• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 금형가공,미세가공,플라스틱가공 공동 심포지엄
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• pp.9-12
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• 2005

The rapid thermal response (RTR) molding is a novel process developed to raise the temperature of mold surface rapidly to the polymer melt temperature prior to the injection stage and then cool rapidly to the ejection temperature. The resulting filling process is achieved inside a hot mold cavity by prohibiting formation of frozen layer so as to enable thin wall injection molding without filing difficulty. The present work covers flow simulation of thin wall injection molding using the RTR molding process. In order to take into account the effects of thermal boundary conditions of the RTR mold, coupled analysis with transient heat transfer simulation is suggested and compared with conventional isothermal analysis. The proposed coupled simulation approach based on solid elements provides reliable thin wall flow estimation fur both the conventional molding and the RTR molding processes

• 한국자동차공학회논문집
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• 제9권5호
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• pp.96-104
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• 2001

The present study experimentally investigates the concentration distribution of liquid and vapor phase with different injection timings in the in-cylinder flow field of a optically accessible engine. The conventional MPI, DOHC engine was modified into DI gasoline engine. The images of liquid and vapor phases in the motoring engine were captured by using exciplex fluorescence method. Dopants used in this study were 2% fluorobenzene and 9% DEMA(diethyl-methyl-amino) in 89% solution of hexane by volume respectively. Two dimensional spray fluorescence images of liquid and vapor phases were acquired to analyze spray behaviors and fuel distribution in the in-cylinder flow field. Measurements were carried out fur four different injection timings, namely BTDC 270$^{\circ}$, 180$^{\circ}$, 90$^{\circ}$, and 50$^{\circ}$. Experimental results indicate that behaviors and distribution of vapor phase were largely affected by in-cylinder tumble flow, and mixture formation process was also greatly affected by in-cylinder flow at early injection mode and by ambient pressure at late injection mode.

• 설비공학논문집
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• 제19권12호
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• pp.811-820
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• 2007

A Study on the optimal design of the AIG(Ammonia Injection Grid) to improve the performance of DeNOx facilities in the HRSG(Heat Recovery Steam Generator) was performed using the CFD analysis. On the basis of the flow analysis results in the case that the AIG in the HRSG was not installed, the numerical analyses according to the positions of AIG, injection angles of nozzle and the control of ammonia injection quantity were carried out. The standard deviation according to factors was calculated for quantitative comparison. As the results, the AIG in the HRSG should be installed in the position that the uniform flow field shows through the exact flow analysis in the previous of the AIG design and installation. In the case the AIG has already been installed and non uniform flow distribution shows, it is recommended that flow correction device or KoNOx catalyst should be used. Otherwise, the control of ammonia injection angle or the ammonia injection quantity using the velocity profile analysis is demanded to accomplish the optimal performance.

• Geomechanics and Engineering
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• 제17권4호
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• pp.367-374
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• 2019

This study concluded the results of a research on the features of cement based permeation grout, based on some important grout parameters, such as the rheological properties (yield stress and viscosity), coefficient of permeability to grout ($k_G$) and the inject ability of cement grout (N and $N_c$ assessment), which govern the performance of cement based permeation grouting in porous media. Due to the limited knowledge of these important grout parameters and other influencing factors (filtration pressure, rate and time of injection and the grout volume) used in the field work, the application of cement based permeation grouting is still largely a trial and error process in the current practice, especially in the local construction industry. It is seen possible to use simple formulas in order to select the injection parameters and to evaluate their inter-relationship, as well as to optimize injection spacing and times with respect to injection source dimensions and in-situ permeability. The validity of spherical and cylindrical flow model was not verified by any past research works covered in the literature review. Therefore, a theoretical investigation including grout flow models and significant grout parameters for the design of permeation grouting was conducted in this study. This two grout flow models were applied for three grout mixes prepared for w/c=0.75, w/c=1.00 and w/c=1.25 in this study. The relations between injection times, radius, pump pressure and flow rate for both flow models were investigated and the results were presented. Furthermore, in order to investigate these two flow model, some rheological properties of the grout mixes, particle size distribution of the cement used in this study and some geotechnical properties of the sand used in this work were defined and presented.

• 한국항공우주학회지
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• 제30권6호
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• pp.53-60
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• 2002

단일 분사 노즐을 갖는 연소기 내부의 혼합과정에 대한 이해를 바탕으로 연료 분사 노즐을 이중으로 갖는 연소기의 혼합과정에 대한 수치연구를 수행하였다. 수치연구를 위하여 3차원 Navier-Stokes 방정식과 k-$\omega$ SST난류 모델을 이용하여 연료 이중 분사 유동을 모사하였다. 이중 분사구 사이의 거리 변화에 따른 혼합특성의 변화를 살펴보기 위하여 파라메터 연구를 수행하였다. 연료 이중 수직분사에서 두 분사기의 유동 및 혼합특성은 서로 상당히 다른 경향을 보이며, 후방 분사기의 유동 및 혼합특성은 전방 분사류의 영향을 받아 더 크게 팽창하고 침투거리가 증가하는 것으로 나타났다. 어떤 특정 거리가 되기 전까지 분사기 사이의 거리가 증가할수록 전체적인 혼합률과 침투거리가 증가하는 등 혼합특성이 개선되지만, 특정 거리보다 크게되면 오히려 혼합특성이 악화되는 것으로 나타났다. 이는 이중분사기에서 최적인 혼합특성을 위한 두 분사기 사이의 거리가 존재함을 의미하는 것으로 판단된다.

• 소성∙가공
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• 제12권1호
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• pp.3-10
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• 2003

The formation of surface defects associated with Jotting in injection molding is related to the geometries of cavity and fate, operational conditions and the rheological properties of polymer. In this study we have examined jetting phenomena in injection molding process for the throe kinds of PCs which have different molecular weights and structures, PBT and PC/ABS alloy with several injection speeds. We have used various cavity shapes those are tensile, flexural and impact test specimens with various gates and cavity thicknesses. Through this study we have observed that the jetting is related to the dic swell of material. This means that the jotting is strongly affected by the elastic flow property rather than the viscous flow property in viscoelastic characteristics of molten polymer. Different resins have different elastic properties, and elastic flow behavior depends on the shear rate of flow, i.e. injection speed. Large die swell would eliminate jetting however, the retardation of die swell would stimulate jetting. In the point of mole design, reducing the thickness ratio of cavity to gate can reduce or eliminate jetting regardless of amount of elasticity of polymer melt.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2011년도 제37회 추계학술대회논문집
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• pp.116-121
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• 2011

SITVC 시스템의 이차분사 노즐 분사 조건 변화에 따른 시스템 성능 변화를 수치적으로 연구하였다. 해석에 사용된 형상은 3차원 종형 수축-팽창 노즐이고 측면에 8개의 이차분사 노즐을 가진다. 노즐 내부 유동은 전압이 70bar이며 300K의 cold flow로 가정하였다. 이차 유동의 유량 변화와 노즐 작동 조건 변화를 고려하였다. 상용코드인 Ansys Fluent v.13을 통해 해석하였고, 난류모델은 Spalart-Allmaras model(1- equation)를 사용하였다. 충격파의 수치적 진동을 막고 충격파의 불연속성을 잘 해석하기 위해 AUSM+ scheme을 사용하였다. Axial thrust, side force, system specific impulse ratio 와 같은 성능 변수를 사용해 시스템 성능을 평가하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제29회 추계학술대회논문집
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• pp.293-296
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• 2007

호주국립대학의 T3 자유충격파관을 이용하여, 마하수 3.7의 유입 유동에 대해 비분사유동, 공동이전 경사분사유동, 공동내부 평행분사유동, 공동내부 역분사유동에 대해 주파수를 확인하고, 공동 유동 특성을 살펴보았다. 비분사유동은 고조파 형태의 주파수가 나타나지 않았으나 10 kHz 부근에서 비교적 큰 압력 스펙트럼이 나타났다. 공동 이전 경사분사는 공동의 앞전에서 박리되는 전단층의 두께를 증가시켜 공동 뒷전에서 발생하는 유동의 진동 현상을 현저히 감소시켰다. 공동 내부 평행분사는 공동의 뒷전에 분사 유동이 직접 부딪히게 되고, 공동의 진동 현상을 오히려 증가시켰다.

• 한국자동차공학회논문집
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• 제11권1호
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• pp.1-6
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• 2003

Engine emission regulations are becoming more stringent nowadays. In cold transient regime, about 80% THC is exhausted to the atmosphere in the first 200s (US FTP cycles). Accordingly, reducing emission levels in the cold period immediately after the engine start before the catalysts reach their working temperature will be an especially critical factor in meeting more stringent regulations in the future. In this study, the total hydrocarbon quantities are measured using a Fast FID with gasoline fuel for a 4-cylinde. Sl engine, including Secondary Air Injection (SAI) system. Commercial SAI device's direction is reverse to the exhaust flow. In this study, a swirl flow type SAI system which is positioned between the exhaust manifold and exhaust port, was developed. We compared the swirl type secondary air injection with a commercial secondary air injection of .everse flow. The swirl type SAI showed better results in reducing HC by 26% than the commercial flow type SAI of reverse flow which was caused by the better mixing between the exhaust gas and the secondary air.

• 한국생산제조학회지
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• 제23권6호
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• pp.561-568
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• 2014

Injection molding industries realize the necessity of developing family molds to improve competitiveness. One of the primary causes of manufacturing defective products is the imbalance of flow in a family mold. In this study, the family mold of a shelf for refrigerators is analyzed by using CAE software. First, the flow balance, clamping force, and injection pressure are analyzed for different gate diameters of two cavities. Second, the flow balance, clamping force, and injection pressure are improved when the two gate valves are open at different times. Finally, the results of filling analysis are compared with the test injection product.