• 설비공학논문집
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• 제13권3호
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• pp.209-216
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• 2001

A numerical study is peformed to investigate the effect of circumferential velocity generated by the guide vane on the nozzle flow of a jet fan, s a way of increasing the penetration force of jet fan with nozzle of 175mm diameter. For the validation of numerical results. the velocity is measured by a 5-hole pitot tube and flow visualization is conducted by the tuft method. Under the inlet condition that the maximum circumferential velocity in the stator outlet of the present jet fan is 1.8m/s, the axial velocity in the nozzle outlet has the feature that the velocity at the axis is low and the velocity near the wall high. Therefore, to increase the throw length of the jet fan, the configuration of the fairing and nozzle needs to be developed and the precise revise of the stator angle is required, In addition, the bigger the circumferential velocity, the smaller the axial velocity at the axis and the bigger non-uniformity of the flow distribution.

• International Journal of Fluid Machinery and Systems
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• 제10권1호
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• pp.47-53
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• 2017

Surface pressure integration and momentum method were respectively performed to evaluate the impeller thrust and the system thrust of a contra-rotating axial flow water jet propulsion, and an interesting phenomenon so-called thrust paradox was revealed. To explain the paradox, the impeller thrust and the system thrust were physically and theoretically analyzed, the results show that the impeller thrust is head involved and is determined by the hydraulic parameters upstream and downstream the impeller, while the momentum method depicted by a classic equation is valid simply under the best efficiency point. Consequently, the role of a water jet propulsion nozzle was deduced that the nozzle is mainly to limit the flow rate that crosses the impeller and to assure the system working under the best efficiency condition apart from its ability to produce momentum difference. Related mathematical formula expressed the nozzle diameter is the dominant variable used to calculate the working condition of the water jet propulsion. Therefore the nozzle diameter can be steadily estimated by the former expression. The system thrust scaling characteristics under various speeds were displayed lastly.

• The Korean Journal of Ceramics
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• 제2권4호
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• pp.216-220
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• 1996

In the present paper, a new type of DC arc plasma torch is disclosed. The principles of the new magnetic and fluid dynamic controlled large orifice long discharge tunnel plasma torch is discussed. Two series of DC Plasma Jet diamond film deposition equipment have been developed. The 20kW Jet equipped with a $\Phi$70 mm orifice torch is capable of deposition diamond films at a growth rate as high as 40$\mu\textrm{m}$/h over a substrate area of $\Phi$65 mm. The 100kW high power Jet which is newly developed based on the experience of the low power model is equipped with a $\Phi$120 mm orifice torch, and is capable of depositing diamond films over a substrate area of $\Phi$110 mm at growth rate as high as 40 $\mu\textrm{m}$/h, and can be operated at gas recycling mode, which allows 95% of the gases be recycled. It is demonstrated that the new type DC plasma torch can be easily scaled up to even higher power Jet. It is estimated that even by the 100kW Jet, the cost for tool grade diamond films can be as low as less than ＄4/carat.

• 한국염색가공학회지
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• 제14권2호
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• pp.109-109
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• 2002

A study has been made of the dry-jet-wet spinning of PAN copolymer fibers using 60% aqueous zinc chloride solution as solvent and 25∼40% aqueous zinc chloride solution as non-solvent. The technological characteristics of this method were that small streams of dope were extruded from the die and allowed to pass through a short distance of air gap(about 10mm) before entering the spinning bath for full coagulation. This work showed the importances which coagulation condition, stretch ratio and fiber tenacity up to 10.5 g/d could be obtained with elongation of 11∼16%. Individual fibers were evaluated on the basis of density and mechanical properties such as tenacity and elongation etc.

• 한국염색가공학회지
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• 제14권2호
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• pp.33-39
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• 2002

A study has been made of the dry-jet-wet spinning of PAN copolymer fibers using 60% aqueous zinc chloride solution as solvent and 25∼40% aqueous zinc chloride solution as non-solvent. The technological characteristics of this method were that small streams of dope were extruded from the die and allowed to pass through a short distance of air gap(about 10mm) before entering the spinning bath for full coagulation. This work showed the importances which coagulation condition, stretch ratio and fiber tenacity up to 10.5 g/d could be obtained with elongation of 11∼16%. Individual fibers were evaluated on the basis of density and mechanical properties such as tenacity and elongation etc.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.102-115
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• 2020

In this study, the SST k - ω turbulence model and the sliding mesh technology based on RANS method have been adopted to simulate the exciting force and hydrodynamic of a pump-jet propulsor in different oblique inflow angle (0°, 10°, 20°, 30°) and different advance ratio (J = 0.95, J = 1.18, J = 1.58).The fully structured grid and full channel model have been adopted to improved computational accuracy. The classical skewed marine propeller E779A with different advance ratio was carried out to verify the accuracy of the numerical simulation method. The grid independence was verified. The time-domain data of pump-jet propulsor exciting force including bearing force and fluctuating pressure in different working conditions was monitored, and then which was converted to frequency domain data by fast Fourier transform (FFT). The variation laws of bearing force and fluctuating pressure in different advance ratio and different oblique flow angle has been presented. The influence of the peak of pulsation pressure in different oblique flow angle and different advance ratio has been presented. The results show that the exciting force increases with the increase of the advance ratio, the closer which is to the rotor domain and the closer to the blades tip, the greater the variation of the pulsating pressure. At the same time, the exciting force decrease with the oblique flow angle increases. And the vertical and transverse forces will change more obviously, which is the main cause of the exciting force. In addition, the pressure distribution and the velocity distribution of rotor blades tip in different oblique flow angles has been investigated.

• Carbon letters
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• 제11권3호
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• pp.176-183
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• 2010

PAN precursor fibers were produced via wet-spinning process, and effects of polymerization and spinning processes, especially the stretching process, were investigated on mechanical properties and micro-morphologies of precursor fibers. An increase in molecular weight, dope solid and densification and a decrease in surface defects were possible by controlling polymerization temperature, the number of heating rollers for densification and the jet stretch ratio, which improved the mechanical properties of precursor fibers. The curves for strength, modulus, tensile power and diameter as a function of stretch ratio can be divided into three stages: steady change area, little change area and sudden change area. With the increase of stretch ratio, the fiber diameter became smaller, the degree of crystallization increased and the structure of precursor fibers became compact and homogeneous, which resulted in the increase of strength, modulus and tensile power of precursor fibers. Empirical relationship between fiber strength and stretch ratio was studied by using the sub-cluster statistical theory. It was successfully predicted when the strengths were 0.8 GPa and 1.0 GPa under a certain technical condition, the corresponding stretch ratio of the fiber were 11.16 and 12.83 respectively.

• 한국터널지하공간학회 논문집
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• 제20권2호
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• pp.501-511
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• 2018

최근 '도로터널 방재시설 설치 및 관리지침'의 개정으로 인해 터널 내 제연용 제트팬의 용량 산정 시에는 열부력을 고려하도록 규정하고 있다. 그러나 열부력을 고려하는 세부방법론에 대한 규정이 없어, 이에 대한 세부적인 추가 연구가 필요한 실정이다. 본 연구에서는 터널 내 화재 시 열부력을 고려하기 위하여 3차원 수치해석 시뮬레이션을 수행하여 터널 내열부력을 계산하고, 화재차량의 진행방향에 따라 열부력과 차량항력의 관계, 즉, 화재차량의 위치에 따른 터널 내 제연용 제트팬 용량 산정방법에 대하여 검토를 수행하였다. 분석결과에 따르면, 하향경사 터널의 경우에는 열부력이 터널 내 저항력으로 작용하며, 터널 내 화재연기를 제연하기 위해 필요한 제연팬의 승압력은 단순히 터널 입구부의 열부력 값과 출구부의 차량항력값에 의해 단순히 결정되지 않으며, 터널 내 화재차량의 위치에 따라 종합적인 검토가 필요한 것으로 분석되었다.

• 한국터널지하공간학회 논문집
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• 제21권1호
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• pp.189-199
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• 2019

본 연구에서는 배연댐퍼 또는 제트팬과 같은 방재시설이 설치된 터널형 구조물(방음터널)에 대하여 방재시설 가동에 따른 화재연기의 거동을 수치해석적으로 고찰하고 해석결과를 비교 검토하여 다음과 같은 결론을 얻었다. 화재차량 천장부 개방 유무에 따라 방음터널 내 화재양상이 확연하게 달라지는 것을 확인하였으며, 방음터널의 주요 자재인 PC와 PMMA의 임계온도를 초과하지 않는 것으로 나타났다. 또한 배연댐퍼의 설치간격에 따른 해석결과, 방음터널 내 발생하는 최대 온도가 미설치시에는 최대 $552^{\circ}C$인 반면, 설치간격이 50 m인 경우에는 $405^{\circ}C$로 나타났으며, 제트팬 가동 여부에 따른 해석결과, 방음터널 내 발생하는 최대 온도는 제트팬 미가동시에는 $549^{\circ}C$인 반면, 가동시에는 $86^{\circ}C$로 나타나 화재시 피난환경과 방음자재보호에 있어 매우 유리한 환경을 조성할 것으로 예상되며, 향후 다양한 목적을 가진 터널을 대상으로도 이러한 기초연구의 활성화가 필요할 것으로 사료된다.