锌电极电化学行为研究(Ⅴ)——有机缓蚀剂对碱液中无汞锌膏电极充放电的影响

利用电化学阻抗技术及循环伏安法,对碱性电液中无汞锌膏电极的电化学行为进行了研究,并讨论了一些有机缓蚀剂对静置、充电和放电状态下的无汞锌膏电极的阻抗行为及循环伏安行为的影响及缓蚀机理。     

Analysis of the ∈-Expansion in Turbulence Theory: Approximate Renormalization Group for Diffusion of a Passive Scalar in a Random Velocity Field

The validity of the -expansion in the turbulence problem is discussed using the example of diffusion of a passive scalar in a random velocity field. A generalization of Wilson's rule for calculating a diagram of arbitrary order is introduced. The resulting perturbation series, while having zero radius of convergence, is summed exactly yielding amplitudes which differ from those obtained to lowest order in the -expansion by only a few percent. The properties of the expansion are analyzed in detail and it is shown that various subsets of diagrams, while differing by an infinite number of terms, give close results in the vicinity of the fixed point. This indicates nontrivial compensation of high-order interactions in turbulence. The irrelevance of high-order couplings is demonstrated for arbitrary values of . The quality the approximation is tested by comparison with numerical experiments on diffusion of a passive scalar in a band-limited random velocity field in the limit of infinite Peclet number.     

COMPUTATION OF THE FLOW FIELD IN A RECIRCULATING TURBULENT GAS JET

As part of an overall investigation of flash-smelting processes, numerical computations were performed for the turbulent recirculating flow field of a gas jet in a confined cylindrical system. The two-equation (k - e) model was used to describe turbulence. The two-dimensional elliptic partial differential equations cast into finite difference forms were solved by the TEACH code (Gosman and Pun, 1973), and the pressure field was computed by the SIMPLER method (Patankar, 1980). Various correlations for the dissipation rate of turbulent kinetic energy at the inlet were tested, and the relation yielding the best results was obtained as E= C_μK^1.5/(0.015d_e where d_e = 4 x hydraulic radius. Extensive comparisons have been made between the computed results using the proposed form of e at the inlet and experimental data taken from the literature. Much better predictions than previously possible have been obtained     

Analysis of a new type of high pressure homogeniser. Part B. study of droplet break-up and recoalescence phenomena

Calculation of the flow pattern in a new small homogenising valve design (Stansted, U.K.), able to reach operating pressure as high as , was investigated in the first part of this paper using a Computational Fluid Dynamics method. Numerical simulation results are used in the present paper to better understand the emulsification process in the Stansted high-pressure homogeniser.Deformation of drops is supposed to occur in the intense elongational flow caused by the restriction between the piston and the seat of the valve. Deformation may be mainly followed by drop disruption in the narrow valve gap. Break-up probably also occurred in the highly turbulent region, located just at the exit of the gap, and underlined by the numerical investigation. Cavitation and the rate of recoalescence, first assumed from numerical results, are determined thank to experimental methods. Intensities of both phenomena strongly increase with homogenising pressure. Final droplet size of model oil-in-water emulsions is then the result of equilibrium between droplet break-up and recoalescence, which strongly depends on operating pressure.     

火电厂循环冷却水系统防腐技术试验与应用

针对火力发电厂循环冷却水系统溶解氧腐蚀、冲刷腐蚀及电化学腐蚀进行了分析,通过添加特效缓蚀剂使金属表面形成牢固、均匀、致密的保护膜层,使金属同循环水介质隔离而起到保护。达到了“GB50050—95”标准中铜及铜合金腐蚀速率宜小于0.005m/a的要求,现场应用效果良好。     

Evaluation of Mean Velocity and Turbulence Measurements with ADCPs

To test the ability of acoustic Doppler current profilers (ADCPs) to measure turbulence, profiles measured with two pulse-to-pulse coherent ADCPs in a laboratory flume were compared to profiles measured with an acoustic Doppler velocimeter, and time series measured in the acoustic beam of the ADCPs were examined. A four-beam ADCP was used at a downstream station, while a three-beam ADCP was used at a downstream station and an upstream station. At the downstream station, where the turbulence intensity was low, both ADCPs reproduced the mean velocity profile well away from the flume boundaries; errors near the boundaries were due to transducer ringing, flow disturbance, and sidelobe interference. At the upstream station, where the turbulence intensity was higher, errors in the mean velocity were large. The four-beam ADCP measured the Reynolds stress profile accurately away from the bottom boundary, and these measurements can be used to estimate shear velocity. Estimates of Reynolds stress with a three-beam ADCP and turbulent kinetic energy with both ADCPs cannot be computed without further assumptions, and they are affected by flow inhomogeneity. Neither ADCP measured integral time scales to within 60%.     

Experimental Study of Fine Sand Particle Settling in Turbulent Open Channel Flows over Rough Porous Beds

Results are presented from laboratory studies investigating the behavior of fine sand particles within turbulent open channel flow conditions flowing over rough, porous beds. A particle tracking technique was employed to record and analyze sand particle motion within the flow, while mean and fluctuating flow velocities were measured by an acoustic Doppler velocimeter probe. Measured particle settling rates show a strong influence from flow turbulence, being generally enhanced in the near-bed and intermediate flow regions and retarded in the outer flow region, compared to their fall velocity in still water conditions. Experiments also reveal the relative degree of settling enhancement to increase with decreasing particle size. Correlation between particle and small-scale fluid motions is demonstrated through a quadrant analysis technique, with higher-order events for the two phases found to be dominated by ejections and sweeps associated with the bursting process. Particle interactions with large-scale turbulent flow structures, revealed through flow visualization with a moving frame of reference, are found to result in particle accumulation in peripheral trajectories on the downflow side of local eddy structures. Analytical and theoretical considerations suggest that both these turbulence scales provide preferential transportation mechanisms that will account for the enhanced sand particle settling rates observed.     

Power Law Velocity Profile in Fully Developed Turbulent Pipe and Channel Flows

The power law velocity profile has been analyzed in terms of the envelope of the friction factor which gives the friction factor log law. The power law index α and prefactor C are shown as the function of the friction Reynolds number, as well as the function of the alternate variable the nondimensional friction velocity. The fully developed turbulent superpipe flow data of McKeon et al. and fully developed channel flow data of Zanoun et al. have been analyzed and the power law index α and prefactor C data have been estimated, first as a function of the friction Reynolds number and second as function of the nondimensional friction velocity. Based on analysis, several correlations have been proposed that have been supported by the data.     

Numerical simulation of wind flow near a forest edge

This paper presents a computational fluid dynamics (CFD) model to simulate wind flow near a forest edge for the purpose of wind energy applications. The model uses a porous media analogy combined with a modified k–ε turbulence model to simulate momentum losses and turbulence generation within the forest. The momentum losses are represented by a drag coefficient and a leaf area density. Two directions were investigated: wind flow entering and wind flow leaving the forest. A fully developed solution with original boundary conditions was used as the inlet boundary condition in the two-dimensional CFD model for wind flow leaving the forest. Original boundary conditions were also proposed for the ground boundary within the forest. The model was solved using FLUENT 6.2 and validated against field measurements from three different authors. A sensitivity analysis was performed on two key parameters: drag coefficient and leaf area density. The results obtained using the proposed method show good agreement with the wind velocity and turbulence intensity measured experimentally.     

NaNO3对含Cl^—衣康酸溶液中316L不锈钢的缓蚀作用

通过失重法和电化学法以及表面膜ＸＰＳ分析，研究了ＮａＮＯ３对含Ｃｌ＾－衣康酸介质中３１６Ｌ不锈钢的缓蚀性能，结果表明：溶液中一定量的ＮａＮＯ３可使不锈钢的点蚀电位显著提高，有效地撸制点蚀，缓 蚀效率达８１－９５％温度、