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A Simple Model to Predict the Hydraulic Jump Location in a Not Fully Filled Horizontal Pipe Flow
Jae-Kwang Seo(서광재),Seung-Yeob Ryu(유승엽),Juhyeon Yoon(윤주현),Sung-Qunn Zee(지성균) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
Hydraulic jump is a local nonuniform flow phenomenon which occurs when the supercritical flow decelerates to a subcritical flow. It may be seen from a not fully filled pipe flow equation that when the Froude number of the fluid approaches unity with a value greater than 1, the differential variation of the fluid level in the direction of the flow becomes infinity. The result, then, is a marked discontinuity on the surface, characterized by the steep upward slope of the profile. In this study, a simple concept where the excessive energy of the supercritical flow is set equal to the energy dissipated by the wall friction is suggested to predict the location of the jump in a pipe flow. Then the location of the jump is simply determined by using the Manning formula. The feasibility of this concept is confirmed indirectly through an evaluation of the water level distribution of the reactor coolant during a mid-loop operation in a real reactor plant.
Jae-Kwang Seo(서재광),Han-Ok Kang(강한옥),Juhyeon Yoon(윤주현),Sung-Qunn Zee(지성균) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
A once-through steam generator (OTSG) with a modular feedwater line (MFL) is located inside a reactor vessel. A sufficient heating of the feedwater in the MFL can cause an aperiodic instability especially at low flow and low pressure conditions. Aperiodic instability is an instability related to the change of a flow direction in individual steam generating U-shaped channels operating at given pressure difference. The nature of an aperiodic instability is close to a Ledinegg instability related to the presence of multiple flows at the full hydraulic curve of a U-shaped channel. In this paper, the conditions for a reverse flow at the OTSG with a tube-in-tube MFL are studied. From the results of the studies, it is revealed that the change of a flow direction in the MFL is due to the boiling of the feedwater in the downcomer branch of the U-shaped pipe and that multiple flows start in the area of the extreams corresponding to the minimum pressure difference of the hydraulic curves.
이재선(Jae-Seon Lee),김종인(Jong-In Kim),김지호(Ji-Ho Kim),박홍윤(Hong-Yune Park),지성균(Sung-Qunn Zee) 한국트라이볼로지학회 2003 한국트라이볼로지학회 학술대회 Vol.37 No.-
Water-lubricated frictional characteristics of stainless steel ball bearing is not well known compared to oil-lubricated frictional characteristics. Furthermore study on friction at high temperature is rare because bearing maintenance strategy for water-lubricated or chemicals-lubricated bearings of equipment is mostly based on change of failed bearings and parts. Ball bearings and ball screw are installed on the power transmission for a developing integral reactor and these are lubricated with high temperature and high pressure chemically-controlled pure water. Bearings and power transmitting mechanical elements for an atomic reactor needs high reliability and high performance during estimated lifetime, and it should be verified. In this paper, experimental research results of frictional characteristics of water-lubricated ball bearing as a preliminary investigation.