Grid insensitive modelling of convective heat transfer fluxes in CFD simulations of medium-scale pool fires

Focusing on convective heat transfer modelling of pool fires, different approaches for calculating the convective heat fluxes at the pool surface have been employed, namely to resolve them; model them based on Nusselt correlations for forced or natural convection; model them based on the stagnant film theory. Large eddy simulations of medium-scale, 30 cm in diameter, alcohol pool fires (methanol, ethanol and acetone) are conducted and compared against experimental convective and radiative heat flux measurements. Overall, the best approach is the one based on the stagnant film theory which is only slightly grid sensitive, and provides satisfactory predictions for all the different fuels tested. The predictions using the other approaches are highly grid dependent, due to a fuel rich region formed just above the pool surface when the grid size is refined, which greatly influence the calculation of the convective heat fluxes using the first grid cell values. •Different methods for modelling the convective heat fluxes are investigated.•The convective heat fluxes are grid sensitive if based on the first grid temperature.•The method based on the stagnant film theory performed best and was grid insensitive.