Detonation velocity Detonator

The Chapman-Jongnet (CJ) theory is a one-dimensional model that treats the detonation shock wave as a discontinnity with infinite reaction rate. The conservation equations for mass, momentum, and energy across the one-dimensional wave gives a unique solution for the detonation velocity (CJ velocity) and the state of combustion products immediately behind the detonation wave. Based on the CJ theory it is possible to calculate detonation velocity, detonation pressure, etc. if the gas mixtnre composition is known. The CJ theory does not require any information about the chemical reaction rate (i.e., chemical kinetics). 

Density is an important characteristic of explosives. Raising the density (e.g. by pressing or casting) improves -> Brisance and Detonation Velocity (- Detonation, Hydrodynamic Theory of Detonation). Low-density explosives, in contrast, produce a milder thrust effect (- also Loading Density - Cartridge Density). 

Primary explosives are substances which unlike secondary explosives show a very rapid transition from combustion (or deflagration) to detonation and are considerably more sensitive towards heat, impact or friction than secondary explosives. Primary explosives generate either a large amount of heat or a shockwave which makes the transfer of the detonation to a less sensitive secondary explosive possible. They are therefore used as initiators for secondary booster charges (e.g. in detonators), main charges or propellants. Although primary explosives (e.g. Pb(N3)2) are considerably more sensitive than secondary explosives (e.g. RDX), their detonation velocities, detonation pressures and heat of explosions are as a rule, generally lower than those of secondary explosives (Tab. 2.1). 

The performance potential of an explosive cannot be described by a single parameter. It is determined by the amount of gas liberated per unit weight, the energy evolved in the process (-> Heat of Explosion), and by the propagation rate of the explosive (detonation velocity -> Detonation). If an explosive is to be detonated in a borehole, the... 

Table 8-2. Detonation velocity, detonation density, and computed detonation pressure at the CJ point of energetic materials. 

Nitromethane RDX Aluminum flakes Ethyl ether Viscosity Density Detonation velocity Detonation temperature Detonation pressure... 

DETONATION VELOCITY DETONATION PRESSURE STRENGTH ENERGY BRISANCE SENSITIVITY FIvtMMABlLITY PERMISSIBILITY WATER RESISTANCE FUME Cl ASSIFICATION... 

In the past 15 years, the fibreoptic technique has been widely used for the determination of different detonation parameters such as detonation velocity, detonation wave shape, detonation temperature, etc. (Lu et al., 1985 Xianchu et al., 1985 Xinghai, 1985). 

Several photographic exposures are taken of the detonation front, the shock waves in the water, and the expanding tube-water interface (or bubble-water interface if the tube is absent). The optical data, shown schematically in Figure 2.12. are used to infer detonation velocity, detonation pressure (C-J states), and the release isentrope of the detonation products. A collection of aquarium test data is available in the data volume entitled Los Alamos Explosives Performance Data and on the CD-ROM. An animation of a NOBEL calculation of a PBX-9502 aquarium test is on the CD-ROM in the /MOVIE/AQUAR.MVE directory. 

Detonation Velocity. Detonation velocity can be determined in any of several ways the choice of a method probably depends more on the availability of equipment and well tested procedures than on any inherent advantage of a given method. 

Detonation. In a detonation, the flame front travels as a shock wave, followed closely by a combustion wave, which releases the energy to sustain the shock wave. The detonation front travels with a velocity greater than the speed of sound in the unreacted medium. 

The purpose of the well completion is to provide a safe conduit for fluid flow from the reservoir to the flowline. The perforations in the casing are typically achieved by running a perforating gun into the well on electrical wireline. The gun is loaded with a charge which, when detonated, fires a high velocity jet through the casing and on into the formation for a distance of around 15-30 cm. In this way communication between the wellbore and the reservoir is established. Wells are commonly perforated after the completion has been installed and pressure tested. 

Computer codes are used for the calculational procedures which provide highly detailed data, eg, the Ruby code (70). Rapid, short-form methods yielding very good first approximations, such as the Kamlet equations, are also available (71—74). Both modeling approaches show good agreement with experimental data obtained ia measures of performance. A comparison of calculated and experimental explosive detonation velocities is shown ia Table 5. 

Explosive Detonation pressure, GPa Bulk specific gravity Detonation velocity, km/s Contains high explosives Heat of detonation kj /g Excavated vol relative to equal wt of TNT... 

The calculated detonation velocity in room temperature acetylene at 810 kPa is 2053 m/s (61). Measured values are about 1000-2070 m/s, independent of initial pressure but generally increasing with increasing diameter (46,60—64). In a time estimated to be about 6 s (65), an accidental fire-initiated decomposition flame in acetylene at ca 200 kPa in an extensive piping system traveled successively through 1830 m of 76—203-mm pipe, 8850 m of 203-mm pipe, and 760 m of 152-mm pipe. 

Obtaining explosives with the proper energy, form, and detonation velocity is difficult. 

Explosives. The pressure, P, generated by the detonating explosive that propels the prime plate is direcdy proportional to its density, p, and the square of the detonation velocity, (25) ... 

The detonation velocity is contioUed by adjusting thepacking density oi the amount of added ineit matetial (26). 

In commercial practice, powdered explosives on an ammonium nitrate basis are used in most cases. Typical detonation velocities are between 1800 and 3500 m/s depending on the metal system to be bonded. The lower detonation velocity range is preferred for many metal systems in order to minimize the quantity of solidified melt associated with the bond-zone waves (12). In addition, subsonic detonation velocity explosives are required for the parallel cladding technique in order to avoid attached shock waves in the coUision region, which preclude formation of a good bond. 

Flame plating (D-gun) employs oxygen and fuel gas. In this method, developed by the Union Carbide Corporation, the gas mixture is detonated by an electric spark at four detonations per second. The powders, mixed with the gas, are fed under control into a chamber from which they are ejected when detonation occurs. The molten, 14—16-pm particles are sprayed at a velocity of 732 m/s at distances of 5.1—10.2 cm from the surface. The substrate is moved past the stationary gun. 

Deflagration to Detonation Transition A reaction front that starts out with velocities below the speed of sound and subsequently accelerates to velocities higher than the speed of sound in the unreacted material is said to have undergone a Deflagration to Detonation Transition. The possibility of transition is enhanced by confinement/turbulence generators in the path of the reaction front. 

Detonation A propagating chemical reaction of a substance in which the reaction front advances into the unreacted substance at equal to or greater than the sonic velocity in the unreacted material. 

The propagation of a shock wave from a detonating explosive or the shock wave induced upon impact of a flyer plate accelerated, via explosives or with a gun, result in nearly steady waves in materials. For steady waves a shock velocity U with respect to the laboratory frame can be defined. Conservation of mass, momentum, and energy across a shock front can then be expressed as... 

Figure 4.9. Shock pressure versus particle velocity for engineering materials, geological material, and explosive detonation products. Intersection of detonation product curves with nonreactive media predicts shock pressure and particle velocity at an explosive sample interface. (After Jones (1972).)...

DETONATION Explosion in which the flamefront advances at more than supersonic velocity. 

Chemical explosives detonate, or deflagrate. Detonating explosives (e.g., TNT or dynamite) rapidly decompose to produce high pressure and a shock front (travels faster than the velocity of sound). Deflagrating explosives (e.g., black and smokeless powders) bum fast, prodr er... 

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