Flame spread along a fuel rod in the absence of gravity
An analysis is carried out of the steady spread of a flame with infinitely fast kinetics over a thermally thin solid rod in the absence of gravity. Due to the radial convergence on the solid surface of the heat flux heating and vaporizing the fuel, the spread rate is found to be higher than for a flame spreading over a slab, and the region of the gas around the flame which is affected by molecular transport is large compared with the radius of the rod. The effects of radiation, of a buoyancy force opposing flame propagation and of axial heat conduction in the solid are discussed briefly
Opposed-Flow Flame Spread over Solid Fuels in Different Burning Regimes
Author(s): Carmignani, Luca | Advisor(s): Seshadri, Kalyanasundaram; Bhattacharjee, Subrata | Abstract: Several aspects of opposed-flow flame spread are experimentally investigated because of their relevance in fire safety studies. Different burning regimes based on the intensity of the opposed flow velocity are identified for acrylic fuels. In downward flame spread, where the flow around a flame is only naturally induced by gravity, the spread rate is highly dependent on fuel size and geometry. The fuel cross-sectional shape is experimentally varied, and a formula which takes into account geometrical effects is proposed by extending previous solutions for two-dimensional flames.The burning region of a solid fuel shows a consistent slope due to the competition between flame spread and surface regression. The angle at the vertex of the pyrolysis region, called burn angle, can be used to indirectly calculate the fuel burning rate. The burn angle depends on fuel thickness; a numerical model and a scale analysis are used to explore the reasons for this behavior.Next, the effect of a forced flow is investigated. The extreme case of blow-off extinction over thin fuels is considered, with flames extinguishing at locations determined by the flow velocity. Results suggest that the interaction between fuel and flow field is more important than the dependence on fuel thickness. The evolution of flame structure and pyrolysis also appear to be driven by flow interactions. A scale analysis is used to explore these dependencies.Finally, previous microgravity experiments are used to explore differences and similarities with ground-based results. By suppressing the buoyant flow, flame radiation becomes essential for the flame spread process. The experimental conditions are simulated numerically to describe the importance of a developing boundary layer in this regime.A numerical parametric study of the radiative emission of flames in microgravity, inspired by the experimental data, shows its dependence on flame area, mass burning rate and flame temperature by changing the burning conditions. For these small flames, soot does not seem to dominate flame radiation, although its generation increases with fuel thickness, oxygen concentration and flow velocity.The experiments in microgravity considered in this work showed flame extinction in a quiescent environment. However, two acrylic cylinders at higher oxygen concentrations from a previous investigation can burn vigorously. To clarify whether these flames are stable, a scale analysis is used to study the influence of surface curvature on radiation losses.
Tortuosity or aneurysm? The palaeopathology of some abnormalities of the vertebral artery
The anatomy of the vertebral artery (VA) and two pathological conditions which affect it—tortuosity and aneurysm—are described. The changes which these lesions produce in the cervical vertebrae are also described and we present two cases in which these changes have been found. One case is of a female aged at least 45 years at the time of death from a 15th century medieval cemetery site in Britain with what we consider to be tortuosity of the VA. The second case is of a male aged between 25 and 35 years at the time of death from a Coffin period site in Japan, dating to ca 1600 years BP. The changes in this skeleton are considered to be more in keeping with a diagnosis of aneurysm of the VA. Copyright © 2002 John Wiley & Sons, Ltd.