Effect of gas phase heat sink on suppression of downward flame spread over thin solid fuels

Abstract

A two-dimensional numerical model of opposed flow flame spread over thin solid fuel is formulated and modeled to study effect of gas phase heat sink (a wire-mesh placed parallel to the fuel surface) on the flame spread rate and flame extinction. The work focuses on the performance of the wire-mesh in normal gravity environment of 21 % oxygen concentration. The simulations were carried out for various mesh parameters (wire diameter, ‘\( \overline{d}_{wr} \)’ and number of wires per unit length, ‘N’) and mesh distance perpendicular to fuel surface (Ymesh). Experiments were carried out for wire mesh with \( \overline{d}_{wr} = 0.035\,{\text{cm}} \) and N = 5 and were found to complement numerical predictions. Both simulations and experiments show that wire mesh is effective in reducing flame spread rate when placed at distance less than flame width (which is about 0.50 cm). Mesh wire diameter is determined to not have major influence on heat transfer. However, smaller wire diameter is preferred on account better aerodynamics and for increasing heat transfer surface area (here prescribed by parameter ‘N’). Computations show that meshes with more number of wires per unit length are more effective heat sinks. However, the flame extinction occurs only if mesh is located very close to the fuel surface (of the order of 0.15 cm) and at this distance flame suppression is relatively insensitive to number of wires per unit length.