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Eingeladener Vortrag
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Modelling of detonation wave parameters, initiation and hazard of chemically active bubble systems
(2002)
The detonation processes in chemically active bubble systems at high initial pressures are calculated numerically. The dependences of detonation wave velocity at sub- and supersonic regimes of propagation on molar fraction of gas in the mixture and on initial pressure have been calculated for the first time. The Chapman-Jouguet condition for supersonic bubble detonation wave is obtained. The principal possibility for a different detonation wave structure in the case of propagation in the mixture with high initial pressure and longitudinal gradient of bubble volume fraction is predicted.
The dynamics and ignition of a chemically active bubble in a field of external pressure is analyzed. It is shown, that an inert diluent addition can increase the explosion hazard of heterogeneous gas - liquid systems. Calculations demonstrate the possibility of chemically active bubble ignition on the second pulsation. It is shown, that single chemically active bubble ignition is possible also owing to a decompression impulse.
An algorithm for the calculation of thermodynamic parameters of chemically equilibrium hydrocarbon gas with soot particles has been suggested. It is shown, that soot formation can have an essential influence on the dynamics of single bubble in chemically active hydrocarbon-oxygen (organic solvent (liquid) - oxidizer (gas)) heterogeneous systems.
The detonation processes in chemically active bubble liquids under elevated initial pressures are investigated theoretically. It is shown, that supersonic regimes of wave propagation can exist, if the initial pressure is relatively high and the volume fraction of the bubbles is relatively small. Characteristic values of the bubble detonation wave pressure at sub- and supersonic regimes differ by an order of magnitude.
The principal possibility of detonation wave structure transformation in the case of propagation in the mixture with high initial pressure and longitudinal gradient of bubble volume fraction is predicted. The leading shock may transform into a smooth wave of compression.
The Chapman-Jouguet conditions for self-sustaining supersonic bubble detonation wave is obtained.
A model of shock induced single bubble dynamics and ignition taking into account the real properties of the liquid, inter-phase transition processes, mechanical mixing of phases, ignition delay and continuous shift of chemical equilibrium have been described. Calculations for the oxygen containing bubble in liquid cyclohexane have been performed.
Safety behaviour of a chemically active organic bubbly medium induced by gas explosion above it
(2003)
Bubble explosions
(2004)
Safety behavior of a chemically active organic bubbly meduim induced by gas explosion above it
(2003)
The possibility of explosion of a compressed oxygen bubble in liquid cyclohexane due to interaction with a spherical shock wave emitted by a nearby exploded bubble has been experimentally and theoretically investigated. Calculations for the explosion limits of a single bubble have been performed too. It is shown that in order to prevent bubble explosions inside a chemical reactor, the operating conditions (temperature and pressure) should be within a certain range.
The present work discusses the role of the distance between single explosive bubbles on their explosion behavior after the passage of an incident shock wave. The investigated system was liquid cyclohexane containing oxidizer bubbles. High speed optical and pressure measurements were applied. It was found that if the distance is short enough, then the shock wave caused by a bubble explosion can ignite a nearby compressed bubble. The experimental finding that bubbles can be ignited by shock waves emitted during nearby bubble explosions, indicates that a process of synchronization of bubble explosions can occur. This synchronization process offers a better understanding of the propagation mechanism of self-sustaining bubble detonation waves inside bubbly media.
An approximate two-stage kinetic model of the chemical reaction in hydrogen-oxygen mixtures containing hydrogen peroxide, water, and inert diluents is developed. The model includes one differential equation for the calculation of the molar mass of the gas after the induction period and algebraic formulas for the calculation of the heat release, internal energy and thermodynamic parameters of the mixture. Based on this model, 2D numerical simulations of a multifront gas detonation wave are performed. These pioneering simulations correspond to the stoichiometric hydrogen-oxygen mixture with hydrogen peroxide and argon additions.
An approximate model of chemical equilibrium in heterogeneous gas-condensed phase systems containing hydrogen peroxide is presented.
In safety engineering, one position of interest inside heterogeneous systems of the type liquidgas is the contact surface between these two phases. Under certain conditions, e.g. shock wave impact, phenomena can take place at this position that can have a significant influence on the explosion behavior of the system. In this work an investigation is presented about the existence of such phenomena on the surface of liquid cyclohexane with or without the existence of oxygen containing bubbles. The observations have been performed during the time before, as well as after, a detonation wave reflection on that surface. High-speed pressure and optical measurements have been applied. Apart from the experimental observations, also a theoretical analysis and discussion is presented in this contribution, which contains the comparison between calculated and experimental values.