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RISS 인기검색어
- 검색키워드
- 주제어 : Steam chimney (검색결과 3 건)
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Yeo, D.Y.,NO, H.C. Elsevier 2017 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.108 No.1
<P><B>Abstract</B></P> <P>The model was developed to predict the heat transfer within the Chalk River Unidentified Deposit (CRUD), which is a kind of fouling found on the fuel rods of pressurized water reactors (PWR). The CRUD tends to develop steam chimneys that separate the liquid from the vapor phase. Therefore, the model describes the CRUD as a porous medium with steam chimneys. Unlike the previous approaches that assume that the evaporation takes place at the lateral surfaces of the chimneys, in the present study it is postulated that the vapor is generated by the bubble nucleation at the CRUD–clad interface, as observed via the visualization study for the chimney-structured porous medium. The generated bubble escapes through the steam chimney. The heat transfer in the CRUD can be described by three mechanisms of heat removal, which are nucleate boiling, liquid convection in the CRUD, and forced convective heat removal from the surface of the CRUD. The predicted CRUD–clad interface temperatures and overall heat transfer coefficients were compared to the experimental results, which were produced under the simulated PWR conditions (approximately 15MPa, 300°C). The prediction data presented better agreement with the experimental data; the normalized Root Mean Square Error (RMSE) of the present model is 18.6% in contrast with the 42.4% obtained with the Cohen model. After the validation with the experimental data, the prediction of temperature in the model was used to investigate how the heat transfer characteristics tended to change within the CRUD. Furthermore, the parametric study regarding the CRUD properties revealed that the effect of permeability on heat transfer is not significant in the nucleate boiling regime.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We propose a new heat transfer model and boiling model for the porous medium in PWRs. </LI> <LI> We validate the model against experimental data under the simulated PWR conditions. </LI> <LI> The liquid convection in the deposits contributes significantly to heat transfer. </LI> <LI> The effect of permeability on heat transfer is found to be insignificant. </LI> </UL> </P>
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Modeling film boiling within chimney-structured porous media and heat pipes
Yeo, D.Y.,NO, H.C. Elsevier 2018 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.124 No.-
<P><B>Abstract</B></P> <P>A porous medium with separated paths for liquid and vapor flows does not fail even after part of the porous medium is dried out. Instead, a vapor film resides within the porous medium, and it grows very slowly. This heat transfer regime was named as “confined film-boiling regime” in this study, and a heat transfer model for this regime was suggested in this paper. Especially, this paper mainly focuses on heat transfer of a CRUD (Chalk River Unidentified Deposit), which is a naturally occurring porous medium found in nuclear reactors. In the present model, the balance between capillary pressure and pressure drops of liquid and vapor flows determined thickness of the vapor film. In addition, we assumed that capillary pressure was changed with applied heat flux. This assumption was validated with a planar heat pipe case: the root-mean-square-error (RMSE) was 16% for the model with the heat flux dependent capillary pressure, while one for a model with the constant capillary pressure was 790%. Furthermore, this approach also turned out to be valid for the case of the CRUD: the model predicted the wall superheat during the film boiling of the CRUD, and its relative error was only within 20% when it was compared with the measured wall superheats. Finally, sensitivity analysis for CRUD parameters found that the heat transfer performance of the CRUD is largely sensitive to chimney density and pore size.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Applied heat can increase capillary pressure during the film-boiling regime of the porous media. </LI> <LI> Film boiling of the chimney-structured porous media and heat pipe is analogous to the capillary limit. </LI> <LI> There is the optimum density of chimneys that maximize heat transfer through the porous medium. </LI> <LI> The chimney-structured porous medium with small pores is worse in heat removal than one with large pores. </LI> </UL> </P>
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Modeling heat transfer through corrosion product deposits on fuel rods in pressurized water reactors
Yeo, D.Y.,NO, H.C. Elsevier 2019 Nuclear engineering and design Vol.342 No.-
<P><B>Abstract</B></P> <P>CRUD is the corrosion product deposit found on a fuel rod surface of pressurized water reactors (PWRs). Problematic phenomena caused by CRUD – CRUD Induced Power Shift (CIPS) and CRUD Induced Localized Corrosion (CILC) – are closely related to the heat transfer mechanism of CRUD. However, heat transfer regimes of CRUD are still not well clarified. Therefore, the heat transfer regimes of CRUD were investigated using existing database from the CRUD heat transfer experiment. As a result, it was found that there are three heat transfer regimes: (i) liquid-saturated regime, (ii) wick-boiling regime, and (iii) film-boiling regime. In addition, the boiling curves from the experiment were categorized according to their heat transfer regimes so that models for CRUD can be validated with appropriate database for the heat transfer regime where they are concerned. After obtaining the categorized databases, the model for the film boiling of CRUD was suggested. Unlike the conventional approaches that use capillary force as a unique source of the liquid supply in pores, the model we present in this paper adopted the disjoining force as an additional liquid supply term. This assumption was validated with the previous heat pipe experiment; the root-mean-square error (RMSE) for the prediction of the vapor film thickness was notably reduced from 790% to 18.7% by including the disjoining force to the supply term. The supply term considering the disjoining force was also applied to a model for the CRUD film boiling. The model estimates the wall superheat by balancing the supply term and the hydraulic resistance terms from fluid flows within CRUD. The model we present in this paper successfully predicted the wall superheat during the film boiling; the RMSE was 19% when the predicted wall superheats were compared with ones from the database categorized as film boiling. Finally, it was found from the sensitivity study using the model we present in this paper that the heat transfer performance of CRUD during the film boiling is highly sensitive to the pore radius.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Liquid-saturated regime, wick-boiling regime, and film-boiling regime are heat transfer regimes of CRUD. </LI> <LI> Vapor film exist within the CRUD during the heat transfer regime beyond the wick-boiling regime. </LI> <LI> Disjoining force becomes dominant during film boiling when heat flux is large. </LI> <LI> Heat transfer rate during film boiling is highly sensitive to pore radius. </LI> </UL> </P>
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