Experimental investigation on thermal-hydrodynamic behavior of annular pool fires under cross air flow: evolution of flame length and height

Annular pool fires commonly occur in the early stage of rim-seal fires in floating-roof tanks and may develop into full-surface pool fires under unfavorable conditions. This study experimentally investigates the flame length and flame height of n-heptane annular pool fires under crosswind conditions, with particular emphasis on the effects of crosswind speed and the inner-to-outer diameter ratio. The results indicate that flame length increases with increasing crosswind speed and with a larger inner-to-outer diameter ratio ( D in / D out ). In contrast, flame height decreases with increasing crosswind speed, but increases with D in / D out at a fixed wind speed. Existing models show progressively larger deviations from the experimental measurements as both wind speed and diameter ratio increase. To address this limitation, a combined velocity is introduced through plume entrainment analysis, coupling the buoyancy-induced plume rising velocity with the crosswind speed. Based on this parameter, new correlations are developed to predict flame length and flame height of annular pool fires under crosswind conditions. The proposed models enhance predictive capability for fires with annular geometries and provide useful references for fire risk assessment, safety distance determination, and mitigation strategies in tank farms and chemical industrial parks.