Numerical investigation of explosion suppression by inert particles in straight ducts

This paper is devoted to the mitigation of explosions in long galleries by means of an inert dust cloud. In practice, this technique bases on mounting shelves under the roof, on which the inert dust is distributed. This issue was numerically investigated in this research. The medium was assumed to be a two-phase mixture consisting of a fast flowing gas (representing the explosion) and a cloud of solid particles (representing the dust phase). The model makes use of the Eulerian-Lagrangian approach, where the solid particles are modelled as moving points, interacting with the gas flow. The objective was to analyse the suppression process and compare with experimental findings.     

Production of rapidly solidified magnesium powders by gas atomisation

Abstract

Rapidly solidified powders of magnesium were produced in a pilot plant gas atomiser. Argon gas at 1·85 MPa was used as the atomising agent in a ‘confined design’ nozzle operating vertically upwards. Oxygen was introduced into the plant at a level of 1% to cause controlled oxidation to passivate the particles. Powders were sized using dry sieving down to 32 μm and wet sieving for smaller sizes. Sauter mean diameter varied between 18·45 and 21·40 μm depending on the rate of production. The distribution of sizes was typically bimodal with the separation point of the peaks at ~34 μm. This supported the particle formation theory developed earlier which predicted that atomised metal powders consisted of two families of particles. The fine range of the particles was spherical up to ~30 μm in diameter. In the coarse range, which was virtually free of satellites, the overall round nature of the particles was preserved, but some oblong shapes were also observed. Comparison with the atomisation of aluminium shows that, despite having a lower surface tension, magnesium powders are marginally coarser than those of aluminium produced under the same conditions. This is explained in terms of the faster acceleration of magnesium droplets (by virtue of lower density) in flight during secondary breakup.

MST/915     

水中爆炸参数测试方法研究

本文结合某次测量试验的实例,介绍了水中爆炸参数测试的方法及测试系统的组成,还就阻抗匹配、防水和抗干扰等问题进行了探讨.     

Evaluating pressure generated by the electric explosion of a foil ring in water

The pressure developed by an acoustic shock wave and the integral of action of the electric discharge formed during the electric explosion of a flat foil ring in a condensed medium are evaluated by assuming a quasi-stationary character of the process.     

Pressure waves generated by a nanosecond electric explosion of a tungsten wire in water

We have studied pressure waves generated during a nanosecond electric explosion of 70-μm-thick tungsten wires in water. The measurements were performed at a distance of 3–8 mm from the exploding conductor. In order to reduce the error caused by two-dimensional effects, we used pressure sensors with dimensions not exceeding 3 mm. The results of measurements revealed a two-component structure of the electric-explosion-induced shock wave.     

The effect of thermal explosion in a supercritical water

The conversion of hydrocarbons (eicosane, naphthalene, and synthetic bitumen) dissolved in super-critical water (SCW) was studied in a batch reactor at a pressure of P=30 MPa and a range of temperatures from 450 to 75°C. It was established that water participates in the conversion process on a chemical level: in particular, oxygen from water molecules is involved in the formation of carbon oxides. Even in the absence of added molecular oxygen, the process of naphthalene and bitumen conversion in a certain temperature interval exhibited an exothermal character. Upon adding O₂ into SCW, the oxidation reaction may proceed in a burning regime with self-heating of the mixture. Under certain conditions, the self-heating process may lead to the thermal explosion effect accompanied by ejection of the substance from the reactor, which is explained by the high rate of hydrocarbon burning in SCW.     

Passive navigation from image sequences by use of a volumetric approach

The paper describes a volumetric approach to depth estimation for robot navigation with use of only an approximately calibrated translating camera. Our approach is related to techniques for photo-realistic object reconstruction but with the emphasis on issues associated with navigation. The technique performs three-dimensional matching by a process of image interpolation and can adjust for errors in camera position. The reconstruction is achieved from a small angular range of scene views, and the technique is demonstrated to be insensitive to large errors in the camera positions. The ability to correct for more critical errors such as the camera orientation is shown to significantly improve the algorithm's performance. Our technique is demonstrated on real image sequences and compares favorably with techniques based on optical flow.     

Homogeneous heating,evaporation and explosion of a water aerosol drop

Pre-explosion heating of a drop of aqueous aerosol is considered for conditions where thermal conductivity and pressure gradients within the drop may be neglected.Translated from Inzhenerno-fizicheskii Zhurnal, Vol. 61, No. 2, pp. 253–261, August, 1991.     

Amorphous silica containers for germanium ultrapurification by zone refining

We have studied the wetting behavior of molten germanium on silica ceramics and amorphous silica coatings in vacuum at a pressure of 1 Pa and a temperature of 1273 K. The results demonstrate that the wetting of rough surfaces of ceramic samples and coatings by liquid Ge is significantly poorer than that of the smooth surface of quartz glass. The contact angle of polished glass is ~100°, and that of the ceramics and coatings increases from 112° to 137° as the total impurity content of the material decreases from 0.120 to 1 × 10^–3 wt %. Using experimental contact angle data, we calculated the work of adhesion of molten Ge to the materials studied. Its value for the surface of the ceramics and coatings decreases from 0.45 to 0.20 J/m² with decreasing impurity content, whereas the work of adhesion to a smooth glass surface is 0.55 J/m². We have fabricated fused silica test containers coated with high-purity amorphous silica. Using horizontal zone refining, we obtained germanium samples with a carrier concentration difference on the order of 10¹¹ cm^–3.     

Rapid, nondestructive near-infrared assay for water in sealed dimethyl sulfoxide compound repository containers

Water contamination in dimethyl sulfoxide (DMSO) compound libraries is a recognized problem in the pharmaceutical industry. We describe a nondestructive, near-infrared (NIR) assay for water contamination inside the sealed containers used for compound libraries. This assay does not require opening the containers. We also report our observation of the permeation of water from laboratory air through the sealed container and into the DMSO solution over a period of months, as well as the rate of water absorption by DMSO directly exposed to laboratory air.     

Gasdynamic regimes of evaporation and explosion of a water aerosol droplet

The heating, evaporation, and explosion regimes for a homogeneous water aerosol droplet are studied. Numerous theoretical and experimental results are analyzed and compared.Translated from Inzhenerno-fizicheskii Zhurnal, Vol. 64, No. 1, pp. 29–33, January, 1993.     

The roles of foam ceramics in suppression of gas explosion overpressure and quenching of flame propagation

In order to substantially suppress the shock waves resulting from gas explosions in coal mines as well as to reveal the mechanism of explosion flame quenching by foam ceramics, a rectangular explosion test pipe was designed, which has a 200 mm × 200 mm cross-section and is similar in shape to the roadways in coal mines. Explosion flame propagation characteristics in empty pipe and in the presence of Al₂O₃ and SiC foam ceramics were experimentally investigated. To obtain direct observations, the flame propagation was photographed by a high-speed camera. Furthermore, the mechanism of foam ceramics affecting gas explosion propagation was analyzed. The results demonstrate that the foam ceramics attenuate drastically the maximal explosion overpressure by up to fifty percent; the interconnected micro-network structure of the foam ceramics contribute to quenching gas explosion flame and suppressing shock wave overpressure. These important findings hint that, if properly designed and deployed, this material is expected to be developed into a new suppression and isolation technique against multiple and continuous gas explosions that are presently a grave threat to production safety of coal mines across China and the rest of the world.     

Preparation of alumina and alumina-silica powders by wire explosion resulting from electric discharge

Wires of aluminium and aluminium-silicon alloys containing 5.2 and 12.1 wt% Si were exploded in air by electric discharge, and the properties of the powders obtained were examined. The powders consisted of large particles of several micrometres and very fine spherical ones, which were formed from the metallic droplets and vapours, respectively, and were mostly oxidized. The large particles decreased with an increase in the charged energy. Although the particle-size distribution was broad, the average particle sizes were small and were increased from 0.7 m to 1.3 m with an increase in the charged energy. These powders were identified as -alumina, amorphous alumina-silica compound and a small amount of the metal. The amorphous phase crystallized to mullite in the temperature range 1153–1243 K, and the crystallization temperature fell with increase in the charged energy because the amount of fine particles formed from the vapours increased.     

On the role of exothermal chemical reaction during wire explosion in water

The explosion of a metal wire in water, accompanied by exothermal chemical reaction with evolution of a large amount of heat, gives rise to thermal ionization of the reaction products. As a result, a dense plasma is generated and energy on the order of or greater than that initially accumulated in the storage battery is liberated.     

典型战斗部水下爆炸侵彻仿真

为了研究典型战斗部水下侵彻情况,采用ANSYS-LS/DYNA 3D有限元仿真软件,对圆柱形装药和半球形空穴装药水中爆炸情况进行数值模拟,并分析了两者冲击波压力、气泡直径的变化。结果表明:25μs时,半球形空穴装药近距离产生的冲击波压力是圆柱形装药的3倍多,但随着距离的增大,不同装药的影响逐渐减小;500μs时,半球形空穴装药水中爆炸形成的气泡轴向直径是圆柱形装药的1.5倍。采用ANSYS-LS/DYNA 3D有限元仿真软件,对圆锥形装药战斗部和半球形装药战斗部爆炸成型和水中侵彻情况进行数值模拟,结果表明:半球形装药战斗部形成的射流外形良好,侵彻水层的速度降较小,更适合水中侵彻破坏。     

Time efficiency and physical workload in manual picking from large containers

A common task in both trade and manufacturing, manual picking from large containers often involves considerable physical workload, as well as low efficiency and varying picking times. With quantitative evidence from an industrial setting, the paper provides detailed insights into how physical workload and picking time vary in picking from large containers. Components at a short horizontal distance from the picker and at the top instead of the bottom of the pallet are associated with shorter picking time and lower physical workload. Moreover, pallets tilted 45° towards the picker are associated with picking times that are significantly shorter on average and display smaller variations than horizontal pallets. The effects that the tilting of the pallets has on physical workload differs depending on component characteristics and from which section of the containers picking was performed. In the study, the greatest values of physical workload were observed for the tilted pallets.     

典型战斗部水下爆炸侵彻仿真

为了研究典型战斗部水下侵彻情况,采用ANSYS-LS/DYNA 3D有限元仿真软件,对圆柱形装药和半球形空穴装药水中爆炸情况进行数值模拟,并分析了两者冲击波压力、气泡直径的变化。结果表明:25μs时,半球形空穴装药近距离产生的冲击波压力是圆柱形装药的3倍多,但随着距离的增大,不同装药的影响逐渐减小;500μs时,半球形空穴装药水中爆炸形成的气泡轴向直径是圆柱形装药的1.5倍。采用ANSYS-LS/DYNA 3D有限元仿真软件,对圆锥形装药战斗部和半球形装药战斗部爆炸成型和水中侵彻情况进行数值模拟,结果表明:半球形装药战斗部形成的射流外形良好,侵彻水层的速度降较小,更适合水中侵彻破坏。     

水压爆破拆除钢筋砼污水池

介绍了利用水压爆破拆除钢筋砼污水池的施爆方案,采用多个药包双雷管并串并复式网路取得满意的爆破效果.