Modeling of solid-state combustion in thermally and chemically heterogeneous media

A thermally and chemically heterogeneous medium is modeled by a set of cylinders pressed from a mixture of solid reagents with coaxially aligned cylindrical rods made from an inert material. The change in velocity of combustion waves propagating over one cylinder is studied by numerical methods under the assumption that there is no heat release from the cylinder surface. The mean velocity of the combustion front in the specimen is shown first to decrease and then to increase with increasing thermal conductivity of the inert rod. Spinning waves are obtained in the range of low velocities of the combustion front. The laws of variations of the maximum temperature in the combustion front are determined. It is shown that the inert rod may serve as a heat sink from the hot charge mixture, may be manifested as dilution by an inert component, enhance heat recuperation, and increase the combustion-wave velocity. Introduction of the inert rod may either destabilize combustion-wave propagation in the region of a stable plane front or stabilize the combustion wave in the range of parameters where the plane front is unstable. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 6, pp. 21–30, November–December, 2007.     

Propagation of a one-spot spinning wave in a thick-walled cylinder under adiabatic conditions

Propagation of a one-spot spinning wave in a cylindrical specimen with a coaxial internal channel is studied by numerical methods under the assumption of the absence of heat removal from the outer surface of the specimen and from the channel surface. Variations of the spinning wave characteristics [maximum temperature, longitudinal and circumferential (tangential) velocities, “pitch,” and time of rotation of the hot spot around the specimen centerline] are tracked for a specimen of a particular size with a varied channel radius, for specimens of different sizes with a fixed channel radius, and for specimens with a constant wall thickness. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 4, pp. 41–49, July–August, 2006.     

Properties of the surface layer and combustion behavior of metallized solid propellants

The properties of the surface layer of burning metallized solid propellants are analyzed on the basis of available experimental data. A general physical concept of processes in the surface layer is developed. The structure called a skeleton layer is shown to play a key role in combustion. The factors influencing the properties of the skeleton layer are determined, and the effect of these of properties on the properties of condensed combustion products and the propellant burning-rate law is studied. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 4, pp. 156–165, July–August, 2009.     

Reflection of a shock wave in a dusty cloud

The problem of shock-wave passage along a cloud of particles adjacent to a solid surface is studied numerically and analytically. The wave pattern of the flow near the shock wave reflected from this surface is analyzed within the framework of the equilibrium approximation of mechanics of heterogeneous media. The conditions of the transition from regular to irregular reflection from the substrate of the refracted shock wave inside the cloud are obtained analytically. The results of numerical simulations of a nonequilibrium flow in the two-velocity two-temperature approximation are compared with data obtained in the equilibrium approximation. Nonequilibrium and equilibrium flows are found to become more similar as the particle size decreases. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 1, pp. 121–131, January–February, 2007.     

Effect of protonation media on chemically and electrochemically synthesized polyaniline

Polyaniline films have been prepared both chemically and electrochemically using formic (‘Pani‐Formic’), boric (‘Pani‐Boric’) or acetic acid (‘Pani‐Acetic’) as protonation media. Among the three, formic acid seems to be a better protonating medium because it selectively yields the conducting phase of polyaniline. The variation of potential with the amount of oxidizing agent suggests one dimensional growth of polymer chain, which proceeds through a PG/EM mechanism as indicated by spectral data. The Pani‐Boric and Pani‐Acetic acid demonstrate three‐ and four‐step decomposition patterns, respectively, with complete decomposition at about 760 °C. Pani‐Formic acid, in contrast, reveals a three‐step decomposition pattern with 90% weight loss at about 900 °C and shows a tendency to react with the Pt sample holder. The films of polyaniline generated electrochemically also suggest formic acid to be a better protonating medium for achieving a relatively greater fraction of conducting emeraldine salt. However, boric acid produces excellent quality adherent films with very high deposition rate. Morphological features give strong support to this observation. The films of Pani‐Formic and Pani‐Acetic acids show a spongy network and globular morphology, respectively, while Pani‐Boric acid yields an extremely uniform surface coating. Furthermore, cyclic voltammetry reveals different patterns depending upon the formation of different oxidation states and the results are in accordance with optical absorption studies. © 2000 Society of Chemical Industry     

Effect of non‐isothermal condition on heterogeneous flow through biofilter media by lattice Boltzmann simulation

BACKGROUND: Biofiltration technology has received much attention due to its effectiveness, low cost and environment friendly properties. It is used to remove odors caused chiefly by hydrogen sulfide (H2S) via biological treatments. RESULTS: In this study, numerical simulations using the thermal lattice Boltzmann method are implemented to investigate the effect of non‐isothermal conditions on heterogeneous flow through three biofilter models that are partly filled with porous media. The generalized Navier–Stokes model based on the Brinkman‐Forchheimer–extended Darcy model is used to make several assumptions. CONCLUSIONS: The numerical results indicate that the Rayleigh number has significant influence on the removal efficiencies of biofilters. There also exist critical Rayleigh numbers for biofilters under non‐isothermal conditions. If the Rayleigh number is less than the critical value, the flow heterogeneity will reduce with increasing Rayleigh number; otherwise, the flow heterogeneity will enhance with increasing Rayleigh number. Moreover, it was found that the performances of biofilters can be improved by designing non‐isothermal conditions between the porous media layers, i.e. by adjusting the Rayleigh number to optimize the detention time of waste air. © 2012 Society of Chemical Industry     

Electromotive force for solid-flame combustion of heterogeneous systems in loose and pressed states

By an example of condensed 3Zr + 2WO₃ and Al + Ni systems, it is demonstrated that the electromotive force of solid-flame combustion measured by probing in loose systems is significantly higher than that in the same systems in a pressed state. An explanation for this phenomenon is offered, based on the difference in electrical conductivity in different zones of the combustion wave in loose and pressed condensed systems. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 4, pp. 71–77, July–August, 2006.     

多孔介质内低热值乙烯燃烧的污染物排放特性试验研究

近年来低热值气体的利用慢慢进入大众视野。为了加大对低热值气体的利用,实现低热值气体的清洁排放,自行搭建了多孔介质实验台,探究乙烯在自由堆积氧化铝小球中的预混燃烧的污染物排放规律。在改变当量比、流速以及空隙率等工况下进行乙烯的燃烧并对出口烟气进行数据采集,分析在不同工况时的污染物排放情况以及乙烯转换率。实验结果表明多孔介质燃烧技术是一种可以高效清洁处理热值气体的燃烧方式,在较好的实验工况下CO的排放可以降低至125~187 mg/m³,NO的排放与当量比有关,和流速以及空隙率关系不大,整个实验过程中的NO出口浓度低于16 mg/m³。稳定燃烧情况下乙烯的转化率在80%～90%之间。实验结果对于高效清洁地处理低热值气体具有一定指导意义。     

Effect of confinement on the bubble points of hydrocarbons in nanoporous media

The bubble point of reservoir petroleum fluids in nanoporous media is an important parameter in shale oil production. We present experimental results on the bubble points of octane and decane confined in controlled‐pore glasses (CPGs) with pore sizes of 4.3 and 38.1 nm. Differential scanning calorimetry (DSC) is used to measure the temperature at which the vapor phase begins to form (i.e., the bubble point). We find that the bubble point is dramatically affected by pore diameter: at 38.1 nm the confinement effect is insignificant, but at 4.3 nm two distinct bubble points appear, suggesting two distinct populations of evaporating fluid. Deviations are as great as ±15 K for both peaks relative to the bulk bubble point for 4.3 nm CPGs. Thermogravimetric analysis is consistent with DSC, supporting the validity of these results. Based on these experiments and previous simulations, we propose a two‐state model for the nanoconfined hydrocarbons. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1772–1780, 2016     

多孔介质内气泡熟化特性孔隙尺度研究

多孔介质内的气泡熟化行为广泛存在于CO₂封存等领域,为探究多孔介质内气泡的熟化特性,本文采用空气作为模拟气体,通过可视化实验和数值计算,对双孔隙和四孔隙气泡熟化过程进行了研究,阐释了多孔介质非均质性对熟化过程的影响规律。结果表明：在双孔隙气体饱和度较小情况下,虽然也发生正向熟化,但是孔隙结构的存在使熟化速率明显低于自由流体情况;四孔隙研究显示多孔介质非均质性对气泡熟化过程影响显著,由于孔隙的几何限制,气泡在某些情况下会发生逆Ostwald熟化,即生长的气泡在充满当前孔隙空间后会停止生长并反向熟化导致尺寸缩小;在非均质多孔介质中,由于熟化作用,气泡有传质到大孔隙区域趋势,导致大孔隙区域富集大气泡,存在泄漏风险,从而影响封存。     

Stability of the combustion wave in a viscoelastic medium to small one-dimensional perturbations

The problem of stability of the conversion front in a viscoelastic medium is formulated. The stability study is performed by the method of small perturbations. Nonlinear equations are derived for decrements of decay and complex frequency. Several particular cases are analyzed. A significant effect of the time of relaxation of viscous stresses on the flammability limits for both high-velocity and low-velocity regimes is demonstrated. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 4, pp. 50–60, July–August, 2006.     

Effect of the addition of ultrafine aluminum powders on the rheological properties and burning rate of energetic condensed systems

The effect of small additives (1.25–5.00%) of ultrafine aluminum powders (UFAP) on the rheology and combustion of model four-component energetic condensed systems is studied. It is found that the addition of UFAP decreases the temperature of HMX decomposition. Small additives of UFAP increase the burning rate of model energetic condensed systems and decrease the exponent ν in the burning rate law without deteriorating the rheological characteristics of the model propellants. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 1, pp. 54–59, January–February, 2007.     

Influence of the boundary conditions on capillary flow dynamics and liquid distribution in a porous medium

After depositing a wetting liquid onto a porous medium surface, and under the influence of the capillary pressure, the liquid is imbibed into the porous medium creating a wetted imprint. The flow within the porous medium does not cease once all the liquid is imbibed but continues as a secondary capillary flow, where the liquid flows from large pores into small pores along the liquid interface. The flow is solved using the capillary network model, and the influence of the boundary condition on the liquid distribution within the porous medium is investigated. The pores at the porous medium boundaries can be defined as open or closed pores, where an open pore is checked for the potential threshold condition for flow to take place. In contrast, the closed pore is defined as a static entity, in which the potential condition for flow to take place is never satisfied. By defining the pores at distinct porous medium boundaries as open or closed, one is able to obtain a very different liquid distribution within the porous medium. The liquid saturation profiles along the principal flow direction, ranging from constant to steadily decreasing, to the profile with a local maximum, are found numerically. It is shown that these saturation profiles are also related to the geometrical dimension that is perpendicular to the flow principal direction, and changing the boundary type from open to closed allows the liquid distribution within the porous medium to be controlled. In addition to the liquid distribution, the influence of the boundary conditions on capillary pressure and relative permeability is investigated, where both parameters are not influenced by variation of the boundary condition types. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Effect of radiative heat transfer on the combustion wave propagation in a model of a heterogeneous system

The subject of investigation was the behavior of integral curves of the problem of combustion-wave propagation in a model of a heterogeneous system. The influence of radiative heat transfer on steady combustion regimes was considered. It was shown that for sufficiently large gaps between the plates in the system (when a quasihomogeneous temperature distribution still exists) in the regime of weak retardation by the growing product layer, the radiation can result in a notable acceleration of the combustion wave. In the regime of strong retardation with the remaining conditions being the same, the radiation can be neglected. Translated fromFiz. Goreniya i Vzryva, Vol. 34, No. 3, pp. 69–76, May–June 1998.     

Condensed combustion products of aluminized propellants. IV. Effect of the nature of nitramines on aluminum agglomeration and combustion efficiency

The condensed combustion products of two model propellants consisting of ammonium perchlorate, aluminum, nitramine, and an energetic binder were studied by a sampling method. One of the propellants contained HMX with a particle size D ₁₀ ≈ 490 μm, and the other RDX with a particle size _{D 10} ≈ 380 μm. The particle-size distribution and the content of metallic aluminum in particles of condensed combustion products with a particle size of 1.2 μm to the maximum particle size in the pressure range of 0.1–6.5 MPa were determined with variation in the particle quenching distance from the burning surface to 100 mm. For agglomerates, dependences of the incompleteness of aluminum combustion on the residence time in the propellant flame were obtained. The RDX-based propellant is characterized by more severe agglomeration than the HMX-based propellant — the agglomerate size and mass are larger and the aluminum burnout proceeds more slowly. The ratio of the mass of the oxide accumulated on the agglomerates to the total mass of the oxide formed is determined. The agglomerate size is shown to be the main physical factor that governs the accumulation of the oxide on the burning agglomerate. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 4, pp. 78–92, July–August, 2006.     

矿石回收率与贫化率关系的实验研究

分析了非均匀散体在放矿吕的流动特点，通过模拟试验，查明了放矿过程中矿岩接触面在下移过程中，矿，岩颗粒的掺杂情况，以及在多分段放矿过程中矿石回收率与贫化率之间的关系。     

非均匀度与矿石损失贫化率关系的实验研究

分析了非均匀崩落矿岩散体在放矿过程中流动特点，通过相似模拟实验，得出了矿岩散体非均匀度与放出矿石损失贫化率的关系，即在其它条件相同时，非均匀度越大，矿石的损失和贫化率也越大。这为非均匀矿岩的低贫化放矿提供了一条切实可行的技术途径。     

Experimental study of the combustion characteristics of methanol‐gasoline blends pool fires in a full‐scale tunnel

The combustion characteristics of methanol‐gasoline blends pool fires were studied in a series of full‐scale tunnel experiments conducted with different methanol and gasoline blends. The parameters were measured including the mass loss rate, the pool surface temperature, the fire plume centerline temperature, the ceiling temperature, the smoke layer temperature profile, the flame height, and the smoke layer interface height. The gasoline components were analyzed by GC‐MS. The effects of azeotropism on the combustion characteristics of the different blends were discussed. On the basis of the results of the fire plume centerline temperature, the ceiling temperature, and the flame height, it shows that the tunnel fire regime gradually switches from fuel controlled to ventilation controlled with increasing gasoline fractions in the blends. The fire plume can be divided into 3 regions by the fire plume centerline temperature for the different blends. The N‐percentage rule to determine the smoke layer interface height is found to be applicable for tunnel fires with different blends for N = 26.     

包覆层可靠性对高燃速火药燃速测试的影响及改进

利用恒压燃速测试法,测试了经硅橡胶包覆的高燃速药柱的燃速.结果表明,在30～80MPa时,样品燃速出现骤增现象.经分析得出,由于在高压下包覆层与高燃速药柱之间的黏结力降低,导致燃烧过程出现传火现象而使测得的燃速在高压下反常升高.通过采用新的包覆材料及包覆工艺后对药柱进行测试,结果表明,在高压下包覆可靠、燃烧稳定.指出选择传热系数小、黏接可靠的包覆材料是保障高压高燃速火药测试准确性的关键技术.