Turbulent pulsations of the microelectrode limiting diffusion current

Flat mounted microelectrodes, for which the longitudinal length,L, is small in comparison with the diffusion entrance region are used to measure wall shear stress fluctuations. However, microelectrode turbulent noise depends both on wall shear stress fluctuations (i.e. longitudinal velocity pulsations) and on normal pressure gradient fluctuations (i.e. normal velocity pulsations). The relative value of these two factors depends on the microelectrode length. The influence of normal and longitudinal velocity pulsations on the microelectrode turbulent noise are the same order of magnitude if the lengthL is approximately 10 or 20 times the thickness of the viscous sublayer. Consequently it is possible to determine statistical characteristics of normal and longitudinal velocity fluctuations by using a number of microelectrodes of different lengths in the flow direction.This paper was presented at the Workshop on Electrodiffusion Flow Diagnostics, CHISA, Prague, August 1990.     

Turbulent diffusion in the flame of a rotary kiln

Conclusions Experimental data on the distribution of velocities in the stream in the flow of air from models of a burner with a normal annular Laval nozzle and a burner with an increase in the angle of opening of the stream under supersonic conditions was obtained. The results of the work may be used in the design of burners for rotary kilns. According to the experimental data the coefficient of turbulent diffusion reaches a value of 0.0071 m²/sec for a pure flow and is reduced by 30% with an increase in the dust content from 0 to 1 kg/kg. It is desirable to use the data obtained in calculations of the flame processes and selection of means of intensification of the process of mixing of the fuel with the oxidizer in the presence of dust.Translated from Ogneupory, No. 1, pp. 46–49, January, 1986.     

LNG垂直喷射源连续泄漏扩散的模拟

对液化天然气(LNG)扩散的物理过程进行了理论分析。针对垂直喷射源连续泄漏扩散特点,将液化天然气扩散过程分为重气扩散与被动扩散两个阶段。结合烟羽抬升计算,在两个阶段分别采用SLAB稳态烟羽模型与高斯烟羽模型,建立了液化天然气扩散过程数学模型。研究了垂直喷射源泄漏形式和不同环境条件下的扩散情形。对液化天然气泄漏后混合云团扩散形成的浓度场、温度场和其他特征参数进行了模拟。得到重气扩散阶段随下风向距离增大,扩散云团高度、宽度、温度、密度、云团中液化天然气蒸气含量、水含量的变化规律,被动扩散阶段云团中液化天然气质量分数的变化情况。可以为事故危害范围的测定、事故后人员的疏通和补救工作的指导提供帮助。     

气固射流扩散火焰形态研究

利用文丘里效应,自行设计气固射流扩散火焰（气固喷射火）实验装置,分别采用147 μm和178 μm两种粒径均匀的白色石英砂以近似恒定速率卷吸入火焰中,来研究固体颗粒对火焰形态的影响,特别地,通过关闭侧面进砂口所形成的气态射流扩散火焰（气态喷射火）与之相比较。理论分析和实验结果表明,砂子进入火焰中会降低火焰温度,并且粒径为147 μm的砂子进入火焰的质量大于178 μm砂子,导致小粒径气固喷射火具有更低的火焰温度,从而具有更低的层流燃烧速度和更大的火焰Froude数,最终使其具有更高的推举高度和火焰高度。对比分析气固喷射火和气态喷射火实验结果,也表明固体颗粒对火焰温度的冷却作用导致气固喷射火更容易产生推举现象并具有更高的火焰高度。     

Research on the LNG dense gas diffusion: A continuous horizontal jet release

结合SLAB稳态烟羽模型,针对液化天然气（LNG）连续泄漏、水平喷射源的重气扩散过程进行了模拟研究,分析了液化天然气泄漏后混合云团扩散形成的浓度场、温度场和其它特征参数。利用MATLAB语言编制液化天然气连续泄漏扩散模拟程序,对两种试验环境条件（不同风速、大气温度、大气稳定度、相对湿度和地表粗糙度等环境参数）下扩散云团的特性参数进行模拟计算,得到各云团参数随下风向距离的变化规律。     

Useful Extensions of the statistical theory of sintering

The statistical theory of sintering is modified to account for the new concept of pore coordination number (after Lange) as well as other refinements of the original assumptions (after Kuczynski). When pores are located in the grain boundaries, the theory postulates that for a given dihedral angle, a critical pore coordination number, n_crmc, exists such that when n < n_c, pores shrink, whereas when n > n_c pores grow. A general morphological kinetic equation is developed for uniform microstructures with pores located at the grain boundaries. This equation provides for contributions of grain boundary and volume diffusion to densification and is unrestricted with respect to the type of firing schedule imposed. Using this modified model, one may evaluate the significant parameter x, a measure of ‘the path of microstructural evolution’. For reasonably uniform compacts, the equation also provides a quantitative estimate of the relative width of the pore size distribution, y, during the later stages of sintering.     

A statistical theory for the strength of concrete

Several earlier studies of size effects on the strength of concrete are based on the weakest link concept. However, the inherent progressive microcracking of concrete with loading, invalidates the applicability of the weakest link concept. In this paper, a study is made to examine the suitability of a size-dependent strength distribution function which is derived taking into account progressive cracking of the material. Using the test data reported by other investigators, it is shown that the theoretical and experimentally observed strength distributions compare well.     

Velocity of combustion of a turbulent diffusion flame jet

Conclusions The investigation carried out showed that the velocity of transverse expansion of a reduced flow of combustion products can be used as the characteristic velocity of diffusion combustion, and the width of this flow can be used as a linear dimension, characterizing the degree of burnup.The physical basis for the velocity of diffusion combustion coincides completely with the well-known ideas in the literature concerning the velocity of laminar and turbulent homogeneous combustion, and therefore it is possible to compare the intensities of all three types of combustion. During the experimental investigations of turbulent homogeneous combustion, it was more useful to measure not the flame propagation velocity with respect to its leading edge, as is usually done, but the combustion velocity, which is unambiguously related to the rate of heat release.The preliminary comparison, carried out between the velocities of diffusion and homogeneous combustion, indicates the significant reduction of the heat-release intensity in a diffusion flame jet in comparison with a homogeneous flame jet, which, obviously, is explained by the complexity of the mixing process which precedes the chemical reaction.Institute of Problems of Mechanics, Academy of Sciences of the USSR, Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 12, No. 4, pp. 483–493, July–August, 1976.     

Some aspects of the chlorination of bauxite

Removal of iron and titanium impurities in bauxite by selective chlorination has been obtained by controlling the addition doses of coke and restricting the temperatures to below 323 K. The chlorination of iron and titanium free bauxite has been studied as regards the effect of coke addition, Cl₂ flow rates and partial pressures and temperatures. The rate equation 1-(1 - R)^1/3 = kt has been shown to fit the experimental data. It is concluded that the diatomic Cl₂ molecule does not dissociate to atomic Cl during chlorination.     

Some aspects of the electrophoretic enamel deposition

The electrophoretic deposition of suitable enamel frits from aqueous suspension and on various metal sheets was investigated. Influence of conductive salts and parameters related to the electrochemistry during deposition show the limits of this coating procedure.     

Turbulent mixing and fast chemical reaction in the confined jet flow at large Schmidt number

Turbulent mixing with fast chemical reaction was modeled in the confined jet flow at large Schmidt number (Sc～1000). The Reynolds-Averaged-Navier–Stokes approach was employed to describe the turbulence–chemistry interaction. Numerical results were validated against data obtained by the two-color planar laser-induced fluorescence method. Based on these data the dissipation rates of the mixture fraction and the product reaction concentration were calculated. Their comparison showed essential differences both in dynamics and values. The influence of different-order finite-difference schemes for scalar gradient determination and of the noise-signal ratio on the dissipation rates was estimated. More accurate higher-order schemes caused both noised and corrected dissipation rates to increase. Eliminating the noise leveled essentially the order-effect of finite-difference schemes.The analysis of the mixing models was demonstrated that the mixing model with the constant mechanical-to-scalar time ratio R and the Multi-Time-Scale model overestimated the mixture fraction variance σ_f in comparison with experiment. To predict the dissipation in the jet flow at Sc～1000 the low-Reynolds-number effects were considered: in the transport equation for σ_f the ratio R and the turbulent Schmidt number Sc_σ were the functions of turbulent Reynolds number. The accuracy of the used standard k–ε model was improved by coordinating the values of the model constants С_μ and C_ε2 with the jet velocity decay and the expansion radius (С_μ=0.06 and C_ε2=1.87).The examination of the known reaction rate models for the gas flow (Sc～1) (the segregation intensity approach, the EDC-model or the PDF method) showed that the reaction rate was overestimated by these models in comparison with the one obtained from the measurements in the liquid flow. The proposed modification of the EDC-model took into account the specific micromixing in vortex structures of flow at Sc?1.     

A statistical theory of polymer network degradation

A statistical theory was proposed for the degradation (random scission of chains) of a network having f-functional nodes in the case where all chains contain equireactive groups and a chain scission event does not create new groups or suppress more than one group. Closed-form relations were established between the conversion ratio of the degradation process and the crosslink density. Emphasis was put on the value of the conversion ratio for which the gel disappears. Some limited cases already considered in the literature were recovered, but a general solution was proposed for networks having any number of reactive groups per chain, be it uniform or not, and for conversion ratios up to the degelation point. The results were applied successfully to recent experiments regarding the hydrolysis of a polyester.     

Some aspects of electrochemical engineering

After a short discussion of the concept of electrochemical engineering, the immediate history of electrochemical process engineering (EPE) is briefly mentioned. Topics then considered are electrolytic reactor design, process modelling and optimisation, and the development and scale-up of electroorganic processes. The article concludes with an assessment of the present state of EPE.