熔融物与下封头间球形窄缝通道内CHF理论研究

严重事故下熔融物与下封头间球形窄缝通道的存在对于下封头结构的完整性有一定的积极意义。本工作通过理论分析，在汽液两相间逆向对流限制机理的基础上提出了球形窄缝通道内的CHF机理模型和预测关系式，预测结果与实验数据符合较好，验证了所建模型的正确性，并进一步分析了系统压力、熔融物半径、间隙尺寸等关键参数对临界热流密度的影响规律。利用本工作的预测模型对三哩岛（TMI-2）事故后堆芯熔融物特性进行了计算分析，结果表明，熔融物与下封头内壁面间的球形窄缝可有效带走堆芯余热，保证了下封头的完整性。     

A feasibility assessment of the use of nanofluids to enhance the in-vessel retention capability in light-water reactors

Nanofluids, colloidal dispersions of nanoparticles, exhibit a substantially higher critical heat flux (CHF) compared to water. As such, they could be used to enhance the in-vessel retention (IVR) capability in the severe accident management strategy implemented by certain light-water reactors. It is envisioned that, at normal operating conditions, the nanofluid would be stored in dedicated storage tanks, which, upon actuation, would discharge into the reactor cavity through injection lines. The design of the injection system was explored with risk-informed analyses and computational fluid dynamics. It was determined that the system has a reasonably low failure probability, and that, once injected, the nanofluid would be delivered effectively to the reactor vessel surface within seconds. It was also shown analytically that the increase in decay power removal through the vessel using a nanofluid is about 40%, which could be exploited to provide a higher IVR safety margin or, for a given margin, to enable IVR at higher core power. Finally, the colloidal stability of a candidate alumina-based nanofluid in an IVR environment was experimentally investigated, and it was found that this nanofluid would be stable against dilution, exposure to gamma radiation, and mixing with boric acid and lithium hydroxide, but not tri-sodium phosphate.     

Experimental study of the effect of non-circular flow geometry on the critical heat flux

An experimental study of the effect of flow geometry (circular, rectangular, triangular, and dumb-bell shaped) on the critical heat flux (CHF) was performed using R-134a as a coolant. The CHF is affected by the following geometric parameters: hydraulic-equivalent diameter, heated length, gap size, channel shape, and curvature. It may also be affected by the thermal conductivity of the wall material and wall thickness. The effect of flow geometry on CHF is influenced by flow parameters. The effect of these parameters on CHF was examined, and recommendations for predicting the CHF in non-circular geometries have been made.     

CHF characteristics of R-134a flowing upward in uniformly heated vertical tube

An experimental study of the critical heat flux (CHF) using R-134a in uniformly heated vertical tube was performed and 182 CHF data points were obtained from the present work to investigate the CHF characteristics of R-134a. The investigated flow parameters in R-134a were: (1) outlet pressures of 13, 16.5, 23.9 bar, (2) mass fluxes of 285-1300 kg/m² s, (3) subcooling temperatures of 5-40 °C. The CHF tests were performed in a 17.04 mm I.D. test section with heated length of 3 m. The parametric trends of CHF show a general agreement with previous understanding in the water. To assess the suitability of the CHF test using R-134a for modeling the CHF in water, Bowring correlation and Katto correlation were used in the present investigation. It was found that the present test results coincided well with the data predicted with both correlations. It demonstrates that the R-134a can be used as the CHF modeling fluid of water for the investigated flow conditions and geometric condition.     

Critical heat flux performance for flow boiling of R-134a in vertical uniformly heated smooth tube and rifled tubes

In the present paper, critical heat flux (CHF) experiments for flow boiling of R-134a were performed to investigate the CHF characteristics of four-head and six-head rifled tubes in comparison with a smooth tube. Both of rifled tubes having different head geometry have the maximum inner diameter of 17.04 mm while the smooth tube has the average inner diameter of 17.04 mm. The experiments were conducted for the vertical orientation under outlet pressures of 13, 16.5, and 23.9 bar, mass fluxes of 285-1300 kg/m²s and inlet subcooling temperatures of 5-40 °C in the R-134a CHF test loop. The parametric trends of CHF for the tubes show a good agreement with previous understanding. In particular, CHF data of the smooth tube for R-134a were compared with well-known CHF correlations such as Bowring and Katto correlations. The CHF in the rifled tube was enhanced to 40-60% for the CHF in the smooth tube with depending on the rifled geometry and flow parameters such as pressure and mass flux. In relation to the enhancement mechanism, the relative vapor velocity is used to explain the characteristics of the CHF performance in the rifled tube.     

PFC emission‐reduction strategy for the LCD industry

Abstract— The perfluorocarbons (PFCs) used as etching‐process and chamber‐cleaning gases in the manufacture of LCD devices have a high global‐warming potential and a long atmospheric lifetime. Thus, to voluntarily reduce these environmentally harmful PFCs, in 2001 the Japanese LCD association established the World LCD Industry Cooperation Committee (WLICC), together with its counterpart associations in the Republic of Korea and Taiwan. Since that time involving many discussions, the WLICC reached a consensus on reducing the aggregate absolute PFC emissions to the equivalent of less than 0.82 million metric tons of carbon by 2010. Each association has been taking whatever emission reduction steps it considers best to achieve this goal. Thanks to these measures, the PFC emissions from the Japanese LCD industry have remained at the same level, or less, than those of the year 2000, in spite of the fact that PFC purchases have continually increased. In the interim, the Japanese LCD association has been obtaining experimental data for the 2006 IPCC Inventory Guidelines, which will give the emission factors needed to estimate the PFC emissions. As a result, some data are quite different from emission factors given in the current 2000 Inventory Guidelines. All the data obtained have been submitted to the IPCC to be adopted in the new 2006 Guidelines.     

Effect of nanoparticles on CHF enhancement in pool boiling of nano-fluids

To investigate the characteristics of CHF (Critical Heat Flux) enhancement using nano-fluids, pool boiling CHF experiments of two water-based nano-fluids with titania and alumina nanoparticles were performed using electrically heated metal wires under atmospheric pressure. The results showed that the water-based nano-fluids significantly enhanced CHF compared to that of pure water. SEM (Scanning Electron Microscopy) observation subsequent to the pool boiling experiments revealed that a lot of nanoparticles were deposited on heating surface during pool boiling of nano-fluids. In order to investigate the role of the nanoparticle surface coating on CHF enhancement of nano-fluids, pool boiling CHF of pure water was measured using a nanoparticle-coated heater prepared by pool boiling of nano-fluids on a bare heater. It was found that pool boiling of pure water on the naonoparticle-coated heater sufficiently achieved the CHF enhancement of nano-fluids. It is supposed that CHF enhancement in pool boiling of nano-fluids is mainly caused by the nanoparticle coating of the heating surface.     

模拟压水堆小破口失水事故喷放阶段临界时间的实验研究

CHF是压水堆中的一个重要的物理现象,t_(CHF)决定了压水堆发生失水事故后安全保护系统必须投入的时间,因此对瞬态CHF和t_(CHF)的研究具有重要的理论和实际意义,对压水堆运行具有参考价值。本文通过模拟小破口,利用直接通电均匀加热的垂直圆管作为实验段以及精心设计的喷放段,对t_(CHF)进行研究,给出了定量的结论。本实验的工况参数范围是:P=0.7～2.2 MPa,△T_(sub)=50～120℃,G=1750～2800 kg/m~2·s,q=0.3～1×10~5W/m~2     

低流速下临界热流密度（CHF）关系式分析

本文介绍了国外开展低流速下临界热流密度实验研究的概况，通过对两个常用于低流速下临界热密度（ＣＨＦ）预测的经验关系式的分析，说明了进一步开展低流速下临界热流密度实验研究的必要性，同时对将来的研究工作提出了建议。