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>

Minimum heat flux and minimum film-boiling temperature on a completely wettable surface: Effect of the Bond number

Kang, Jun-young,Kim, Tong Kyun,Lee, Gi Cheol,Park, Hyun Sun,Kim, Moo Hwan Elsevier 2018 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.120 No.-

<P><B>Abstract</B></P> <P>We investigated the effect of Bond number of sphere <I>Bo</I> <SUB>s</SUB> and surface super-hydrophilicity at minimum film-boiling temperature <I>T</I> <SUB>MFB</SUB> and minimum heat flux <I>q</I>″<SUB>min</SUB> using quenching experiment at atmospheric pressure and the saturation temperature of water. In particular, we focused on the vapor-releasing dynamics in film boiling and evaluated the main parameters such as vapor-bubble releasing frequency <I>f</I> <SUB>b</SUB> and vapor-bubble departure diameter <I>D</I> <SUB>b</SUB>. We selected two sizes of quench sphere (sphere diameter <I>D</I> <SUB>s</SUB> = 15 mm and 25 mm) based on critical Bond number <I>Bo</I> <SUB>C</SUB> to evaluate the vapor-releasing dynamics depending on the <I>Bo</I> <SUB>s</SUB>. The super-hydrophilic surface was prepared by the anodic oxidation on zirconium (Zr-702) sphere. High speed visualization and inverse heat transfer calculation facilitate a qualitative and quantitative analysis of film boiling heat transfer. The surface super-hydrophilicity of the quench sphere increases <I>T</I> <SUB>MFB</SUB> and <I>q</I>″<SUB>min</SUB>: 12% and 366% increase for <I>D</I> <SUB>s</SUB> = 15 mm and 20% and 305% increase for <I>D</I> <SUB>s</SUB> = 25 mm, respectively. <I>D</I> <SUB>b</SUB> strongly depends on <I>D</I> <SUB>s</SUB> and exhibits a relatively weak dependency to the surface super-hydrophilicity. <I>f</I> <SUB>b</SUB> is affected by the <I>D</I> <SUB>s</SUB> and the surface super-hydrophilicity. The increase in <I>T</I> <SUB>MFB</SUB> is explained by the liquid-solid contact in film boiling. The D25-CWS exhibits the large area fraction of liquid-solid contact versus total heat transfer surface compared to the D15-CWS. The increase in <I>q</I>″<SUB>min</SUB> is related to minimum frequency of vapor-bubble releasing to sustain the stable liquid-vapor interface <I>f</I> <SUB>b,min</SUB> because the large <I>f</I> <SUB>b,min</SUB> indicates the fast destabilization of the liquid-vapor interface in film boiling during quenching.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The surface super-hydrophilicity results in increase in minimum film-boiling temperature <I>T</I> <SUB>MFB</SUB> and minimum heat flux <I>q</I>″<SUB>min</SUB>. </LI> <LI> The increase in T<SUB>MFB</SUB> and <I>q</I>″<SUB>min</SUB> is strongly related to the Bond number of sphere <I>Bo</I> <SUB>s</SUB> (or, diameter of sphere <I>D</I> <SUB>s</SUB>). </LI> <LI> The increase in T<SUB>MFB</SUB> and <I>q</I>″<SUB>min</SUB> can be explained by the vapor bubble releasing dynamics in film boiling. </LI> </UL> </P>

Numerical investigation on ballooning and rupture of a Zircaloy tube subjected to high internal pressure and film boiling conditions

Van Toan Nguyen,Hyochan Kim,Byoung Jae Kim Korean Nuclear Society 2023 Nuclear Engineering and Technology Vol.55 No.7

Film boiling may lead to burnout of the heating element. Even though burnout does not occur, the heating element is subject to deformation because it is not sufficiently strong to withstand external loads. In particular, the ballooning and rupture of a tube under film boiling are important phenomena in the field of nuclear reactor safety. If the tube-type cladding of nuclear fuel ruptures owing to high internal pressure and thermal load, radioactive materials inside the cladding are released to the coolant. Therefore, predicting the ballooning and rupture is important. This study presents numerical simulations to predict the ballooning behavior and rupture time of a horizontal tube at high internal pressure under saturated film boiling. To do so, a multi-step coupled simulation of conjugated film boiling heat transfer and ballooning using creep model is adopted. The numerical methods and models are validated against experimental values. Two different nonuniform heat flux distributions and four different internal pressures are considered. The three-step simulation is enough to obtain a convergent result. However, the single-step simulation also successfully predicts the rupture time. This is because the film boiling heat transfer characteristics are slightly affected by the tube geometry related to creep ballooning.

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>

Direct-contact heat transfer of single droplets in dispersed flow film boiling: Experiment and model assessment

Park, Junseok,Kim, Hyungdae Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.8

Direct-contact heat transfer of a single saturated droplet upon colliding with a heated wall in the regime of film boiling was experimentally investigated using high-resolution infrared thermometry technique. This technique provides transient local wall heat flux distributions during the entire collision period. In addition, various physical parameters relevant to the mechanistic modelling of these phenomena can be measured. The obtained results show that when single droplets dynamically collide with a heated surface during film boiling above the Leidenfrost point temperature, typically determined by droplet collision dynamics without considering thermal interactions, small spots of high heat flux due to localized wetting during the collision appear as increasing We_n. A systematic comparison revealed that existing theoretical models do not consider these observed physical phenomena and have lacks in accurately predicting the amount of direct-contact heat transfer. The necessity of developing an improved model to account for the effects of local wetting during the direct-contact heat transfer process is emphasized.

주행하는 고온 강재의 상하부 동시 냉각 과정 수치해석

권면재(Myeon Jae Kwon),박일석(Il Seouk Park) 대한기계학회 2014 大韓機械學會論文集B Vol.38 No.12

열간 압연을 거친 800℃ 이상의 고온 철강 판재는 일반적으로 다중 봉상 수분류(multiple circular water jets)에 의해서 급속 냉각된다. 이 과정은 소재의 온도가 냉각수의 끓는점보다 훨씬 높기 때문에 소재 표면과 냉각수 사이에 막비등 열전달 현상이 발생하며 소재 표면에 매우 얇은 증기층이 형성되며, 이 증기층은 소재와 냉각수의 열교환을 방해하는 중요한 열저항으로 작용한다. 본 문제에는 비등 열전달 이외에도 소재 표면에 쌓이는 체류수의 자유표면 유동, 소재의 고속 주행 등 복잡한 물리현상들이 복합적으로 작용하고 있다. 본 논문에서는 이 모든 물리현상들을 동시에 고려할 수 있는 해석 절차를 적용하여 일정한 속도로 주행하는 고온 철강 판재의 상하부 동시 냉각 과정을 3 차원 수치해석 하였으며, 소재 상부 및 하부 면의 냉각 특성을 비교하였다. After hot rolling, a high-temperature steel plate with a temperature higher than 800°C is rapidly cooled by multiple circular water jets. In this cooling process, because the temperature of the steel plate is much higher than the boiling point of the cooling water, film-boiling heat transfer occurs and a very thin steam layer forms between the plate surface and the cooling water. The steam layer acts as a thermal resistance that prevents heat transfer between the cooling water and the steel plate. In addition to the film-boiling heat transfer, complex physical phenomena such as the free-surface flow of residual water that accumulated on the material and the material"s high-speed motion also occur in the cooling process. In this study, the simultaneous cooling process of the upper and lower sides of a running hot steel strip is investigated using a three-dimensional numerical model and the cooling performances and characteristics of the upper-side cooling and lower-side cooling are compared.

하드보일드 탐정소설의 장르적 특성 연구: 레이먼드 챈들러의 『깊은 잠』

신혜원 ( Hye Won Shin ) 한국아메리카학회 2012 美國學論集 Vol.44 No.2

Having emerged as a distinct literary genre during the 1930s, hard-boiled crime fiction differs from classical detective stories such as the works of Edgar Allan Poe and Agatha Christie. Classical detective stories show how chaotic realities are scientifically explained by rational procedures so that temporarily disrupted social order may be restored in the end. On the other hand, in hard-boiled detective novels, though crimes are solved, the culprits of powerful businessmen, politicians, organized criminals go unpunished. This fictional chaos reflects the ethical uncertainty and cynicism of American society going through the corruption of the Prohibition era and the despair of the Great Depression. Raymond Chandler`s The Big Sleep (1939) exemplifies the above characteristics of hard-boiled fiction. Revealing the pessimism of the interwar-period America, his novel is not a simple "pulp fiction" but a serious modernist novel criticizing the widespread violence, corruption, and greed of the modern city. Despite the apparent darkness, Chandler creates a private-eye hero, Philip Marlowe, who voluntarily retreats from the sinful world to preserve his moral integrity. Embodying the ethos of American individualism, Marlowe is also a modern-day knight who is more loyal to his own conscience and ethical principles than to his client-his "lord." Exploring these issues, this essay examines the hard-boiled formulas used in The Big Sleep as well as the generic variants derived from classical detective stories and the medieval romance. In addition, it investigates Howard Hawks`s adaptation of the novel in his film noir classic, The Big Sleep (1946). The comparison between these two works suggests the film`s loss of the radical social criticism seen in the orignal novel. Deflected by the Hays Code and Hollywood commercialism, the film`s sanitization is most obviously illustrated by the gender relations and hypermasculinity portrayed in the movie, anticipating the postwar political conservatism.

하방비등 조건에서 그래핀 표면개질이 슬러그 기포 거동에 미치는 영향

김지민 한국기계기술학회 2020 한국기계기술학회지 Vol.22 No.5

This paper reports slug bubble dynamics on modified surface with two-dimensional graphene film in downward-facing nucleate boiling. Behaviors of slug bubbles were observed with high speed camera, and post-processing was followed to measure departing speed, frequency, and diameter of slug bubbles, which were important to analyze boiling performance change. The graphene-modified surface showed enhanced boiling heat transfer coefficient (BHTC) and critical heat flux (CHF). The effect of surface modification on slug bubble dynamics was quantitatively analyzed; bigger slugs departed from the modified surface with faster speed but same frequency, compared with the bare. It seems that the BHTC enhancement is caused by increase of bubble diameter, resulting in increase of its departing speed. The higher speed of departing bubble could extend the hydrodynamic limit of vapor removal from downward-facing surface, so that CHF performance could be enhanced.

Extended validation of a developing post-dryout heat transfer correlation over a wide range of pressure conditions

Nguyen, Ngoc Hung,Moon, Sang-Ki,Song, Chul-Hwa Elsevier 2018 Nuclear engineering and design Vol.338 No.-

<P><B>Abstract</B></P> <P>The present paper deals with the validation of a post-dryout heat transfer correlation, which has been proposed by Nguyen and Moon (2015), to show its extended applicability to developing post-dryout region. It is also shown that the well-known film-boiling look-up table (LUT) method currently having limited application to fully-developed flow can be improved to extend its applicability to the developing post-dryout region. In order to show that the correlation can be utilized for nuclear reactor safety analysis, eight different sets of post-dryout data covering flow conditions both in both large break loss-of-coolant accident (LB LOCA) and prolonged station blackout (SBO) scenarios have been assessed. It turns out that the correlation predicts well the measured wall temperature with a total average error of 3.81% and a root-mean-square error of 13.46% in case of given CHF (dryout) condition. The prediction accuracy of the correlation is strongly influenced by how well the local vapor temperature and the CHF locations can be predicted.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A post-dryout heat transfer correlation for developing regime was validated over a wide range of flow conditions. </LI> <LI> The dryout location is estimated using the CHF look-up table. </LI> <LI> Good prediction results are obtained over wider pressure conditions. </LI> </UL> </P>

필름 느와르(film noir)의 역사적 특수성에 관한 연구

전평국 ( Pyeong Kuk Jeon ) 한양대학교 현대영화연구소 2014 현대영화연구 Vol.10 No.3

본 논문은 1940년대 미국에서 발생한 필름 느와르의 여러 가지 시대적, 사회적 배경과 또 탄생의 직, 간접적으로 영향을 준 역사적 사건들이 무엇인지 탐구함을 목적으로 한다. 1920년대 시행된 금주법의 부작용은 불법과 범죄로 불합리와 부조리한 현실이 존재한다는 것을 인식하게 하였고 1930년 전후에 발생한 대공황의 경제적 침체와 혼란은 전통적인 미국적 가치와 정체성을 심각하게 위협하였으며, 2차 세계대전과 이에 따른 성과 폭력에 대한 영화검열완화 그리고 하드보일드 소설의 서사구조와 캐릭터, 주제와 스타일 등의 영향과 역사적 흐름이 하나의 통일된 기제로 작용해 필름 느와르를 배태시켰다. 필름 느와르는 2차 세계대전이라는 큰 역사의 전후에서 점차 암울해져가는 세계관과 문화적 태도를 스크린위에 반영했다. 대중들은 필름 느와르를 통해 현실의 모순과 불합리, 부도덕성을 인식하고 그 속에서 현실도피와 대리만족의 카타르시스를 경험했다. 결과적으로 필름 느와르는 자체가 지니고 있는 특성과 그 배경이 되는 역사적, 사회적 특수성이 누적 연계되어 미국식 표현주의라고 하는 새로운 리얼리즘의 영화미학인 하나의 스타일을 창조함으로써 영화의 숨겨진 역할을 수행했다. 영화는 삶과 역사의 투영이고 필름 느와르또한 그 원칙에서 벗어날 수 없기 때문이다. The purpose of this study is to explore various historical and social background of film noir occurred in the United States in 1940s and to explore what historical events had directly and indirectly influenced its birth. The side effects of Volstead Act has made aware of the existence of unreasonable and absurd reality due to illegality and criminality, and the economic downturn and chaos of the Great Depression occurred before and after the 1930 have serious threatened the traditional American values and identity, and the mitigation of film censorship on sex and violence following the Second World War with the effect of narrative structure and character of hard-boiled fiction, impact of themes and styles, and a single unified mechanism of historical flow gave birth to the film noir. The film noir has reflected the ever increasing murky worldview and cultural attitudes on the screen before and after the great history called the Second World War. The public has recognized the immorality and contradiction and absurdity of reality through film noir and within it experienced the catharsis of escapism and vicarious satisfaction. In conclusion, with the accumulation and association of characteristics of film noir and the historic and social distinctiveness which becomes its background, it has played a hidden role of film by creating a style of film aesthetics of new realism called the American expressionist. It is because the film is the projection of life and history and the film noir also cannot escape from its principles.