Fire Induced Flow Field - Theory And Experiment

An experimental technique is described for accurately measuring the steady-state fuel consumption rates in small scale pool fires, less than 7 cm in diameter. The iechnique is applied to studying ethanol fires burning in vessels ofvarious geometries and constructedfrom various materials. The results indicate that the distance between the top of a vessel (lip height or freeboard) and the fuel surface influences profoundly the properties of liquid pobl fires, including their structure and their burning rates. For combustion in glass cylinders, the burning rates decrease exponentially with increasing freeboard until a critical height is attained. At this height, the fuel begins to bum on the inside of the vessel, and the burning rate tends to grow slightly. With a further increase of the lip height, flame instabilities develop leading ultimately to flame self-extinction. The exponential decline in fuel consumption with the lip height depends trongly on the vessel's material of construction. For fires in copper and mild steel cylinders, the ethanol starts to boil beyond a certain critical freeboard. The appearance of this phenomenon redefines the fuel consumption curve. Finally, free convection leads to non-negligible heat losses, especially from more conductive (copper and steel) vessels, with the burning rates becoming dependent on the outside surface area ofthe cvlinders.

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