Flame speed solid surface

From Figure 8.8, Vf > vp, so cbcf/dxp > 1. Hence, transient effects will cause a lower speed for wind-aided spread. Again, since the gas phase response time is much faster than the solid, we can use steady gas phase results for qf and <5f in these formulas for flame spread on surfaces. 

Figure 8.4 displays a thermally thin solid of thickness d, insulated at its back face and undergoing surface flame spread. Any of the modes shown in Figure 8.1 are applicable. We consider the case of steady flame spread, but this constraint can be relaxed. The surface flame spread speed is defined as... 

---