• 제목/요약/키워드: Downward-Facing Boiling

검색결과 16건 처리시간 0.024초

Experimental study of bubble behaviors and CHF on printed circuit board (PCB) in saturated pool water at various inclination angles

  • Tanjung, Elvira F.;Alunda, Bernard O.;Lee, Yong Joong;Jo, Daeseong
    • Nuclear Engineering and Technology
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    • 제50권7호
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    • pp.1068-1078
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    • 2018
  • Experiments were performed to investigate bubble behaviors and pool boiling Critical Heat Flux (CHF) on a thin flat rectangular copper heater fabricated on Printed Circuit Board (PCB), at various inclination angles. The surface inclination angles were $0^{\circ}$, $45^{\circ}$, $90^{\circ}$, $135^{\circ}$, and $180^{\circ}$. Results showed the Onset of Nucleate Boiling (ONB) heat flux increased with increasing heater orientation from $0^{\circ}$ to $90^{\circ}$, while early ONB occurred when the heater faced downwards ($135^{\circ}$ and $180^{\circ}$). The nucleate boiling was observed to be unstable at low heat flux (1-21% of CHF) and changed into typical boiling when the heat flux was above 21% of CHF. The result shows the CHF decreased with increasing heater orientation from $0^{\circ}$ to $180^{\circ}$. In addition, the bubble departure diameter at the heater facing upwards ($0^{\circ}$, $45^{\circ}$, and $90^{\circ}$) was more prominent compared to that of the heater facing downward ($135^{\circ}$). The nucleation site density also observed increased with increasing heat flux. Moreover, the departed bubbles with larger size were observed to require a longer time to re-heat and activate new nucleation sites. These results proved that the ONB, CHF, and bubble dynamics were strongly dependent on the heater surface orientation.

하향 평판에서의 풀비등 임계열유속에 관한 실험적 연구 (An Experimental Study of the Pool-Boiling CHF on Downward-Facing Plates)

  • Yang, Soo-Hyung;Baek, Won-Pil;Chang, Soon-Heung
    • Nuclear Engineering and Technology
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    • 제26권4호
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    • pp.493-501
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    • 1994
  • 하향 가열 평판에서의 풀비등 임계열유속 실험이 수행되었다. 이는 원자로에서의 노심용융사고 발생시 그 결과를 완화시키는 한 방법으로 고려되고 있는 원자로용기 외부 냉각 (Ex-Vessel Flooding) 개념과 연관된다. 대기압하, 포화상태 물에서 너비가 다른 두 개의 평판 (20mm$\times$200mm및 25mm$\times$200mm)을 이용, -90$^{\circ}$(평형 하향), -88$^{\circ}$, -86$^{\circ}$, -84$^{\circ}$, -60$^{\circ}$와 -40$^{\circ}$의 경사 가도에 대한 임계열유속이 측정되었다. 실험 결과 너비가 큰 평판에서, 그리고 수직 위치로부터의 각도가 클수록 임계열유속이 낮게 나타났다. 이는 가열면에서 발생된 기포들의 이탈이 어려워지기 때문인 것으로 판단된다. 경사가도에 따른 전체적 인 임계열유속 경향은 기존 연구들과 대체로 일치하나, 임계열유속 감소율이 변화하는 천이 각도가 -80$^{\circ}$ 근방에서 발견되었다.

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초음파에 의한 평판에서의 임계열유속 증진에 대한 실험적 연구 (Experimental Study on CHF Enhancement of Plate by Ultrasonic)

  • 김대훈;권영철;정지환
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2003년도 춘계학술대회
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    • pp.1512-1517
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    • 2003
  • Augmentation of CHF by ultrasonic is experimentally studied under subcooling pool boiling condition. Experiment is carried out for downward-facing plate with and without the ultrasonic. The working fluid is distilled water. Experimental apparatus is composed of a bath, power supply, test section, ultrasonic generator, DAQ system. Experiment is performed with the subcooling temperature of $5^{\circ}C$, $20^{\circ}C$, $40^{\circ}C$ and the inclined angle of $0^{\circ}$, $10^{\circ}$, $20^{\circ}$, $45^{\circ}$, 90. From the experimental results, it is found that ultrasonic effect enhances CHF of the downward-facing plate. As increasing the degree of subcooling, the rate of CHF increase is enhanced. As increasing the inclined angle, the rate of CHF increase decreases. Also, we can see that the heat transfer mechanism of CHF augmentation is closely connected with the dynamic behavior of bubble generation and departure.

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EXPERIMENTAL STUDY OF CRITICAL HEAT FLUX WITH ALUMINA-WATER NANOFLUIDS IN DOWNWARD-FACING CHANNELS FOR IN-VESSEL RETENTION APPLICATIONS

  • Dewitt, G.;Mckrell, T.;Buongiorno, J.;Hu, L.W.;Park, R.J.
    • Nuclear Engineering and Technology
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    • 제45권3호
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    • pp.335-346
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    • 2013
  • The Critical Heat Flux (CHF) of water with dispersed alumina nanoparticles was measured for the geometry and flow conditions relevant to the In-Vessel Retention (IVR) situation which can occur during core melting sequences in certain advanced Light Water Reactors (LWRs). CHF measurements were conducted in a flow boiling loop featuring a test section designed to be thermal-hydraulically similar to the vessel/insulation gap in the Westinghouse AP1000 plant. The effects of orientation angle, pressure, mass flux, fluid type, boiling time, surface material, and surface state were investigated. Results for water-based nanofluids with alumina nanoparticles (0.001% by volume) on stainless steel surface indicate an average 70% CHF enhancement with a range of 17% to 108% depending on the specific flow conditions expected for IVR. Experiments also indicate that only about thirty minutes of boiling time (which drives nanoparticle deposition) are needed to obtain substantial CHF enhancement with nanofluids.

충돌수분류(衝突水噴流)에 의한 서브쿨 Burnout열류속(熱流束)에 관한 연구 (Subcooled Burnout Heat Flux on a Heated Surface with Impinging Water Jet)

  • 엄기찬;이종수;박성연
    • 설비공학논문집
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    • 제8권4호
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    • pp.527-536
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    • 1996
  • Convective nucleate boiling and burnout heat flux have been studied on a flat, downward facing, constant heat flux surface cooled by an impinging water jet. The tests are progressed from low, nonboiling power to high, burnout heat flux power. The jet velocity and the subcooling do not affect the nucleate boiling curve of $q{\sim}{\Delta}T_{sat}$ diagram, but the supplementary water height affects the curve. For the case of dimensionless height of supplementary water S/D=1, the boiling curve shift to the heigher heat flux than that of S/D=0 or S/D=2. Burnout heat flux is enhanced with increasing jet velocity and subcooling. Also. by using the supplementary water(S/D=1 or S/D=2), burnout heat flux is larger than that of the simple water jet(S/D=0). A generalized correlation for the burnout heat flux data in the present boiling system with an impinging water jet is successfully evolved.

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Effect of Inclination Angle and Size of Heated Surface on Pool Boiling CHF

  • Yang, Soo-Hyung;Baek, Won-Pil;Chang, Soon-Heung
    • 한국원자력학회:학술대회논문집
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    • 한국원자력학회 1999년도 춘계학술발표회요약집
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    • pp.155-155
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    • 1999
  • Pool boiling critical heat flux (CHF) have been investigated using plate type test sections with different widths (3 cm & 4 cm) and lengths (10 cm, IS cm & 20 cm) under various incli- nation angles. As the inclination angle increases from $0^{\circ}$ (horizontally facing downward plate) to $30^{\circ}$, CHF sharply increases. After that angle, CHF gradually increases with the increase of the inclination angle. There must be a transition angle between $0^{\circ}$ and $30^{\circ}$, at which the CHF increase rate remarkably changes. According to the comparison of present and previous ex- periments, the transition angle may be affected by heater size and increase with the increase of heater size. The size effect of heated surface on CHF is noticeable in the L15 & L20 series and W4 series; however, it seems to be difficult to find the size effect in L10 series and W3 series.

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