Improvement of horizontal stratification criteria in the SPACE code

Lee, Jong Hyuk,Kim, Byoung Jae,Kim, Kyung Doo Elsevier 2019 Annals of nuclear energy Vol.133 No.-

<P><B>Abstract</B></P> <P>The flow regime for two-phase flow plays an important role in nuclear safety analysis, because different physical models for two-phase flow are used depending on the flow regime. This paper deals with the flow regime criteria for horizontal stratification, which frequently occurs in the hot or cold leg during a loss-of-coolant accident (LOCA). Although there are several horizontal stratification criteria based on the Kelvin-Helmholtz theory, the condition for the onset of waves leading to a wavy-stratified flow or a non-stratified flow is still unclear. This study approached the horizontal stratification criteria from the perspective of viscous/inviscid flow instability theories. The criterion between smoothly stratified flow and transition region was adopted with viscous Kelvin-Helmholtz (VKH) analysis. The onset of ill-posedness for the governing equation set, which is related to the inviscid Kelvin-Helmholtz (IKH) analysis, was used to determine the transition criterion between the transition region and non-stratified flow. These criteria were incorporated into the SPACE thermal-hydraulic system code. Simulation results show good agreements with experimental data, and the predictability of horizontal stratification is thereby further improved.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The criteria of horizontal stratified flow were modified by adopting with inviscid/viscous Kelvin-Helmholtz analyses. </LI> <LI> These criteria are implemented into the SPACE code. </LI> <LI> The simulation results show the predictability of horizontal stratification is further improved. </LI> </UL> </P>

Experimental investigation of droplet entrainment and deposition in horizontal stratified wavy flow

Bae, Byeonggeon,Kim, Taeho,Kim, Kyungdoo,Jeong, Jae Jun,Yun, Byongjo Elsevier 2019 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.144 No.-

<P><B>Abstract</B></P> <P>An experimental study of the local droplet parameters for an atmospheric horizontal stratified wavy flow was conducted in a horizontal circular pipe with an inner diameter of 40 mm and a length of 5.5 m. The local distributions of the droplet fraction, droplet velocity, droplet diameter, and droplet mass flux in the cross section of the pipe were measured using single optical fiber probes at four locations with length-to-diameter ratios of 17.5, 55.0, 80.0, and 105.0 from the inlet of the test section. The average droplet mass flow rate along the axial direction of the flow channel was also obtained from the droplet parameters. The combination of the droplet entrainment and deposition rate models of Schimpf et al. was evaluated for droplet mass flow rates obtained from five different experiments including the present experiment in the horizontal stratified flow. However, its prediction accuracy was not good for the present and REGARD data. Finally, new droplet entrainment and deposition rate models for the horizontal stratified flow were proposed based on those five experiments. The applicable ranges of the proposed models are 65,500–571,400 and 170–11,000 for the gas ( <SUB> Re g </SUB> ) and liquid ( <SUB> Re l </SUB> ) Reynolds numbers, respectively.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The local droplet parameters in the horizontal pipe were measured using SC-OFP sensor. </LI> <LI> The droplet and liquid interfacial wave were separated on the basis of critical time difference. </LI> <LI> New droplet entrainment and deposition models for horizontal stratified wavy flow were proposed. </LI> </UL> </P>

Characteristics of an interfacial wave in a horizontal air-water stratified flow

Bae, Byeonggeon,Ahn, Taehwan,Jeong, Jaejun,Kim, Kyungdoo,Yun, Byongjo Elsevier 2017 International journal of multiphase flow Vol.97 No.-

<P><B>Abstract</B></P> <P>Interfacial wave parameters, in this case the frequency, height, velocity, and slope, were investigated experimentally in a horizontal air-water stratified flow. Experiments were conducted with a parallel wire conductance sensor and PIV visualization in a rectangular channel, of which the width and height are 40 mm and 50 mm, respectively. In the experiments, the flow condition covered the liquid Reynolds number Re<SUB>l</SUB> range of 450 to 3540 and the gas Reynolds number Re<SUB>g</SUB> range of 14,000 to 70,000. The results revealed that the observed wave types according to the flow conditions in the rectangular channel are similar to those in a horizontal pipe. The frequency, height, and slope of the interfacial wave show complicated tendencies according to the combination of Re<SUB>g</SUB> and Re<SUB>l</SUB>, which affects the coalescence and breakup of the wave. Specifically, the wave height and wave slope have opposite tendencies regarding the criterion of Re<SUB>g</SUB> = 34,000. For cases in which Re<SUB>g</SUB> ≥ 34,000, the interfacial drag force significantly affects the height and slope of the disturbance wave. In contrast, for Re<SUB>g</SUB> < 34,000, the growth of the wave has an important effect on the wave parameters. Finally, new empirical correlations for the frequency, height, and slope of the interfacial wave were proposed for application to the development of a droplet entrainment model in a horizontal stratified flow.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The frequency, height, velocity, and slope of interfacial wave are investigated experimentally in horizontal stratified flow. </LI> <LI> Characteristics of wave parameters are closely related to the wave types appeared depending on the combination of Re<SUB>g</SUB> and Re<SUB>l</SUB>. </LI> <LI> Correlations for the frequency, height, and slope of the interfacial wave are proposed. </LI> </UL> </P>

Quantitative observation of co-current stratified two-phase flow in a horizontal rectangular channel

이성태,어동진,김석,송철화 한국원자력학회 2015 Nuclear Engineering and Technology Vol.47 No.3

The main objective of this study is to investigate experimentally the two-phase flow characteristics in terms of the direct contact condensation of a steam–water stratified flow in a horizontal rectangular channel. Experiments were performed for both air–water and steam–water flows with a co-current flow configuration. This work presents the local temperature and velocity distributions in a water layer as well as the interfacial characteristics of both condensing and noncondensing fluid flows. The gas superficial velocity varied from 1.2 m/s to 2.0 m/s for air and from 1.2 m/s to 2.8 m/s for steam under a fixed inlet water superficial velocity of 0.025 m/s. Some advanced measurement methods have been applied to measure the local characteristics of the water layer thickness, temperature, and velocity fields in a horizontal stratified flow. The instantaneous velocity and temperature fields inside the water layer were measured using laser-induced fluorescence and particle image velocimetry, respectively. In addition, the water layer thickness was measured through an ultrasonic method.

An empirical model of the wetted wall fraction in separated flows of horizontal and inclined pipes

Ahn, Taehwan,Moon, Jeongmin,Bae, Byeonggeon,Jeong, Jaejun,Bae, Byounguhn,Yun, Byongjo Elsevier 2018 Chemical engineering science Vol.178 No.-

<P><B>Abstract</B></P> <P>This study reports an experiment to investigate the wetted wall fraction (WWF), which represents the shape of the continuous interface of the air–water stratified and wavy flow regimes, in horizontal and inclined pipes with an inner diameter of 40 mm. Using the experimental data, a semi-empirical model to predict the WWF was developed based on the energy balance for the liquid phase in separated flows. The model used a relationship between the WWF and the center of gravity of the liquid phase with a concave interface that can describe continuous changes to the flow regime from a stratified to an annular. The coefficients of the model were empirically determined based on a wide range of experimental data from the literature obtained in the air and various liquids covering a void fraction of greater than 0.79, a pipe with inner diameter in the range 24–150 mm, density differences varying from 812 to 1052 kg/m<SUP>3</SUP>, a range of liquid phase viscosity of 0.87–5.66 mPa s, surface tension ranging from 27.9 to 72.7 mN/m, a wide range of inclination angles from −27° for a downward flow to +3° for an upward flow, and gas and liquid Reynolds numbers based on a superficial velocity of up to 219,000 and 7500, respectively. This WWF model was tested using an extensive experimental database of the WWF and void fraction in the stratified and wavy flow regimes, and yielded the best agreement compared with existing models in the literature.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Circumference distribution of liquid film thickness was measured in inclined pipes. </LI> <LI> Empirical coefficients in a concave interface model were derived to predict the wetted wall fraction. </LI> <LI> Eight prediction models for the wetted wall fraction were investigated and evaluated. </LI> </UL> </P>

수평관 기포유동 실험 데이터를 이용한 3차원 2상유동 해석코드 CUPID 평가

이동훈(D.H. Lee),이승준(S.J. Lee),윤한영(H.Y. Yoon),정재준(J.J. Jeong) 한국전산유체공학회 2018 한국전산유체공학회지 Vol.23 No.1

Bubbly flows may occur in horizontal pipes during an accident in a nuclear power plant. Horizontal bubbly flows are characterized by asymmetric distribution of main parameters, such as void fraction and velocity, and slip ratio less than 1. Thus, three-dimensional simulation capability is needed for horizontal bubbly flows. In this study, horizontal bubbly flows were simulated using the CUPID code. The model evaluation results showed that the particle based 2-fluid momentum equation simulated more physically reasonable slip ratio than standard 2-fluid momentum equation and the turbulent dispersion force was the most important factor in the prediction of void fraction. In the quantitative assessments, it was shown that the CUPID code predicted well the axial pressure drop within the error range of 10%. Also, the code estimated well axial development process of void fraction. However, it was found that the code can not simulate asymmetric distribution of flow parameters and phenomena which gas phase moves slower than liquid phase. To improve the prediction ability, the modification of turbulence model such as turbulent shear stress, bubble induced turbulence, and so on, or the additional term in momentum equation are needed.

수평 T형 분지관 내 냉매 이상유동 분배특성에 미치는 변수들의 영향

태상진,조금남 대한설비공학회 2006 설비공학 논문집 Vol.18 No.1

The present study has been experimentally investigated the effect of geometric and operating parameters on the two-phase flow distribution of refrigerants in a horizontal T- junction. The operating parameters were the kind of refrigerants(R-22, R-134a, and R-410A), saturated temperature, and the inlet mass flux and quality. The geometric parameters were the tube diameter and the tube diameter ratio. The measured data of refrigerants were compared with the values predicted using the models developed by several researchers for air/ water or steam/water two-phase flow. Among the operating parameters, the inlet quality was the most sensitive to the mass flow rate ratio. Between the geometric parameters, the tube diameter ratio was more sensitive than tube diameter.

Numerical analysis study on the application of three-lobed vortex tube in low-production wells

Ruyi Gou,Chenchen Kang,Xun Luo 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.6

In order to solve the problem of fluid accumulation in horizontal gas wells and improve the fluid-carrying capacity and recovery efficiency of gas wells, this paper simulates three internal vortex tools using the commercial software ANSYS FLUENT, and analyzes the drainage recovery efficiency of the three vortex structures and the vortex characteristics of the downstream section vortex field. The results show that the axial velocity of the three-bladed spiral tube in the cyclonic field rotates quasi-periodically with the flow field compared with the internal vortex tube and the rifled tube, and the axial velocity, tangential velocity and vortex intensity of the three-bladed vortex tube guided flow field are the highest; meanwhile, the axial velocity, tangential velocity and vortex intensity of the three-bladed spiral tube guided flow field decay the fastest, and the line rifled tube decays the slowest. The liquid phase in the cyclonic field exhibits obvious spiral motion and maintains a long-distance cyclonic flow state under the action of cyclonic flow. The enhancement of the vortex intensity easily leads to the increase of liquid volume fraction and liquid film thickness at the tube wall. Through the analysis of the energy efficiency of the three structures, it is found that the three-leaf spiral tube is more suitable for the initial phase of drainage transport, while the internal vortex tube is more favorable for the stable phase of transport. The study of the gas-liquid swirl flow of the three swirl tools demonstrated the feasibility of the internal swirl tool for application in horizontal wells. It can provide theoretical guidance and practical basis for effective liquid filling with internal vortex tools in the future.

수평 흐름형 미생물 연료전지에서 유체의 흐름 형태에 따른 전력수율 평가

이채영(Chae-Young Lee),박수희(Su-Hee Park),송영채(Young-Chae Song),유규선(Kyu-Seon Yoo),정재우(Jae-Woo Chung),한선기(Sun-Kee Han) 유기성자원학회 2013 유기물자원화 Vol.21 No.1

본 연구에서는 수평 흐름 미생물 연료전지에서 유체 흐름이 전력 수율에 미치는 영향을 평가하고자 하였다. 본 연구에서는 산화전극 반응조의 바닥에 아크릴 막대를 설치하여 각각 4가지 유체의 흐름을 유도하였다. 각 반응조 형상에 따라 최대전력수율을 평가하였으며 추적자 실험을 통해 유체 흐름을 해석하였다. 분극 곡선 실험 결과 반응조별 최대 전력수율은 case 1, 2, 3 및 4에서 각각 95.7, 129.1, 190.9 및 114.2 mW/m2로 나타났다. 좌우 도류벽을 설치하여 S 형태의 유체 흐름을 유도한 case 3 반응조에서 가장 높은 전력이 생산되는 것으로 나타났다. 추적자 실험의 Morrill 분산지수 값에 따르면 case 4 반응조의 경우 반응조 전체에 기질이 골고루 분포하여 미생물 활성을 높일 수 있을 것으로 나타났다. 그러나 월류 현상에 의해 안정적인 운영을 할 수 없을 것으로 판단된다. 따라서 case 3 반응조의 경우 안정적인 운영 및 높은 전력수율을 얻을 수 있으므로 미생물 연료전지로 이용하기에 효과적일 것으로 나타났다. This study evaluated the effect of fluid flow on the power density in a horizontal-flow microbial fuel cell (MFC). The maximum power densities in four types of flow induced by different channel types in the anode chamber were investigated. The fluid flow at each channel was analyzed using tracer tests. Results of polarization curves showed that the maximum power densities of case 1, 2, 3 and 4 were 95.7, 129.1, 190.9 and 114.2 mW/m2, respectively. Case 3 with a set of guide walls where flow had an S type-like shape showed the highest power density. Based on the Morrill Dispersion Index (MDI) value of case 4, microbial activity would be enhanced since the reactor allows even distribution of substrate but the overflow occurrence would not guarantee stable performance. Therefore, case 3 could be an effective reactor type for MFC because of high electricity generation and stable performance.

수평 유동을 고려한 정육면체의 이동 거리 추정

이유정(Yujeong Lee),정소미(Somi Jung),나원배(Won-Bae Na) 한국해양환경·에너지학회 2021 한국해양환경·에너지학회 학술대회논문집 Vol.2021 No.10

물의 흐름은 자유낙하 하는 물체를 이동시키고 결국에는 해저에 도달하는 위치를 결정 짓는 데 영향을 준다. 본 연구에서는 수평 유동의 영향을 받으며 자유낙하 하는 정육면체 모델의 이동 거리를 추정한다. 이를 위해, 정육면체 모델의 이동 거리를 추정하는 모형실험과 수치해석을 수행하였다. 방법론의 검증을 위해 실험 결과와 수치해석 결과를 비교하였고, 약 5% 이내의 오차가 발견되었다. 연구 결과는 물속에서 중력과 수평 유동의 영향을 받는 고체의 이동거리 또는 낙하 거리를 예측하는 데 사용할 수 있다. It is important to consider horizontal water flow because it makes a free-falling body move horizontally and eventually determines its arriving location in the seabed. Therefore, we estimated the movement distance of a free-falling cube model in the presence of horizontal water flow. Experimental and numerical works have been performed to estimate the movement distance of the cube model. Those eresults were compared for the verification of the methodologies, and the errors were found within 5%. As a result, the results can be used to predict either of movement distance or falling distance of underwater moving solids subjected to gravity and horizontal water flow.