Stereoscopic micro-PTV기법의 개발

유청환(Cheong-Hwan Yu),김형범(Hyoung-Bum Kim) 한국가시화정보학회 2007 한국가시화정보학회 학술발표대회 논문집 Vol.- No.-

Stereoscopic micro-PIV기법을 이용한 충돌제트 유동 측정

유청환(Cheong-Hwan Yu),김형범(Hyoung-Bum Kim) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10

Micro flow measurement is important to understand the physics of micro fluidic devices such as MEMS actuator, pumps, etc. Micro-PIV became the essential tool for this purpose due to the good performance of it. Micro-PIV is basically two dimensional measurement method and many micro fluidic devices generate three dimensional flow. In this study, we developed stereoscopic micro-PIV(SMPIV) which is basically the combination of conventional stereoscopic PIV method with stereoscopic microscope. This SMPIV method is applied to the impinging jet flow for validating the performance. The results showed this SMPIV method can measure out-of-plane velocity of test plane precisely.

수분류 추돌제트 열전달의 비등 특성

유청환(Cheong-Hwan Yu),이정호(Jungho Lee) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5

Liquid jet impingement cooling has been widely used in the iron/steel making industries and nucleate power plants as an effective method of removing high heat flux. Liquid jet impinging on hot surface passes through a phase change heat transfer such as single-phase forced convection, nucleate boiling, transition boiling, and film boiling. Especially, a strict understanding of boiling phenomena is significant to ensure high quality products in iron/steel making industry. An actual hot-steel cooling process requires wider band of nucleate boiling rather than transient boiling, because there are sudden changes in heat transfer rate within transient boiling regime. In this study, a variety of parameters has been experimentally considered to investigate the role of boiling in heat transfer characteristics of liquid jet impinging on hot surface extremely up to higher temperature of 900℃. The result shows a higher cooling rate with increased CHF (critical heat flux) by increasing flow rates.

미세제트 유동의 Stereoscopic micro-PIV측정

유청환(Cheong-Hwan Yu),김형범(Hyoung-Bum Kim) 한국가시화정보학회 2007 한국가시화정보학회지 Vol.5 No.1

Micro-PIV(particle image velocimetry) has been widely used to measure the velocity of micro flow. Although this micro-PIV method can give accurate 2D instantaneous velocity information of measurement plane, it cannot resolve the out of plane component of velocity vectors. Lots of the micro fluidic devices generate three-dimensional flow and 3D measurement of velocity is useful to understand the physics of micro flow phenomena. In this study, we constructed stereoscopic micro-PIV(SMPIV) system and applied this method to the impinging micro jet flow. The results show that this method can produce accurate 3D reconstruction of micro jet flow.

〈학술논문〉 또는 〈응용논문〉 : Cavity Bubble 이 벤투리 유량측정의 불확도에 미치는 영향

이정호(Jungho Lee),유청환(Cheong-Hwan Yu),윤석호(Seok Ho Yoon),도규형(Kyu Hyung Do) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11

벤투리 유량계는 유량측정 시 압력손실이 적어 많은 공업적 응용분야에서 유체 유량을 측정하는데 널리 사용되어 왔다. 이러한 공업적 및 산업적인 응용에 있어서, 유체가 증기압 이하로 압력이 강하될 때 발생하는 공동현상은 흔히 접하게 되고, 이와 같이 주 유동에 공동현상이 발생하는 경우에 있어 벤투리를 사용한 유량측정에서는 이상유동의 영향이 고려되어야 한다. 본 연구에서는 유체의 기포율이 벤투리 유량측정에 미치는 영향을 파악하기 위해 미국기계학회에서 추천하는 ASME PTC 19.1-2005 에 근거하여 불확실성 해석을 수행하였고, 측정 불확도를 줄이기 위한 방법을 확인해 보았다. 벤투리 유량측정의 불확도는 기포율이 증가함에 따라 증가하는 결과를 보여준다. Venturi has been widely used to measure flow rate of liquids and gases in a variety of engineering applications due to relatively low pressure losses. In these engineering applications, a two-phase bubbly flow occurs on most industrial flow fields in which the pressure of the liquid falls below its vapor pressure and its effect needs to be considered for flow rate measurement by venturi. The present study focuses on making detailed estimation of measured uncertainties, as the void fraction affects uncertainty of the main water flow in the circulating-loop test. The measurement uncertainty of flow rate has been performed by a quantitative uncertainty analysis that is based on the ANSI/ASME PTC 19.1-2005 standard. The best way to reduce error in measuring flow rate is also investigated for evaluating its measurement uncertainty. The results show that the uncertainty of flow rate measurement can be increased by increasing void fraction.

대류열전달계수의 불확실성 해석 및 응용

이정호(Jungho Lee),유청환(Cheong-Hwan Yu),도규형(Kyu Hyung Do) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11

The analysis of the uncertainties in experimental measurements and results is a powerful tool, particularly when it is used in the planning and design of experiments. The uncertainty analysis, when used in the initial planning phase of an experiment, can identify such situations and save the experimentalist much time, money and embarrassment. The current study focuses on making detailed determination and estimation of the convective heat transfer coefficient as it is frequently encountered in the field of thermal engineering applications. The quantitative uncertainty analysis was carried out based on the ANSI/ASME PTC 19.1-2005 standard. The actual application of the uncertainty analysis is provided by the detailed example which is performed at the submerged impinging jet heat transfer case. The results show that the convective heat transfer coefficient can be determined by its individual contributors of measurands.

냉각수 온도에 따른 수분류 충돌제트의 열전달 특성 연구

이정호 ( Jung Ho Lee ),유청환 ( Cheong Hwan Yu ),도규형 ( Kyu Hyung Do ) 한국열처리공학회 2010 熱處理工學會誌 Vol.23 No.5

Water jet impingement cooling has been widely used in a various engineering applications; especially in cooling of hot steel plate of steelmaking processes and heat treatment in hot metals as an effective method of removing high heat flux. The effects of cooling water temperature on water jet impingement cooling are primarily investigated for hot steel plate cooling applications in this study. The local heat flux measurements are introduced by a novel experimental technique that has a function of high-temperature heat flux gauge in which test block assemblies are used to measure the heat flux distribution during water jet impingement cooling. The experiments are performed at fixed flow rate and fixed nozzle-to-target spacing. The results show that effects of cooling water temperature on the characteristics of jet impingement heat transfer are presented for five different water temperatures ranged from 5 to 45˚C. The local heat flux curves and heat transfer coefficients are also provided with respect to different boiling regimes.

냉각수온 효과에 따른 고온 강판의 스프레이 냉각 열전달 특성 연구

이정호(Jungho Lee),유청환(Cheong-Hwan Yu),박상진(Sang-Jin Park) 대한기계학회 2011 大韓機械學會論文集B Vol.35 No.5

수분류 스프레이 냉각은 900℃ 이상의 고온에서 강판을 냉각하는데 매우 중요한 기술이다. 본 연구는 냉각수온이 고온 강판의 수분류 스프레이 냉각에 미치는 영향을 고찰하였다. 이 때의 열유속은 시편, 카트리지히터, 열전대의 조합으로 고안된 열유속게이지를 제작하여 엄밀하게 측정되었다. 스프레이는 fullcone 노즐로부터 생성되고 냉각실험은 일정한 스프레이 질량유속과 노즐과 표면 사이의 거리 조건에서 수행되었다. 냉각수온의 효과는 5℃에서 45℃까지 다섯 가지의 서로 다른 수온에 대한 수분류 스프레이 냉각의 열전달 현상을 비교 및 평가하였다. 여기서 열유속곡선과 열전달계수는 고온강판의 냉각공정에서 실제 스프레이 냉각을 위한 기본 데이터로 활용될 수 있다. Water spray cooling is a significant technology for cooling of materials from high-temperature up to 900℃. The effects of cooling water temperature on spray cooling are mainly provided for hot steel plate cooling applications in this study. The heat flux measurements are introduced by a novel experimental technique that has a function of heat flux gauge in which test block assemblies are used to measure the heat flux distribution on the surface. The spray is produced by a fullcone nozzle and experiments are performed at fixed water impact density of G and fixed nozzle-totarget spacing. The results show that effects of water temperature on forced boiling heat transfer characteristics are presented for five different water temperatures between 5 to 45℃. The local heat flux curves and heat transfer coefficients are also provided to a benchmark data for the actual spray cooling of hot steel plate cooling applications.

냉각수온 효과에 따른 고온 강판의 스프레이 냉각 열전달 특성 연구

이정호(Jungho Lee),유청환(Cheong-Hwan Yu),박상진(Sang-Jin Park) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.5

수분류 스프레이 냉각은 900℃ 이상의 고온에서 강판을 냉각하는데 매우 중요한 기술이다. 본 연구는 냉각수온이 고온 강판의 수분류 스프레이 냉각에 미치는 영향을 고찰하였다. 이 때의 국소열유속은 시편, 카트리지히터, 열전대의 조합으로 고안된 열유속게이지를 제작하여 엄밀하게 측정되었다. 스프레이는 fullcone 노즐로부터 생성되고 냉각실험은 일정한 스프레이 질량유속과 노즐과 표면 사이의 거리 조건에서 수행되었다. 냉각수온의 효과는 5℃에서 45℃까지 다섯 가지의 서로 다른 수온에 대한 수분류 스프레이 냉각의 열전달 현상을 비교 및 평가하였다. 여기서 국소 열유속곡선과 열전달계수는 고온 강판의 냉각공정에서 실제 스프레이 냉각을 위한 기본 데이터로 활용될 수 있다. Water spray cooling is an important technology for the cooling of materials from high-temperature up to 900℃. The effects of cooling water temperature on spray cooling for hot steel plate cooling applications are provided in this study. The local heat flux measurements are introduced by a novel experimental technique in which test block assemblies are used to measure the heat flux distribution on the surface as a function of heat flux gauge. The spray is produced by a function nozzle and experiments are performed at fixed water impact density of G and fixed nozzle-to-target spacing. The results show that effects of water temperature on forced boiling heat transfer characteristics are presented for five different water temperatures between 5 to 45℃. The local heat flux curves and heat transfer coefficients are also provided to a benchmark data for the actual spray cooling of hot steel plate cooling applications.

고온 열유속게이지 가열특성에 대한 시뮬레이션 연구

이정호(Jungho Lee),유청환(Cheong-Hwan Yu),이공훈(Kong-Hoon Lee) 대한설비공학회 2010 대한설비공학회 학술발표대회논문집 Vol.2010 No.6

A sort of numerical simulations are highly significant in the design-stage of a high-temperature heat flux gauge and also are helpful to understand heat transfer characteristics under a general heating process up to 900℃. In present study, a numerical simulation using a commercial finite element analysis software, COMSOL Multiphysics<SUP>?</SUP>. was employed to validate the heating characteristics of a heating block with a function of a novel high-temperature heat flux gauge. Moreover, the appropriate method of a heating was compared between a constant heat flux condition and an electric heating condition with PID control. The results show that the heating block was quickly reached a uniformly constant temperature, and an electric heating using PID control exhibits more realistic heating behavior than heating with a constant heat flux boundary condition.