Russell E. Duff

Shock‐Tube Performance at Low Initial Pressure

An electron beam densitometer has been used to investigate the behavior of a conventional 1⅛‐in. i.d. shock tube operating at initial pressures of the order of 1 mm Hg. These experiments show that such a shock tube does not perform as predicted by simple theory. Most of the experiments were performed in argon with shock Mach numbers ranging between 1.2 and 7.0. The most striking observation was that for a given shock velocity, Ms = 1.6, the distance between the shock wave and contact surface as observed at the densitometer was proportional to initial pressure and independent of expansion chamber length over a tenfold range of tube length. At an initial pressure of 0.5 mm Hg the time interval between the arrival of the shock and the contact surface varied between 600 μsec at Ms = 1.2 and 20 μsec at Ms = 7.0. The diaphragm pressure ratio (Ar ‐ Ar) required to produce a shock of velocity Ms = 1.6 varied from 200 at an initial pressure of 0.25 mm Hg to 20 at an initial pressure of 50 mm Hg. For a given diaphr...

Effects of Diffusion on Interface Instability between Gases

Experiments are described concerning the interface instability which arises when an argon‐bromine mixture falls under gravity into air or into helium. Existing theories which include viscosity effects fail to explain the observed amplitude growth rate, but it is shown that approximate inclusion of diffusion effects allows calculation of all features of early perturbation growth accurately to within experimental error.

Equilibrium Composition of the C/H System at Elevated Temperatures

Thermodynamic functions for a large number of C–H molecules were computed from the molecular parameters presented in the preceding paper. These functions and others taken from the literature were used to calculate the equilibrium composition of the C/H gas phase system over the composition range C/H=1/10, ¼, ½, 1, 2, 3. The temperature range was 500–5000°K, and the pressures used were 0.1, 1.0, and 10 atm. In additional calculations solid carbon was assumed to be present. Representative graphs of the results are presented. They show that the familiar, stable hydrocarbons are not important in characterizing the equilibrium composition above 2000°K. Acetylenic molecules and their radicals dominate the composition at high temperatures.

Calculation of Reaction Profiles behind Steady-State Shock Waves. I. Application to Detonation Waves

A numerical procedure for the integration of an arbitrary system of kinetic equations subject to the constraints imposed by steady state shock hydrodynamics is described. The detonation profile has been calculated for a 2H2+O2+Xe mixture at an initial pressure of 30 mm Hg. These conditions correspond to those used by Kistiakowsky and Kydd in a measurement of the wave profile. The calculated profile is in qualitative agreement with the measured one. The calculation provides empirical evidence that a frozen sound speed definition of the Chapman‐Jouguet state cannot correspond to reality.

Measurement of the Chapman‐Jouguet Pressure and Reaction Zone Length in a Detonating High Explosive

The Chapman‐Jouguet pressure and the reaction zone length in detonating Composition B containing 63 percent RDX at a density of 1.67 g/cc have been measured by determining the initial free surface velocity imparted to aluminum plates as a function of plate thickness. The C‐J pressure is 0.272 megabar and the reaction zone length is 0.13 mm. The experimental free surface velocity‐plate thickness curve provides powerful confirmation for the pressure profile in a detonating explosive predicted by the hydrodynamic theory of detonation proposed by Zeldovich, von Neumann, and Doring.

Investigation of Spinning Detonation and Detonation Stability

The stability of a detonation wave and the nature of a spinning detonation have been investigated by observing the patterns inscribed by the wave in soot coatings on films located on the circumference of the detonation tube and on the end plate. The detonation instability reported by others persists to an initial pressure of over 2 atm and to wave velocities at least 75% greater than the equilibrium value. The wave front of a simple spinning detonation contains a complex Mach interaction with wave inclinations as high as 37° to the tube diameter. The acoustic theory of spinning detonation does describe high‐order spin if it is assumed that two or more modes of vibration coexist.

Kinetic Studies of Hydroxyl Radicals in Shock Waves. I. The Decomposition of Water between 2400° and 3200°K

The decomposition of water vapor has been studied at temperatures between 2400° and 3200°K generated in plane shock waves by following changes in the concentration of OH with time. Specific radiation absorbimetry permits these measurements to be made with microsecond resolution. The source of OH radiation used was a flash lamp containing water vapor. Measurements were made on the gas behind reflected shock waves in argon at initial pressures near 50 mm Hg and containing the reactant, H2O vapor, in amounts of the order of 1 mole %. The shock tube and associated electronic and optical equipment are described. Problems of purity, chemical analysis, and reduction of data are discussed. Absorption by OH was calibrated with the equilibrium mixtures resulting from the decomposition of H2O and from the reaction of H2 and O2. The rate of formation of OH from H2O is proportional to the H2O concentration and nearly independent of the argon pressure. The effective activation energy is about 50 kcal/mole. Addition of ...

Precision Measurement of Detonation and Strong Shock Velocity in Gases

A simple system is described for determining the velocity of detonation or strong shock waves, with temperatures above 3000°K, by using the conductivity behind the wave. Wave contact is made by two 36‐mil wires set 0.1 inch apart in a Teflon plug mounted in the experimental tube. When a wave passes, signals are produced across a 30‐K resistor in series with these wires and a 0.001 μf capacitor charged to 300 v. Any number of circuits may be paralleled across a single signal resistor if a diode is added to each circuit to prevent signal deterioration. The arrival time of a wave at a pin can be determined with an accuracy of almost 10−8 sec from an oscilloscope record of the signals. The principal advantages of this system are excellent space resolution and very simple basic circuitry. An amplifier is described which can be used with an individual pin circuit to fire a thyratron and extend the range of applicability of this system to waves with temperatures as low as 1000°K.

Equation of State of Gases by Shock Wave Measurements. II. The Dissociation Energy of Nitrogen

The results of equation of state measurements made behind strong shock waves in nitrogen are consistent only with the higher of the two spectroscopically acceptable values of the dissociation energy of nitrogen, 9.764 ev.

Precision Flash X‐Ray Determination of Density Ratio in Gaseous Detonations

An x‐ray densitometer has been used to measure the density ratio across a detonation wave in a number of different gaseous mixtures involving C2H2, C2N2, or H2 with O2 and Kr. In a 3‐in. i.d. tube at an initial pressure of 60 cm the density ratios observed were between 1.64 and 1.67. Investigations of the influence on density ratio of tube diameter at constant initial pressure and of initial pressure at constant tube diameter both indicate an extrapolated infinite diameter density ratio of 1.70 for a 0.3 C2H2 + 0.3 O2 + 0.4 Kr mixture. This result is significantly lower than the ratio 1.79 which corresponds to the tangent point on the equilibrium Hugoniot from the initial state. At the present time these observations cannot adequately be explained by detonation theory.