• Title/Summary/Keyword: Pool boiling

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나선형 튜브 열교환 방식의 포화 상태 액체질소의 비등열전달 특성에 대한 실험적 연구 (Experimental Research of Characteristic of Pool Boiling Heat Transfer of Saturated Liquid Nitrogen with Helical Coil Type Heat Exchanger)

  • 서만수;이지성;김정한;강선일
    • 한국추진공학회지
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    • 제24권3호
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    • pp.59-70
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    • 2020
  • 본 논문에서는 기존 적층형 배관의 총 열전달 계수 경험식을 활용할 때 발생하는 한계점을 해결하고자, 외부 총 열전달 계수의 강제 대류 열전달 계수 항을 독립적으로 도출하는 간소화된 모델링을 제안하고, 이를 극저온 환경의 실험 결과로 확인하였다. 액체 산소 냉각 나선형 열교환기가 액체 질소와 열교환하는 실험 장치를 구성하고 열교환기의 열전달량을 계측하여, 외부 총 열전달 계수를 도출하였다. 측정된 외부 총 열전달 계수가 모델링으로 예측 곡선과 일치함을 확인하였다.

초음파 진동에 의한 대류 및 비등 열전달 촉진 원리에 관한 연구 (Mechanisms of Convective and Boiling Heat Transfer Enhancement via Ultrasonic Vibration)

  • 김이구;김호영;강승민;강병하;이진호
    • 대한기계학회논문집B
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    • 제27권5호
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    • pp.612-619
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    • 2003
  • This work experimentally studies the fundamental mechanisms by which the ultrasonic vibration enhances convection and pool boiling heat transfer. A thin platinum wire is used as both a heat source and a temperature sensor. A high speed video imaging system is employed to observe the behavior of cavitation and thermal bubbles. It is found that when the liquid temperature is below its boiling point, cavitation takes place due to ultrasonic vibration while cavitation disappears when the liquid reaches the boiling point. Moreover, when the gas dissolved in liquid is removed by pre-degassing, the cavitation arises only locally. Depending on the liquid temperature, heat transfer rates in convection, subcooled boiling and saturated boiling regimes are examined. In convection heat transfer regime, fully agitated cavitation is the most efficient heat transfer enhancement mechanism. Subcooled boiling is most enhanced when tile local cavitation is induced after degassing. In saturated boiling regime, acoustic pressure is shown to be a dominant heat transfer enhancement mechanism.

국부적인 발열부분을 가진 표면에서의 잠김 비등열전달 -전자부품 액침 냉각에서의 응용- (Boiling Heat Transfer from a locally Heated Surface -A Simulated Electronic Device under Liquid Immersion Cooling-)

  • 하광순;최상민
    • 대한기계학회논문집
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    • 제15권2호
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    • pp.685-692
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    • 1991
  • The pool boiling behavior of a heated surface has been investigated experimentally, focusing on the cases when only a part of the contact surface is heated. Characteristic boiling curves are obtained with circular metal surface test pieces heated below while immersed in Refrigerant-113. Locally heated test pieces are fabricated by inserting a heating block at the center inside a larger conducting block. Overall heat transfer rates are measured while the experimental conditions are systematically varied. The local temperature profiles along the radius are measured for conducting blocks. It is found that the conjugated boiling condition exists and the total heat fluxes should be correlated to a suitably defined temperature difference.

평활관군 내 R-123/오일의 흐름비등 (Flow Boiling of R-123/Oil Mixture in a Plain Tube Bundle)

  • 이진욱;이재호;김내현
    • 설비공학논문집
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    • 제22권10호
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    • pp.704-709
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    • 2010
  • The effect of oil on flow boiling of R-123 in a plain tube bundles was experimentally investigated for a range of quality and heat flux. It is shown that the heat transfer coefficient decreased as the oil concentration increased. Comparison with the previous pool boiling data reveals that the reduction of heat transfer coefficient by oil is more pronounced in pool boiling, and the difference increased with the increase of oil concentration and heat flux. Within the experimental range, the variation of mass flux or quality has negligible effect on the heat transfer coefficient.

하부 유로단면적이 수직 환상공간 내부 풀비등열전달에 미치는 영향 (Effects of Bottom Inflow Area on Pool Boiling Heat Transfer in a Vertical Annulus)

  • 강명기;유주식
    • 대한기계학회논문집B
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    • 제31권7호
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    • pp.604-610
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    • 2007
  • To investigate effects of the inflow area on pool boiling heat transfer in a vertical annulus, the inflow area at its bottom has been changed from 0 to $1060.3mm^2$. For the test, a heated tube of 34 mm diameter and water at atmospheric pressure have been used. To elucidate effects of the inflow area on heat transfer results of the annulus are compared to the data of a single unrestricted tube. The change in the inflow area at the bottom of the annulus results in much variation in heat transfer coefficients. When the inflow area is $113.1mm^2$ the deterioration point of heat transfer coefficients gets moved up to the higher heat fluxes because of the convective flow at the bottom regions.

Local Pool Boiling Coefficients on Horizontal Tubes

  • Kang Myeong-Gie
    • Journal of Mechanical Science and Technology
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    • 제19권3호
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    • pp.860-869
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    • 2005
  • Local pool boiling on the outside and inside surfaces of a 51 mm diameter tube in horizontal direction has been studied experimentally in saturated water at atmospheric pressure. Much variation in local heat transfer coefficients was observed along the tube periphery. On the outside surface the maximum and the minimum are observed at ${\theta}=45^{\circ}$ and $180^{\circ}$, respectively. However, on the inside surface only the minimum was observed at ${\theta}=0^{\circ}$. Major mechanisms on the outside surface are liquid agitation and bubble coalescence while those on the inside surface are micro layer evaporation and liquid agitation. As the heat flux increases liquid agitation gets effective both on outside and inside surfaces. The local coefficients measured at ${\theta}=90^{\circ}$ can be recommended as the representative values of both outside and inside surfaces.

액체과냉도가 하부폐쇄 수직환상공간 내부의 풀비등 열전달에 미치는 영향 (Effect of Liquid Subcooling on Pool Boiling Heat Transfer in Vertical Annuli with Closed Bottoms)

  • 강명기
    • 대한기계학회논문집B
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    • 제29권2호
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    • pp.239-246
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    • 2005
  • Effects of subcooling on pool boiling heat transfer in vertical annuli with closed bottoms have been investigated experimentally. For the test, a tube of 19.1mm diameter and the water at atmospheric pressure have been used. Three annular gaps of 7.05, 18.15, and 28.20 have been tested in the subcooled water and results of the annuli are compared with the data of a single unrestricted tube. The increase in pool subcooling results in much change in heat transfer coefficients. At highly subcooled regions, heat transfer coefficients for the annuli are much larger than those of a single tube. As the heat flux increases and subcooling decrease, a deterioration of heat transfer coefficients is observed at the annulus of 7.05mm gap. Single-phase natural convection and liquid agitation are the governing mechanisms for the single tube while liquid agitation and bubble coalescence are the major factors at the bottom closed annuli.

EFFECTS OF GEOMETRIC PARAMETERS ON NUCLEATE POOL BOILING OF SATURATED WATER IN VERTICAL ANNULI

  • Kang, Myeong-Gie
    • Nuclear Engineering and Technology
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    • 제41권3호
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    • pp.271-278
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    • 2009
  • Nucleate pool boiling of water in vertical annuli at atmospheric pressure has been studied experimentally and two empirical correlations have been suggested to obtain effects of geometric parameters on heat transfer. Data of the present and the previous tests range over a tube length of 0.50-0.57 m, a diameter of 16.5-34.0 mm, and an annular gap size of 3.7-44.3 mm. Through the analysis, tube bottom confinement (open or closed) has been investigated, as well. The developed correlations predict experimental data within a ${\pm}25%$ error bound. It has been identified that effects of the diameter and the length of heated tubes as well as the annular gap size should be counted into the analyses to estimate heat transfer coefficients accurately.

수직 환상 공간 내부의 풀핵비등 열전달 (Nucleate Pool Boiling Heat Transfer in Vertical Annuli)

  • 강명기
    • 대한기계학회논문집B
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    • 제25권8호
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    • pp.1113-1121
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    • 2001
  • Effects of gap sizes(3.9 and 15mm) of vertical annuli and the bottom blockage on the nucleate pool boiling heat transfer at atmospheric pressure condition have been examined experimentally, and the results were compared to those with a single tube without confinement. The annular geometry resulted in significant increase in heat transfer coefficient. The effect is much enhanced with the bottom blockage. The heat transfer coefficient for the closed bottom condition is three times greater than the unconfined tube at 30kW/㎡ when the gap size is 3.9mm. However, with further increase of the heat flux much more than 70kW/㎡, all these effects were diminished.

POOL BOILING HEAT TRANSFER IN A VERTICAL ANNULUS WITH A NARROWER UPSIDE GAP

  • Kang, Myeong-Gie
    • Nuclear Engineering and Technology
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    • 제41권10호
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    • pp.1285-1292
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    • 2009
  • The effects of the narrowed upside gap on nucleate pool boiling heat transfer in a vertical annulus were investigated experimentally. For the study, a stainless steel tube with a diameter of 25.4 mm and saturated water that kept an atmospheric condition were used. The ratio between the gaps measured at the upper and the lower regions of the annulus ranged from 0.18 to 1. Two different lengths of the modified gap also were investigated. The change in heat transfer due to the modified gap became evident as the gap ratio decreased and the length of the gap increased. As the gap ratio became less than 0.51, a significant decrease in heat transfer was observed compared to the plain annulus. The longer gap size resulted in an additional decrease in heat transfer. The major cause for the tendency was attributed to the formation of lumped bubbles around the upper region of the annulus followed by the increased flow friction between the fluid and the surface around the modified gap.