Silver Azide Pellet Research Articles

Blowoff mechanism of airburst blast extinguishment of a methane air jet diffusion flame with micro explosive

In the study, experiments of airburst blast extinguishment of a methane-air jet diffusion flame have been conducted with 20 mg silver azide pellets, and the extinguishing processes have been observed using a high-speed camera and schlieren method. From the experimental results, we have examined the extinguishing mechanisms. When the blast wave interacts with the diffusion flame, vortex pair is generated in the flame due to the baroclinic effect which is caused by the misalignment between the pressure gradient of the blast wave and the density gradient in the combustion region. The vortical motion leads to the local extinction, and finally, the whole flame is blown off. In airburst, a reflected shock wave occurs on the ground surface. Depending on the height of burst and the distance between the explosion location and the extinguishing target, the reflected blast wave merges with the incident blast wave and the Mach stem is formed before the blast wave interferes with the diffusion flame. As a result, it is found that the extinguishing effectiveness is increased by the presence of the Mach Stem. Moreover, the optimal height of burst in the airburst blast extinguishment is clarified.

OS24-4 Effective Range of Blast Extinguishment with Silver Azide Pellets(Scale modeling on heat and mass transfer,OS24 Scale modeling,FLUID AND THERMODYNAMICS)

OS24-4 Effective Range of Blast Extinguishment with Silver Azide Pellets(Scale modeling on heat and mass transfer,OS24 Scale modeling,FLUID AND THERMODYNAMICS)

132 水面近傍で発生する膨張波および気泡現象(流体工学IV,一般講演)

This paper reports a preliminary experimental result of the expansion wave and cavitation bubble generation near the water surface. Underwater spherical shock wave generated by detonating of micro explosive of a 10 mg silver azide (AgN_3)pellets propagated and reflected from the water surface. The reflected wave is an expansion wave. The process of expansion wave and cavitation bubble generation near the water surface were observed by shadowgraph method and recorded by a high-speed camera. The pressure distribution near the water surface was measured by a PVDF needle hydrophone.

Pressure Generation from Micro-Bubble Collapse at Shock Wave Loading

This paper reports the result of a primary experimental and analytical study used to explore a reliable technology that is potentially applicable to the inactivation of micro-creatures contained in ship ballast water. A shock wave generated by the micro-explosion of a 10mg silver azide pellet in a 10mm wide parallel test section was used to interact with a bubble cloud consisting of bubbles with average diameter 10µm produced by a swirling flow type micro-bubble generator. Observations were carried out with a high-speed camera, IMACON200, and the corresponding rebound pressures of the collapsing bubbles were measured with a fiber optic probe pressure transducer that provides high spatial and temporal resolutions. We found that micro-bubbles collapse in several hundred nanoseconds after the shock exposure and the resulting peak pressure pulses that repeatedly occurred exceeded well over 200MPa measured at the 20mm distance from the explosion center. These continued for well over 20µs. The experimental pressure responses were explained by solving the one-dimensional bubble Rayleigh-Plesset equation. Such high peak pressures could be used effectively for the inactivation of micro-creatures contained in ship ballast water.

Shock Hugoniot and equations of states of water, castor oil, and aqueous solutions of sodium chloride, sucrose and gelatin

This paper reports a result of experiments for the determination of reliable shock Hugoniot curves of liquids, in particular, at relatively low pressure region, which are needed to perform precise numerical simulations of shock wave/tissue interaction prior to the development of shock wave related therapeutic devices. Underwater shock waves were generated by explosions of laser ignited 10 mg silver azide pellets, which were temporally and spatially well controlled. Measuring temporal variation of shock velocities and over-pressures in caster oil, aqueous solutions of sodium chloride, sucrose and gelatin with various concentrations, we succeeded to determine shock Hugoniot curves of these liquids and hence parameters describing Tait type equations of state.

衝撃波作用による微小気泡群の崩壊と衝撃圧生成(流体工学,流体機械)

This paper reports the result of a primary experimental and analytical study used to explore a reliable technology that is potentially applicable to the inactivation of micro-creatures contained in ship ballast water. A shock wave generated by the micro-explosion of a 10mg silver azide pellet in a 10mm wide parallel test section was used to interact with a bubble cloud consisting of bubbles with average diameter 10µm produced by a swirling flow type micro-bubble generator. Observations were carried out with a high-speed camera, IMACON200, and the corresponding rebound pressures of the collapsing bubbles were measured with a fiber optic probe pressure transducer that provides high spatial and temporal resolutions. We found that micro-bubbles collapse in several hundred nanoseconds after the shock exposure and the resulting peak pressure pulses that repeatedly occurred exceeded well over 200MPa measured at the 20mm distance from the explosion center. These continued for well over 20µs. The experimental pressure responses were explained by solving the one-dimensional bubble Rayleigh-Plesset equation. Such high peak pressures could be used effectively for the inactivation of micro-creatures contained in ship ballast water.

Experimental Determination of Shock Hugoniot for Water, Castor Oil, and Aqueous Solutions of Sodium Chloride, Sucrose and Gelatin

Shock waves are indispensable tools for medical applications, and hence their interactions with human tissue become one of the most important basic research topics. In this paper, the determination of shock Hugoniot curves for liquids that can model human tissue, namely water, castor oil, and aqueous solutions of sodium chloride, sucrose and gelatin, at 10 and 20 weight percent are presented. Underwater shock waves were generated by ignition of 10 mg silver azide pellets and time variations of over-pressures were measured and simultaneously the shock speed was measured by the time of flight technique. Then shock Hugoniot curves were obtained, by assuming the Tait type equation of state, to relate the estimated density and measured pressure values. Results show in the cases of aqueous solutions that increasing amount of additives into water causes only a very minute decrease in the compressibility of the solution. This difference was more pronounced in the case of sodium chloride, less for gelatin, and almost none for sucrose aqueous solution.

Implosion of a spherical shock wave reflected from a spherical wall

The paper describes results of experiments of a converging spherical shock wave reflected from a spherical wall. In order to visualize the motion and the flow field behind the shock waves, an aspheric lens-shaped transparent test section made of acrylic PMMA (polymethyl methacrylate) with an inner spherical cavity was designed and constructed. This test section made optical flow visualization with collimated object beams possible. Spherical shock waves were produced at the centre of the spherical cavity by explosion of silver azide pellets ranging from 1.0 to 10.0 mg with corresponding energies of 1.9 to 19 J. The charges were ignited by irradiation of a pulsed Nd:YAG laser beam. Pressures were also measured at two points with pressure transducers mounted flush at the inner wall of the test section. The pellet was simultaneously ignited on two sides or was shaped to produce a uniform diverging spherical shock wave. This spherically diverging shock wave was reflected from the spherical inner wall of the test section to form a converging spherical shock wave. We visualized the shock-wave motion by using double exposure holographic interferometry and time-resolved high-speed video recording. The sequence of diverging and converging spherical shock-wave propagations and their interaction with gaseous explosion products were observed. The convergence, acceleration and stability of the imploding shock wave in the test section were studied.

Experimental and numerical studies of underwater shock wave attenuation

The attenuation of an underwater shock wave by a thin porous layer is studied both experimentally and numerically. The shock waves are generated by exploding 10 mg silver azide pellets and the pressures at different distances from the explosion center are measured. Measurements are also carried out with a gauze layer placed between the explosion source and the pressure gauge. The results with and without the gauze layer are compared evaluating the shock wave attenuation. Numerical simulations of the phenomenon are also carried out for a simple wave attenuation model. The results are compared with the experimental data. Despite the simple mathematical model of wave attenuation, the agreement between the experimental and numerical results is reasonable.

アジ化銀ペレットのレーザ起爆で 発生する衝撃波の初期形状

本論文は,実験室内で発生可能な微小爆発を利用した大規模爆発のアナログ実験手法開発に向けた基礎研究として,微小爆薬で発生させた衝撃波の初期伝播様態を可視化計測と数値解析を用いて検討し,球状衝撃波が得られるまでの伝播様態を詳細に明らかにした. 微小爆発は,アジ化銀ペレット（AgN3,直径1.5 mm,長さ1.5 mm,質量10 mg）のレーザ起爆で発生させた. 可視化手法は,方向指標型カラーシュリーレン法（Direction-Indicating Color Schlieren method: DICS）である. DICSは,従来型のカラーシュリーレン法と異なり,可視化面の密度こう配ベクトルを色分布として表現する特長を持つ. 起爆方法に関しては,光ファイバ経由でレーザ光を微小爆薬に伝達する方法と空中で直接照射する方法により計4種類の起爆様式を検討した. これらにより発生初期（起爆後180 μs）の衝撃波をそれぞれ計測した. その結果,ペレットから発生する爆発生成気体噴流が,衝撃波形状に強く影響を与えていることを確認した. そこで,噴流発生の支配要因としてペレット形状と起爆点に着目し,実験と数値解析で考察した. 実験は,10 mgペレットを砕いて作成した質量 500 μgの不定形アジ化銀微小片をレーザ起爆し,超高速フレームカメラを用いた連続撮影法で発生した衝撃波の伝播様態の可視化計測を行った. その結果,不定形アジ化銀の起爆では,噴流が衝撃波に影響を与えないことを確認した. 次に,起爆点の影響を衝撃解析コード（AUTODYN-2D）で評価した結果,衝撃波形状及び反応生成気体噴流形状など,可視化計測での観測結果とよく一致する結果を得た. さらに,衝撃波が受けた影響（形状の歪み等）は,伝播するにつれ小さくなり,中心から距離約120 mm 以遠では,完全な球状衝撃波を形成することを確認した.

Formation of a Liquid Jet by Interaction between a Laser-Induced Bubble and a Shock Wave

There are some problems such as a narrow therapeutic time window and severe side effects of fibrinolytics in the therapy of cerebral embolisms. Therefore, it is necessary to develop a new method to remove a cerebral thrombus more rapidly with fewer fibrinolytics. A Q-switch pulsed holmium (Ho): YAG laser with 86 mJ/pulse, pulse duration of 200ns and wavelength of 2.1 mm was used. The laser beam was transmitted through a 0.6 mm diameter quartz optical fiber. Experiments were conducted in a stainless steel container equipped with observation windows . The test chamber was filled with distilled water at 283K. At first, the formation of laser-induced bubbles in a 4 mm diameter glass tube was observed. The bubble gradually expanded and reached a maximum size at about 1 ms after irradiation. A shock wave induced by ignition of silver azide pellet was interacted with it at 500mus before Ho:YAG laser irradiation, which resulted in forming a liquid jet. This liquid jet penetrated into an artificial thrombus made of gelatin, and its maximum penetration depth was 4.2 mm, which was nearly twice deeper than the laser irradiation only (2.2 mm). Combination of this liquid jet and fibrinolytics will realize more rapid recanalization with fewer drugs.

Holographic interferometric visualization of weak shock waves in castor oil packed with equal-diameter gelatine spheres

The attenuation of shock waves in castor oil in which equal-diameter gelatine spheres were packed was measured with hydrophones at various stand-off distances. The motion of shock waves was quantitatively visualized by using double exposure holographic interferometry. Diameters of gelatine spheres under study were 3.0 mm ±1%, 4.5 mm ±1%, and 6.0 mm ±1%. Shock waves were produced at the center of a chamber in which gelatine spheres of total 4 L in volume were densely immersed in castor oil. In order to generate shock waves, irradiation of a pulsed YAG laser beam on silver azide pellets were used. The weight of silver azide pellets ranged from 3 μg to 10 mg, with their corresponding energy of 4.5 mJ to 15 J. The effect of the nonuniformity on the shock-wave attenuation created due to the multiple interaction of shock waves with the gelatine spheres was experimentally clarified. The result will be useful to establish a model of human tissue in numerically simulating the complex interaction of underwater shock waves with human tissue which takes place in shock-wave therapies.

Liquid jets, accelerated thrombolysis: a study for revascularization of cerebral embolism

A prior study has reported that a rapid recanalization therapy of cerebral embolism, using liquid jet impacts generated by the interaction of gas bubbles with shock waves, can potentially penetrate through thrombi in as little as a few μs with very efficient ablation (Kodama et al. 1997). The present study was undertaken to examine the liquid jet impact effect on fibrinolysis in a tube model of an internal carotid artery. First, the conditions for generating the maximum penetration depth of liquid jets in the tube were investigated. Gelatin was used to mimic thrombi. The shock wave was generated by detonating a silver azide pellet weighing about a few μg located in a balloon catheter. The collapse of the inserted gas bubbles and the subsequent liquid jet formation were recorded with high-speed photography. Second, thrombi were formed using fresh human blood from healthy volunteers. The fibrinolysis induced by the liquid jet impact with urokinase was explored. This was conducted under selected conditions based on the experiment using the gelatin. Fibrinolysis was calculated as the percentage of the weight loss of the thrombus. Fibrinolysis with urokinase alone and with a single liquid jet impact with urokinase was 1.9 ± 3.7% (n = 16) and 20.0 ± 9.0% (n = 35), respectively, for an incubation time of 60 min. Statistical differences were obtained between all groups (ANOVA). These results suggest that liquid jet impact thrombolysis has the potential to be a rapid and effective therapeutic modality in recanalization therapy for patients with cerebral embolism and other clinical conditions of intra-arterial thrombosis.

Analog experiments of tissue damage generated during ESWL treatments

Among the possible causes of ESWL tissue damage, the interaction of shock waves with cavitation bubbles is believed to be the most responsible. A series of analog experiments has been carried out for clarifying the mechanism of tissue damage during ESWL. Interactions of shock waves with single air bubbles in water were examined, including the formation of a rebound shock wave and the generation of liquid microjets. The collapse of air bubbles which were attached to gelatin walls and exposed to shock waves was quantitatively observed using double-exposure holographic interferometry and high-speed cinematography. In these analog experiments, shock waves were created via microexplosives: 10-mg silver azide pellets were pasted on the tip of an optical fiber and detonated with the radiation of a pulsed YAG laser beam. Details of the bubble collapse were well resolved. More complex materials analogous to human tissue have been tested and will be presented also.

Cavitation phenomena in extracorporeal microexplosion lithotripsy

An experimental investigation was made of cavitation phenomena induced by underwater shock wave focusing applied to the extracorporeal microexplosion lithotripsy (microexplosion ESWL). Firstly an underwater microexplosion generated by detonation of a 10 mg silver azide pellet was studied and secondly underwater shock focusing and its induced cavitation phenomena were investgated. Underwater shock wave was focused by using a semi-ellipsoidal reflector in which a shock wave generated at the first focal point of the reflector was reflected and focused at the second focal point. It is found that an explosion product gas bubble did not produce any distinct rebound shocks. Meantime cavitation appeared after shock focusing at the second focal point where expansion waves originated at the exit of the reflector were simultaneously collected. A shock/bubble interaction is found to contribute not only to urinary tract stone disintegration but also tissue damage. The cavitation effect associated with the microexplosion ESWL was weaker in comparison with a spark discharge ESWL. The microexplosion ESWL is an effective method which can minimize the number of shock exposures hence decreasing tissue damage by conducting precise positioning of urinary tract stones.

104 衝撃波作用による気泡の挙動

The interaction of a shock wave with a gas bubble was visualized by double exposure holographic interferometry or shadowgraph for four combinations of liquid/gas, such as, silicone-oil (1.0 cSt)/air, silicone-oil (10cSt)/air, water/air, and water/helium. The gas bubble was exposed to a spherical shock wave generated by detonating a 10 mg silver azide pellet. The gas bubble contracted by hitting of the shock, and aa liquid jet formed, as the case may be. Eventually, one or plural rebound shock waves occurred. It was found that there are at least three types of rebound shocks. The generation of these for each type is explained by sequential flow visualizations. Numerical simulations were also carried out using GRP/MIT scheme.

Focusing of underwater shock waves and the mechanism of high pressure generation.

Underwater spherical shock focusing can be obtained in a closed ellipsoidal-shaped cavity by the explosion of a small silver azide pellet. The present paper reports on an experimental and numerical study of the generation of high pressure and its mechanism. The shock focusing pressure was measured in a 500mmx700mm ellipsoidal cavity with a PVDF pressure transducer which has a wide frequency response. A high pressure of 3000bar was obtained for a 100mg silver azide pellet. The process of shock focusing was also studied numerically by the TVD finite difference scheme. A quantitative agreement was obtained between the experiment and the simulation. It was demonstrated that the underwater shock focusing is one of the most efficient methods to obtain a controlled high pressure in a small region.

16 水中衝撃波フォーカッシングの可視化と数値シミュレーション

Recently, underwater shock wave focusing has been applied to the non-invasive disintegration of kidny stones. However, due to the highly non-linearity, the shock wave focusing phenomenon is stil unresolved. Therefore, it is crucial to clarify this complicated phenomenon. In this paper, the experimental and computational study of the underwater shock wave focusing is presented. The underwater shock wave was generated by using a 5mg lead azide (Pb(N3)2) pellet and a 10mg silver azide (AgN3) pellet, and reflected by an ellipsoidal cavity, and focuses at 2nd focal point. The focusing process was visualized by using holographic interferometry. The peak pressure along the axis of the reflector were also measured by Kstler 601H pressure transducer. The interferometric results were compared with the numerical simulation conducted by using a Total Variation Diminishing (TVD) finite difference scheme. A good agreement was obtained between the computation and experiment.

17 水中衝撃波と気泡の干渉について

The present paper reports the visualization study of the initiation of a shock wave generated by a rebounding bubble and a micro-jet induced when the bubble is collapsed. The underwater spherical shock wave is obtained by using a 10 mg silver azide(AgN3) pellet, and visualized by using double exposure holographic interferometry. In order to understand the quantitative properties of this phenomenon, the density and pressure distributions were evaluated by measuring the interference fringes and using Tait equation. Consequently, the sudden pressure change when the shock wave is generated by the rebounding bubble and the structure of the micro-jet were clarified