加熱된 回轉水平圓管에서 自然對流에 관한 硏究

牟洋佑,李行男 조선대학교 동력자원연구소 1988 動力資源硏究所誌 Vol.10 No.2

An analysis and experimental investigation of natural convection heat transfer from a horizontal cylinder dissipating a uniform heat flux is carried out. This paper is expected to contribute to the understanding of rotating cylinder with the combined effects of rotation free stream flow and natural convection. The first application of problem, which show the relation magnitudes of the independent variables concerned in the problem(Re, Re_w, and Ra) with respect to each other and net their absolute values that defines the heat transfer regime. It is the most important that natural convection is quite enhanced by rotation, especilly very slow rotation. The main goal of this work is to determine the dependence of the heat flux from the rotating cylinder, represented by the Nusselt number on the free stream Reynolds number, rotational Reynolds number and the Rayleigh number.

圓形管에 있어서 脈動流의 亂流流動 現象에 관한 硏究

牟洋佑,李行男 조선대학교 동력자원연구소 1988 動力資源硏究所誌 Vol.10 No.2

Turblent Pulsating Circular tube flow was measured at the time-averaged Reynolds number of 6.0×10^4 and over wide range of both frequency and velocity amplitude ration. In addition, test Sections are Composed of hydrodynamically Smooth and rigid Copper tube of 5m in length, 5㎜ in wall thickness, and the inside diameter of tested tube is 80㎜ for water flow. The results obtained from analytical and experimental studies are as follows ; 1) The flow pattern in an incompressible turblent pulsating circular tube flow is described by four characteristic parameters of Φ_t·n, Φ_z·n, β_t·n and β_z·n. 2) It Can be Considered that velocity amplitude ration, A_1has no effect on the flow pattern. 3) The flow patterns are classified in three types of qusi-steady, intermediate, and inertia dominant flow region. 4) characteristic parameters of Φ_t·1, Φ_z·1, β_t·1, Calculated from the four-region model for V_M agree well with the experimental results only in the inertia dominant region.

원심압축기의 선회실속특성에 관한 연구

모양우,나기대,유영태,김지환 朝鮮大學校 機械技術硏究所 2003 機械技術硏究 Vol.6 No.2

In the present study, the performance characteristics and the number of stall cell during rotating stall of a centrifugal air compressor were experimentally investigated. Rotating stall in the vaneless diffuser were investigated by measuring unsteady pressure fluctuations at several different diffuser radius using a high frequency pressure transducer. The number of stall cell and their rotational speeds are distinctive features of the rotating stall phenomenon. The present study is mainly forced on the analysis for the stall cell number and its propagation speed unstable operating region of the compressor. The interpretation method of visualization is based on the pressure distribution in the circumference pressure fields while plotting the pressure and its harmonics variations in time in polar coordinates. To obtain the visualize the existence rotating stall, auto-correlation function and the frequency spectra of the pressure fluctuations were measured at rh-2 = 1.52. When the flow coefficient is lower than 0.150, the static pressure at impeller inlet is higher than that at inlet duct of the Compressor. And the flow coefficient is lower than 0.086, several stall cell groups of discrete frequencies are observed.

정상유동에서 원통형 Choke의 유동특성에 관한 연구

모양우,유영태,홍성삼 조선대학교 생산기술연구소 1994 生産技術硏究 Vol.16 No.2

It is important to know the flowrate or controlling fluid machinery because the power of it can be appeared the product of flowrate and pressure. Cylindrical chokes are widely used in hydrostatic pumps, hydrostatic actuators, hydrostatic control valves and many other kinds of hydrostatic machinery and were favorite hydraulic components. In the designing of hydrostatic machinery containing cylindrical chokes, it is important to know pressure-flow rate part of rate characteristics of cylindrical chokes. Thus, it is used cylindrical chokes to measure flowrate of a circular pipe and must know the coefficient of flowrate of cylindrical chokes. The widely applicable formulas of flow coefficients of cylindrical chokes are given as the function of dimensionless choke number σ=Q/νl (Q=flow rate, ν=kinematic viscosity of fluid, l=length of choke). The strain gauge type Pressure conductor was used to meassure pressure drop for defining the coefficient of flowrate in this paper. The calibration of flowrate was used ultrasonic flowmeter. It is proposed the flowrate formular that was used cylindrical chokes experimentally.

원관에서 원통형초크의 비정상유동의 유동특성함수

모양우,유영태,위광한 조선대학교 동력자원연구소 1994 動力資源硏究所誌 Vol.16 No.2

A new instantaneous flowmeter for water hydraulic by means of cylindrical chokes is developed. In this method the instantaneous flowrate through chokes is predicted in real time from measurement of pressure difference on both sides of cylindrical choke. The experimental study for the flowrate of pulsating flow in a pipe is carried out to measure differential pressure drop by using a strain gauge pressure transducer with data acquisition and processing system. A pulsating flow is verified by visualization method. In the present study, the flow charcteristic variables of laminar pulsating flow are investigated analytically and experimentally in a circular pipe. Characteristics parameters of ratio of inertia term and pressure term(Φ_t.1) and ratio of viscous term and pressure term (Φ_z.1) are introduced to describe the flow pattern of laminar pulsating flow.

曲管에 있어서 脈動流에 關한 硏究

牟洋佑,河鈺男,金基馨 조선대학교 동력자원연구소 1990 動力資源硏究所誌 Vol.12 No.1

An experiment study on pulsating flow was carried out. The axial velocity of a laminar, fully-developed pulsating flow in curved circular pipes has been made experiment in a widerage of various parametters. j.e. radius ratio of pipes R/a, mean Dean number D. Womersley number α and Reynolds number Re and flow ratio η. The experimental results agree well with the solution of the numerical analysis. The relation between the kinetic energy of the secondery flow and the influence of curvature on the flow is discussed The instantaneous velocity measured is classified into time-mean and varing components and the effects of porameters on them are discussed. Experimenton are given for the complicated behavior of the curved pipe pulsating flow.

矩形斷面을 갖는 曲管內의 振動流

牟洋佑,河鈺男 조선대학교 동력자원연구소 1990 動力資源硏究所誌 Vol.12 No.2

Fluid flow in curved pipes has attractedmuch attention because curved pipe or tubegeo-metries arise in bio-fluid-mcchanics, es-pecially blood flow in the aortu, as wellas in engineering appeications to heat exchnagers bends in piping systems, intakes in airchaft, etc. However, most of them are concerned with steady flows. Velocity profiles, stream lines of secondary flow and disstribution of wall shearing stresses were calculated in a wide range of various paramerters, i, e. mean Dean D, Wonrersley number a and flowrate ??. It was found that one to four pairs of Vortices were induced in the cross section in a cycle at moderate values of α.

원관에서 원통형 초크의 차압을 이용한 맥동유동의 유량 측정법

모양우,유영태,홍성삼 조선대학교 생산기술연구소 1994 生産技術硏究 Vol.16 No.2

A new instantaneous flowmeter is developed by means of cylindrical chokes. In this method the instantaneous flowrate through chokes is predicted in real time from measurement of pressure difference on both sides of cylindrical choke. The experimental study for the flowrate of pulsating flow in a pipe is carried out to measure differential pressure drop by using a strain gage pressure transducer with data acquisition and processing system. A pulsating flow is verified by visualization method.

유압관로의 비정상유동에 따른 임피던스 전달특성

모양우,유영태,나기대,김지환 한국공작기계학회 2004 한국생산제조학회지 Vol.13 No.6

Design for quite operation of fluid power system requires the understanding of noise and vibration characteristics of the system. This paper presents a dynamic response of design of hydraulic circuit. Experimental investigations on the attenuation of pressure ripple in automotive power steering hydraulic pipe line is examined. Also, a mathematical model of hydraulic pipe is proposed to support a design of the hydraulic circuit. and the impedance characteristics of pressure ripple is analyzed. It is experimentally shown that power steering hydraulic pipe attenuates pressure ripple with high frequency.

곡관에서 층류맥동유동의 유동특성에 관한 연구

모양우,유영태,홍성삼 조선대학교 동력자원연구소 1992 動力資源硏究所誌 Vol.14 No.2

The flow characteristics of laminar pulsating flows are studied experimentally in a curved pipe. Velocity profiles, wall shear stress distributions and pressure gradients are investigated both analytically and experimentally for fully developed laminar pulsating flows of a curved pipe. Velocity profiles and pressure gradients in a curved pipe flow are measured over ranges of Reynolds number and dimensionless frequencies. A laminar pulsating flow in a curved pipe was analyzed solution and following conclusions were obtained: 1) In the case of large flow rate ratio, the axial velocity has maximum value a little outside of center of the pipe for a small Womersley number. 2) When the flow rate trtio becomes smaller, two pairs of vortices are found thorugh a cycle. The wall shearing stress has large value at the outer wall and outside of upper and lower walls. 3) As η decreases, the velocity profile becomes similar to one in the steady flow. 4) As the Wormersly number becomes 10, some of the secondary vortices disappear and new vortices which repeat combination and disjunction are formed in the cross section.