Two-parameter model of two-phase turbulent nonisothermal flow with particles,burning in the vapor-phase regime

Tyumen'. Translated from Fizika Goreniya i Vzryva, Vol. 25, No. 5, pp. 62–69, September–October, 1989.     

Model of micro- and macroscale chemical condensations in a gas mixture with solid particles flowing in a channel with a heated wall

A model of the mutual influence of micro- and macroscales for the competing processes of chemical condensation in a finely dispersed mixture of a reacting gas and solid particles is studied. A kinetic model of chemical and phase transformations is used to calculate the fields of concentrations, temperatures, particle size distribution for the finely dispersed solid phase, and other characteristics at different values of similarity parameters. This model can be used to estimate the phase structure and morphology of the condensed product and the dynamics of the growth or evaporation of the particles.     

Experimental investigation of cocurrent two-phase flow in a vertical rectangular channel

New time averaged data of two-phase flow in bubbly and slug regimes are presented. A modified dual spherical tipped optical fiber probe is used to measure local void fractions, gas velocity and bubble sizes. Hot film anemometry was used to measure the local mean liquid velocity axially. The void fraction, gas and liquid velocities values were presented as averages over the long and short dimensions respectively. Also core values of these variables are presented along the smaller dimension of 12.7 mm, near the plane of symmetry of the longer dimension, to show the most general trend of the different bubbly and slug flow runs. Bubble sizes obtained experimentally were compared with predictive models applied to circular geometries and were found to have a reasonable agreement. It was also interesting to find that local void fractions measured using hot film anemometers were comparable to those found by optical fiber probes. Frequencies of interfacial passage of bubbles and slugs are presented which show rather flat profiles across the channel. It is hoped that these data can be further used in predictive two-phase two-fluid models in the future. Lastly of interest is the fact that slip values near the boundaries were shown to be less than 1.0 for some cases in bubbly flow similar to those observed in circular geometries.     

Detonation of a mixture of RDX particles partially filling a cylindrical channel

Using a mathematical model of a two-phase, two-velocity medium, detonation in an annular layer of a suspension of volatile secondary explosives adjacent to the wall of a cylindrical channel is numerically investigated. The dynamics of formation and the special features of the structures of a two-dimensional reaction zone of a detonation wave in a gas mixture of RDX particles are discussed. A detonation regime with a vortex structure of the reaction zone is obtained in calculations for the first time. The geometrical limits of detonation in a channel are determined. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 4, pp. 79–87, July–August 1999.     

Modeling of flame propagation in a mixture of combustible gases and particles

A physicomathematical model of flame propagation over a gas suspension composed of a mixture of gases (oxidizing, combustible, and inert components) and the particles of a condensed material that reacts heterogeneously with the oxidizing component is formulated. Numerical simulations are used to obtain a dependence of the flame velocity on the parameters related to the mass concentration of the particles, the particle size, the activation energy of a heterogeneous reaction on the particle surface, the heat of the heterogeneous reaction, and the mass exchange of the particles. Depending on the ratio of the dispersed-phase parameters, the flame velocity in this medium can increase severalfold in comparison with the flame velocity in a dust-free gas mixture or decrease. In the latter case, the effect of the particles is similar to the effect of the inert dispersed phase. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 2, pp. 3–9, March–April, 2000.     

Modeling the gas absorption in a spray scrubber with dissolving reactive particles

The absorption of a gaseous species into a spherical slurry droplet with internal circulation that contains reactive, sparingly soluble microparticles is studied. The droplet recirculation is assumed to be similar to Hill's vortex flow, and the chemical reaction is assumed to be either instantaneous or of second order. Reactive gas species diffusion, chemical reaction and particle dissolution are numerically modeled using droplet recirculation streamlines as a coordinate. Parametric calculations are performed, and are utilized to assess the adequacy of the widely used film theory, and to examine the effect of particle size variation on the absorption rate. A transient model is also developed that utilizes the aforementioned quasi-steady droplet mass transfer and reaction models and calculates the time variation of the average solid particle size in the droplet. Parametric calculations are presented that confirm the importance of particle size and its variation as a result of dissolution. Transient parametric calculations show a declining total absorption rate with time as a result of the shrinkage of the average particle size. The results are everywhere sensitive to droplet internal circulation, however. Partial suppression of droplet internal circulation leads to significant reduction in absorption rate, even with a high concentration of particles. The calculation results thus demonstrate that several parameters should be considered for optimal design of a slurry spray scrubber.     

Numerical simulation of aerodynamics and combustion of a gas mixture in a channel with sudden expansion

A physicomathematical model and results of numerical simulations of aerodynamics and combustion of a swirled flow of an aluminum-air mixture in an axisymmetric channel with sudden expansion are presented.     

非线性振动下水平通道气液两相流动

将振动装置与气液两相流实验回路相结合,对非线性振动工况下水平通道内气液两相流进行实验研究。重点考察了不同振动参数对流型转换界限及摩擦压降的影响。流型图表明,非线性振动工况和稳态工况下的气液两相流动形式不同,提高振动的频率和幅度会导致流型转换界限发生改变。由实验得到的气液界面分布结果表明,振动频率对相界面波动程度有显著影响,而振动幅度则主要影响截面含气率。最后对比了非线性振动工况下的摩擦压降和经验公式的计算结果,发现两者在数值和分布上均无明显差异,说明稳态下两相流摩擦压降计算公式同样适用于非线性振动工况。     

气/液-固两相流中的粒子速度

通过实验研究和理论分析,考察了提升管中颗粒相的质量守恒;发现在传统的两相流研究中,对颗粒速度的时间平均和算术平均存在着误用。在传统理论中,由于引入了颗粒相的体积分率项,实际上是对离散的颗粒进行了连续化的假设。由此不可避免地造成颗粒速度时间平均和算术平均的混淆。在微观尺度上对气/液-固两相流中颗粒速度时间平均的物理意义进行了分析,给出了计算非连续流场中颗粒时均速度的表达式,并提出了分析颗粒相质量守恒的方法。     

开孔金属泡沫内气液两相流动的可视化

开孔金属泡沫内流动特性的研究多局限于局部流动特性的分析,大尺寸（100cm²以上）金属泡沫内气液两相宏观流动特性的研究目前较为缺乏。为了深入认识金属泡沫内气液两相流动特性,本文通过光学可视化手段,对金属泡沫多孔介质薄层内的气/液驱替、液/气驱替两相流动过程进行研究,分析了入侵流体的流速及金属泡沫的孔径对泡沫薄层内两相流动的影响。结果表明：在气/液驱替流动方面,随着空气流速的增大,气液两相的界面形态由毛细指状结构过渡到黏性指状结构,随着泡沫孔径的减小,部分排水现象愈加显著;在液/气驱替流动方面,气液界面较为规则,近似呈锥形,且流速越大,界面锥角越大、长度越小,试验中仅在最小孔径的金属泡沫中捕捉到明显的部分驱替现象,并且随着水流速的减小愈加显著。