Al2O3/H2O纳米流体球形下封头表面气泡脱离行为模拟

压力容器内滞留（IVR）策略可在反应堆发生严重事故后,有效地将堆内熔融物滞留在压力容器内,是防止放射性物质外泄的关键技术。纳米流体是将粒径小于100 nm的固体颗粒加入到基液中以提高换热特性的稳定悬浮液,其热物性以及换热特性与传统固液悬浮液相比有较大区别,适宜的纳米流体种类及配比可强化换热。本文采用引入了无网格对流格式的移动粒子半隐法（MPS方法）研究了体积份额为1.0%的Al₂O₃/H₂O纳米流体和纯水中加热面朝下时气泡在加热面上的成长、脱离以及附着形成气膜的过程,探索了气泡脱离的临界角度及其影响因素,为加速纳米流体的工业应用、增强IVR能力提供理论基础。     

全局减方差方法在大空间γ辐射场计算中的应用

为了提高大空间γ辐射场全局计算效率,开展了全局减方差(Global Variance Reduction,GVR)方法在大空间γ辐射场计算中的应用研究。针对计数栅元/网格体积差异造成的过度分裂问题,引入体积修正因子修改全空间权窗参数。体积修正后的基于通量的GVR方法计算的全局品质因子(FOM_G)比直接模拟提高约39倍。针对非计数区计算耗时问题,提出了非计数区修正方法,使得FOM_G因子进一步提高40%。在引入体积和非计数区修正的基础上,在大空间γ辐射场计算中与基于粒子误差、权重、径迹、数目、能量、碰撞和通量的7种GVR方法进行对比。结果表明：7种GVR方法计算的FOM_G因子比直接模拟提高2～3个量级,基于误差的标准差σ降低2～3个量级;而基于权重的GVR方法计算的FOM_G因子比直接模拟提高2 304倍,在所有GVR方法中减方差效果最好。在基于通量的GVR方法中引入光滑因子SI后,模拟计算的权窗下限随SI增加而减小,FOM_G因子随SI的增加先增加后减小。当SI=0.8时,该方法计算...     

失水事故引起反应堆堆内结构动响应分析的声学有限元方法

失水事故引起的反应堆堆内结构动响应是反应堆结构动力学的重要问题。现有的分析计算方法主要是基于计算流体动力学(Computation Fluid Dynamics,CFD)的单向/双向流固耦合分析方法,数值预测精度较高但计算成本过高。本文基于以流体和固体位移和流体压力为基本未知量的势流体声学有限元理论,采用商用有限元软件ADINA和流固界面共节点网格技术,对德国HDR(Heiss Dampf Reaktor)实验堆V32破口失水事故进行了数值模拟。声学有限元-结构耦合计算结果与文献中的实验测试结果和基于CFD的双向流固耦合结果吻合良好,但比CFD方法更易于实现且具有较高的计算效率。研究结果为反应堆失水事故下堆内结构动响应提供了一种简单而高效的分析方法。     

LiH和LiT与H2O反应机理研究

氢材料在微量H₂O、CO₂、O₂和N₂存在下可能发生物理化学反应,使材料的物理品位下降。由于反应过程十分复杂,很难从实验上准确获取这类反应的最佳通道和具体产物信息,因此,从理论上研究氢材料分子的物理化学性质及其化学反应机制,了解化学反应过程具有十分重要的意义。本文使用Gaussian03软件包和Gaussview工具软件,在6-311G(d)全电子基函数水平上,应用二阶微扰理论优化得到了⁶LiH、⁶LiT与H₂O反应的中间体、过渡态及产物的结构,总能量,振动频率和零点能等。通过计算发现⁶LiH、⁶LiT均只有1个反应通道,⁶LiH与H₂O反应的焓变、活化能和反应速率常数分别为-156.99 kJ/mol、8.95 kJ/mol和3.75×10¹⁰(mol•dm^-3)^-1/s,⁶LiT与H₂O反应的焓变、活化能和反应速率常数分别为-159.02 kJ/mol、9.92 kJ/mol和1.72×10¹⁰ (mol•dm^-3)^-1/s。     

Neutron noise and random trees links between past and present Special Lecture SMORTH VIII — Göteborg, 27–31 May 2002

After reviewing personal reminiscences about the history of reactor noise research, the generalized notion of neutron importance is discussed and advantages of the backward generating function equation are shown by calculating the space-time fluctuations of the neutron density in a simple virtual (one-dimensional) reactor. Similarities between chain reactions and randomly evolving trees are used to study the special properties of branching processes. It is assumed that at t = 0 the tree consists of a single living node called root which, after a certain time τ ≥ 0, may produce η ≥ 0 new living nodes and then becomes dead. τ and η are random variables with known distribution functions. Each new living node evolves further independently of the others as does the root. The time dependence of the expectation value of the living nodes number is determined by the average number q₁ of the new nodes produced by one dying node. Depending on whether q₁ < 1 or q₁ = 1 or q₁ > 1 the randomly evolving tree is called subcritical, critical, and supercritical, respectively. The probability distributions of the tree lifetime and the tree size are determined in two exactly solvable models, and it is proven that a supercritical tree may be finite even at t = ∞ with non-zero probability.     

ESR法研究Pt催化N2H4分解机制

采用电子自旋共振谱（ESR）法，研究了酸性条件下•NH₂的转化，HClO₄体系下反应时间对溶液中自由基产生的影响、pH值对N₂H₄断键的影响以及HNO₃中N是否对溶液中的•NH₂有贡献，确定了Pt催化N₂H₄分解的反应机理。结果表明：在酸性条件下•NH₂被DMPO捕捉时反应式为•NH⁺₃+HO-H+DMPO=NH⁺₄+DMPO(•OH)，硝酸在Pt催化N₂H₄体系中不会发生断键产生•NH₂，所产生的•NH₂是由N₂H₄断键形成的；在HClO₄体系中，随着Pt催化N₂H₄反应时间的延长，N₂H₄中N-N断键的趋势逐渐减小，N-H断键的趋势逐渐增大；随pH值的增大，N₂H₄中N-N断键的速率先快速减小，pH>3后缓慢增大；Pt催化N₂H₄分解反应中N-N断键和N-H断键两种方式共存，但N-N断键占优；反应体系中N₂H₄与H^＋浓度之比决定了N-N断键生成•NH₂的速率，而•NH₂与H^＋的浓度又决定了•NH₂转化成产物的速率，这两方面共同决定了N₂H₄分解的速率。     

Pt催化N2H4还原U(Ⅵ)制备U(Ⅳ)过程中N2H4断键机制研究

为优化硝酸介质下Pt催化N₂H₄还原U(Ⅵ)制备U(Ⅳ)的工艺条件，确定此反应过程的控制步骤，有针对性地提高控制步骤的反应速率，以确定N₂H₄还原U(Ⅵ)制备U(Ⅳ)过程中的反应历程以及反应机理，通过实验研究确定了N₂H₄在Pt催化剂上的断键方式和分解机理。采用气相色谱法、分光光度法、滴定法及排水法对硝酸介质下Pt催化N₂H₄还原U(Ⅵ)制备U(Ⅳ)过程中的产物进行分析，确定反应过程中N₂H₄的断键机制。结果表明，硝酸介质下Pt催化N₂H₄还原U(Ⅵ)制备U(Ⅳ)反应过程中没有叠氮酸、氮氧化物及氢气生成，产物主要是N₂，生成的N₂的量与消耗的N₂H₄的量接近1∶1；当存在U(Ⅵ)时，生成的NH⁺₄产量较低，当U(Ⅵ)反应完全后，NH⁺₄的产生速率急剧增大；N₂H₄以N-N断键和N-H断键两种方式共存；反应温度升高有利于加快由U(Ⅵ)制备U(Ⅳ)还原反应的进行。     

Insulation characteristics of triple mixtures of c-C4F8/N2/CO2 under lightning impulse voltage

This paper has researched the insulation characteristics of 10%c-C₄F₈/N₂/CO₂ mixtures under lightning impulse voltage by experiment. It is shown that the positive and negative lightning impulse breakdown voltages of 10%c-C₄F₈/N₂/CO₂ gas mixtures rise linearly as the electrode gap distance and gas pressure increase and under the same conditions, the positive lightning impulse breakdown voltage of the gas mixtures is always higher than the negative lightning impulse breakdown voltage. As the gas mixtures have a little higher liquefied temperature than SF₆ and the comprehensive GWP is about 5% of SF₆ , and the positive and negative lightning impulse breakdown voltages can both reach 60% of SF₆ , 10%c-C₄F₈/N₂/CO₂ gas mixtures can be applied as insulation gas in electrical equipment such as C-GIS, GIT, GIL and so on.     

Study of partial discharge characteristics in HFO-1234ze(E)/N2 mixtures

HFO-1234ze(E)(trans-1,3,3,3-tetrafluoropropene, chemical formula: C₃H₂F₄) is an extremely environmentally friendly SF₆ alternative gas with high electrical strength. In this paper, the partial discharge (PD) characteristics of HFO-1234ze(E)/N₂ mixtures were studied using the gas insulation test platform. The PD inception voltage of insulating gas under positive and negative half cycles of power frequency was tested. Using SF₆/N₂ mixtures as a control group, the effects of electrode spacing, mixing ratio and pressure on the insulation performance of HFO-1234ze(E)/N₂ mixtures were explored. The test results show that the PD inception voltage of the negative half-cycle of pure HFO-1234ze(E) under short electrode spacing can reach 0.96–1.04 times of pure SF₆ under different pressures; the PD inception voltage of 40%HFO-1234ze(E)/60%N₂ mixtures at 0.3 MPa is 0.67–0.89 times that of SF₆/N₂ mixtures under the same conditions, which has great application prospect.     

Study of the permeability of thin films of a-Si:H using MeV ion beams

MeV heavy ion irradiation of hydrogenated plasma-deposited silicon nitride induces formation of the volatile molecules H₂ and N₂ inside the material. This type of nitride appears permeable for these molecules and they effuse at relatively low temperature. These effusing molecules are used to study the low temperature permeation in a 100 nm hydrogenated amorphous silicon layer, deposited onto the nitride. Upon irradiation of the double layer stack with 43.3 MeV Ag ions, appearance of D₂ and N₂ from the bottom deuterated silicon nitride layer in the vacuum does not take place up to an ion fluence of 3×10¹² ions/cm². This shows that the 100 nm plasma-deposited hydrogenated amorphous silicon top layer is initially not permeable for D₂ and N₂ molecules.     

Characteristics of a nitrogen-jet system in KUR-ISOL

The basic characteristics of a N₂-jet system coupled with a surface-ionization type ion source have been investigated at KUR-ISOL. The yields of transported activities and ionized ions have been measured under various conditions for both the He- and N₂-jets. The effects of N₂ gas upon the ionization and skimmer efficiency have been investigated. It was found that N₂ gas has almost no effect upon the ionization efficiency, but causes poorer skimmer efficiency than He gas owing to the large opening angle of aerosol particles at the outlet of a capillary. A mixture of He and N₂ gases was also tested.     

The effect of gas additives on reactive species and bacterial inactivation by a helium plasma jet

In this paper,the influences of gas doping(O_2,N_2,Air)on the concentrations of reactive species and bactericidal effects induced by a He plasma jet are studied.Firstly,results show that gas doping causes an increase in voltage and a decrease in current compared with the pure He discharge under the same discharge power,which might be attributed to the different chemical characteristics of O_2 and N_2 and verified by the changes in the gaseous reactive species shown in the optical emission spectroscopy(OES) and Fourier transform infrared(FTIR)spectroscopy.Secondly,the concentrations of aqueous reactive oxygen species(ROS) and reactive nitrogen species(RNS) are tightly related to the addition of O_2 and N_2 into the working gas.The concentrations of aqueous NO_2~- and NO_3~- significantly increase while the concentrations of aqueous ROS decrease with the admixture of N_2.The addition of O_2 has little effect on the concentrations of NO_2~- and NO_3~- and pH values; however,the addition of O_2 increases the concentration of O_2~- and deceases the concentrations of H_2O_2 and OH.Finally,the results of bactericidal experiments demonstrate that the inactivation efficiency of the four types of plasma jets is He?+?O_2??He+AirHeHe+N_2,which is in accordance with the changing trend of the concentration of aqueous O_2~-.Simultaneously to the better understanding of the formation and removal mechanisms of reactive species in the plasma–liquid interaction,these results also prove the effectiveness of regulating the concentrations of aqueous reactive species and the bacteria inactivation effects by gas doping.     

Effect of N_2 and O_2 on OH radical production in an atmospheric helium microwave plasma jet

UV-pulsed laser cavity ringdown spectroscopy of the hydroxyl radical OH(A–X)(0–0)band in the wavelength range of 306–310 nm was employed to determine absolute number densities of OH in the atmospheric helium plasma jets generated by a 2.45 GHz microwave plasma source.The effect of the addition of molecular gases N_2 and O_2 to He plasma jets on OH generation was studied.Optical emission spectroscopy was simultaneously employed to monitor reactive plasma species.Stark broadening of the hydrogen Balmer emission line(H_β)was used to estimate the electron density nein the jets.For both He/N_2 and He/O_2 jets, newas estimated to be on the order of 10~(15)cm~(-3).The effects of plasma power and gas flow rate were also studied.With increase in N_2 and O_2 flow rates, netended to decrease.Gas temperature in the He/O_2 plasma jets was elevated compared to the temperatures in the pure He and He/N_2 plasma jets.The highest OH densities in the He/N_2 and He/O_2 plasma jets were determined to be 1.0?×10~(16)molecules/cm~3 at x?=?4 mm(from the jet orifice)and 1.8?×?10~(16)molecules/cm~3 at x=3 mm, respectively.Electron impact dissociation of water and water ion dissociative recombination were the dominant reaction pathways, respectively, for OH formation within the jet column and in the downstream and far downstream regions.The presence of strong emissions of the N_2~+ bands in both He/N_2 and He/O_2 plasma jets, as against the absence of the N_2~+ emissions in the Ar plasma jets, suggests that the Penning ionization process is a key reaction channel leading to the formation of N_2~+ in these He plasma jets.     

Ni-MOF-74制备及其对CO的吸附性能

通过水热合成法制备了Ni-MOF-74材料，采用全自动表面积吸附仪、PXRD、扫描电子显微镜、同步热分析仪对材料的孔隙结构、晶体形貌和热稳定性进行了表征，并采用静态吸附法测定了CO、N₂、CH₄和CO₂在Ni-MOF-74上的吸附等温线；采用挤压成型方法制备了Ni-MOF-74成型材料，并研究了挤压成型后Ni-MOF-74晶体结构和微孔结构的变化及对CO的吸附性能的影响。结果表明，制得的Ni-MOF-74材料比表面积达1 212.61 m²/g ，其孔径主要集中在0.8～1.0 nm之间，对CO的吸附量远高于相同条件下对N₂和CH₄的吸附量，具有良好的热稳定性；Ni-MOF-74对CO的吸附作用力明显高于对N₂、CH₄和CO₂的；挤压成型后Ni-MOF-74的完整晶体数量明显减少，且部分微孔结构遭到破坏，成型后对CO的吸附性能明显下降。