• Nuclear Engineering and Technology
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• 제33권4호
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• pp.397-408
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• 2001

A marine reactor shows very different thermal-hydraulic characteristics compared to a land- based reactor. Especially, study on the variation of flow field due to ship motions such as inclination, heaving and rolling is essential since the flow variation has great influence on the reactor cooling capability. In this study, the natural circulation characteristics of integral type marine reactor with modular steam generators were analyzed using computational fluid dynamics code, CFX-4, for inclined conditions. The numerical analyses are performed using the results of natural circulation experiments for integral reactor which are already conducted at Seoul National University. From the results, it was found that the flow rate in the ascending steam generator cassettes increases due to buoyancy effect. Due to this flow variation, temperature difference occurs at the outlets of the each steam generator cassettes. which is mitigated through downcomer by thermal mixing. Also, around the upper pressure header the flow from descending hot leg goes up to the ascending steam generator cassettes due to large natural circulation driving force in ascending steam generator cassettes. From this result, the increase of How rate in the ascending steam generator cassettes could be understood qualitatively.

• 대한기계학회논문집B
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• 제35권2호
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• pp.145-152
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• 2011

컴퓨터용 방열기의 헤더부 튜브 삽입길이에 따른 열전달 및 유동특성을 파악하기 위하여 수치해석을 수행하였다. 튜브삽입길이 0, 5, 10mm의 3가지 해석모델을 선정하였으며 해석결과의 타당성 검증을 위해 삽입길이가 5mm 일 때 샘플을 실험결과와 비교하였다. 유량분배의 균일성을 판단하기 위해 각 튜브에서 유량비를 분석하였고, 유량분배 특성을 정량적으로 비교하기 위하여 유량균일도를 정의하였다. 해석결과를 통하여 모든 샘플에서 열전달량과 압력강하는 질량유량이 증가함에 따라 점차 증가하였으며, 튜브삽입길이가 10mm(h/D=0.5)인 샘플 3의 열전달량과 압력강하는 가장 크게 나타났다. 유량균일도(Stotal )를 조사하였을 때 튜브삽입길이가 0mm(h/D=0)인 샘플 1이 0.0052로 가장 균일한 유량분포를 보였다.

• 설비공학논문집
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• 제18권12호
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• pp.1007-1016
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• 2006

Although the advance in electronic technology enables a large number of circuity to be packed in a small volume, it is simultaneously required to remove the high heat load produced by them. In this study, the heat transfer and pressure drop characteristics of a mini-channel heat exchanger, which is designed for liquid cooling of electronic components, are investigated by varying operating conditions. Water and FC-72 were used as working fluids. The mini-channel heat exchanger was made with circular shape channels having din-meters of 2, 3, and 4 mm in regular intervals, and the channel length was 100 mm. The header and inlet guide pathway to provide uniform inflow were attached at the inlet of the test section. Copper block including the heaters was attached at the sidewall of the test section as a heat source, which provided the heat flux from 5 to $15W/cm^2$. The entrance effects enhanced the heat transfer coefficient in the mini-channel significantly. In addition, the single-phase pressure drop in the mini-channel was very similar to that predicted by the laminar flow correlation except that the transition Re decreased due to flow instability in the entrance region.