• Proceedings of the KSME Conference
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• 2003.11a
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• pp.828-833
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• 2003

This work analyzes the effects of the independent variation of different geometric dimensions of compressor valves on the effective flow and force areas using a circular valve plate, such as different geometry of the valve seat, and the valve reed is opened and closed by pressure pulsation, the flow characteristic of the refrigerant passing the valve is very important. In the present study, a circular disk with inclination is assumed to be the valve reed of a reciprocating compressor and numerical analysis of three dimensional velocity fields are performed for theradial flow through the valve model. The effective flow and force area which are required to predict the efficiency of the valve are required to predict the efficiency of the valve are measured and compared with the numerical analysis in this research.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.1
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• pp.34-40
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• 2022

In this paper, a flow analysis of a swash-plate type hydraulic piston pump installed on a hydraulic flow supply system for marine vessels is presented. A model and governing equations for computational fluid dynamics (CFD) analyses of swash-plate type hydraulic piston pumps were built, and simulation results regarding the internal flow field of the pump were obtained. By analyzing the internal flow of the swash-plate type hydraulic piston pump, we can confirm the time-dependent stroke of each piston as the pump rotates. We also verified that by analyzing the pulsating flow against the slope of the swash plate, the simulation results match well with the experimental results. The natural frequency of the system was computed to be approximately 380 Hz by applying and analyzing the fast Fourier transform (FFT) of each swash plate slope evaluated.

• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.567-571
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• 2008

PEM Fuel Cell operation mode can be classified into dead-end mode or open mode by whether the outlet port is blocked or not. Generally, dead-end type fuel cell has some merits on the pressure drop and system efficiency because it can generate more power than the open type fuel cell due to high operating pressure condition. However, the periodic purging process should be done for removing water which is formed as product of a reaction in the gas diffusion layer. In this study, cathode side dead-end type operation has been conducted. Moreover, pulsating flow generator at the outlet of cathode side has been suggested for increasing the period to purge the formed water because the pulsating flow can make formed water scattered uniformly over the whole channel. As a result, the purging period with pulsation increased by 1.5-2 times longer than that without pulsating.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.1
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• pp.1-11
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• 2002

Flow of fluid has been studied in various fields of fluid engineering. To hydraulic engineers, the unsteady flow such as pulsation and liquid hammering in pipes has been considered as a serious trouble. So we are supposed to approach the formalized mathematical model by using more exact momentum equation for fluid transmission lines. Most of recent studies fur pipe line have been studied without considerations of variation of viscosity and temperature, which are the main factors of pressure loss causing the friction of fluid inside pipe line. Frequency response experiments are carried out with use of a rotary sinusoidal flow generator to investigate wave equation take into account viscosity and temperature. But we observed that measured value of gains are reduced as temperature increased. And it was respectively observed that the measured value of gains are reduced and line width of gain is broadened out, when temperature was high in the same condition. As we confessed, pressure loss and phase delay are closely related with the length, diameter and temperature of pipe line. In addition, they are the most important factors, when we decide the momentum energy of working fluid.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.2 s.107
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• pp.190-197
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• 2006

It is well known that the acoustic characteristics of the sea are significantly affected by bubbles which have their own inherent characteristics at the undersea. In this study, the shape and acoustic characteristics of air bubbles generated by an underwater nozzle are calculated numerically, and are measured with a high speed camera and a hydrophone at various air flow rates in the experimental apparatus. As a result of analysis, the shape calculated numerically well matched with measured values at low flow rates, but in case of relatively higher flow rates. the use of correction coefficient is needed for more accurate estimation of the bubble shape. And also the rising velocity of a single bubble is constant regardless of both the bubble size and the flow rate. and the acoustic signal generated when the bubble is produced by an underwater nozzle has the same characteristic of natural frequency of the bubble pulsation, and is agreed with Minnaert's equation if the correction coefficient is considered in accordance with the flow rate.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.3
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• pp.355-361
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• 2012

Though a micro pump is a crucial element in miniaturized bio-fluidic systems or drug delivery systems, it has some intrinsic disadvantages such as backward flow, pulsation of flow, low repeatability and producibility, and high cost. To overcome these limitation, a PZT disc actuated micro pump including a novel ring-shaped multi-flap check valve is introduced. To enhance the performance of the micro pump, the static behaviour of flap valve module and the micro fluidic behavior of fluids are numerically modelled and analyzed. As results of the numerical analysis, the optimal dimension and configuration of the ring-shaped multi flap valve are $1{\times}0.05$ mm and 2 (inlet side)${\times}1$ (outlet side) type. The obtained maximum flow rates and flow resolution are about 90 ml/min and 30 ${\mu}l$/stroke respectively.

• Journal of the Korean Society of Industry Convergence
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• v.4 no.1
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• pp.21-26
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• 2001

A method for the control of pulsating pressure transients in the hydraulic brake system has been presented and experimentally verified. This control is accomplished by installing flow restricting devices at appropriate locations in the brake oil pipe line. The experimental results presented are expected to provide a basis for transient control design of hydraulic brake systems.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.05a
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• pp.322-326
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• 1997

The condensate in a single vertical reflux condenser with a tube of the large L/D ratio could carried over in both ways of fill-and-dump and the annular occurrent to steam flow. From the experimental observation made, a theoretical model based on the lumped parameter method is made to understand the dynamics of the reflux condenser. The present model predicts well the time period of fill-and-dump model and the natural vibrational frequency of the water column. This could be a first step to understand the complex phenomena in the reflux condenser such as itd improved thermal performance due to the well controlled pulsation in steam flow and the tube-to tube effect in the multi tube reflux condenser.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.591-595
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• 1997

In analysis of piping vibration of petrochemical plant, the forcing functions mainly depend upon the equipment working mechanism and vibration resources in the piping systems. In general, harmonic function is used for the system with rotary equipments. Mechanical driving frequencies, wave functions, and response spectrum are used for reciprocating compressors, surge vibration of long transfer piping, and seismic/wind vibration, respectively. In this study, for the spray injection case inside the pipe, forcing function was modeled, in which two different fluids are distributed uniformly. To confirm the results, the scheme used for the forcing function was applied for real piping system. The vibration mode of the real system was consistent with the 4th mode obtained by simulation using the forcing function formulated in this study.

• Proceedings of the KSMRM Conference
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• 1999.04a
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• pp.34-42
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• 1999

의료영상에서 인공물(Artifacts) 이라 함은 영상이 얻어지는 신체부위와 아무런 관련이 없으나 얻어진 영상에는 마치 영상의 일부분으로 나타나는 모든 것을 가리킨다. 따라서 영상에서 이들 인공물들은 실제 조직의 해부학적인 구조를 나타내지 않으므로 영상 판독에 영향을 주어 잘못된 진단을 초래할 수도 있다. 그러나 MR 영상이 가능한 이래로 새로운 여러 종류의 MR 인공물들이 많이 발견 되었으나 다행스럽게도 거의 모든 MR 인공물들은 쉽게 설명이 가능하며, 따라서 이들 인공물들에 의한 진단 오류의 가능성은 매우 희박한 실정이다. 그러나 새로운 영상방법이나 혹은 새로운 펄스대열이 계속 고안됨에 따라 새로운 종류의 인 공물들이 생겨날 가능성은 항상 존재하고 있다. 지금까지 알려진 여러 MR 인공물들은 그 생겨난 원인에 따라 다음과 같이 크게 세 가지로 분류가 가능하다. I. Motion Artifacts 1. Voluntary motion 2. Involuntary motion 1) Bowel Peristalsis 2) Respiration 3) Cardiac and vessel pulsation 4) Swallowing 3. Fluid motion 1) Blood flow 2) Cerebrospinal fluid flow II. Reconstruction Artifacts 1. Aliasing 2. Partial volume averaging 3. Truncation (Ringing) 4. Central point III. Magnetic and RF Field Related Artifacts 1. Chemical shift 1) First kind 2) Second kind 2. Susceptibility 1) Dental 2) Metal 3. Magic angle 4. Zipper 5. Bad data point 6. RF field inhomogeneity 7. Magnetic field inhomogeneity 8. Eddy current 9. slice overlapping 10. Zebra 11. RF overflow