Techn. University, Diss., 2005--Berlin.

When a large area of open gob collapses suddenly, a windblast is produced that can cause considerable damage throughout the infrastructure of a mine. In a few cases, the windblast has been accompanied by ignitions of methane and/or coal dust. Analytical and numerical analyses investigated the transient behavior of the air through the small time period during which the roof is falling. This is sufficiently short to allow adiabatic compression of the air, i.e. negligible heat transfer to rock surfaces. Controlled escape of the air via interconnecting entries limits the build-up of air pressure. However, this same phenomenum causes the potential energy of the falling strata to be concentrated into a diminishing mass of air. Computer simulations predicted that the temperature of the air would increase rapidly as the roof descends, reaching values that are capable of igniting either methane or coal dust. This thesis concentrates on a series of laboratory tests involving the compression of mixtures of air, methane and coal dust under a falling weight and while allowing controlled escape of the mixture. The transient responses on pressure and temperature sensors were recorded. In addition to an analysis of those records, the thesis highlights those conditions in which ignitions occurred. / Master of Science

A smoke explosion is generally considered as a deflagration of the accumulated unburned fuel inside a closed compartment. However, the term smoke explosion has been widely misused for decades with a great deal of confusion, and very little research has been done towards this topic. The purpose of this research is to study the smoke explosion phenomenon in much more detail through the development of a fire scenario under various experimental conditions including ventilation size, fuel elevation and fuel mass, so that a more comprehensive understanding of this phenomenon can be achieved. A total of twenty experiments are carried out including both exploratory and final experiments. Thirteen experiments result in smoke explosions, among which there are five experiments result in more than one smoke explosion. A phenomenon referred as smoldering decay is observed in all experiments with smoke explosions, making it one of the precursors of the smoke explosion phenomenon. The smoldering decay is often indicated by an exponential decay of the temperature and is caused by the low oxygen concentration within the compartment. Based on the analysis, it is found that the vent size must be at least 50 mm in diameter in order for smoke explosions to occur. The fuel elevation has no influence on the occurrence of the smoke explosion. However when the fuel is placed near the ceiling, the temperature, the mass flow rate and the heat release rate are all lowered significantly. The size of the fuel also has no significant influence except for the duration of the experiment. The concentration of CO is scattered in the range of 1.9% and 4.3% when explosions occur. Hence, the accumulation of CO is considered not to be the direct cause for the smoke explosion. The triggering factor for smoke explosions is believed to be the flammable limit formed by the mixture of hydrocarbon and CO. The pressure difference caused by the explosion inside the compartment has to be at least 27 Pa for it to be considered as a smoke explosion.

The impact of rapid rotation of the supernova progenitor star (white dwarf) on its explosion (type Ia supernova) is investigated. Different explosion mechanisms are employed. / Die Auswirkung schneller Rotation des Supernova-Vorläufersterns (Weißer Zwergstern) auf die Explosion (Typ Ia Supernova) dessen wird unter verschiedenen Explosionsmechanismen untersucht.

"This study investigates the interaction of micron- sized coal particles entrained into lean methane €“ air premixed flames. In a typical axisymmetric burner, coal particles are made to naturally entrain into a stream of the premixed reactants using an orifice plate setup. Pittsburgh seam coal dust, with three particle sizes in the range of 0 to 25 µm, 53 to 63 µm, and 75 to 90 µm is used. The effects of different coal dust concentrations (10 €“ 300 g/m3) at three lean equivalence ratios, ϕ (methane-air) of 0.75, 0.80 and 0.85 on the laminar burning velocity are determined experimentally. The laminar burning velocity of the coal dust-methane-air mixture is determined by taking a shadowgraph of the resulting flame and using the cone-angle method. The results show that the addition of coal dust in methane-air premixed flame reduces the laminar burning velocity at particle size of 53 to 63 µm and 75 to 90 µm. However, burning velocity promotion is observed for 0 to 25 µm particles at ϕ = 0.80. Two competing effects are assumed involved in the process. The first is burning velocity promotion effect that the released volatile increases the gaseous mixture equivalence ratio and thus the burning velocity. The second is the heat sink effect of the coal particles to reduce the flame temperature and accordingly the burning velocity. A mathematical model is developed based on such assumption and it can successfully predict the change of laminar burning velocity at various dust concentration. Furthermore, the implication of this study to coal mine safety is discussed."

In this report I will describe how an art-directed fluid effect for motion picture can be achieved. This effect will be an explosion with a visual style that is congruent with Pixar's movie Up. To begin with I will analyze the visual components that are used in Up and control the fluid simulation to get the desired visual style. I will briefly explain the background of my thesis, why it is interesting to create designed effects and why it is hard to design fluid effects. In the method I will explain my work process and some of the challenges that arises. In the end of my report I will look into my result and present my findings.

In the U.S. Chemical Safety and Hazard Investigation Board (CSB) report, Improving Reactive Hazard Management, there are 37 out of 167 accidents, which occurred in a storage tank or a storage area. This fact demonstrates that thermal runaway problems in chemical storage processes have not been give enough attention. Hydroxylamine Nitrate (HAN) is an important member of the hydroxylamine compound family and its diluted aqueous solution is widely used in the nuclear industry for equipment decontamination. It is also used as a solid or aqueous propellant. Due to its instability and autocatalytic behavior, it has been involved in several incidents at the Hanford and Savannah River Sites (SRS). Much research has been conducted on HAN in different areas, such as combustion mechanism, decomposition mechanism, and runaway behavior. However, the autocatalytic behavior of HAN at runaway stage has not been fully addressed due to its highly exothermic and rapid decomposition behavior. This work focuses on extracting its autocatalytic kinetics mechanism and studying its critical behavior from adiabatic calorimetry measurements. The lumped autocatalytic kinetics model, the associated model parameters and HAN critical condition are determined for the first time. The contamination effect of iron ions and nitric acid on diluted hydroxylamine nitrate solution is also studied. This work also identified the safe storage conditions for a small quantity HAN diluted solution with thermal explosion theory. Computational Fluid Dynamics (CFD) was used to further study the influence of natural convection and system scale on the critical behavior for a large quantity of chemical and thus proposed the practical storage guidelines for industrial practice.

Reproduction de : Thèse de doctorat : Systèmes automatiques : Toulouse 3 : 2007. / Titre provenant de l'écran-titre. Bibliogr. p. 131-136.

In a kraft recovery dissolving tank, high temperature molten smelt droplets fall into an aqueous solution and dissolve. The rapid heat transfer between molten smelt and water can lead to violent dissolving tank operation, and in severe cases, a dissolving tank explosion. In this study, an experimental apparatus was built to investigate the interaction between a molten synthetic smelt droplet and water. Smelt-water interaction was documented, and the effects of water and smelt temperatures on droplet explosion probability, explosion delay time, and explosion intensity were examined. The results show that explosions always occur below a lower critical water temperature, which is a function of smelt temperature, and never explodes above an upper critical water temperature. Up to the upper critical water temperature, as the water temperature increases, the explosion probability decreases, and the explosion delay time and the explosion intensity increases. A Smelt-Water Interaction Temperature (SWIT) diagram was constructed to describe the explosion probability at different smelt and water temperatures.

In a kraft recovery dissolving tank, high temperature molten smelt droplets fall into an aqueous solution and dissolve. The rapid heat transfer between molten smelt and water can lead to violent dissolving tank operation, and in severe cases, a dissolving tank explosion. In this study, an experimental apparatus was built to investigate the interaction between a molten synthetic smelt droplet and water. Smelt-water interaction was documented, and the effects of water and smelt temperatures on droplet explosion probability, explosion delay time, and explosion intensity were examined. The results show that explosions always occur below a lower critical water temperature, which is a function of smelt temperature, and never explodes above an upper critical water temperature. Up to the upper critical water temperature, as the water temperature increases, the explosion probability decreases, and the explosion delay time and the explosion intensity increases. A Smelt-Water Interaction Temperature (SWIT) diagram was constructed to describe the explosion probability at different smelt and water temperatures.