• Title/Summary/Keyword: Critical Heat Flux(임계열유속)

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Study on the Oxidation Treatment of Nanoparticles for the Critical Heat Flux (임계열유속 향상을 위한 나노물질의 산화처리에 대한 연구)

  • Kim, Woo-Joong;Jeon, Yong-Han;Kim, Nam-Jin
    • Journal of the Korean Solar Energy Society
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    • v.37 no.6
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    • pp.39-49
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    • 2017
  • Pool boiling, one of the key thermal-hydraulics phenomena, has been widely studied for improving heat transfer efficiencies and safety of nuclear power plants, refrigerating systems, solar-collector heat pipes, and other facilities and equipments. In the present study, the critical heat flux (CHF) and heat-transfer coefficients were tested under the pool-boiling state using graphene M-5 and M-15 nanofluids as well as oxidized graphene M-5 nanofluid. The results showed that the highest CHF increase for both graphene M-5 and M-15 was at the 0.01% volume fraction and, moreover, that the CHF-increase ratio for small-diameter graphene M-5 was higher than that for large-diameter graphene M-15. Also at the 0.01% volume fraction, the oxidized graphene M-5 nanofluid showed a 41.82%-higher CHF-increase ratio and a 26.7%-higher heat-transfer coefficient relative to the same nanofluid without oxidation treatment at the excess temperature where the CHF of distilled water occurs.

Critical Heat Flux in Uniformly Heated Rod Bundle Under Wide Range of System Pressures (광범위한 압력조건하에서 균일 가열 수직 봉다발에서의 임계열유속)

  • Moon, Sang-Ki;Chun, Se-Young;Choi, Ki-Yong
    • Proceedings of the KSME Conference
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    • 2001.06d
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    • pp.195-200
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    • 2001
  • An experimental study on critical heat flux (CHF) has been performed for water flow in a uniformly heated vertical 3 by 3 rod bundle under low flow and a wide range of pressure conditions. The objective of this study is to investigate the parametric trends of CHF with 3 by 3 rod bundle test section where three unheated rods exist. The general trends of the CHF are coincident with previous understandings. At low flow and system pressure above 3 MPa, some critical qualities are larger than 1.0 due to counter-current flow in test sections. Since there is a supply of water to the heated section from unheated section, the maximum CHFs at system pressure between 2 and 4 MPa are not shown.

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Experimental Investigations on Pool Boiling CHE of Nano-Fluids (나노유체의 풀비등 임계열유속에 대한 실험적 연구)

  • Kim, Hyung-Dae;Kim, Moo-Hwan
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.31 no.11
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    • pp.949-956
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    • 2007
  • Pool boiling critical heat flux (CHF) of nanofluids with oxide nanoparticles of $TiO_2$ or $Al_2O_3$ was experimentally investigated under atmospheric pressure. The results showed that a dispersion of oxide nanoparticles significantly enhances the CHF over that of pure water. Moreover it was found that nanoparticles were seriously deposited on the heater surface during pool boiling of nanofluids. CHF of pure water on a nanoparticle-deposited surface, which is produced during the boiling of nanofluids, was not less than that of nanofluids. The result reveals that the CHF enhancement of nanofluids is absolutely attributed to modification of the heater surface by the nanoparticle deposition. Then, the nanoparticle-deposited surface was characterized with parameters closely related to pool boiling CHF, such as surface roughness, contact angle, and capillary wicking. Finally, reason of the CHF enhancement of nanofluids is discussed based on the changes of the parameters.

Experimental Study on the Thermal Mixing and the Critical Heat Flux in the 5${\times}$5 Rod Bundle with the Hybrid Mixing Vane (복합혼합날개를 장착한 5${\times}$5 봉다발에서 부수로 혼합 및 임계열유속 실험 연구)

  • Kang, K.H.;Shin, C.H.;Choo, Y.J.;Youn, Y.J.;Park, J.K.;Moon, S.K.;Chun, S.Y.
    • Proceedings of the KSME Conference
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    • 2007.05b
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    • pp.2303-2308
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    • 2007
  • Experiments were performed to determine the thermal (or turbulent) diffusion coefficient (TDC) and to investigate the critical heat flux (CHF) performance in the 5${\times}$5 rod bundle with 5 unheated rods which are supported by Hybrid Mixing Vane. In this study, HFC-134a fluid was used as working fluid and the fluid temperature were measured in the important subchannels. To determine the TDC value, the measured fluid temperatures were compared with the predicted values obtained from the MATRA code. The best optimized value of ${\beta}$ was found to be 0.02 by considering prediction statistics, i.e., average and standard deviations of the differences between the experimental results and code calculations. Using the best optimized value of ${\beta}$ as 0.02, the MATRA code predicts the test results of the fluid temperature within ${\pm}$1.0 % of error. According to the experimental results on CHF of 5 non-heating guide tubes, the case with non-heating guide tube showed a little good performance in terms of CHF.

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Hydrodynamic effects of heater lengths on pool boiling critical heat flux (히터 길이가 수조비등 임계열유속에 미치는 수력학적 영향)

  • Su Cheong Park;Do Yeon Kim;Seon Ho Choi;Chang Hoon Lee;Younghun Lim;Chi Young Lee;Yeon Won Lee;Dong In Yu
    • Journal of the Korean Society of Visualization
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    • v.21 no.1
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    • pp.67-73
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    • 2023
  • In the study, pool boing critical heat flux (CHF) was experimentally investigated depending on the length of heaters. A smooth silicon oxide surfaces are used as the boiling surfaces. As the results of pool boiling experiments based on distilled water in ambient pressure condition, the CHF decreased as the length of the heater increased. By the high speed imaging, it was shown that the number of vapor columns increased as the length of the heater increased. Comparing the number of vapor columns and the CHF according to the heater length, the change in the CHF according to the heater length was analyzed based on the hydrodynamic instability.