V. Conclusions and Recommendations
5.2 Recommendations
１２４
5.1.2 Quenching Performance Enhancement of SiC and GO Nanofluids
The present works were conducted to investigate the effect of nanofluids on reflood heat transfer in a long vertical tube (1,300 mm in the heating length). When the potential application of nanofluids comes to Emergency Core Cooling System (ECCS), the situation of interest is quenching phenomena of fuel rods during reflood of emergency coolants. The following results are obtained.
- The reflood tests have been performed using SiC/water nanofluid and GO/water nanofluid as a coolant, instead of water. We have observed a more enhanced cooling performance in the case of the nanofluid reflood.
- A more enhanced cooling performance is attributed to a high wettability of a thin layer formed on a heating surface by a deposition of nanoparticles. The enhancing cause of the cooling performance after the quenching experiments using the nanofluids were investigated through macroscopic observation, SEM, contact angles and SEM-EDS of the inner surface of the test section.
- Also, a more enhanced cooling performance is caused to increase of thermal activity related to thermal conductivity and thickness.
- A cooling performance is enhanced more than 20 seconds for SiC/water nanofluid and GO/water nanofluid.
- The increase of quenching velocity for nanofluids is attributed to rupture of vapor blanket/film due to turbulence enhancement.
- At the severe accident, a more enhanced cooling performance can be decreased amount of hydrogen. So, this can reduce the degree of hydrogen explosion.
１２５
observed a more enhanced cooling performance in the case of the nanofluid reflood. As a result, a cooling performance is enhanced more than 20 seconds for SiC/water nanofluid and GO/water nanofluid.
Therefore, effects of SiC/water and GO/water nanofluids show the enhancement of safety margin for advanced nuclear reactors in terms of CHF enhancement and an enhanced quenching performance as shown in Figure 5-3.
Figure 5-3. Effects of SiC/water and GO/water nanofluids on critical heat flux and quenching for advanced nuclear reactors.
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- “2.4 Application of Nanofluids” is reproduced in part with permission of “Lee, S. W.; Park, S. D.;
Kang, S.; Shin, S. H.; Kim, J. H.; Bang, I. C., Feasibility study on molten gallium with suspended nanoparticles for nuclear coolant applications, Nuclear Engineering and Design 2012, 247, 147-159”.
2012 Elsevier B.V. All rights reserved.
- “2.5 Dispersion of Nanoparticles in Liquid” is reproduced in part with permission of “Lee, S. W.;
Park, S. D.; Bang, I. C., Critical heat flux for CuO nanofluid fabricated by pulsed laser ablation differentiating deposition characteristics, Int. J. Heat Mass Transfer 2012, 55, 6908-6915”. 2012 Elsevier Ltd. All rights reserved.
- Chapter III is reproduced in part with permission of “Lee, S. W.; Park, S. D.; Kang, S.; Kim, S. M.;
Seo, H.; Lee, D. W.; Bang, I. C., Critical heat flux enhancement in flow boiling of Al2O3 and SiC nanofluids under low pressure and low flow conditions, Nuclear Engineering and Technology 2012, 44, 429-436” and “Lee, S. W.; Kim, K. M.; Bang, I. C., Study on flow boiling critical heat flux enhancement of graphene oxide/water nanofluid, Int. J. Heat Mass Transfer 2013, 65, 348-356”. 2013 Elsevier Ltd. All rights reserved.
- “4.2.1 Preliminary Experiment: Part 1” is reproduced in part with permission of “Lee, S. W.; Chun, S. Y.; Song, C. H.; Bang, I. C., Effect of nanofluids on reflood heat transfer in a long vertical tube, Int.
J. Heat Mass Transfer 2012, 55, 4766-4771”. 2012 Elsevier Ltd. All rights reserved.
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- “4.2.2 Preliminary Experiment: Part 2” is reproduced in part with permission of “Lee, S. W.; Kim, S.
M.; Park, S. D.; Bang, I. C., Study on the cooling performance of sea salt solution during reflood heat transfer in a long vertical tube, Int. J. Heat Mass Transfer 2013, 60, 105-113”. 2012 Elsevier Ltd. All rights reserved.
１３２
Acknowledgement (감사의 글)
UNIST 에 입학하여 석박사 통합과정을 마치기까지 5 년 가까운 세월이 지나갔습니다.
5 년 동안 많은 일들이 있었습니다. 정말 소중하고 감사한 시간이어서 빨리 지나간 것 같습니다. 또한 함께 해주신 소중한 분들 덕분에 석박사 통합과정을 무사히 마칠 수 있었습니다. 학위를 마친다고 하니 많은 아쉬움이 남습니다만, 연구실에서 실험하고 고민했던 여러 날들이 이젠 소중한 추억들로 간직되면서, 새로운 시작을 앞두고, 박사 학위 논문을 마무리할 수 있도록 많은 분들의 도움이 있어 가능하였기에 이 자리를 빌어 감사의 마음을 전하려 합니다.
우선 석박사 통합과정 내내 실험 및 코드에 대해서 관심과 조언을 아끼지 않으시고, 열의를 다해 지도해주시고, 사랑과 관심을 베풀어 주시며, 올바른 가르침으로 저를 이끌어 주신 방인철 교수님께 머리 숙여 진심으로 감사를 드립니다. 아직까지 부족한 점이 많아 죄송스럽기만 합니다. 그 동안 배운 가르침을 바탕으로 발전하는 모습을 보일 수 있도록 노력할 것입니다. 귀중한 시간을 내어, 논문이 나아가야 할 방향과 부족한 부분에 대해 세심한 가르침과 꾸준한 지도로 격려해주셨던 최기용 박사님, 허선 박사님, 김지현 교수님, 박형욱 교수님께도 깊이 감사 드립니다.
석박사 통합과정 5년 동안 함께 열심히 연구하고, 즐거운 대학원 생활을 할 수 있도록 이끌어 준 연구실 동료들에게도 고마운 마음을 전합니다. 나보다 한 학기 늦게 들어왔지만, 가끔은 선배처럼 실험하는 것을 도와 주고 조언을 아끼지 않았던 성대, 남은 기간 동안 영어 점수 만들고, 멋진 연구해서 사회에서 보자. 성대랑 같이 들어와 여자 혼자 외롭게 연구한 사라, 성대랑 같이 남은 기간 동안 후배들 잘 챙겨주고, 코드의 대가가 되서 대전에서 보자. 지금은 졸업했지만, 항상 한결 같은 모습으로 묵묵히 연구실
１３３
생활한 성만이, 항상 최선을 다하면 결국 좋은 결실 있을꺼야. 어리지만, 나이 든 형들, 누나 챙겨주느라 고생한 한이, 군대 생활 대신 한다는 마음으로 조금만 더 하고 후배들 잘 챙겨주면 좋은 결과 나올꺼야. 유동비등 임계열유속 및 급랭 실험을 이어 받은 경모, 핵연료 열전도도 실험을 이어 받은 인국이, 경모랑 같이 들어온 성보, 석빈이, 그리고 앞으로 들어올 효, 영신이, 교수님이 조언해 주신데로만 하면 주어진 시간 내에 졸업하고 좋은 곳에 취직할 수 있으니, 대학원 생활 열심히 해. 그리고 힘들면 대전 와서 연락해 술 한 잔 사줄께. 아무것도 없었던 UNIST 원자력공학과에 같이 들어온 상훈이, 종진이, 고생 많았어. 조금만 더 고생해서 사회에서 보자. 지금은 졸업해서 없지만, 대학원 생활하면서 웃음을 잃지 않았던 정석이, 주앙이, 재료랩에 있으면서 실험하는데 많이 도와주었던 경준이, 상일이, 승현이, 태호, 광범아 고마워. 방사선랩에 속해 있는 동한이, 건희, 핵연료랩에 속해 있는 병진이, 주영이, 지현이, 관윤이, 제균이, 태원이, 노심랩에 속해 있는 태우, 현석이, 수영이, 치동이, 지원이 모두 어리숙한 선배 도와주느라 고생 많았어. 싫은 내색 없이 그래핀을 만들어준 인엽아 고마워. 그리고, KAIST 에서 비슷한 연구를 해서 항상 저를 도와줬던 종혁씨, 태승씨, 사회에서 뵈요.
어렸을 때부터 수많은 추억을 함께 했던 친구들, 대학교 친구들, 인화원 동기들, LG 전자 휴대폰 사업부 동기들에게도 고마운 마음을 전합니다.
오늘의 제가 있기까지 모든 정성으로 키워주신 아버지, 어머니의 무한한 은혜에 머리 숙여 진심으로 감사드리며, 언제나 잘한다고 칭찬해 주시고 인자하게 대해주신 장인어른, 장모님께 가슴 깊이 감사의 마음을 전합니다. 물심양면으로 도와주신 후원자이자 커다란 힘이 되어준 누나, 형, 형수님, 처형, 형님들께도 진심으로 깊은 감사의 마음을 전합니다.
많은 응원을 보내주고 이모부, 작은 아빠, 고모부에게 용기를 준 지영이, 준영이, 지호,