Ceiling heat transfer during fire plume and fire impingement

Abstract

AbstractThe impingement of turbulent fires and fire plumes on a horizontal ceiling was considered. Free flame heights, impinging flame lengths along the ceiling and ceiling heat fluxes were measured for both unconfined and confined ceilings. The study was limited to the initial stage of ceiling heating by fire under conditions where convection dominates the flow. Fire sources were simulated by burning liquid methanol, ethanol, 1‐propanol or n‐pentane from the top surface of a cylindrical wick. Test variables include fire heat release rate of 50–7890 W, ceiling diameters of 610 and 660 mm, ceiling heights of 58–940 mm, wick diameters of 10–107 mm and curtain wall lengths (for confined ceilings) as large as the ceiling height. Simplified models were employed to suggest expressions for data correlation. Flame lengths increased up to 40% when the ceiling was confined. Ceiling heat fluxes were relatively independent of position in the stagnation region (radius along ceiling <20% of the ceiling height). Heat fluxes in the stagnation region for plumes were 25–40% of those measured for impinging jets at comparable conditions. In the ceiling jet region, at larger distances from the point of impingement, the heat flux decreased with increasing radius, in agreement with other studies. Confinement tended to increase ceiling heat fluxes in both regions. Ceiling heat fluxes for impinging flames and plumes were approximately the same, for flame lengths along the ceiling up to 25% of the ceiling height; however, stagnation point heat fluxes decreased for longer flame lengths.