循环系统中闪蒸换热特性的实验研究

本文针对循环系统中闪蒸的换热特性进行了实验研究,通过可视化系统对闪蒸形态进行了记录和分析,并得出了换热系数与各影响参数之间关系的实验关联式.实验结果表明:当循环水流量为0.028kg/s时,随着过热度的增大,换热系数变化较小,而循环水流量为0.056 kg/s和0.083 kg/s时,换热系数随过热度的增大而减小;同时发现换热系数随水膜厚度的增大而减小.可视化分析表明,闪蒸形态随闪蒸室内饱和压力的减小而变剧烈,闪蒸换热系数随之减小.     

Laser flash photolysis of fluorinated aryl azides in neutral and acidic solutions

Laser flash photolysis of perfluoro-4-biphenyl azide andN-propyl-4-azido-2,3,5,6-tetrafluorobenzylamide in acetonitrile, water-acetonitrile mixtures, and HCl-containing solutions was studied. The absorption spectra of primary intermediates, singlet arylnitrenes(2a(S) and2b(S), respectively), were recorded. The absolute rate constants of their intersystem crossing in MeCN were measured, and the corresponding Arrhenius parameters were found from the temperature dependences of the rate constants of isomerization of singlet arylnitrenes2a(S) and2b(S) to azirines. Protonation of singlet arylnitrenes2a(S) and2b(S) was observed, the rate constants of their protonation were measured, and the transient absorption spectra of arylnitrenium ions were recorded. It was shown by quantum-chemical calculations (the hybrid B3LYP method) that the arylnitrenium ions that formed have the singlet ground state and the singlet-triplet gap is ∼20 kcal mol⁻¹. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 49–54, January, 2000.     

A property of certain multistage linear programs and some applications

In this paper, we present a property of certain linear multistage problems. To solve them, a method which takes this property into account is presented. It requires the resolution of 2N–1 subproblems, if there areN stages in the original problem. A sufficient condition is given on the matrix of the constraints for the property to be true. When only a submatrix has this property, we propose to use the Dantzig-Wolfe decomposition principle. We then can solve the subproblem with the proposed method. Applications to linear and nonlinear programming are presented.This work was done while the author was Visiting Scholar at the Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, California.     

烟煤快速加氢热解的研究Ⅵ．煤和半焦中氮化学形态剖析

采用电子能谱(XPS)测定了我国以烟煤为主的10种煤样以及对应快速加氢热解半焦中氮的化学形态。研究结果表明我国煤的XPS谱图在398.8(±0.1)和400.2(±0.1)eV的位置上出现氮峰,其相应氮化合物是吡啶和吡咯,随煤种不同氮的形态不尽一致,但主要是吡啶和吡咯,且多数煤以吡咯氮为主。快速加氢热解半焦与煤有相同的氮出峰位置,即半焦与煤有相同的氮化学形态,加氢热解过程总体为吡咯氮相对含量的增加和吡啶氮的减少。     

Diagnostics of an RF Plasma Flash Evaporation Process Using the Monochromatic Imaging Technique

The high densities and high gas temperature of rf plasmas at pressures near 1 atm are favorable for the development of plasma sources capable of evaporating solid precursors in the plasma zone. In the cooler region downstream of the plasma, the evaporated material condenses to nanoparticles and/or coatings. The complete evaporation of precursors injected into a thermal plasma depends on plasma and precursor parameters and is studied in this paper. Since many parameters contribute to the evaporation, fast experimental techniques are necessary to carry out a systematic study of the evaporation process. The monochromatic imaging technique applied in this work uses an intensified CCD camera with optical filters for the detection of characteristic plasma emission lines. The high spatial and temporal resolution of this technique results in a detailed picture of plasma emission and particle evaporation for different process parameters. These results are compared to model calculations for particle evaporation.     

Primal—Dual Constraint Aggregation with Application to Stochastic Programming

The special constraint structure and large dimension are characteristic for multistage stochastic optimization. This results from modeling future uncertainty via branching process or scenario tree. Most efficient algorithms for solving this type of problems use certain decomposition schemes, and often only a part of the whole set of scenarios is taken into account in order to make the problem tractable.We propose a primal–dual method based on constraint aggregation, which constructs a sequence of iterates converging to a solution of the initial problem. At each iteration, however, only a reduced sub-problem with smaller number of aggregate constraints has to be solved. Number of aggregates and their composition are determined by the user, and the procedure for calculating aggregates can be parallelized. The method provides a posteriori estimates of the quality of the current solution approximation in terms of the objective function value and the residual.Results of numerical tests for a portfolio allocation problem with quadratic utility function are presented.     

4MV/80kA IVA型脉冲X射线照相装置研制进展

介绍了西北核技术研究院研制的4 MV脉冲X射线闪光照相装置("剑光二号")系统组成和实验结果。装置基于感应电压叠加器(IVA)驱动阳极杆箍缩二极管(RPD)技术,主要由前级脉冲功率源、感应电压叠加器和RPD等组成。前级脉冲功率源由两台3.2 MV低电感Marx发生器和四路同轴水介质线组成。每台Marx同时给两路脉冲形成线(特征阻抗6Ω、电气长度30 ns)充电,充电峰值时间约370 ns。每路水介质线采用两级脉冲压缩,为感应腔馈入约1 MV/160 kA/60 ns电脉冲。电触发SF6气体开关、自击穿水开关分别用作主同步开关和脉冲陡化开关。感应电压叠加器采用四级1.5 MV感应腔串联,每级感应腔采用单点馈入结构。次级采用真空绝缘传输线实现电压叠加和功率传输,特征阻抗由30Ω线性增大至120Ω。采用4 MV电压下综合性能较优的RPD来产生强脉冲X射线。装置目前达到技术指标:输出电压4.3 MV、脉冲前沿(10%~90%)21 ns、半高宽约70 ns、二极管电流85 kA,X射线半高宽约55 ns,整机延时(从Marx触发器输出到X射线产生)约749 ns,标准偏差约7 ns。当RPD阳极采用直径2 mm钨针时,正前方1 m处剂量约15.5 rad(LiF),正向焦斑约1.4 mm。     

Experimental investigation of steel spheres as a passive enhancement technique for flash boiling of HCFC-22

An experimental investigation was conducted to study the influence of a layer of 3.6-mm-diameter steel spheres on the mass flow during flash boiling in a glass pressure vessel. It was observed that the steel spheres added numerous heterogeneous nucleation sites within the liquid and promoted abundant vapor bubble growth during depressurization. The steel spheres were in contact with each other and with the interior of the glass vessel. The data from these experiments were compared with baseline experimental results primarily with regard to the mass flow. Each test was run for 60 s, using controlled variables of orifice diameters (1.59 and 5.56 mm), initial refrigerant amounts (0.23, 0.45, and 0.68 kg), initial pressures (575 and 840 kPa), and vessel geometries (665 and 1110 ml). Pressures, temperatures, and mass flow rates, along with calculated saturation temperatures, amount of superheat, mass flux, and total mass flashed, were used to compare the baseline experiments with the enhanced boiling method. Results showed an increase in the total mass flashed at each test condition, ranging from an average of 22% to 81% with respect to baseline experiments.