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마이크로채널 열교환기에서 R-134a의 증발열전달 특성에 관한 실험적 연구
이해승(Haeseung Lee),김선창(Seon-Chang Kim),김영률(Young-Lyoul Kim),김용찬(Yongchan Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
Experimental investigations have been carried out to verify the evaporative heat transfer characteristics of R-134a in micro-channel heat exchanger. The micro-channel heat exchanger used in this study is a sort of plate heat exchanger. Micro-channels are fabricated on the SUS304 plate by photo etching process : 13 sheets of plate are stacked and bonded by diffusion bonding process. Effects of evaporating temperature, inlet temperature of water and mass flowrate of R-134a have been examined. The relationship of effectiveness and NTU have been also investigated under the various inlet temperatures of refrigerant and water. As the difference between temperature of inlet refrigerant and that of water increases, the heat transfer rate increases. Evaporative heat transfer coefficients obtained in this study range from 3.30 ㎾/㎡ㆍ℃ to 12.98 ㎾/㎡ㆍ℃.
마이크로채널 열교환기에서 R-134a의 증발열전달 특성에 관한 실험적 연구
이해승(Haeseung Lee),전동순(Dong-Soon Jeon),김영률(Young-Lyoul Kim),김용찬(Yongchan Kim),김선창(Seon-Chang Kim) 대한기계학회 2010 大韓機械學會論文集B Vol.34 No.2
마이크로채널 열교환기에서 R-134a의 증발열전달 특성에 관하여 실험적 연구를 수행하였다. 마이크로 채널은 금속박판인 SUS304에 포토에칭 공정으로 식각되었으며, 13개의 금속박판은 차례로 적층되어 확산접합 공정을 통하여 접합되었다. 본 연구에서는 R-134a의 증발온도, 질량유속 그리고 물의 입구온도의 변화에 따른 열전달 특성을 대향류 조건에서 실험하였다. 실험결과 R-134a와 물의 입구온도차가 클수록 증발열전달량은 증가하였으며, 증발열전달계수는 0.67 ㎾/㎡ ?℃에서 6.23 ㎾/㎡ ?℃이었다. 아울러 마이크로채널 열교환기에서 R-134a와 물의 열교환에 따른 증발열전달 특성에 영향을 미치는 Reynold수와 무차원 온도비 θ를 도출하여 Nusselt수에 관한 실험적 상관식을 제안하였다. An experimental investigation was carried out to examine the evaporative heat transfer characteristics of R-134a in a micro-channel heat exchanger. The micro-channel heat exchanger used in this study was a sort of plate heat exchanger. Micro-channels were fabricated on the SUS304 plate by the photo-etching process: 13 sheets of plates were stacked and bonded by the diffusion bonding process. The effects of the evaporating temperature, mass flux of R-134a, and inlet temperature of water were examined. As the difference between the inlet temperatures of R-134a and water increased, the heat transfer rate increased. The evaporative heat transfer coefficients obtained in this study range from 0.67 to 6.23 ㎾/㎡ ?℃. The experimental correlation for the Nusselt number as a function of the Reynold number and θ was suggested for the micro-channel heat exchanger.
채널 형상에 따른 마이크로채널 열교환기의 증발열전달 특성 및 압력강하에 관한 실험적 연구
이해승(HaeSeung Lee),김선창(Seon-Chang Kim),김영률(Young-Lyoul Kim),전동순(Dong-Soon Jeon),김용찬(YongChan Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
Experimental investigations have been carried out to examine the evaporative heat transfer characteristics of R-134a in micro-channel heat exchangers with straight and zigzag 15° and 30° channel. The micro-channels heat exchangers used in this study is a sort of plate heat exchanger. Micro-channels were fabricated on the SUS304 plate by photo-etching process : 13 sheets of plate were stacked and bonded by diffusion bonding process. Effects of difference in Reynolds number with R-134a and that of difference in heat transfer areas have been examined under counter flow condition. The heat transfer rate of zigzag 15° and 30° has increased about 1.1~1.2 times compared with the straight, and the pressure drop also increased about 1.1~1.4 times. The evaporative heat transfer coefficients obtained in this study range from 0.97 ㎾/㎡ㆍ℃ to 7.85 ㎾/㎡ㆍ℃.
조립품 심(seam)의 갭(gap)에 대한 정량적 심미평가의 기초연구
이해승(Haeseung Lee),이래우(Raewoo Lee),임현준(Hyunjune Yim) (사)한국CDE학회 2011 한국CDE학회 논문집 Vol.16 No.5
Esthetic appeal of a product is often affected by the appearance quality of seams forming between components of the product. The appearance quality of seams is, however, assessed in a very subjective and qualitative manner that heavily depends on the evaluator. This paper presents a preliminary study to quantify such assessment by formulating a quantitative index which is a linear function of the seam gap sizes, seam gap ranges, and the size uniformity of seam gaps. By considering a highly simplified problem of a drawer system and utilizing subjective assessments by twenty evaluators, the index has been formulated. The validity of this index has been confirmed by observing its behavior with changes of the component tolerances. Also, the utility of this index has been demonstrated through a selective assembly scheme applied to the drawer system problem. Though the index formulated in this study for seam appearance quality may be useful, future studies are necessary to make the model readily applicable to real problems.
증분 회절이론을 이용한 완전도체 산란체의 레이다 단면적 해석
이소영(Soyeong Lee),이해승(Haeseung Lee),신호근(Hokeun Shin),윤대영(Daeyeong Yoon),박용배(Yong Bae Park) 한국전자파학회 2021 한국전자파학회논문지 Vol.32 No.10
본 논문에서는 고주파 근사기법인 증분 회절이론을 이용하여 완전도체 재질을 갖는 임의의 산란체의 레이다 단면적을 계산한다. 산란체 표면에서의 반사파는 기존의 shooting and bouncing rays (SBR)로 계산하고, 모서리에서의 회절파는 증분 회절이론을 이용하여 계산한다. 서로 다른 크기를 가진 두개의 직육면체로 이루어진 산란체의 모노스태틱 및 바이스태틱 레이다 단면적을 계산하고, 상용 소프트웨어의 시뮬레이션 결과와 비교하여 계산 방법을 검증한다. 또한, 단순선박에 대한 바이스태틱 레이다 단면적을 계산하여 기존의 physical theory of diffraction (PTD) 기법에서 갖는 발산 문제를 해결할 수 있음을 보인다. This paper presents the calculation of the radar cross-section (RCS) of an arbitrary scatterer with a perfect electric conductor by using the incremental theory of diffraction (ITD), a high-frequency technique. The reflected field at the surface of the scatterer is calculated using conventional shooting and bouncing rays (SBR), and the diffracted field at the edge is calculated using the ITD. The proposed method is verified by calculating the monostatic and bistatic RCS of a scatterer composed of two cubes of different sizes and comparing it with the simulation results from CST Microwave Studio. Furthermore, it is demonstrated by calculating the bistatic RCS for a simplified ship that the divergence problem in the physical theory of diffraction can be solved using the proposed method.
표면 전류를 기반으로 한 유한 배열 I-모양 메타물질의 TM 편파 전자기 산란 모델
장지웅(Ji-woong Jang),이해승(Haeseung Lee),고일석(Il-suek Koh),서일성(Ilsung Seo),이용식(Yongshik Lee) 한국전자파학회 2014 한국전자파학회논문지 Vol.25 No.6
일반적으로 메타물질의 성질은 무한히 배열된 단위 셀 구조로 해석한다. 그러나 실제 응용 구조의 설계/구현 과정에서 메타물질은 유한하게 배열할 수밖에 없고, 유한 배열의 효과를 해석하는 방법이 필요하다. 본 논문에서는 유한한 대형 배열 메타물질 구조의 산란 특성을 full-wave 해석 없이 계산하기 위한 방법을 제안하였다. 제안한 모델은 다음과 같다. TM 편파에 대해 유한히 배열한 메타물질 구조의 표면 전류와 무한 배열 표면 전류 비를 4차 다항식으로 근사하였다. 다항식의 계수를 금속 패치의 물리적 길이에 대한 함수로 계산하여, 임의의 I-모양 메타물질이 균일하게 배열된 유한배열 구조의 전류 분포를 쉽게 계산할 수 있다. 그리고 제안된 전류 분포 모델을 기반으로 예측한 표면 전류를 통해 유한한 메타물질 배열 구조의 산란파를 계산하였다. 또, 제안한 모델을 이용하여 계산한 레이더 반사 단면적(Radar Cross Section: RCS)을 측정 결과와 비교함으로써 제안한 모델의 정확도를 실험적으로 확인하였다. Generally, the properties of metamaterials are analyzed based on the infinite array of the unit cells. In real application of the metamaterial, however, the array has to be finite. Hence, it is important that a method can analyze the effect of the finite array of the metamaterial. In this paper, a model is proposed which can calculate the scattering by a large-size finite array of an I-shaped metamaterial without a full-wave simulation. The proposed model is based on the surface current estimation of each unit cells. The ratio of the current distribution on a finite array of the metamaterial to that of the infinite array of the same metamaterial for a TM polarized incident wave is approximated as a quartic polynomial. The coefficients of the polynomial are a function of the physical dimension of the metallic patch. Hence, the current distribution of the finite metamaterial can be estimated based on the proposed polynomial and the current of the infinite array. The scattered field is calculated by using the surface current model. The proposed model is numerically and experimentally verified by comparing calculated and measured RCS(Radar Cross Section) data.