Experimental study of external condensation and flashing-induced instability for passive containment cooling system피동 원자로건물 냉각계통 적용을 위한 외부응축현상 및 증발기인 유동불안정성에 관한 실험적 연구

Cited 0 time in webofscience Cited 0 time in scopus
  • Hit : 313
  • Download : 0
This research investigated the condensation heat transfer and the flashing-induced instability, which were the two primary heat transfer mechanisms of the passive containment cooling system (PCCS) in iPOWER. In the first part, the present research focused on the experimental study of the condensation phenomena with the presence of non-condensable gas on a slender vertical cylinder to apply the PCCS in iPOWER. The condensation experiments were performed using 1m long, 31.75mm diameter tube in 2~5 bar, 0.1~0.8 of air mass fraction, and 10~60$^\circ K$ of wall subcooling degrees. The experimental heat transfer coefficients were increased at the higher pressure conditions. Also, the heat transfer coefficients were increased in the decreasing of the air mass fraction and the wall subcooling degrees. During the experiments, the condensate flow characteristics were observed. In the high condensation rate condition, the high growth rate of drop-wise condensation was taken place in the top surface of the tube. In the middle and bottom of the tube surface, the active rivulet flow was observed. The rivulet flow could increase the condensation driving force. In the low condensation rate condition, the stagnant droplets covered the whole surface of the tube. The rivulet flow effect was indirectly tested by CFD analysis considering the liquid film flow in a CFD model. The CFD analysis showed that the liquid film flow was not significant effects on the heat transfer mechanism, only limited in 20% of enhancement effect. The diffusion layer model with the heat and mass transfer analogy has been widely adopted in the condensation modeling with the presence of non-condensable gas. The film-wise condensation-based diffusion layer model produced about 10~40% of under-prediction in the low wall subcooling degree at the low pressure condition while it predicted the lower heat transfer coefficients by about 50~100% than the experimental data in the low wall subcooling degree at the high pressure condition. As a result, we postulated that the drop-wise condensation was significant effects on the condensation heat transfer. Based on the relevant analysis and the observed phenomena, a new correction factor was empirically introduced into the diffusion layer model to account for rivulet flow-induced condensation enhancement and the drop-wise condensation. It was confirmed that the new diffusion model produced accurate condensation heat transfer coefficients with 4.2% of the mean absolute deviation in comparison with the present experimental data. Also, predictions by the new model were in good agreement with the prototype experimental results with 6.5% of the mean absolute deviation. We can say that the present model has a good prediction capability for the longer tube and the expandability to the low wall subcooling region. In the second part, the present research focused on the development of flashing-induced instability (FII) maps for PCCS in iPOWER. The nodalization of PCCS was modeled using the original plant design data. A series of sensitivity analysis were performed to identify the sensitivities of the nodalization scheme, selection of time step size, and alternative models and correlations in the MARS code. The coarse nodalization of the riser section induced artificial flashing oscillations, and fine nodes were preferred to estimate accurate vapor generation in the riser section. The oscillation patterns were not much sensitive to the selection of the time step size, but marginally sensitive to alternative user options in MARS code. Based on the standard input and the analysis methodology, the stability maps for the PCCS were developed. Typically, the instability was initiated as a sinusoidal instability near the stability boundary, and the sinusoidal instability changed to the intermittent instability at the high phase change number. In respect to the stability boundary criterion, we found out that the calculated equilibrium quality at the exit of the riser as a stability boundary was approximately 1.2% above 5 kW/$m^2$, which was in good agreement with Furuya’s results. However, in a very low heat flux condition, the onset of the FII occurred at the lower equilibrium quality than the experimental data. Also, it was confirmed that inlet throttling reduced the unstable region. However, the design of the inlet restrictor for minimizing FII should be carefully determined by considering its negative effect on the heat removal performance of the natural circulation system.
Advisors
Lee, Jeong Ikresearcher이정익researcherNO, Hee Cheonresearcher노희천researcher
Description
한국과학기술원 :원자력및양자공학과,
Publisher
한국과학기술원
Issue Date
2020
Identifier
325007
Language
eng
Description

학위논문(박사) - 한국과학기술원 : 원자력및양자공학과, 2020.2,[viii, 127 p. :]

Keywords

Condensation▼aDrop-wise Condensation▼aNon-condensable gas▼aDiffusion layer model▼aRivulet flow▼aFlashing-induced Instability; 응축▼a적응축▼a비응축성기체▼a확산경계층모델▼a리뷸릿유동▼a증발기인-유동불안정성

URI
http://hdl.handle.net/10203/283517
Link
http://library.kaist.ac.kr/search/detail/view.do?bibCtrlNo=902016&flag=dissertation
Appears in Collection
NE-Theses_Ph.D.(박사논문)
Files in This Item
There are no files associated with this item.

qr_code

  • mendeley

    citeulike


rss_1.0 rss_2.0 atom_1.0