• 에너지공학
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• 제23권3호
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• pp.27-35
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• 2014

본 연구에서는 기존에 알려진 수직 원형관내 혼합대류 유동영역지도에 대하여 원 문헌의 분석과 재구성을 통해 지도의 유효성 검토를 수행하였다. 지도를 구성하는 원 문헌을 수집하여 내용을 정리하였고 조사한 데이터와 대류열전달 상관식을 활용하여 독립적으로 지도를 재구성하고 기존의 지도와 비교하였다. 재구성한 지도에는 혼합대류 영역이 곡선이 아니라 직선으로 나타났으며 천이영역을 나타내는 것은 재현되지 않았다. 일부 데이터만 포함된 기존의 지도와 달리 재구성 지도에는 상당히 많은 양의 데이터가 포함됐다. 기존의 유동영역지도는 활용된 데이터가 선택적으로 사용되었고, 혼합대류와 천이영역을 나타내는 실선 대해 언급되지 않았으며 불확실도 분석을 통한 정보를 제공하지 않았기 때문에 신뢰할 수 없다고 판단된다. Metais와 Eckert의 연구 이후, 혼합대류에 관한 많은 연구가 수행되었으나 대류의 유동영역을 구분하는 방법으로 기존의 지도가 지금까지 활용되고 있다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1075-1079
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• 2004

Steam was vertically discharged into water through mini nozzles of various diameters (d=0.115, 0.520, 1.55mm). The condensation was observed and categorized into several types of condensation regimes for each of the nozzles. Compared with the regimes in the previous researches, the regimes of 'internal necking with attached bubble' and 'internal chug with detached bubble' were newly observed. Depending on a nozzle, some regimes expanded, shrank, or moved in the regime map. For the nozzle of 1.55mm, the regime map was similar to Chan and Lee (1982) except that the regime of 'internal chug' was not observed. For the nozzle of 0.115mm, the regime of 'internal chug' appeared even at high pool temperature.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2006년도 전기학술대회논문집
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• pp.59-60
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• 2006

Some useful flow regime data are obtained from the experiments using the flight producing hyper-gravity(2g) conditions and on ground(1g) with the identical flow conditions. The flow regime data obtained at 1g and 2g conditions are compared with new dimensionless flow regime map using Fr, Bo and We number related with gravity, surface tension and inertia force.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.153-154
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• 2002

Wear map of silver coatings on AISI 52100 has been constructed to delineate the wear transition behavior with the change in operating conditions in various environments. Three main regimes were clearly identified: (i) elastic/plastic deformation of silver coating without failure. (ii) mild wear regime after initial failure of silver coating and (iii) severe wear regime. In the mild wear regime, the contact surfaces were covered with transfer layers of agglomerated wear particles. The transfer layer acted as a protective layer and resulted in low friction even after the initial failure of the coated films, whose characteristics were strongly dependent on both the operating and environmental conditions. Also, the existence of the critical sliding speed, above which no transfer layer was able to form, was discussed in the work.

• Journal of Mechanical Science and Technology
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• 제20권8호
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• pp.1275-1283
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• 2006

Condensation heat transfer coefficients in a 7.92 mm inside diameter copper smooth tube were obtained experimentally for R22, R134a, and R410A. Working conditions were in the range of $30-40^{\circ}C$ condensation temperature, $95-410 kg/m^2s$ mass flux, and 0.15-0.85 vapor quality. The experimental data were compared with the eight existing correlations for an annular flow regime. Based on the heat-momentum analogy, a condensation heat transfer coefficients correlation for the annular flow regime was developed. The Breber et al. flow regime map was used to discern flow pattern and the Muller-Steinhagen & Heck pressure drop correlation was used for the term of the proposed correlation. The proposed correlation provided the best predicted performance compared to the eight existing correlations and its root mean square deviation was less than 8.7%.

• Nuclear Engineering and Technology
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• 제54권2호
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• pp.546-553
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• 2022

Narrow rectangular channels are employed in nuclear research reactors that use plate-type nuclear fuels, high heat-flux compact heat exchangers, and high-performance micro-electronics cooling systems. Two-phase flow in narrow rectangular channels is important, and it needs to be better understood because it is considerably different than that in round tubes. In this study, mechanistic models were developed for the flow regime transition criteria for various flow regimes in co-current air-water two-phase flow for vertical downward flow inside a narrow rectangular channel. The newly developed criteria were compared to a flow regime map of downward air-water two-phase flow inside a narrow rectangular channel with a 2.35-mm gap width under ambient temperature and pressure conditions. Overall, the proposed model showed good agreement with the experimental data.

• 한국에너지공학회:학술대회논문집
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• 한국에너지공학회 2003년도 추계 학술발표회 논문집
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• pp.159-164
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• 2003

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1998년도 추계학술발표회요약집
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• pp.137-137
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• 1998

• Journal of Mechanical Science and Technology
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• 제15권7호
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• pp.941-950
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• 2001

A study of counter-current two-phase flow in narrow rectangular channels has been performed. Two-phase flow regimes were experimentally investigated in a 760mm long and 100mm wide test section with 2.0 and 5.0mm gap widths. The resulting flow regime maps were compared with the existing transition criteria. The experimental data and the transition criteria of the models showed relatively good agreement. However, the discrepancies between the experimental data and the model predictions of the flow regime transition become pronounced as the gap width increased. As the gap width increased the transition gas superficial velocities increased. The critical void fraction for the bubbly-to-slug transition was observed to be about 0.25. The two-phase distribution parameter for the slug flow was larger for the narrower channel. The uncertainties in the distribution parameter could lead to a disagreement in slug-to-churn transition between the experimental findings and the transition criteria. For the transition from churn to annular flow the effect of liquid superficial velocity was found to be insignificant.

• 한국전산유체공학회지
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• 제17권1호
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• pp.86-93
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• 2012

A numerical investigation is conducted to search for the optimal flow rate for a rotating-disk chemical vapor decomposition reactor operating at a high temperature and a low pressure. The flow of a gas mixture supplied into the reactor is modeled by a laminar flow of an ideal gas obeying the kinetic theory. The axisymmetric two-dimensional flow in the reactor is simulated by employing a CFD package FLUENT. With operating pressure and temperature fixed, numerical computations are performed by varying rotation rate and flow rate. Examination of the structures of flow and thermal fields leads to a flow regime diagram illustrating that there are a stable plug-like flow regime and a few unfavorable flow regimes induced by mass unbalance or buoyancy. The criterion for sustaining a plug-like flow regime is discussed based on a theoretical scaling argument. Interpretation of the flow regime map suggests that a favorable flow is attainable with a minimum flow rate at the smallest rotation rate guaranteeing the dominance of rotation effects over buoyancy.