A mesoscale CFD model to simulate wood combustion

Shrikar Banagiri, Ishanee Khadakkar, Manjunath Parameswaran, Joseph Meadows, Brian Lattimer

Abstract

Flaming and smoldering wood combustion modes have been studied by various authors in the literature. Traditionally, experiments are performed at either the microscale (milligram weight samples) using a simultaneous thermal analyser (STA) or at the mesoscale (gram weight samples) in a cone calorimeter or fire propagation apparatus. However, quantifying the relative influence of pyrolysis, char oxidation, and gas phase combustion is experimentally difficult since these processes are strongly coupled. Thus, various numerical wood degradation models have been proposed. However, these models are either 1D and/or do not account for finite-rate gas phase chemistry. The current study proposes a comprehensive wood combustion CFD model using user defined functions (UDFs) in Ansys Fluent. The CFD model is constructed using kinetic mechanisms for pyrolysis, char oxidation, and gas phase combustion. The in-house wood pyrolysis mechanism was formulated using STA and gas chromatography (GC) experiments at the microscale. The CFD model was validated at the mesoscale against cone calorimetry experiments at different external heat fluxes and for different sample thicknesses. Using the validated model, the relative impact of solid phase chemistry and heat transfer is quantified.