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Dohoon Kwon,Jinwook Kim,정상권 한국초전도저온학회 2022 한국초전도저온공학회논문지 Vol.24 No.1
A sorption cooler, which utilizes helium-4 as a working fluid, was previously developed and tested in KAIST. The cooler consists of a sorption pump and a thermosyphon. The developed sorption cooler aims to pre-cool a certain amount of the magnetic refrigerant of an adiabatic demagnetization refrigerator (ADR) from 4.5 K to 2.5 K. To simulate the high heat capacitance of the magnetic refrigerant, liquid helium was utilized not only as a refrigerant for the sorption cooling but also as a thermal capacitor. The previous experiment, however, showed that the lowest temperature of 2.7 K which was slightly higher than the target temperature (2.5 K) was achieved due to the radiation heat leak. This excessive heat leak would not occur when the sorption cooler is completely integrated with the ADR. Thus, based on the experimentally obtained pumping speed, the prediction model for the sorption cooler is developed in this study. The presented model in this paper assumes the sorption cooler is integrated with the ADR and the heat leak is negligible. The model predicts the amount of the liquid helium and the required time for the sorption cooling process. Furthermore, it is confirmed that the performance of the sorption cooler is enhanced by reducing the volume of the thermosiphon. The detailed results and discussions are summarized.
Kwon, Dohoon,Jin, Lingxue,Jung, WooSeok,Jeong, Sangkwon Elsevier 2018 Cryogenics Vol.92 No.-
<P><B>Abstract</B></P> <P>Heat transfer coefficient of a mini-channel printed circuit heat exchanger (PCHE) with counter-flow configuration is investigated. The PCHE used in the experiments is two layered (10 channels per layer) and has the hydraulic diameter of 1.83 mm. Experiments are conducted under various cryogenic heat transfer conditions: single-phase, boiling and condensation heat transfer. Heat transfer coefficients of each experiments are presented and compared with established correlations. In the case of the single-phase experiment, empiricial correlation of modified Dittus-Boelter correlation was proposed, which predicts the experimental results with 5% error at Reynolds number range from 8500 to 17,000. In the case of the boiling experiment, film boiling phenomenon occurred dominantly due to large temperature difference between the hot side and the cold side fluids. Empirical correlation is proposed which predicts experimental results with 20% error at Reynolds number range from 2100 to 2500. In the case of the condensation experiment, empirical correlation of modified Akers correlation was proposed, which predicts experimental results with 10% error at Reynolds number range from 3100 to 6200.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Thermal performance of a mini-channel PCHE under cryogenic condition is studied. </LI> <LI> Single-phase, boiling and condensation experiments are conducted. </LI> <LI> Empirical heat transfer correlations are proposed at each experimental condition. </LI> </UL> </P>
사용자 인터페이스 유형별 스마트폰 파지 자세에 대한 우세손, 손 크기, 그리고 기기 크기의 영향 파악
권도훈(Dohoon Kwon),최영근(Younggeun Choi),Xin Cui,김민재(Minjae Kim),유희천(Heecheon You) 대한인간공학회 2021 大韓人間工學會誌 Vol.40 No.5
Objective: This study aims to identify the effects of hand size, hand dominance, and device size on the grip posture of smartphones for physical and graphical UIs. Background: An inappropriate user interface (UI) causes an inappropriate grip posture and is a cause of lowering smartphone usability. Although studies on smartphone UI elements affecting the gripping posture have been conducted in various fields, there has been no study on the effect of hand dominance for physical and graphical UIs together. Method: Forty participants with different hand sizes simulated texting and web-surfing tasks using smartphone mock-ups with screen sizes of 3.0" to 7.0" and their grip postures were recorded using web cameras. Four major grip postures (side grip, back-support grip, bottom-support grip, and upper grip), classified based on the positions of the fingers on the smartphone and the shape of the grip, were identified. Results: It was found that the grip posture distributions for physical UI and graphical UI varied largely by device size (up to 37.1%), moderately by hand size (up to 14.3%), and slightly (up to 3.0%) by hand dominance. Conclusion: This study found that the frequency distribution of use of the grip posture was significantly changed according to the user interface, anthropometric information such as hand length and dominant hand, and smartphone design factors such as device size. Application: The information of the grip posture distributions identified in the present study can be utilized to determine the optimal locations of smartphone interfaces for better usability.
머신러닝 분석 기술을 통한 뇌파 기반 VUI 감성 만족도 평가
권도훈(Dohoon Kwon),김민재(Minjae Kim),장나영(Nayoung Jang),유희천(Heecheon You) 대한인간공학회 2021 대한인간공학회 학술대회논문집 Vol.2021 No.11
Objective: 본 연구는 뇌파 기반 음성 사용자 인터페이스(voice user interface, VUI) 평가를 통해 인터페이스 변화에 따른 감성 만족도를 확인하는 것이다. Background: 사용자 감성은 사용자 만족도와 선호도에 영향을 끼쳐 객관적으로 평가될 필요가 있다. 두피에 전극을 부착하여 영역별로 활성화된 전위를 측정하는 뇌파(electroencephalogram, EEG)는 사용자가 의도적으로 조절할 수 없어 감성을 객관적으로 평가하는데 유용하게 활용되고 있다. Method: 본 연구의 EEG 평가 실험에는 30명의 실험참여자가 모집되었으며, 실험참여자가 음 높이(낮음: 170 ㎐, 보통: 210 ㎐, 높음: 240 ㎐)와 말 빠르기(느림: 285 spm, 중간: 345 spm, 빠름: 405 spm)가 다양한 9가지 VUI를 청취하는 동안 EEG 신호가 측정되었다. EEG 신호 분석은 전처리, 특징 추출 그리고 분류의 절차를 통해 분석되었다. 전처리 단계에서는 EEG 신호의 body artifact와 eye movement noise가 제거되었으며, 분석에 사용될 데이터 선별 과정을 거쳤다. 특징 추출 단계에서는 frequency band에 따라 delta (1 ~ 4 ㎐), theta (1 ~ 4 ㎐), alpha (1 ~ 4 ㎐), beta (1 ~ 4 ㎐), 그리고 gamma (1 ~ 4 ㎐)의 5가지 신호로 분류되었다. 분류 단계에서는 support vector machine (SVM) method와 random forest를 통해 사용자의 감정이 분류되었으며 주관적 평가와 비교되었다. Results: 높은 음 높이와 중간 말 빠르기 조건에서 실험참여자의 명료성과 친근감 그리고 실험참여자의 전두엽에서 측정된 긍정도(valence)가 가장 높은 것으로 평가되었다. 또한, 경고와 일반 사용 조건의 두가지 사용 상황 중 경고 상황에서 말 빠르기가 빠를수록 정보 전달성이 더 높은 것으로 평가되었다. 사용된 machine의 정확도는 SVM과 RF에서 각각 평균 91.3%, 85.7%이다. Conclusion: 본 연구의 뇌파 기반 사용자 감성 만족도 평가/분석 방법은 감성 만족도가 높은 제품 설계에 활용되어 사용자의 제품 사용성과 선호도를 높이는데 활용될 수 있다.
CFD 를 이용한 선박 기관실 공기 공급용 팬 입구 형상에 따른 성능 비교 연구
권도훈(Dohoon Kwon),홍윤균(Youngyun Hong),구성우(Seongwoo Koo) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
The performance of fan for engine room of ship is absolutely important when it take into consideration work efficiency, work condition, and the performance of various equipments. Fan performance test should be carried out during sea trial to satisfy owner’s requirement as above mentioned. We have considered various values to affect fan test result. In here, various values are to be silencer, fan inlet shape, and arrangement of fan room. In general, the shapes of fan inlet is overall circular type because of the shapes of axial fan. So, all vessels built at SHI have been applied fan inlet of circular type. And now, in order to reduce sound of noise from supply fan, big silencer often has been installed at high value vessels. In this case, the capacity of supplied air can be insufficient due to silencer which is an obstructer about air flow. In this paper, we have studied the performance of fan through comparison between a circular shape and a square shape of fan inlet. We also compare with CFD results and experimental results.