• 제목/요약/키워드: Critical pressure ratio

검색결과 240건 처리시간 0.024초

An Experimental Study of Underexpanded Moist Air Jet Impinging on a Flat Plate

  • Lee, D.W.;S.C. Baek;S.B. Kwon;Kim, H.D.
    • 한국추진공학회:학술대회논문집
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    • 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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    • pp.768-773
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    • 2004
  • When a gas expands through a convergent nozzle in which the ratio of the ambient to the stagnation pressures is higher than that of the critical one, the issuing jet from the nozzle is underexpanded. If a flat plate is placed normal to the jet at a certain distance from the nozzle, a detached shock wave is formed at a region between the nozzle exit and the plate. In general, supersonic moist air jet technologies with nonequilibrium condensation are very often applied to industrial manufacturing processes. In spite of the importance in major characteristics of the supersonic moist air jets impinging to a solid body, its qualitative characteristics can not even know. In the present study, the effect of the nonequilibrium condensation on the underexpanded moist air jet impinging on a vertical flat plate is investigated experimentally. Flow visualization and impact pressure measurement are performed for various relative humidities and flat plate positions. The obtained results show the plate shock and Mach disk are dependent on the nozzle pressure ratio and the relative humidity, but for a given nozzle pressure ratio, the diameters of the plate shock and Mach disk depend on the stagnation relative humidity. The impact pressure deviation from the flow of without condensation is large, as the relative stagnation humidity increases.

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열처리 온도 및 분위기 변화에 따른 Bi-2223 초전도 선재에서의 특성변화 (superconducting properties of Bi-2223 tapes with various heat treatment condition)

  • 하동우;이동훈;하홍수;오상수;김홍대;양주생;윤진국;최정규;권영길
    • 한국전기전자재료학회:학술대회논문집
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    • 한국전기전자재료학회 2002년도 하계학술대회 논문집
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    • pp.527-530
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    • 2002
  • A lot of efforts have been focused on the optimization of PIT parameters for Bi-2223/Ag wire. In this paper, initial annealing of Bi-2223/Ag wire to transform Bi-2212 orthorhombic from Bi-2212 tetragonal Precursor was investigated. This initial annealing step at low oxygen partial pressure were to transform Bi-2212 orthorhombic structure and to reduce the formation of second phases at superconducting wire. However Bi-2223 Phases were appeared at higher annealing temperature. Critical currents(Je) of Bi-2223/Ag tapes were sintered at low oxygen Partial pressure were higher than that of the wires sintered at atmosphere condition. In order to investigate the effect of rolling reduction ratio, Bi-2223/Ag HTS tapes were rolled with different reduction ratio. There were no clear difference of Je and filaments shape with various rolling reduction ratio.

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피코초 레이저를 이용한 고세장비 미세 홀가공의 실험적 연구 (Experimental study on micro-hole drilling with high aspect ratio using picosecond laser)

  • 오부국;김종기;김두영;이승기;정수화;홍순국
    • 한국레이저가공학회지
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    • 제18권2호
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    • pp.11-13
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    • 2015
  • Pressure-drop in a micro-channel is critical when a hole diameter is less then 100um with the high aspect ratio, more than 40. To minimize these pressure loss for micro-channel applications is important and there would be the best hole diameter, taper angle, and their combinations. In this work, the parametric study for laser drilling of anodized material is conducted to obtain the micro-channel hole with high aspect ratio.

수평 직사각 덕트 내 임계점 부근 물의 대류열전달 특성 (Convective Heat Transfer to Water near the Critical Region in Horizontal Rectangular Ducts)

  • 이상호
    • 대한기계학회논문집B
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    • 제36권5호
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    • pp.477-485
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    • 2012
  • 수평 덕트 내 임계점부근의 유체 유동 및 열전달특성은 중력과 함께 임계영역에서의 열역학 및 전달 물성치의 많은 변화와 직접적으로 연관되어 있다. 본 연구에서는 수평 직사각 덕트 내 임계점부근의 물에 대한 대류열전달특성을 전산해석을 통하여 분석하였다. 이를 통해 국부적인 열전달계수와 유속, 온도, 그리고 물성치분포를 포함한 대류열전달특성에 대해 임계점 근접효과와 함께 비교하였다. 벽으로부터의 열전달에 따른 유체 밀도감소로 덕트 내 유동방향으로의 유속증가와 함께 유체가 액체에서 기체 같은 상태로 천이하는 형태의 유동장특성을 보여준다. 덕트의 윗면, 옆면, 그리고 아래면 각각의 국부적인 열전달계수분포에 큰 차이가 있으며 준임계점 온도부근에서 난류전달특성의 향상으로 열전달계수의 최대치에 이르게 된다. Nu 수는 덕트 내 압력과 종횡비에 영향을 받으며 임계압에 가까워질수록 최대 Nu 수는 급격히 증가하게 된다. 이와 함께 기존의 열전달상관식을 통한 결과와 예측된 Nu 수 분포를 비교하였다.

부실식 정적연소실내 층상혼합기의 연소특성(II) (Combustion Characteristics of Stratified Mixture in a Constant Volume Combustion Chamber with Sub-chamber (II))

  • 김봉석;권철홍;류정인
    • 한국자동차공학회논문집
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    • 제3권5호
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    • pp.122-134
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    • 1995
  • The present study was investigated combustion characteristics of methane-air mixtures at stratified charge in a constant volume combustion chamber. The main results obtained from this study can be summarized as follows. In case of ${\phi}_s=1.0$, total burning times greatly affected rather than initial time of pressure increase and maximum combustion pressure. In case of ${\phi}_t=1.0$, initial time of pressure increase and total burning times were affected considerably in comparison with the case of ${\phi}_s=1.0$. Also, even the very lean mixture which total equivalence ratio is ${\phi}_t=0.69$(${\phi}_s=1.0$, ${\phi}_m=0.65$), by changing configuration of the critical passage-hole and using a stratified mixture, it is possible to decrease substantially the initial time of pressure increase. total burning times and NOx concentration without deteriorating combustion characteristics such as maximum combustion pressure, rate of heat release etc. in comparison with the use of single chamber(in case of ${\phi}=1.0$) only. Specifically, our trends were revealed remarkably in the case of Type D which is reduced a flame contact area of sub-chamber side of the passage-hole.

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자체반응열 고온합성법을 이용한 Titanium Carbonitride의 합성에 관한 연구 (A Study on the Synthesis of Titanium Carbonitride by SHS(Self-propagating High-temperature Synthesis) Method)

  • 하호;황규민;이희철
    • 한국세라믹학회지
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    • 제31권6호
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    • pp.637-642
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    • 1994
  • Using SHS(Self-propagating High-temperature Synthesis) method, the optimum synthetic condition of titanium carbonitride was established by controlling the parameters such as relative density of mixture (Ti+C), nitrogen pressure, additive amounts of titanium hydride(TiH1.924) and protecting heat loss. Under 1 atm nitrogen pressure, nitridation ratio with changing relative density of the sample compacts has a maximum (87.2%) at about 55%, and in the case of enveloping the pellet with a quartz tube, the highest nitridation ratio of 90% was obtained at about 68%. At relative density of 55%, nitridation ratio with the nitrogen pressure has a miximum (87.3%) at 7 atm. As the amounts of additive titanium hydride increased, nitridation ratio decreased at below 7 atm nitrogen pressure and, increased at above this pressure until percent of addition percent reached 15 wt% and decreased abruptly upon futher increases in titanium hydride. In the synthesis of TiCxNy by combustion reaction, heat transfer from combustion zone to preheating zone and nitrogen gas penetration into the compact were found to be important factors affecting the TiCxNy formation. It was difficult to obtain high nitridation ratio when the conbustion temperature was either too high or too low, and it seems that the retention of high temperature after a combustion wave sweeped through the reactant mixture pellet is critical to obtain a satisfactory nitridation ratio.

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비틀림 및 횡압럭을 받고 있는 복합재 원통쉘의 좌굴 (Buckling of Composite Cylindrical Shells Sugjected ot Torsion of Lateral Pressure)

  • 한병기;이성희;유택인
    • 대한기계학회논문집A
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    • 제20권5호
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    • pp.1436-1444
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    • 1996
  • The problem ofinstability of laminated circular cylindrical shell under the action of torsio or lateral pressure is investigated. The analysis is based on the Sander's theory for finite deformations of thin shell. The buckling is elastic for thin compoisite shell nad the geometry is assumed to be free of initial imperfections. The equilibrium equations are obrained by usitn the p[erturbation technique. Solution procedure is based on the Galerkin mehtod. The computer program for numerical results is made for several stacking sequence, length-to-radius ratio, and radius-to-thickness ratio. The numerical results of buckling load are present.

CFD based simulations of flutter characteristics of ideal thin plates with and without central slot

  • Zhu, Zhi-Wen;Chen, Zheng-Qing;Gu, Ming
    • Wind and Structures
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    • 제12권1호
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    • pp.1-19
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    • 2009
  • In this paper, the airflow around an ideal thin plate (hereafter referred to as ITP) with various ratios of central slot is simulated by using the finite-difference-method (FDM)-based Arbitrary-Lagrangian-Eulerian descriptions for the rigid oscillating body. The numerical procedure employs the second-order projection scheme to decouple the governing equations, and the multigrid algorithm with three levels to improve the computational efficiency in evaluating of the pressure equation. The present CFD method is validated through comparing the computed flutter derivatives of the ITP without slot to Theodorsen analytical solutions. Then, the unsteady aerodynamics of the ITP with and without central slot is investigated. It is found that even a smaller ratio of central slot of the ITP has notable effects on pressure distributions of the downstream section, and the pressure distributions on the downstream section will further be significantly affected by the slot ratio and the reduced wind speeds. Continuous increase of $A_2^*$ with the increase of central slot may be the key feature of the slotted ITP. Finally, flutter analyses based on the flutter derivatives of the slotted ITP are performed, and moreover, flutter instabilities of a scaled sectional model of a twin-deck bridge with various ratios of deck slot are investigated. The results confirm that the central slot is effective to improve bridge flutter stabilities, and that the flutter critical wind speeds increase with the increase of slot ratio.

Analysis of Split Magnetic Fluid Plane Sealing Performance

  • Zhang, Hui-tao;Li, De-cai
    • Journal of Magnetics
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    • 제22권1호
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    • pp.133-140
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    • 2017
  • Split magnetic fluid sealing is a combination of magnetic fluid rotary and plane sealing. Using the theory of equivalent magnetic circuit design as basis, the author theorized the pressure resistance performance of magnetic fluid plane sealing. To determine the pressure resistance of magnetic fluid plane sealing, the author adopted the method of finite element analysis to calculate the magnetic field intensity in the gap between plane sealing structures. The author also analyzed the effect of different sealing gaps, as well as different ratios between the sealing gap and tooth and solt width, on the sealing performance of split magnetic fluid. Results showed that the wider the sealing gap, the lower the sealing performance. Tooth width strongly affects sealing performance; the sealing performance is best when the ratio between tooth width and sealing gap is 2, whereas the sealing performance is poor when the ratio is over 8. The sealing performance is best when the ratio between the solt width and sealing gap is 4, indicating a slight effect on sealing performance when the ratio between the solt width and sealing gap is higher. Theoretical analysis and simulation results provide reference for the performance evaluation of different sealing equipment and estimation of critical pressure at interface failure.

오리피스를 통하는 임계 기체 유동에 관한 연구 (Study of the Critical Gas Flow through an Orifice)

  • 김재형;김희동;박경암
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2003년도 추계학술대회
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    • pp.532-537
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    • 2003
  • Gas flow through orifice is encountered in many diverse fields of engineering applications. In order to investigate the critical gas flow through an orifice system, a computational analysis is performed using axisymmetric, compressible, Navier-Stokes equations which are numerically solved by a fully implicit finite volume method. In the present study, the discharge coefficients of two different types of orifices which are a straight-bore orifice and a sharp-edged orifice, are predicted to obtain the critical flow conditions. The present CFD data are compared with the previous experimental results. The present computational results show that the critical mass flow rate through orifice is well predicted and it is a strong function of Reynolds number. The discharge coefficient increases with the orifice diameter.

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