Effects of cross wind and ullage height on the burning rate of medium-scale pool fires

The impacts of cross wind and ullage height (distance between the fuel surface and the pool's upper edge, h) on the burning rate of medium-scale heptane pool fires were studied. Using a series of 30 cm diameter fuel pools, the study covered crosswind speeds (u) from 0 to 5 m/s and dimensionless ullage heights (h/D) from 0 to 1.48. It was found that the overall burning rate decreased with increasing ullage height. Comparing the experimental mass flux with prior model predictions, classical models were accurate only when ullage height was low (h/D ≤ 0.35), with deviation increasing as ullage height rose. The simulation revealed the formation of a strong clockwise recirculating vortex inside the cavity, with the flame body positioned inside the pool. Changes in ullage height and crosswind speed influenced the recirculation flow velocity (u_c), affecting fuel vapor-air mixing, boundary layer development over the fuel surface, and heat/mass transfer between the plume and fuel body, leading to a higher burning rate. A new mass flux model based on momentum conservation within the pool was developed, addressing the limitations of classical models at high ullage heights and providing a valuable tool for energy safety and emergency planning.