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사각 마이크로채널에서 단상유동 열전달 특성에 대한 실험적 연구
문지현(Ji-Hyun Mun),김선창(Seon-Chang Kim) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
In this paper, experiments were carried out to investigate convective heat transfer characteristics in rectangular microchennels. Rectangular microchannels were made of copper that contained 20 rectangular microchannels in parallel and have hydraulic diameter of 700 ㎛. Distilled water was used as a working fluid. The experiments were conducted with the Reynolds number ranging from 400 to 800, heat flux range 35 ~ 85 ㎾/㎡ and the inlet fluid temperature of 20℃. The heat transfer coefficient has values in the range of 4.51 ~ 6.45 ㎾/㎡℃. Convective heat transfer coefficient obtained in fully developed region and increased with increasing Reynolds number. Also, thermal entry length increased with increasing Reynolds number in the laminar flow. As a result, the experimental correlation for Nusselt number as a function of Reynolds number and Prantl number was proposed, and it was found that this correlation has ±5% of error range.
액체질소 냉각용 극저온 열교환기(Type A, B)의 열전달 및 압력강하 특성 비교
문지현(Ji-Hyun Mun),전동순(Dong-Soon Jeon),김영률(Young-Lyoul Kim) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
This paper presents heat transfer and pressure drop characteristics of cryogenic heat exchanger for cooling liquid nitrogen applicable to stirling cryocooler for cooling of the HTS power cables. Since surface area of cold head in stirling cryocooler was limited, ways to enhance the heat transfer characteristics of heat exchanger have been examined. In this study, two heat exchanger types(type A, B) were considered to evaluate the heat transfer and pressure drop characteristics. Design factors of heat exchanger were channel(Wch, Hch) size and cold head parts(shape, size and surface temperature). Inlet temperature and pressure of liquid nitrogen have been fixed at 82 K and 400 ㎪. As results, we have investigated effects of the factors and compared heat transfer and pressure drop characteristics of the heat exchangers(type A, B). Also, considering the constraints on the design of heat exchanger, cryogenic heat exchanger for cooling liquid nitrogen was proposed for applying to 1 ㎾ stirling cryocooler.
문지현(Ji Hyun Mun),김선창(Seon-Chang Kim) 대한기계학회 2011 大韓機械學會論文集B Vol.35 No.9
본 연구에서는 사각 마이크로 채널의 열전달 특성을 연구하기 위한 실험을 수행하였다. 실험에 사용된 시료의 채널 수력직경은 700 ㎛이며, 채널의 개수는 20개이다. 작동유체는 물이며, 작동유체의 입구 온도는 20 이다. 실험 변수는 Reynolds 수 400 ~ 800 및 열 유속 35 ~ 85 ㎾/㎡ 이다. 결과로, Reynolds 수가 큰 경우일수록 대류 열전달 계수가 증가하는 것으로 나타났으며, 열적으로 완전히 발달된 영역에 대하여 대류 열전달 계수는 약 4.6 ~ 6.4 ㎾/㎡ 로 나타났다. 또한, 사각 마이크로 채널에서의 열적 입구길이는 Reynolds 수가 커지는 경우일수록 길어지는 것을 알 수 있었으나, 열 유속의 변화는 입구길이에 영향을 미치지 않는 것으로 나타났다. 본 연구의 결과로 완전히 발달된 유동영역에 대하여 사각 마이크로 채널의 열적 특성을 나타내기 위한 Nusselt 수 상관식을 제안하였다. In this study, experiments were carried out to investigate the convective heat transfer characteristics of rectangular microchannels. The sample used in the experiments contained 20 rectangular microchannels in parallel. The channels had a hydraulic diameter of 700 ㎛. Distilled water was used as the working fluid. In the experiments, the Reynolds number ranged from 400 to 800, heat flux ranged from 35 to 85 ㎾/㎡, and the inlet fluid temperature was 20℃. As a result, the convective heat transfer coefficient increased upon increasing the Reynolds number and ranged from 4.6 to 6.4 ㎾/㎡/℃ in the thermally fully developed region. Moreover, the higher the Reynolds number, the longer the thermal entry length in the rectangular microchannels. However, it was observed that a variable heat flux did not affect the thermal entry length. In conclusion, a correlation was proposed to indicate the heat transfer characteristics in a thermally fully developed region.
문지현(Ji-Hyun Mun),전동순(Dong-Soon Jeon),김선창(Seon-Chang Kim),김영률(Young-Lyoul Kim) 대한설비공학회 2009 대한설비공학회 학술발표대회논문집 Vol.2009 No.-
In this paper, plain fin-flat tube condenser was proposed to replace existing condenser for a household refrigerator. Existing condenser has a problem which occupies large space in the machine room of the refrigerator. Plain fin-flat tube condenser was designed and manufactured in this study. The volume of plain fin-flat tube condenser decreased by 69% compared with that of existing condenser. Performance tests of the new developed condenser and the refrigerator system adopting the condenser were also performed. As a result, heat capacity of the condenser and EER increased by 5.7% and 10.6% respectively.
열교환식 액체 제습기의 LiCl 수용액 헤더 분배에 관한 실험적 연구
문지현(Ji-Hyun Mun),전동순(Dong-Soon Jeon),김선창(Seon-Chang Kim),김영률(Young-Lyoul Kim) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12
An experimental investigation was carried out to examine the LiCl aqueous solution header distribution performance for heat exchanger type liquid dehumidifier. Design factors were diameter of the semicircular channels(D<SUB>ch</SUB>) and the number of the semicircular channels(N<SUB>ch</SUB>). Diameter of the semicircular channels was 0.3 mm and 0.5 mm. And the number of the semicircular channels was 40 ea and 80 ea. The inlet temperature and concentration of LiCl aqueous solution have been fixed at 43.8℃ and 43% respectively. And mass flow-rate was 0.1 g/s and 0.7 g/s. Mass flow-rate ratios were measured at 10 points by using the tube tray and graduated cylinder. And the standard deviation of mass flow-rate ratios was selected to define the distribution performance. As a result, the higher the mass flow-rate, the smaller the standard deviation of mass flow-rate ratios. Also, standard deviation of mass flow-rate ratios was observed within the range from 0.29 to 1.23.
문지현 ( Ji Hyun Mun ),나현신 ( Hyun Shin Na ) 한국패션비즈니스학회 2010 패션 비즈니스 Vol.14 No.5
The market in the 21st century has drastically changed due to the advances of digital technology. This could be represented by the key words prosumer, do-it-yourself, mass customization, and so on. The net generation is in the center of change and nowadays teenage groups wearing school uniforms is a part of this generation. Therefore the current school uniform hardly fits their tastes and demands. This study aims to provide the fundamental information for developing the school uniforms for the net generation based on the study of the characteristic of net generation and questionnaires targeted at high school students regarding the current school uniform.