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수직 환형유로 내 과냉각비등 유동 가시화 및 국소 유동인자 측정 실험 연구
박일웅,강인엽,이연건 대한기계학회 2022 大韓機械學會論文集B Vol.46 No.10
A series of experiments were conducted to investigate flow structures and local temperatures in subcooled boiling in a vertical heated channel at a pressure approximately equal to atmospheric pressure. The test section was the internally heated annulus with an effective heated length of 2 m and hydraulic diameter of 20 mm; the heat flux, mass flux, inlet subcooling degree, and exit pressure were adjusted in the test. The boiling flow phenomena were recorded with a high-speed camera for three flow conditions. In addition, local void fraction profiles that had been measured by optical fiber probes were identified. Furthermore, the surface temperatures of the heater rod were obtained, and the radial distributions of fluid temperature were measured by traversing precisely the sensing tip of the thermocouples. 본 연구에서는 대기압 주변 조건에서 수직 가열채널 내 과냉각비등 유동장의 유동 구조를 분석하고, 국소 온도를 측정하기 위한 실험을 수행하였다. 유효 가열 길이 2 m, 수력 직경 20 mm의 내측 가열 환형유로를 갖는 비등 실험장치를 이용하여 열속, 질량속, 입구 과냉각도, 그리고 시험부 출구 압력을 제어하였다. 세 가지 유동 조건에 대해 시험부에 높이에 따라 세 군데에 설치된 가시창을 통해 과냉각비등 유동을 초고속 카메라로 촬영하였으며, 광섬유 프로브를 이용하여 측정된 국소 기포율 분포와 연계하여 유동 구조를 분석하였다. 또한, 온도 센서의 측온접점을 이송함으로써 유체 온도의 반경 방향 프로파일을 정밀 측정하였으며, 향후 벽면비등 모델의 검증에 유용하게 활용될 수 있는 가열봉의 외벽온도를 얻었다.
과냉각 유동비등 조건에서 평가된 사각 히트싱크의 유동 불안정 시작점
임지환(Ji Hwan Lim),오훈교(Hoongyo Oh),박민규(Minkyu Park),이수원(Su Won Lee),황돈관(Donkoan Hwang),김무환(Moo Hwan Kim),조항진(HangJin Jo) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
Onset of flow instability (OFI), a phenomenon that rapidly fluctuates the system due to the generation of many vapors inside the heat sink, is a major threat to the operation of the cooling system. However, studies evaluating OFI under one-side high heat load conditions are very scarce. Therefore, in this study, the OFI of a rectangular heat sink was investigated through a sub-cooled flow boiling experiment. In addition, the effects of pressure, flow, and sub-cooling on OFI heat flux were analyzed. Finally, the accuracy of OFI correlations developed under the existing sub-cooled flow boiling condition was evaluated. Unfortunately, the existing correlations showed a high error rate because they were developed based on mini or micro-channel. This shows the need to develop a new correlation suitable for one-side high heat load conditions.
마이크로채널에서의 유동비등 열전달과 2 상 유동 압력강하
허철(Cheol Huh),김무환(Moo Hwan Kim) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
With a single horizontal rectangular microchannel and a series of microheaters made with Micro-Electro-Mechanical Systems (MEMS) technique, two-phase pressure drop and local flow boiling heat transfer of deionized water were investigated. The test microchannel had a hydraulic diameter of 100 ㎛ and a length of 40 ㎜. Tests were performed for mass fluxes of 90 to 267 ㎏/㎡s and heat fluxes of 100 to 700 ㎾/㎡. The experimental local flow boiling heat transfer coefficients and two-phase frictional pressure gradient were evaluated and the effects of heat flux, mass flux, and vapor quality were studied, respectively. Both experimental data were compared with existing correlations. Most correlations did not provide reliable predictions except under certain limited conditions.
2 상 마이크로채널 히트싱크에서의 유동 양식과 비등 열전달계수
허철(Cheol Huh),김무환(Moo Hwan Kim) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.11
The present paper proposes a baseline for new flow boiling heat transfer coefficient correlation in a microchannel heat sink. An experimental measurement and evaluation of boiling heat transfer coefficients were carried out using a horizontal rectangular microchannel heat sink having a hydraulic diameter of 100 ㎛. Test results showed that the measured boiling heat transfer coefficients had week dependence on quality at bubble/elongated bubble flow and no dependence on mass flux at elongated slug/annular flow. A modified new flow boiling heat transfer coefficient correlation using the heat flux, surface tension and hydraulic diameter is proposed. The suggested correlation shows good predictions capability and provides a design guide line for the microchannel heat sinks.
김병주,정은수,손병후 대한설비공학회 2004 설비공학 논문집 Vol.16 No.10
An experimental study on saturated flow boiling heat transfer of R113 was performed in a vertical narrow rectangular channel with offset strip fins. Two-phase pressure gradients and boiling heat transfer coefficients in an electrically heated test section were measured in the range of quality 0∼0.6, mass flux 17∼43 kg/m2s, and heat flux of 500∼3,000 W/m2. Two-phase friction multipliers were determined as a function of Lockhart-Martinelli parameter. Local boiling heat transfer coefficients were analysed in terms of mass flux, heat flux and local vapor quality. Correlation for boiling heat transfer coefficients was proposed, which was in good agreement with experimental data.
김병주(Byong Joo Kim),김건일(Geonil Kim) 대한설비공학회 2011 설비공학 논문집 Vol.23 No.11
Characteristics of flow boiling heat transfer in microchannels were investigated experimentally. The microchannels consisted of 9 parallel trapezoidal channels with each channel having 205 m of bottom width, 800 m of depth, 3.6 o of sidewall angle, and 7 cm of length. Tests were performed with R113 over a mass velocity range of 150~920 kg/m 2 s, heat flux of 10~100 kW/m 2 and inlet pressures of 105~195 kPa. Flow boiling heat transfer coefficient in microchannels was found to be dominated by heat-flux. However the effect of mass velocity was not significant. Contrary to macrochannel trends, the heat transfer coefficient was shown to decrease with increasing thermodynamic equilibrium quality. A new correlation suitable for predicting flow boiling heat transfer coefficient was developed based on the laminar single-phase heat transfer coefficient and the nucleate boiling dominant equation. Comparison with the experimental data showed good agreement.