自然循环欠热沸腾起始点特性

利用适于强迫循环的伯格尔斯和罗斯诺经验方法、Davis和Anderson理论方法，以及本课题组依据自然循环实验提出的预测欠热沸腾起始点的经验公式，对两种类型的欠热沸腾起始点的热力学平衡干度进行比较计算，研究自然循环的欠热沸腾起始点的基本特性。研究结果表明：自然循环欠热沸腾起始点的热力学平衡干度对加热量、进口温度、系统压力有着更大的敏感特性，在同等条件下，更早发生欠热沸腾现象。统计物理的微观角度研究进一步指出：产生这一现象的根本原因在于处于自组织状态的自然循环耗散结构的特点、动力学的涨落力和动量力对热力学平衡的共同影响。此研究结果为今后研究和应用自然循环的欠热沸腾奠定了基础。     

Applications of Artificial Neural Network for the Prediction of Flow Boiling Curves

An artificial neural network (ANN) was applied successfully to predict flow boiling curves. The databases used in the analysis are from the 1960's, including 1,305 data points which cover these parameter ranges: pressure P=100–1,000 kPa, mass flow rate G=40–500 kg/m²-s, inlet subcooling ΔT_sub =0–35°C, wall superheat ΔT_w = 10–300°C and heat flux Q=20–8,000kW/m². The proposed methodology allows us to achieve accurate results, thus it is suitable for the processing of the boiling curve data. The effects of the main parameters on flow boiling curves were analyzed using the ANN. The heat flux increases with increasing inlet subcooling for all heat transfer modes. Mass flow rate has no significant effects on nucleate boiling curves. The transition boiling and film boiling heat fluxes will increase with an increase in the mass flow rate. Pressure plays a predominant role and improves heat transfer in all boiling regions except the film boiling region. There are slight differences between the steady and the transient boiling curves in all boiling regions except the nucleate region. The transient boiling curve lies below the corresponding steady boiling curve.     

Radiation Anneal Hardening of Neutron Irradiated Niobium

Experiments were carried out with a vertical rectangular channel simulating a sub-channel of the upgraded JRR-3 fuel element, in order to investigate the validity and the error of the correlations predicting the superheat at the onset of nucleate boiling. These correlations were used in the core thermal-hydraulic design of the upgraded JRR-3. As the results, the following were made clear: (1) The existing Bergles-Rohsenow correlation gives a good prediction for the relationship of heat flux vs. superheat at the onset of nucleate boiling, with the error of about 1 K against the lower limits of the measured superheat. (2) There are no significant differences in the characteristics of the relationship of heat flux vs. superheat at the onset of nucleate boiling between upflow and downflow. (3) There are no significant differences in the histories of relationship of heat flux vs. superheat from the forced convection single-phase flow to the subcooled boiling between increasing heat flux and decreasing heat flux, with little overshoot of superheat at the onset of nucleate boiling both in the upflow and in the downflow.     

超亲水特性传热面上水喷流冷却时的沸腾换热特性实验研究

研究了在纳米材料涂层形成的超亲水材料传热表面上水喷流冷却时的沸腾换热特性,并与普通金属面上的喷流沸腾特性进行了比较.介绍了流动条件、加热方式、加热条件、超亲水材料涂层等条件对高温沸腾换热、临界热流密度的定量影响和一些基本换热规律.实验发现,超亲水传热表面对沸腾换热特性有十分显著的影响,超亲水传热面强化了喷流沸腾临界热流密度.     

压力容器外部冷却可视化图像分析研究

针对反应堆压力容器外部冷却（ERVC）缩比试验台架的可视化视频数据,基于Matlab商业软件开发相应图像自动分辨和界面捕捉程序IMGPROCS1对下朝向半球形结构的沸腾两相流动可视化数据进行批量处理分析。通过图像分析程序的批量处理,分析了不同工况下ERVC过程中沸腾汽泡的界面演化、汽膜厚度、沸腾循环周期等汽泡行为特征。结果表明:核态沸腾工况下,随着热流密度的增加,汽膜厚度逐渐增大;沸腾循环周期维持一恒定值。      

Experimental investigation of sodium boiling in partially blocked fuel subassemblies

Out-of-pile experiments were conducted to examine local sodium boiling in two wire-wrapped 37-pin bundles simulating LMFBR fuel subassemblies. The central 24 subchannels were blocked in the first bundle, and a edge part of bundle cross-sectional area was blocked in the other. The boiling modes observed in the wake were irregular nucleate, oscillatory and stationary. Three different types of boiling transition were identified, which were characterized by the temperature gradient around the two-phase voiding region. Dryout occurred not in the irregular nucleate boiling mode, but in both the stationary and oscillatory boiling modes. The coolability margin is considered to be 20 to 30% in terms of power-to-flow ratio from the incipient boiling to the occurrence of dryout.     

An investigation of transition boiling mechanisms of subcooled water under forced convective conditions

A mechanistic model for forced convective transition boiling has been developed to investigate transition boiling mechanisms and to predict transition boiling heat flux realistically. This model is based on a postulated multi-stage boiling process occurring during the passage time of the elongated vapor blanket specified at a critical heat flux (CHF) condition. Between the departure from nucleate boiling (DNB) and the departure from film boiling (DFB) points, the boiling heat transfer is established through three boiling stages, namely, the macrolayer evaporation and dryout governed by nucleate boiling in a thin liquid film and the unstable film boiling characterized by the frequent touches of the interface and the heated wall. The total heat transfer rates after the DNB is weighted by the time fractions of each stage, which are defined as the ratio of each stage duration to the vapor blanket passage time. The model predictions are compared with some available experimental transition boiling data. The parametric effects of pressure, mass flux, inlet subcooling on the transition boiling heat transfer are also investigated. From these comparisons, it can be seen that this model can identify the crucial mechanisms of forced convective transition boiling, and that the transition boiling heat fluxes including the maximum heat flux and the minimum film boiling heat flux are well predicted at low qualities/high pressures near 10 bar. In future, this model will be improved in the unstable film boiling stage and generalized for high quality and low pressure situations.     

锆-4在冷却水中的骤冷沸腾传热实验研究

为了研究锆-4在冷却水中的骤冷行为与沸腾传热特性,本文采用可视化方法,并测量了锆-4在骤冷过程中的温度变化。基于一维导热反问题求解,计算得到锆-4表面的热流密度和温度。在骤冷过程中锆-4会依次经历膜态沸腾、过渡沸腾、核态沸腾以及单相对流换热4个阶段,并且分析了轴向高度和冷却水过冷度对骤冷行为以及沸腾传热的影响。结果表明,随着过冷度的增大,骤冷时间减小,最小膜态沸腾温度增大,并且核态沸腾与过渡沸腾传热受加热表面局部特性影响显著,并建立了锆-4表面最小膜态沸腾温度的关系式,对反应堆的安全分析具有重要的意义。      

Core Thermohydraulic Design with 20% LEU Fuel for Upgraded Research Reactor JRR-3

This paper presents the outline of the core thermohydraulic design and analysis of the research reactor JRR-3, which is to be upgraded to a 20 MWt pool-type, light water-cooled reactor with 20% low enriched uranium (LEU) plate-type fuel. For the condition of normal operation, the upgraded JRR-3 core is planned to be cooled by two cooling modes of forced-convection at high power and natural-convection at low power. The major feature of core thermohydraulics is that at the forced-convection cooling mode the core flow is a downflow, under which fuel plates are exposed to a severer condition than an upflow in cases of operational transients and accidents. The core thermohydraulic design was, therefore, done for the condition of normal operation so that fuel plates may have enough safety margins both against the onset of nucleate boiling (ONR) not to allow the nucleate boiling anywhere in the core and against the departure from nucleate boiling (DNB). The safety margins against ONB and DNB were evaluated. The core velocity thus designed is at the optimum condition where fuel plates have the maximum margin against the ONB, and the minimum DNB ratio (ratio of DNB heat flux to the maximum heat flux) was evaluated to be about 2.1, which gives a sufficient margin against the DNB. The core thermohydraulic characteristics were also clarified for the natural-convection cooling mode.     

Steady-State Plasmas in KT5D Magnetized Torus

Steady-state plasma generated by electron cyclotron resonance （ECR） wave in the KT5D magnetized torus was studied using a fast high-resolution camera and Langmuir probes. It was found that both the discharge patterns taken by the camera and the plasma parameters measured by the probes were very sensitive to the working gas pressure and the magnetic configuration of the torus both without and with vertical fields. There existed fast vertical motion of the plasma. Tentative discussion is presented about the observed phenomena such as the bright resonance layer at a high gas pressure and the wave absorption mechanism at a low pressure. Further explanations should be found.     

环形窄通道内过冷沸腾起始点的实验研究

在1.0-4．5MPa的压力范围内研究了1．2mm间隙环形窄缝通道内过冷沸腾起始点．分析了部分热工参量对沸腾起始点的影响。引入双面加热影响因子．对环形窄缝内过冷沸腾起始点的数据进行回归分析,得出了适用于环形窄缝过冷沸腾起始点的实验关系式     

Scattering of Electromagnetic Waves by Drift Vortex in Plasma

In a quasi-two-dimensional model, the scattering of incident ordinary electromag- netic waves by a dipole-electrostatic drift vortex is studied with first-order Born approximation. The distribution of the scattering cross-section and total cross-section are evaluated analytically in different approximate conditions, and the physical interpretations are discussed. When the wavelength of incident wave is much longer than the vortex radius （kia〈〈1）, it is found that the angle at which the scattering cross-section reaches its maxim depends significantly on the approximation of the parameters of the vortex used. It is also found that the total scattering cross-section has an affinitive relation with the parameters of the plasma, while it is irrelevant to the frequency of the incident wave in a wide range of parameters of the vortex. In a totally different range of parameters when incident wave is in the radar-frequency range （then kia 〈〈 1, the wavelength of incident wave is much shorter than the vortex radius）, the numerical procedure is conducted with computer in order to obtain the distribution and the total expression of the scattering crosssection. Then it is found that the total scattering cross-section in the low frequency range is much larger than that in high frequency range, so the scattering is more effective in the low frequency range than in high frequency range.     

Density functional theory study of H,C and 0 chemisorption on UN（O01） and （111） surfaces

We performed density functional theory calculations of H, C, and O chemisorption on the UN（001） and （111） surfaces using the generalized gradient approximation （GGA） and the Hubbard U parameter and revised Perdew-Burke-Ernzerhof （RPBE） exchange-correlation functional at non-spin polarized level with the periodic slab model. Chemisorption energies vs. distance of molecules from UN（001） and UN（111） surfaces have been optimized for four symmetrical chemisorption sites, respectively. The results show that the Hollow, N-top, and Hollow adsorption sites are the most stable sites for H, C, and O atoms with chemisorption energies of 13.06, 25.50 and 27.34 kJ/mol for UN（001 ） surface, respectively. From the point of adsorbent （UN（001） and UN（111） surfaces in this paper）, interaction of O with the chemisorbed surface is of the maximum magnitude, then C and H, which are in agreement with electronegativities of individual atoms. For the UN（001） surface, U-N bond lengths change relatively little （〈 9%） as a result of H chemisorption, however C and O chemisorptions result in remarkable changes for U-N bond lengths in interlayer （〉 10%）. Electronic structure calculations indicate that Bridge position is equivalent with Hollow position, and the most stable chemisorption position for H, C, and O atoms are all Bridge （or Hollow） position for the UN（1 11） surface. Calculated electronic density of states （DOSs） demonstrate electronic charge transfer between .9, p orbitals in chemisorbed atoms and U 6d, 5f orbitals.     

On the dynamics of nucleate region flow boiling

A transfer function to describe boiling dynamics has been developed analytically. Dynamic measurements were performed for pool biling and experimental transfer functions were developed. Flow boiling dynamics were then investigated. Results obtained for negative h region flow boiling dynamics have been presented. The present study concerns nucleate region flow boiling dynamics.     

Density isomer of nuclear matter in an equivalent mass approach

The equation of state of symmetric nuclear matter is studied with an equivalent mass model. The equivalent mass of a nucleon has been expanded to order 4 in density. We first determine the first-order expansion coefficient in the quantum hadron dynamics, then calculate the coefficients of the second to fourth order for the given binding energy and incompressibility at the normal nuclear saturation density. It is found that there appears a density isomeric state if the incompressibility is smaller than a critical value. The model dependence of the conclusion has also been checked by varying the first-order coefficient.     

Study on the Removal of SO2 from Simulated Flue Gas Using Dry Calcium-Spray with DBD Plasma

In this study, lime-hydrate （Ca（OH）2） desulfurizer was treated by plasma with strong ionization discharge of a dielectric barrier. The removal of SO2 from simulated flue gas was investigated. The principles of SO2 removal are discussed. Several factors affecting the efficiency of SO2 removal were studied. They included the ratio of calcium to sulfur （Ca/S）, desulfurizer granularity, residence time of the flue gas, voltage applied to the discharge electrode in the plasma generator, and energy consumption. Experimental results indicate that the increase in Ca/S ratio, the applied voltage and discharge power, the residence time, and the reduction in the desulfurizer granularity all can raise the SO2 removal efficiency. The SO2 removal efficiency was up to 91.3% under the following conditions, namely a primary concentration of SO2 of 2262×10^-6 （v/v） in the emission gas, 21%（v/v） of oxygen, 1.8% （v/v） of water, a Ca/S ratio of 1.48, a residence time of 2.8 s, a 3.4 kV voltage and a 10kHz frequency power applied to the discharge electrodes in the plasma generator, and a flow rate of 100 m^3/h for emission gas.     

Analysis of the Variability of the L-H Transition Power Threshold in a Helium-4 Discharge

In this paper, a mechanism about the variability of the L-H transition power thresh- old PL-H is proposed which is based on the ion orbit losses. Only in the edge where there are enough ion orbit losses and the negative radial electric field Er is high enough can the H-mode be triggered. The ion orbit losses are determined by the ion in the loss region under certain edge conditions. For different mass A and different charge Z, the critical loss energy E Z2/A in the loss region. In H and D charges, because the D＋ loss region is larger than H＋, it can be deduced that the PL-H of H is larger than that of D. In a 4He discharge, experiment finds there exist a considerable number of 4He1＋ in the plasma edge. The actual ion orbit losses are determined by the mixing ratio of a He1＋ and 4He2＋. The 4He1＋ loss region is larger than that of 4He2＋, and the loss region of D＋ interposes between 4He1＋ and 4He2＋. Different 4He1＋ content can cause the edge ion losses in a 4He discharge to be greater than, less than or equal to that in a D discharge. So a 4He discharge can exhibit multiple experimental phenomena in the PL-H.     

Simulation of y spectrum-shifting based on the parameter adjustment of Gaussian function space

Based on the statistical characteristics of energy spectrum and the features of spectrum-shifting in spectrometry, the parameter adjustment method of Gaussian function space was applied in the simulation of spectrum-shifting. The transient characteristics of energy spectrum were described by the Gaussian function space, and then the Gaussian function space was transferred by parameter adjustment method. Furthermore, the spectrum-shifting in measurement of energy spectrum was simulated. The applied example shows that the parameters can be adjusted flexibly by this method to meet the various requirements in simulation of energy spectrum-shifting. This method was one parameterized simulation method with good performance for the practical application.     

A practical image reconstruction and processing method for symmetrically off-center detector CBCT system

CBCT scanners have been widely used in angiography, radiotherapy guidance, mammography and oral maxillofacial imaging. To cut detector size, reduce manufacturing costs and radiation dose while keeping a reasonable FOV, the flat panel detector can be placed off-center horizontally. This scanning configuration extends the FOV effectively. However, each projection is transversely truncated, bringing errors and artifacts in reconstruction. In this paper, a simple but practical method is proposed for this scanning geometry based on truncation compensation and the modified FDK algorithm. Numerical simulations with jaw phantom were conducted to evaluate the accuracy and practicability of the proposed method. A novel CBCT system for maxillofacial imaging is used for clinical test, which is equipped with an off-center small size flat panel detector. Results show that reconstruction accuracy is acceptable for clinical use, and the image quality appears sufficient for specific diagnostic requirements. It provides a novel solution for clinical CBCT system, in order to reduce radiation dose and manufacturing cost.     

Mutagenic Effects of BM302：GO112 Induced by Low-Energy Ion Beam Implantation

Mutant strains of GO112 and BM302 with a high 2-keto-L-gulonic acid （2KLG） transformation rate induced by ion beam implantation were separately and combinatorially compared with the original strains GO29 and BM80 to study the mutagenic effects of ion beam implantation. Both the sole GOl12 and mixed BM302：GOl12 demonstrated improved SNDH activity and 2KLG yield compared to the original strains. The mutant combinations of BM302：GOl12 showed a longer stationary phase and higher biomass than BM80：GO29. The mutant BM302 exhibited a stronger capacity to maintain a stable pH environment at mixed fermentation with Gluconobacter oxydans （G. oxydans） for 2KLG transformation and facilitated the growth of G. oxydans compared with the original strain BM80. The promotive capacity to L-sorbosone dehydrogenase （L-SNDH） from the supernate of BM302 was 1.6-fold higher than that of BM80. Genes encoded SNDH in GO29 and GOl12 were amplified and sequenced, and mutations including three transitions （CG →TA, CG →TA, GC → AT） and one transversion （AT→ TA） were confirmed from GO29 to GOl12. The corresponding amino acid was changed as Leu →Phe, Arg → Gln and Asn → Lys.