Heat transfer in wind-driven fires stabilized under a mixed-convective turbulent flow environment

Abstract

This study experimentally investigates the heat flux distribution over a horizontally placed condensed fuel surface under mixed-convective turbulent flow conditions. The study explores different freestream conditions, including variations in crossflow velocity (ranging from 1 m/s to 1.8 m/s) and turbulent intensity (ranging from 3% to 9%) on local heat fluxes at the condensed fuel surface. Further, to decipher the collective influence of momentum, buoyancy, and turbulence on local heat fluxes, a mixed-convection variable ξx was defined in the form of ξx=Grx1/ψx2n. The defined variable also encapsulates the property of fuel as a function of mass transfer number B, thereby establishing a fuel-dependency factor in the formulation of the mixed-convective parameter (ξx). A methodology was adopted to quantify heat flux components (convective and radiative) with the knowledge of local mass burning rates and local temperature gradients at the condensed fuel surface in the pyrolysis zone. An inverse relationship was observed for incident heat flux with flame standoff distance and ξx. The present study considered the experimental data for two fuels, n-heptane, and ethanol, which showed almost similar trends. However, the radiative heat flux was dominant for the n-heptane case due to the higher sooting propensity of heptane.