inside CWM dropolets is very much affected by the atomizing air pressure and the mean size of pulverized coal particles in CWM slurry.

• 한국분말재료학회지
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• 제22권3호
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• pp.197-202
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• 2015

In this study, porous stainless steel (STS316L) sintered body was fabricated by powder metallurgy method and its properties such as porosity, compressive yield strength, hardness, and permeability were evaluated. 67.5Fe-17Cr- 13Ni-2.5Mo (wt%) powder was produced by a water atomization. The atomized powder was classified into size with under $45{\mu}m$ and over $180{\mu}m$, and then they were compacted with various pressures and sintered at $1210^{\circ}C$ for 1 h in a vacuum atmosphere. The porosities of sintered bodies could be obtained in range of 20~53% by controlling the compaction pressure. Compressive yield strength and hardness were achieved up to 268 MPa and 94 Shore D, respectively. Air permeability was obtained up to $79l/min{\cdot}cm^2$. As a result, mechanical properties and air permeability of the optimized porous body having a porosity of 25~40% were very superior to that of Al alloy.

• 한국분무공학회지
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• 제16권4호
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• pp.176-185
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• 2011

The empirical correlations for the prediction of penetration height of liquid jet in crossflow are reviewed and classified in this study. Around thirty different correlations had been proposed by many investigators. It has generally known that the penetration height of a liquid jet in a cross-flow is a function of the liquid to air momentum flux ratio and the normalized downstream distance from the injector. However, several researchers incorporated the Weber number, liquid-to-water or air viscosity ratio, pressure ratio or Reynolds number, temperature ratio in the empirical correlations. The existing correlations can be grouped as correlations in a power-law, logarithmic, and exponential forms, respectively. Correlations in a power-law form can be further classified as three groups such as basic form, Weber number form and other parameters form. It should be pointed out that correlations in a logarithmic form in terms of Weber number or any other parameters could not be found. Universal correlation has still not been established due to the significant discrepancies between various correlations suggested to date. Several of the studies reported the significant discrepancies of predicted values by the existing correlations. The possible reasons for discrepancies will be summarized as measurement technique, assumptions made in defining terms in the liquid to air momentum flux ratio, difficulties in defining the boundaries of the liquid jets, and nozzle/injector geometry. Evaluation of validity for the correlations proposed recently by several investigators is essentially required. Those include eight power-law forms, two logarithmic forms, and one exponential form.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 1997년도 춘계학술강연 및 발표대회 강연 및 발표논문 초록집
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• pp.34-34
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• 1997

The effect of alloying mode and porosity on the axial tension-tension fatigue behavior of a P/M steel of nominal composition Fe-4w/o Ni-1.5w/o Cu-O.5w/o Mo-O.5w/o C has been evaluated. Alloying modes utilized were elemental powder mixing, partial alloying(distaloy) and prealloying by water atomization; in each case the carbon was introduced as graphite prior to sintering. Powder compacts were sintered($1120{\circ}C$/30 min.) in 7Sv/o $H_2$/25v/o $N_2$ to densities in the range 6.77-7.2 g/$cm^3$. The dependence of fatigue limit response on alloying mode and porosity was interpreted in terms of the constituent phases and the pore and fracture morphologies associated with the three alloying modes. For the same nominal composition, the three alloying modes resulted in different sintered microstructures. In the elemental mix alloy and the distaloy, the major constituent was coarse and fine pearlite, with regions of Ni-rich ferrite, Ni-rich martensite and Ni-rich areas. In contrast, the prealloy consisted primarily of martensite by with some Ni-rich areas. From an examination of the fracture surfaces following fatigue testing it was concluded that essentially all of the fracture surfaces exhibited dimpled rupture, characteristic of tensile overload. Thus, the extent of growth of any fatigue cracks prior to overload was small. The stress amplitude for the three alloying modes at 2x$l0^6$ was used for the comparison of fatigue strengths. For load cycles <3x$l0^5$, the prealloy exhibited optimum fatigue response followed by the distaloy and elemental mix alloy, respectively. At load cycles >2x$l0^6$, similar fatigue limits were exhibited by the three alloys. It was concluded that fatigue cracks propagate primarily through pores, rather than through the constituent phases of the microstructure. A decrease in pore SIze improved the S-N behavior of the sintered steel.

• 한국분무공학회지
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• 제24권1호
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• pp.35-42
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• 2019

Syngas is widely produced by incomplete combustion of coal, water vapor, and air (oxygen) in a high-temperature/high-pressure gasifier through a coal-gasification process for power generation. In this study, a simulation syngas which was mainly composed of $H_2$, CO, $CO_2$, and $N_2$ was fueled with diesel. A modified single cylinder compression ignition (CI) engine is equipped with intake port syngas supply system and mechanical diesel direct injection system for dual fuel combustion. Combustion and emission characteristics of the engine were investigated by applying various syngas composition ratios and compression ratios. Diesel fuel injection timing was optimized to increase indicated thermal efficiency (ITE) at the engine speed 1,800 rpm and part load net indicated mean effective pressure ($IMEP_{net}$) 2 to 5 bar. ITE of the engine increased with the $H_2$ concentration, compression ratio and engine load. With 45% of $H_2$ concentration, compression ratio 17.1 and $IMEP_{net}$ 5 bar, ITE of 41.5% was achieved, which is equivalent to that of only diesel fuel operation.

• 한국추진공학회지
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• 제25권4호
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• pp.59-70
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• 2021

슬링거 연소기 회전연료노즐의 유량과 회전수의 변화에 따른 분무 특성을 관측하기 위한 실험적 연구를 수행하였다. 물 공급장치, 고속 회전모터, 회전연료노즐, 시험용 챔버로 구성된 분무 시험리그를 구성하였으며, 고속카메라와 고출력 광원을 사용하여 회전연료노즐 오리피스로부터 토출되는 물의 분무를 가시화하였다. 실험 결과 유량이 감소하고 회전수가 증가할수록 미립화가 향상됨을 확인하였다. 분무 특성 모드와 성능함수로 구성된 맵을 도출한 결과, 기체의 공기역학적 Weber 수와 액체-기체 모멘텀 플럭스 비는 액체의 주 분열 특성과 관련이 있으며, 액체-기체 모멘텀 플럭스 비와 Rossby 수는 액체 분출 모드와 밀접한 상관관계를 가짐을 확인하였다.

• 대한환경공학회지
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• 제27권10호
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• pp.1081-1089
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• 2005

본 연구에서는 기존에 중유를 사용하는 상용보일러에서 오리멀젼 연료의 활용 가능성을 평가하기 위하여 소형 보일러에서 오리멀젼 연료의 기본적인 연소특성을 실험과 더불어 수치해석하였다. 오리멀젼의 주요 연소특성은 최고 화염온도가 버너로부터 $20{\sim}30\;cm 뒤쪽에 나타나는 화염지연현상과 비교적 넓게 분포하는 화염의 형태로 이는 오리멀젼 제조과정에서 포함된 높은 수분함량과 미세한 수부액적으로 이한 미소폭발 현상에 기인한다. 오리멀젼 연료의 연소특성에 미치는 영향을 평가하기 위하여 연료공급량, 무화유체의 종류, 그리고 계산에 사용된 현상학적인 복사모델과 같은 중요한 설계 및 운전인자에 대한 일련의 변수연구를 수행하였다. 연소특성인 최고 화염온도 지연현상은 연료공급 속도를 조절함으로써 어느 정도 저감시킬 수 있었으며 연소생성물로 CO와 $SO_2$ 그리고 NO가스의 연소로 내 발생특성을 평가하였다. 또한 무화용 유체로 증기를 사용하였을 경우 로내 연소상태는 무화용 공기에 비해 안정화 되고 고온영역이 감소되는 결과를 보였다. 일반적으로 본 연구에서 수행한 실험조건에 대한 수치해석 결과는 물리적으로 일관성 있는 결과를 제시하였으나 오염물질 생성농도에 대한 보다 정확한 예측을 위해서는 추후 현상학적인 모델개선을 필요로 한다. 결국 본 연구로부터 개발된 컴퓨터 프로그램은 기존의 상용화 중유 보일러에서 오리멀젼 연료로 대체 사용시 개선사항 및 유용한 운전 자료를 제공할 것으로 판단된다.