The investigation of pressure drop in moving-beds

The pressure drop of a cross-flow moving-bed was investigated in a two-dimensional rectangular apparatus. The effects of the particle velocity, the superficial gas velocity, the formation and development of cavity/raceway and voidage of particles on the pressure drop were investigated experimentally under the operational conditions of 0.09–1.35 m/s of the superficial gas velocity and 0.95–9.68 cm/min of the particle velocity. The experimental results show that the particle velocity has little influence on the pressure drop, while the phenomena of cavity and pinning occur when the cross-flow velocity is high enough. The development of a cavity or a raceway can result in three types of variations of pressure drop with time: stabilization, slight fluctuation and severe fluctuation. A cavity appears in a process cycle of ‘formation-growing up-collapsing-fluidization’ at a high gas velocity. On the basis of experimental results, a model for calculating the pressure drop after a cavity occurs and a dimensionless relationship of cavity size is developed, which gives a good qualitative account of the experimental data. Translated from The Chinese Journal of Process Engineering, 2006, 6(5): 697–702 [译自: 过程工程学报]     

Effect of the site of heat and mass supply in the near wake of a body of revolution on the body base pressure and drag

It is shown experimentally that in the near wake of a body of revolution in supersonic flow (1.15<M<3.1) there are at least two regions in which the heat and mass supply is more effective than that in the conventional schemes of base drag reduction. The first region is located at a distance from the base edge and the second is upstream of the region of attachment of the separated boundary layer. The effects of heat and mass supply on these regions are approximately identical and lead to an increase in the base pressure practically to the static pressure in the incoming flow. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 4. pp. 23–30, July–August, 2000.     

Drag of nonspherical particles in a flow behind a shock wave

The early stage of velocity relaxation of nonspherical particles in a flow behind an incident shock wave is considered by the method of multiframe shadowgraphy. A procedure of processing the data on the motion of a free body for determining its acceleration is proposed; in combination with the diagnostic method used, the procedure forms something like a noncontact aerodynamic balance. Novel data on the drag of bodies of irregular shape in a flow behind a shock wave with Mach numbers of 0.5–1.5 and Reynolds numbers of 10⁵ typical of dust explosions are obtained. It is found that the values of drag of a nonspherical bluff body and a sphere under these conditions are similar and exceed the drag of a sphere in a steady flow by a factor of 2 to 3.Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 1, pp. 81–88, January–February, 2005.     

Numerical simulation of two-dimensional spouted bed with draft plates by discrete element method

A discrete element method (DEM)-computational fluid dynamics (CFD) two-way coupling method was employed to simulate the hydrodynamics in a two-dimensional spouted bed with draft plates. The motion of particles was modeled by the DEM and the gas flow was modeled by the Navier-Stokes equation. The interactions between gas and particles were considered using a twoway coupling method. The motion of particles in the spouted bed with complex geometry was solved by combining DEM and boundary element method (BEM). The minimal spouted velocity was obtained by the BEMDEM-CFD simulation and the variation of the flow pattern in the bed with different superficial gas velocity was studied. The relationship between the pressure drop of the spouted bed and the superficial gas velocity was achieved from the simulations. The radial profile of the averaged vertical velocities of particles and the profile of the averaged void fraction in the spout and the annulus were statistically analyzed. The flow characteristics of the gas-solid system in the two-dimensional spouted bed were clearly described by the simulation results. __________ Translated from Chemical Engineering (China), 2007, 35(6): 24–28 [译自: 化学工程]     

Particle dynamics and relaxation in bimodal suspensions during drying using multispeckle diffusing wave spectroscopy

The motion of polystyrene particles in a bimodal suspension drop during drying was characterized via multispeckle diffusing wave spectroscopy. The fast and slow dynamics of bimodal particles, which were expressed in terms of autocorrelation function data from two kinds of cameras, were well connected in short and long lag time regimes. Characteristic time of β‐relaxation, representing the rapid movement of bimodal particles, became lower in the short lag time region as the portion of small particles increased, reflecting their fast Brownian motion. The difference in the relaxation features between bimodal suspension with large and small particles and unimodal suspension with only large particles became more evident as the size ratio between particles was high. Drying temperature could encourage the particle movement at the early stages of drying, leading to lower relaxation time, and inversely retard the relaxation behavior when drying time further elapsed, due to the structural rearrangement of particles. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1114–1121, 2017     

Temperature measurements at the leading edge of the conducting zone of a condensed-system combustion wave

An experimental method is proposed for the estimation of the temperature at the leading edge of the conducting zone in combustion waves in nonconducting condensed systems. Experiments using the Zr + WO₃ system demonstrated the effectiveness of the method. The temperature of the leading edge is found to be 2000–2400 K for a combustion temperature of the system of ≈3000 K. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 2, pp. 84–87, March–April, 2000.     

Deformations inside burning specimens

The dynamics of particle motion inside burning specimens producing solid combustion products was studied by flash radiography. In the experiments, we used specimens of aTi+C+20% TiC mixture, inside which marks in the form of strips of a ofZr+WO ₃ mixture or a tantalum powder were placed. The specimens were burnt in a semiclosed rigid casing with exhaust of impurity gases through slags. It is established that, just behind the combustion front, particles of combustion products begin to move in the direction opposite to the direction of motion of the combustion front. In the central zone of specimens, the particle velocity reaches values comparable with the combustion velocity of the specimens (∼20 mm/sec), whereas, on the periphery, the particle velocity is close to zero. Institute of Experimental Physics, Sarov 607190. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 4, pp. 78–83, July–August, 1997.     

The effect of surfactant on terminal velocity of and mass transfer from a fluid sphere in a non-newtonian fluid

The effect of interfacial tension gradients on creeping flow past a fluid sphere (bubble or drop) in a non-Newtonian fluid is investigated. The drag force and the Sherwood number for contaminated fluid spheres moving in a non-Newtonian fluid are obtained by an approximate solution of equations of motion in the creeping flow regime. It has been found that surface-active agents decrease both the terminal velocity and the mass transfer rate. The influence of the flow index of the power-law on both the drag coefficient and the Sherwood number is superimposed over the influence of the interfacial tension gradient. Comparisons between the present analysis and the available experimental data in the literature show reasonable agreement for the terminal velocity and the Sherwood number.     

Effect of the isotopic composition of lithium carriers on the ionic conductivity of lanthanum lithium titanate ceramic

The ionic conductivity of the solid electrolyte La_{2/3 − x} Li_3x TiO₃ at temperatures 20–600°C with different isotopic composition of the lithium current carriers is measured. It is shown that it has two components — low-and high-temperature — with very different activation energies. NMR on ⁷Li nuclei is used to measure the spin-lattice relaxation rate of the carriers. It is determined that the activation energies of short-and long-range carrier motion are the same at temperatures 20–500°C and are sharply different at higher temperatures. The effect of the concentration of cationic vacancies on the motion of carriers with different isotopic composition is investigated. __________ Translated from Steklo i Keramika, No. 7, pp. 31–34, July, 2007.     

Modelling mass transfer coefficient for liquid-liquid extraction with the interface adsorption of hydroxyl ions

A combined model was used for prediction of overall mass transfer coefficient of drops in the liquid-liquid extraction process, prone to the deleterious effect of adsorbed hydroxyl ions onto the interface. The importance is due to the use of different pH waters as aqueous phase. The work is based on single drop experiments with a chemical system of toluene-acetone-water where the pH of the continuous aqueous phase was within the range 5.5–8, appropriate to most industrial waters, and can lead to rigid behavior of circulating drops. The combined model in conjunction with the correlation developed here for the ratio of interfacial velocity to drop terminal velocity that links the film mass transfer coefficients of both sides can be used satisfactorily for design purposes. This model gives a maximum relative deviation of less than ±10% for the mass transfer directions of dispersed to continuous phase and vice versa.     

Particle size effect on the filtration drag of fly ash from a coal power plant

In order to investigate the filtration properties of fly ash from a conventional coal power plant, the filtration drag across the dust cake over an absolute fiberglass filter element was measured. A fluidized bed column was utilized to obtain a well characterized particle stream. The cake resistance coefficient was analyzed by the equation proposed by Endo et al. [1998] in order to observe the effect of particle size and polydispersity. The filtration drag was measured for three kinds of particle stream having the geometric mean particle size of 3.15, 6.07, and 7.83 μm and the geometric standard deviation less than 1.44 in the practical operation conditions for the field applications of face velocity of 0.03–0.06 m/s and area dust load up to 0.2 kg/m². A dust cake of smaller particle size showed larger pressure drop even though the porosity was higher and presented high compressibility according to the face velocity. The particle polydispersity was also a dominant factor affecting the compressibility of the dust cake.     

Interaction of rarefaction waves with a finite-thickness layer near a rigid boundary. Equilibrium approximation

Interaction of a rarefaction wave with a layer of solid particles near the end face of a shock tube is considered. A one-dimensional unsteady approximation of mechanics of heterogeneous media with identical pressures of the phases and with allowance for a finite volume concentration of particles in the layer is used as a mathematical model. The wave pattern of the flow and the mechanism of wave interaction with the layer, including the dynamics of the layer boundary depending on the layer thickness and rarefaction-wave width, are determined. The mathematical model proposed is verified against the dependence of the layer-boundary coordinate on time and also the dependence of the velocity of upward motion of the layer on the difference in pressures between the high-pressure and low-pressure chambers. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 5, pp. 126–135, September–October, 2007.     

Effect of convective motion on the flame structure in combustion waves propagating in heterogeneous systems under natural and artificial gravity conditions

Convective motion in combustion waves arises from natural or artificial gravity (centrifugal effect) for a wide range of heterogeneous systems, such as ammonium perchlorate containing solid additives, metal and nonmetal powders with a gas reagent, thermite mixtures, and hybrid layered structures. The paper summarizes the results obtained by the author and coworkers in studies of the effect of convective motion in combustion of heterogeneous systems for the period from the early 1970s to the present. It is shown that convective processes in combustion waves of heterogeneous systems may determine the structure and propagation mechanism of the combustion waves and the concomitant heat and mass transfer. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 4, pp. 86–92, July–August, 2009.     

Parameters of an accelerating spherical deflagration

A numerical analysis of an accelerating spherical deflagration is performed. It is shown that the deviations of the deflagration parameters from steady values are determined by the degree of increase in velocity in the law of motion for the flame front rather than by the acceleration value. Maximum deviations are observed at a front velocity equal to ≈0.1 of the sound velocity in the starting mixture. Analytical relations are obtained for the main parameters of the resulting flow for velocities up to a front velocity a factor of1.5 higher than the sound velocity in the starting mixture. Bauman Moscow State Technical University, Moscow 107005. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 2, pp. 11–22, March–April, 1997.     

Motion of a shaped-charge jet in a porous medium

The problem of the motion of a shaped-charge jet in a porous medium is equivalent to the problem of a blunt cylinder in a hypersonic flow whose velocity at infinity is equal to the jet velocity in the porous medium. The flow pattern of the medium is the same as in the case of propagation of a blast wave generated by a point explosion of a cylindrical charge. The approximate theory of a strong explosion is used to obtain the basic relations for the shock wave and the expanding cavity in the hypersonic flow of a porous medium around the blunt cylinder. A comparison with experiments on the motion of a copper shaped-charge jet in porous aluminum is performed. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 6, pp. 119–124, November–December 1999.     

Investigation of the combustion dynamics of low-volatile fuel particles by measuring “thermometric” and color temperatures

A new technique for studying the combustion dynamics and entrainment of lowvolatile fuel particles is proposed. It is based on simultaneous measurements of “thermometric” and pyrometric (color) temperatures. The technique permits a detailed study of time phases and mass rates of combustion of fuel particles in a wide range of regime parameters. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 5, pp. 27–30, September–October 1999.     

High P–T Nano-Mechanics of Polycrystalline Nickel

We have conducted high P–T synchrotron X-ray and time-of-flight neutron diffraction experiments as well as indentation measurements to study equation of state, constitutive properties, and hardness of nanocrystalline and bulk nickel. Our lattice volume–pressure data present a clear evidence of elastic softening in nanocrystalline Ni as compared with the bulk nickel. We show that the enhanced overall compressibility of nanocrystalline Ni is a consequence of the higher compressibility of the surface shell of Ni nanocrystals, which supports the results of molecular dynamics simulation and a generalized model of a nanocrystal with expanded surface layer. The analytical methods we developed based on the peak-profile of diffraction data allow us to identify “micro/local” yield due to high stress concentration at the grain-to-grain contacts and “macro/bulk” yield due to deviatoric stress over the entire sample. The graphic approach of our strain/stress analyses can also reveal the corresponding yield strength, grain crushing/growth, work hardening/softening, and thermal relaxation under high P–T conditions, as well as the intrinsic residual/surface strains in the polycrystalline bulks. From micro-indentation measurements, we found that a low-temperature annealing (T < 0.4 T_m) hardens nanocrystalline Ni, leading to an inverse Hall–Petch relationship. We explain this abnormal Hall–Petch effect in terms of impurity segregation to the grain boundaries of the nanocrystalline Ni.     

Numerical simulation of the characteristics of turbulent Taylor vortex flow

Turbulent Taylor vortex flow, which is contained between a rotating inner cylinder and a coaxial fixed outer cylinder with fixed ends, is simulated by applying the development in Reynolds stress equations mold (RSM) of the micro-perturbation. This resulted from the truncation error between the numerical solution and exact solution of the Reynolds stress equations. Based on the numerical simulation results of the turbulent Taylor vortex flow, its characteristics such as the fluctuation of the flow field, the precipitous drop of azimuthal velocity, the jet flow of radial velocity, the periodicity of axial velocity, the wave periodicity of pressure distribution, the polarization of shear stress on the walls, and the turbulence intensity in the jet region, are discussed. Comparing the pilot results measured by previous methods, the relative error of the characteristics predicted by simulation is less than 30%. Translated from Journal of East China University of Science and Technology (Natural Science Edition), 2006, 32(5), 617–622 [译自: 华东理工大学学报 (自然科学版)]     

短纤维链板式松弛热定型机内部流场测试及数值模拟

在对短纤维链板式松弛热定型机内气体流场部分实测数据的基础上,建立了数值计算模型,利用流体动力学软件Fluent对干燥机箱体单元进行了数值模拟分析。结果表明:所研究短纤维链板式松弛热定型机的匀风板开孔率布置不合理,使得干燥机内垂直于链板运动方向流速不均匀,导致干燥效果的不均匀;由于风机的离心力及蜗壳的导流作用,使得干燥机流场具有明显链板移动方向速度分量,该分量有助于加强干燥过程中的对流传质效果。所建模型的数值计算方法与实际测试结果相近,数值分析结果可以用来作为短纤维链板式松弛热定型机结构优化设计,尤其是匀风板开孔和风机蜗壳的设计的依据。