• Journal of Advanced Marine Engineering and Technology
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• v.20 no.4
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• pp.59-69
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• 1996

냉동.공조 및 각종 화학공업에 널리 사용되는 열교환기인 응축기의 고성능화 및 합리적인 설계를 위해서는 냉매의 정확한 응축열전달률 예측과 그 메카니즘 규명이 필수 요건이다. 본 연구에서는 내경 9.7mm, 외경 12.7mm, 길이 1200mm의 수직 이중관 응축기의 압력강하 및 응축열전달특성을 실험적으로 밝혔다. 실험으로부터 Lockart-Martinelli의 상관 관계식을 이용한 수직 응축관내 압력강하 특성을 종래의 실험식들과 비교.검토하고 새로운 압력강하식을 제안하였다. 그리고 종래의 해석방법과는 달리 비환상류 모델을 가정한 해석결과로부터 전 유동양식에 걸쳐 적용할 수 있는 새로운 응축열전달 예측식을 제안하였다.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.20 no.2
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• pp.137-142
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• 1984

An experimental study has been performed on the heat transfer characteristics of condensation by the injecting steam flow in the tube. The comparison between results of experimental data and available data concerning equivalent Reynolds number has studied. As the result, the followings were obtained. 1. The shear stress of the radial direction in the tube when the injecting steam flow was condensed can be written as root($\tau$sub(0)/$\tau$sub(0v))=1+1.46X sub(tt) super(0.20). 2. The effect of the heat transfer in the injecting steam flow was less than the value of equivalent Reynolds number. The reason are the nonuniform fluid film of the axial and radial direction in the tube. 3. The value of N sub(u) by the heat transfer of condensation can be written as N sub(u)=1.08$\times$[{$\rho$ sub(l) d/$\mu$ sub(l)}/{$\delta$+(2.5/P sub(rl)) ln(y sub(i)/$\delta$)}]$\times${$\tau$ sub(0)/ $\rho$ sub(l)} super(1/2).

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.8
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• pp.811-819
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• 2012

An air-cooled condenser is a device that is used for converting steam into condensate by using ambient air. The air-cooled condenser is prone to suffer from a serious explosion when the condensate inside the tubes of a heat exchanger is frozen; in particular, tubes can break during winter. This is primarily due to the structural problem of the tube outlet of an existing conventional air-cooled condenser system, which causes the backflow of residual steam and noncondensable gases. To solve the backflow problem in such condensers, such a system was simulated and a new system was designed and evaluated in this study. The experimental results using the simulated condenser showed the occurrence of freezing because of the backflow inside the tube. On the other hand, no backflow and freezing occurred in the advanced new condenser, and efficient heat exchange occurred.

• Journal of Energy Engineering
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• v.25 no.1
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• pp.56-68
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• 2016

Extensive researches have been carried out for enhancing the safety of nuclear power plants and, especially, the development of passive cooling systems, such as passive containment cooling system (PCCS) and passive residual heat removal system, is increasingly important, where condensation is a crucial heat transfer mechanism. Recently, Ahn & Yun et al. developed a horizontal in-tube condensation heat transfer model as one of the activities for the PCCS development. In this work, we implemented the Ahn & Yun 's condensation heat transfer model into the MARS code and assessed it using the PASCAL experimental data. Based on the results of the assessment, we identified the limitations of the Ahn & Yun 's model and suggested a modified Ahn & Yun 's model, and assessed the model using various experimental data.

• Transactions of the Korean hydrogen and new energy society
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• v.19 no.4
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• pp.331-339
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• 2008

본 논문은 내경 7.73 mm와 5.80mm의 수평관내 프레온계 냉매 R-22와 탄화수소계 냉매 R-290과 600a의 응축 열전달 계수의 실험적 결과를 나타내었다. 실험장치는 압축기, 응축기, 팽창밸브, 증발기 등으로 구성된다. 응축 실험은 질량유속 $35.5{\sim}210.4\;kg/m^2s$이고, 응축온도 40$^{\circ}C$인 조건에서 수행하였다. 주요 결과를 요약하면 다음과 같다. 탄화수소계 냉매 R-290과 R-600a의 평균 열전달 계수는 프레온계 냉매 R-22보다 높게 나타났으며, R-600a의 평균 열전달 계수가 모든 관경에 대해 가장 높게 나타났다. 실험결과와 종래의 상관식을 비교한 결과, 모든 관경과 냉매에 대해 Haraguchi 등의 상관식이 가장 좋은 일치를 보였다. 그 중에서 Cavallini-Zecchin의 상관식은 7.73 mm 관경의 실험데이터와, Dobson 등의 상관식은 내경 5.80 mm 관경의 데이터와 좋은 일치를 보였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.3
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• pp.248-252
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• 2007

This article is related to the possibility for continuous operation of a liquid rocket engine when a portion of cryogenic propellant in the pipeline is vaporized. As a result of experimental studies imitating the formation of vapors in the flow, we confirmed the possibility of full gas-phase condensation in case temperature of cryogenic liquid is lower than it's saturation temperature in the pipeline. Empirical equation allowing to calculate a nonequilibrium condensation region in the steady flow of cryogenic liquid was obtained as a non-dimensional form and the fields of practical application were suggested.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.3
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• pp.271-281
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• 1998

In this study, condensation heat transfer experiments were conducted with two small diameter(ø7.5, ø4.0) tubes. Comparison with existing in-tube condensation heat transfer correlations indicated that the correlations overpredict the present data. For example, Akers correlation overpredicts the data upto 104%. The condensation heat transfer coefficient of the ø4.0 I.D. tube was smaller than that of the ø7.5 I.D tube; at the mass velocity of 300kg/$m^2$s, the difference was 12%. The pressure drop data of the small diameter tubes ware highly(two to six times) overpredicted by the Lockhart-Martinelli correlation. Subcooled forced convection heat transfer test confirmed that Gnielinski's single phase heat transfer correlation predicted the data reasonably well.

• Journal of the Korean Society of Visualization
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• v.14 no.2
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• pp.18-24
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• 2016

This paper presents an experimental investigation to visualize cross-sectional two-phase flow structure and identify liquid-gas interface for condensation of steam at a low mass flux in a slightly inclined tube using the axial-viewing technique, which permits to look directly into flow during condensation of steam. In this technique, two-phase flow is viewed along the axis of a pipe by locating a high-speed video camera in front of a viewer that is fitted at the outlet of the pipe. A short section of the pipe is illuminated and is recorded through the viewer, which is kept free of liquid by mildly introducing air. Experiments were conducted in a pipe of 19.05 mm in inner diameter at atmospheric pressure. Cross-sectional two-phase flow structure is obtained at a steam mass flux of $2.62kg/m^2s$ as a function of steam quality in the range from 0.5 to 0.9. The results show that stratified-wavy flow is a unique flow pattern observed in the scope of the present study. Condensate film thickness, stratification angle and void fraction were measured from the obtained flow structure images. Finally, heat transfer coefficient was calculated using the measurement data and discussed in comparison with existing correlations.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 2003.11a
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• pp.241-246
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• 2003

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.17 no.1
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• pp.83-91
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• 1988