이상 유동에 놓인 관군의 표면에 작용하는 압력 분포

심우건(Woo Gun Sim) 대한기계학회 2013 大韓機械學會論文集B Vol.37 No.1

이상 횡 유동은 응축기, 증발기와 원자로 증기발생기와 같은 쉘과 튜브의 열 교환기에서 볼 수 있다. 이상 유동장에 놓인 구조물에 작용하는 수동력을 이해하기 위해서는 이상유동의 특성을 이해하는 것이 중요하다. 이상 유동의 유동특성과 유동변수를 소개하고 관군에서의 압력손실과 실린더에 작용하는 압력분포에 의한 수동력을 평가하기 위한 실험을 수행하였다, 실험부 입구에서 이상유동은 혼합되었으며 실험은 횡 방향 이상 유동장에 놓인 정규 삼각형 배열을 갖는 관군을 사용하여 수행하였다. 관군에서의 흐름방향 압력손실을 측정하여 이상유동의 마찰승수를 계산하고 이론적 결과와 비교하였다. 또한 특정 실린더에 작용하는 원주 방향 압력 분포의 측정결과와 이상유동의 기초이론에 근거하여 압력손실계수의 분포 및 항력계수에 미치는 체적건도와 단위면적당 질량유량의 효과를 평가하였다. 튜브 표면에 작용하는 측정된 압력을 수치해석방법으로 적분하여 항력계수를 계산하였다. 작은 질량 유량의 경우에 측정된 마찰 승수는 기존의 이론 결과와 잘 일치하며 압력분포에 의한 항력계수에 작용하는 기공률의 영향은 기존의 실험결과와 정성적으로 유사한 경향을 보이고 있다. Two-phase vapor-liquid flows exist in many shell and tube heat exchangers such as condensers, evaporators, and nuclear steam generators. To understand the fluid dynamic forces acting on a structure subjected to a two-phase flow, it is essential to obtain detailed information about the characteristics of a two-phase flow. The characteristics of a two-phase flow and the flow parameters were introduced, and then, an experiment was performed to evaluate the pressure loss in the tube bundles and the fluiddynamic force acting on the cylinder owing to the pressure distribution. A two-phase flow was pre-mixed at the entrance of the test section, and the experiments were undertaken using a normal triangular array of cylinders subjected to a two-phase cross-flow. The pressure loss along the flow direction in the tube bundles was measured to calculate the two-phase friction multiplier, and the multiplier was compared with the analytical value. Furthermore, the circular distributions of the pressure on the cylinders were measured. Based on the distribution and the fundamental theory of two-phase flow, the effects of the void fraction and mass flux per unit area on the pressure coefficient and the drag coefficient were evaluated. The drag coefficient was calculated by integrating the measured pressure on the tube by a numerical method. It was found that for low mass fluxes, the measured two-phase friction multipliers agree well with the analytical results, and good agreement for the effect of the void fraction on the drag coefficients, as calculated by the measured pressure distributions, is shown qualitatively, as compared to the existing experimental results.

단열 원관내 공기-물 기-액 이상류의 유동특성

최부홍(B. H. Choi),조대환(D. H. Cho),김준효(J. H. Kim) 한국동력기계공학회 2004 한국동력기계공학회 학술대회 논문집 Vol.- No.-

Two-phase loop systems using the latent heat capacity of their working fluids can meet the increasing power requirements and are well suited to thermal management systems of future large applications, due to its abilities to handle large heat loads and to provide them at uniform temperatures regardless of the changes in the heat loads. However, more reliable design of thermal transport, power acquisition and thermal management systems requires a through understanding of the flow hydrodynamic. Therefore some experiments were performed for an water-air two-phase flow through 10㎜ diameter adiabatic test section with 600㎜ length of transparent acrylic resin tube. The obtained experimental data covered a range of liquid and gas flow rates with the liquid superficial velocity ranging from 0.095㎧ to 2.56 Necessities of high power level demands for thermal management systems in future space applications have stimulated research on gas-liquid two-phase flows under microgravity condition. Two-phase flow is an excellent alternative to the conventional single-phase system in transporting large amount of thermal energy at a uniform temperature regardless of variations in the heat loads. In addition, two-phase flows exist in a wide range of applications and enabling technologies in space. These include material processing and ceramics at ultra high temperatures, life-support systems, storage and transport of cryogenics, and in the design of many cold plate assemblies where heating or cooling takes place at the instrument interface. More reliable design of such systems requires a through understanding of the mechanics of the two-phase flow at variable gravity conditions, since two-phase flow characteristics differ when subjected to earth gravity, to hyper-gravity, to Moon or Mars gravity, or to microgravity environment. The essential factors to the designers of such systems are also the flow patterns in a conduit, the void fraction, and the pressure drop at different gas and liquid flow rates. Recent progress in the study of gas-liquid two-phase flows at variable gravity conditions will be reviewed and discussed in this paper., and the gas superficial velocity ranging from 0.032㎧ to 21.08㎧. As results, The flow patterns were depended on the superficial velocity of each phase. It showed that the increasing jL resulted in a significant increase in the frictional pressure loss for all flow patterns, at a constant jc. The experimental results were also evaluated with some of existing flow pattern and frictional pressure drop models and correlations.

Measurement of Two-Phase Flow with a High Frame-Rate Dynamic Neutron Radiography in HANARO Reactor

Jae-Eun Cha(차재은),In-Cheol Lim(임인철),Chul-Muu Sim(심철무),Hee-Ryoung Kim(김희령),Byung-Ho Kim(김병호) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6

A dynamic neutron radiography(DNR) has a complementary characteristics to X-ray radiography and is suitable for a visualization and measurement of a multi-phase flow research in a metallic duct and a liquid metal flow. Two kinds of experiments were conducted to visualize the water-air two-phase flow and the liquid-metal two-phase flow. The void fraction and the two-phase flow patterns in a channel simulating the HANARO fuel channel were investigated in the D₂O-air two-phase condition. The DNR technique was also applied to visualize the flow field in the gas-liquid metal two-phase flow with the HANARO-beam facility. The two-phase flow images were taken at various combinations of the liquid flow and gas flow with a high frame-rate neutron radiography at 1000 fps. The study showed that the dynamic neutron radiography is a good technique to measure the two-phase flow behavior in the complex rod-bundle geometry and the liquid-metal two-phase flow.

기액 이상류를 응용한 우주용 열관리 시스템의 개발

최부홍(B. H. Choi) 한국동력기계공학회 2004 한국동력기계공학회 학술대회 논문집 Vol.- No.-

Necessities of high power level demands for thermal management systems in future space applications have stimulated research on gas-liquid two-phase flows under microgravity condition. Two-phase flow is an excellent alternative to the conventional single-phase system in transporting large amount of thermal energy at a uniform temperature regardless of variations in the heat loads. In addition, two-phase flows exist in a wide range of applications and enabling technologies in space. These include material processing and ceramics at ultra high temperatures, life-support systems, storage and transport of cryogenics, and in the design of many cold plate assemblies where heating or cooling takes place at the instrument interface. More reliable design of such systems requires a through understanding of the mechanics of the two-phase flow at variable gravity conditions, since two-phase flow characteristics differ when subjected to earth gravity, to hyper-gravity, to Moon or Mars gravity, or to microgravity environment. The essential factors to the designers of such systems are also the flow patterns in a conduit, the void fraction, and the pressure drop at different gas and liquid flow rates. Recent progress in the study of gas-liquid two-phase flows at variable gravity conditions will be reviewed and discussed in this paper.

자동차용 고분자 연료전지 수소 재순환 시스템의 이상 유동해석

곽현주(Hyun Ju Kwag),정진택(Jin Taek Chung),김재춘(Jae Choon Kim),김용찬(Yongchan Kim),오형석(Hyung Seuk Oh) 대한기계학회 2008 大韓機械學會論文集B Vol.32 No.6

The purpose of this paper is to analyze two-phase flows of the hydrogen recirculation system. Two-phase flow modeling is one of the great challenges in the classical sciences. As with most problems in engineering, the interest in two-phase flow is due to its extreme importance in various industrial applications. In hydrogen recirculation systems of fuel cell, the changes in pressure and temperature affect the phase change of mixture. Therefore, two-phase flow analysis of the hydrogen recirculation system is very important. Two-phase computation fluid dynamics (CFD) calculations, using a commercial CFD package FLUENT 6.2, were employed to calculate the gas-liquid flow. A two-phase flow calculation was conducted to solve continuity, momentum, energy equation for each phase. Then, the mass transfer between water vapor and liquid water was calculated. Through an experiment to measure production of liquid water with change of pressure, the analysis model was verified. The predictions of rate of condensed liquid water with change of pressure were within an average error of about 5%. A comparison of experimental and computed data was found to be in good agreement. The variations of performance, properties, mass fraction and two-phase flow characteristic of mixture with resepct to the fuel cell power were investigated.

2차원 압축공기-물의 압축성 이상 유동 수치 해석

박찬욱(Chan Wook Park),이승수(Sungsu Lee) 대한기계학회 2008 大韓機械學會論文集B Vol.32 No.6

Two-phase compressible flow fields of air-water are investigated numerically in the fixed Eulerian grid framework. The phase interface is captured via volume fractions of each phase. A way to model two phase compressible flows as a single phase one is found based on an equivalent equation of states of Tait's type for a multiphase cell. The equivalent single phase field is discretized using the Roe's approximate Riemann solver. Two approaches are tried to suppress the pressure oscillation phenomena at the phase interface, a passive advection of volume fraction and a direct pressure relaxation with the compressible form of volume fraction equation. The direct pressure equalizing method suppresses pressure oscillation successfully and generates sharp discontinuities, transmitting and reflecting acoustic waves naturally at the phase interface. In discretizing the compressible form of volume fraction equation, phase interfaces are geometrically reconstructed to minimize the numerical diffusion of volume fraction and relevant variables. The motion of a projectile in a water-filled tube which is fired by the release of highly pressurized air is simulated presuming the flow field as a two dimensional one, and several design factors affecting the projectile movement are investigated.

사각 미니채널 내 공기-물 이상유동 영역 판별 및 압력강하 특성에 관한 실험적 연구

송정연(Jung-Youn Song),신홍철(Hong-Cheol Shin),김성민(Sung-Min Kim) 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.12

An air-water two-phase flow experiment is performed to identify the flow patterns and pressure drop characteristics in a 55 cm long rectangular mini-channel with 1.88 mm in width and 5.78 mm in height. A highspeed video camera is used to visualize the two-phase pattern, and differential pressure transducer is used to measure the frictional pressure drop in channel. The experimental data are obtained over a superficial liquid velocity range of 0.018-3.70 m/s and superficial gas velocity range of 0.27-46.47 m/s. Six different flow patterns including the dispersed-annular, smooth-annular, wavy-annular, slug, stratified and transition flow are observed. A flow regime map is constructed with the acquired flow pattern data and compared with previously published flow regime maps. In addition, pressure drop oscillations for different flow patterns are examined to capture dominant flow characteristics of each flow pattern.

배열회수보일러(HRSG)에서 이상 유동(Two phase) FAC 고찰

서상일 한국동력기계공학회 2022 동력시스템공학회지 Vol.26 No.5

FAC(Flow Accelerated Corrosion)는 복합화력발전소에서 HRSG 튜브 손상의 주요 원인 중 하나이다. 발전설비에서 발생한 FAC에 대한 연구가 오랫동안 진행되어 왔으며, 관련 자료도 쉽게 접근할 수 있다. 그러나 대부분 비교적 빈번하게 발생하는 단상 유동 FAC에 대한 자료이며, 국내에서 드물게 발생한 사례도 대부분 단상 유동에서 발생한 FAC이다. 특히 국내 복합발전소에서는 이상 유동 FAC 발생사례가 거의 없어 관련 보고서나 자료가 전무한 상태이다. 이로 인해 최근 현장에서는 FAC가 발생할 경우 대책 마련에 혼선을 빚고 있다. 본 논문은 FAC 관련 자료를 바탕으로 단상 유동과 이상 유동의 FAC 발생 요인과 위치, 손상상태 및 대책 방안 등에 대해 차별성을 기술하였으며, 또한 국내 복합화력발전소에서 최근 발생한 FAC 사례소개를 통해 유동 상태에 따른 FAC의 구분을 명확히 할 수 있게 하였다. 따라서 본 논문을 통해 복합화력발전소에서 FAC가 발생했을 경우 보다 명확한 대응책을 마련할 수 있게 되었다.

터빈 유량계를 사용한 이상유동의 측정

심재우(W. Jaewoo Shim) 한국해양공학회 1998 韓國海洋工學會誌 Vol.12 No.2

In this study turbine flowmeters were used to predict volumetric flow rate of each phase in two-phase, gas-liquid, flowing in a vertical tube. To determine volumetric flow rates of two-phase, air-water, flowing vertically upward through the polycarbonate tube(57㎜ ID-inside diameter), two turbine flow meters were used. For void fraction measurements, two gamma densitometers were used at each location of the turbine flow meter, one at the upstream and the other at the downstream. It was determined that the turbine flowmeter's outputs were a function of actual volumetric flow rate of each of the two phases. A two-phase flow model was developed.

이상유동(Two-phase)을 고려한 착화기 내부 연소 모델 개발

차승원(Seung-Won Cha),오석환(Seok-Hwan Oh),이강규(Kang-Kyu Lee),장진성(Jin-Sung Jang),노태성(Tae-Seong Roh) 한국추진공학회 2016 한국추진공학회 학술대회논문집 Vol.2016 No.5

착화기 내부유동은 기상과 고상으로 이루어져 있기 때문에 이상유동을 고려해서 성능 해석을 수행하여야 한다. 본 연구에서는 기상과 고상에 각각의 지배방정식을 적용하고 Eulerian-Lagrangian 좌표계를 사용하여 착화기 내부 연소 모델을 개발하였다. 이상유동을 고려한 착화기 모델의 성능결과를 Lumped-parameter method로 구한 해석결과와 비교하였다. 차후 이 연소모델은 PMD(Pyrotechnic Mechanical Device) 성능해석을 위해 사용될 예정이다. A flow analysis model for gas-generator combustion has to consider the two-phase flow model with gas - solid phase. In this study, the two-phase flow model with governing equations of each phase and the Eulerian-Lagrangian coordinated system have been adopted to analyze the gas-generator combustion flow. The performance results of the combustion model considering the two-phase flow have been compared with the results of the lumped-parameter method. The combustion model will be applied to the analysis of PMD(Pyrotechnic Mechanical Device) at later.