• Nuclear Engineering and Technology
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• 제48권6호
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• pp.1404-1411
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• 2016

Pipe wall thinning in the secondary piping system of a nuclear power plant is currently a major problem that typically affects the safety and reliability of the nuclear power plant directly. Regular in-service inspections are carried out to manage the piping system only during the overhaul. Online thickness monitoring is necessary to avoid abrupt breakage due to wall thinning. To this end, a transducer that can withstand a high-temperature environment and should be installed under the insulation layer. We propose a thin plate type of embedded ultrasonic transducer based on magnetostriction. The transducer was designed and fabricated to measure the thickness of a pipe under a high-temperature condition. A number of experimental results confirmed the validity of the present transducer.

• 대한기계학회논문집B
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• 제29권10호
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• pp.1092-1100
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• 2005

In the present study, characteristics of steady state laminar flows of a straight duct connected to a 180$^{o}$ curved duct were examined in the entrance region through experimental and numerical analyses. For the analysis, the governing equations of laminar flows in the Cartesian coordinate system were applied. Flow characteristics such as velocity profiles and secondary flows were investigated numerically and experimentally in a square cross-sectional straight duct by the PIV system and a CFD code(STAR CD). For the PIV measurement, smoke particles produced from mosquito coils. The experimental data were obtained at 9 points dividing the test sections by 400 3m. Experimental and numerical results can be summarized as follows. 1) Reynolds number, Re was increased, dimensionless velocity profiles at the outer wall were increased due to the effect of the centrifugal force and secondary flows. 2) The intensity of a secondary flow became stronger at the inner wall rather than the outer wall regardless of Reynolds number. Especially, fluid dynamic phenomenon called conner impact were observed at dimensionless axial position, x/D$_{h}$=50.

• Nuclear Engineering and Technology
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• 제23권3호
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• pp.275-284
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• 1991

핵연료봉의 정방형 또는 삼각형 배열내의 2차 난류 유동의 해석은 연료봉내의 온도분포와 열전달 과정의 해석에 있어서 중요한 문제이다. 비등방성 난류모델과 등방성 난류모델을 사용하여 속 도장을 구하였고 열수력학적 성질이 일정하다는 가정하에 지배방정식을 유한 요소법을 사용하여 수치해석적인 방법으로 해를 구하였다. 또한 연료봉 표면 근처에서는 유체의 유동이 난류가 아니기 때문에 축 방향 속도는 벽의 법칙에 의해서 계산하였다. 이러한 방법에 의해서 구해진 해는 실험 결과와 비교되었고 비교적 잘 일치하였다.

• Plant Biotechnology Reports
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• 제5권1호
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• pp.1-7
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• 2011

Secondary walls have recently drawn research interest as a primary source of sugars for liquid biofuel production. Secondary walls are composed of a complex mixture of the structural polymers cellulose, hemicellulose, and lignin. A matrix of hemicellulose and lignin surrounds the cellulose component of the plant's cell wall in order to protect the cell from enzymatic attacks. Such resistance, along with the variability seen in the proportions of the major components of the mixture, presents process design and operating challenges to the bioconversion of lignocellulosic biomass to fuel. Expanding bioenergy production to the commercial scale will require a significant improvement in the growth of feedstock as well as in its quality. Plant biotechnology offers an efficient means to create "targeted" changes in the chemical and physical properties of the resulting biomass through pathway-specific manipulation of metabolisms. The successful use of the genetic engineering approach largely depends on the development of two enabling tools: (1) the discovery of regulatory genes involved in key pathways that determine the quantity and quality of the biomass, and (2) utility promoters that can drive the expression of the introduced genes in a highly controlled manner spatially and/or temporally. In this review, we summarize the current understanding of the transcriptional regulatory network that controls secondary wall biosynthesis and discuss experimental approaches to developing-xylem-specific utility promoters.

• 설비공학논문집
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• 제15권10호
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• pp.809-820
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• 2003

The present study investigates effects of flow velocity on the convective heat/mass transfer characteristics in wavy ducts of a primary surface heat exchanger application. Local heat/mass transfer coefficients on the wavy duct sidewall are determined by using a naphthalene sublimation technique. The flow visualization technique is used to understand the overall flow structures inside the duct. The aspect ratio and corrugation angle of the wavy duct is fixed at 7.3 and 145$^{\circ}$ respectively, and the Reynolds numbers, based on the duct hydraulic diameter, vary from 100 to 5,000. The results show that there exist complex secondary flows and transfer processes resulting in non-uniform distributions of the heat/mass transfer coefficients on the duct side walls. At low Re (Re<1000), relatively high heat/mass transfer regions like cell shape appear on both pressure and suction side wall due to the secondary vortex flows called Taylor-Gortler vortices perpendicular to the main flow direction. However, at high Re (Re>1000), these secondary flow cells disappear and boundary layer type flow characteristics are observed on pressure side wall and high heat/mass transfer region by the flow reattachment appears on the suction side wall. The average heat/mass transfer coefficients are higher than those of the smooth circular duct due to the secondary flows inside wavy duct. And also friction factors are about two times greater than those of the smooth circular duct.

• Journal of Advanced Marine Engineering and Technology
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• 제23권4호
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• pp.533-542
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• 1999

In this study the flow characteristics of developing turbulent pulsating flows in a square-sec-tional 180。 curved duct are investigated experimentally. The experimental study of air flow in a square-sectional curved duct is carried out to measure axial velocity distribution secondary flow velocity profiles and wall shear stress distributions by using a Laser Doppler Velocimetry system with the data acquisition and processing system of Rotating Machinery Resolver (RMR) and PHASE software at the entrance region of the duct which is divided into 7 sections from the inlet(${{\o}}=0_{\circ}$) to the outlet (${{\o}}=180_{\circ}$) in $30_{\circ}$ intervals. The results obtained from the study are summarized as follows: (1) The time-averaged critical Dean number of turbulent pulsating flow(De ta, cr) is greater than $75{\omega}+$ It is understood that the critical Dean number and the critical Reynolds number are related to the dimensionless angular frequency in a curved duct. (2) Axial velocity profiles of turbulent pulsating flows are of an annular type similar to those of turbulent stead flows. (3) Secondary flows of trubulent pulsating flows are strong and complex at the entrance region. As velocity amplitudes(A1) become larger secondary flows become stronger. (4) Wall shear stress distributions of turbulent pulsating flows in a square-sectional $180_{\circ}$ curved duct are exposed variously in the outer wall and are stabilized in the inner wall without regard to the phase angle.

• Corrosion Science and Technology
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• 제17권6호
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• pp.317-323
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• 2018

Assumptions have always been that wall thinning on the secondary side piping in nuclear power plants is mostly caused by Flow-Accelerated Corrosion (FAC). Recent studies have showed that wall thinning on the secondary side piping is caused by Liquid Droplet Impingement Erosion (LDIE), Solid Particle Erosion (SPE), cavitation, and flashing. To manage those aging mechanisms, several software such as CHECWORKS, COMSY, and BRT-CICERO have been used in nuclear power plants. Korean nuclear power plants have been using the CHECWORKS program since 1996 to date. However, many site engineers have experienced a lot of inconveniences and problems in using the CHECWORKS program. In order to work through the inconveniences and to remedy problems, KEPCO-E&C has developed a "3D-based pipe wall thinning management program (ToSPACE)" based on the experience of over 30 years in relation to the pipe wall thinning management. This study compares the results of FAC and LDIE analysis using both the CHECWORKS and ToSPACE programs with respect to validation of the wall thinning analysis results.

• 한국전산유체공학회지
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• 제8권2호
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• pp.57-63
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• 2003

Two nonlinear κ-ε models with the wall function method are applied to the fully developed turbulent flow in a square duct. Typical predicted quantities such as axial and secondary velocities, turbulent kinetic energy and Reynolds stresses are compared in details both qualitatively and quantitatively with each other. A nonlinear κ-ε model with the wall function method capable of predicting accurately duct flows involving turbulence-driven secondary motion is presented in the present paper. The nonlinear κ-ε model of Shih et al.[1] adopted in a commercial code is found to be unable to predict accurately duct flows with the prediction level of secondary flows one order less than that of the experiment.

• 한국전산유체공학회지
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• 제8권2호
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• pp.8-15
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• 2003

Three nonlinear κ-ε models with the wall function method are applied to the fully developed turbulent flow in a triangular subchannel of a bare rod bundle. Typical predicted quantities such as axial and secondary velocities, turbulent kinetic energy and wall shear stress are compared in details both qualitatively and quantitatively with both each other and experimental data. The nonlinear κ-ε models by Speziale[1] and Myong and Kasagi[2] are found to be capable of predicting accurately noncircular duct flows involving turbulence-driven secondary motion. The nonlinear κ-ε model by Shih et aL.[3] adopted in a commercial code is found to be unable to predict accurately noncircular flows with the prediction level of secondary flows one order less than that of the experiment.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1980-1985
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• 2003

Two nonlinear ${\kappa}-{\epsilon}$ models with the wall function method are applied to the fully developed turbulent flow in a square duct. Typical predicted quantities such as axial and secondary velocities, turbulent kinetic energy and Reynolds stresses are compared in details both qualitatively and quantitatively with each other. A nonlinear ${\kappa}-{\epsilon}$ model with the wall function method capable of predicting accurately duct flows involving turbulence-driven secondary motion is presented in the present paper. The nonlinear ${\kappa}-{\epsilon}$ model adopted in a commercial code is found to be unable to predict accurately duct flows with the prediction level of secondary flows one order less than that of the experiment.