A 3D Numerical Study on Opposed Flow Flame-Spread over Thin Parallel Fuel Sheets of Finite Widths in Microgravity
01 Jan 2017-pp 551-558
TL;DR: In this article, a model of flame spread over an array of fuel sheets of finite width size has been modeled and numerically investigated for opposed, low convective flows in microgravity, and steady flame spread rates were observed for all separation distances up to the separation distance of flame extinction.
Abstract: Flame spread over an array of fuel sheets of finite width size has been modeled and numerically investigated for opposed, low convective flows in microgravity. As opposed to the previous studies based on 2D models, steady flame spread rates were observed for all separation distances up to the separation distance of flame extinction. The flame spread rate increased with decrease in separation distance up to a point where it was maximum, further reduction in separation distance, reduced the flame spread rate. The flammability map as a function of separation distance was also obtained for different fuel widths. While the extinction map qualitatively matches with the flammability map obtained from the 2D model, the flame extinguished at higher oxygen levels with the decrease in fuel width due to radiation heat losses.
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TL;DR: In this article, the authors analyzed the flame front speed in the downward combustion of multiple parallel samples of thermally thin fuels at normal gravity and far from extinction conditions and derived an analytical approximation for the burning rate that generalizes the classical de Ris formula for those cases where radiative effects cannot be neglected.
Abstract: We analyze the flame front speed in the downward combustion of multiple parallel samples of thermally thin fuels at normal gravity and far from extinction conditions. In contrast with the single sample case, where conduction through the gas-phase is the dominant heat transfer mechanism, in the multiple parallel samples case, radiative heat fluxes may become very relevant, which compromises the application of the well-known formula of de Ris for determining the burning rate. Here we study the downward combustion of multiple parallel sheets by (1) obtaining new experimental data at different oxygen atmospheric levels; (2) generalizing a previous comprehensive energy balance model now expected to be valid for a wide range of scenarios; and (3) deriving an analytical approximation for the burning rate that generalizes the classical de Ris formula for those cases where radiative effects cannot be neglected. The comparison with own as well as with external data reveals the strengths and weaknesses of these type...
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