12.9 A turbulent methane-air flame is stabilized in the wake of a circular rod (d=6.4 mm) held perpendicular to the flow. For inlet conditions of 1 atm and 298 K, the blowout velocity is 61 m/s when the equivalence ratio is unity. The recirculation zone behind the rod is six diameters long. Estimate the turbulent thermal diffusivity, . How does this value compare with the molecular thermal diffusivity, a? (Use air properties for a.) 12.9 A turbulent methane-air flame is stabilized in the wake of a circular rod (d=6.4 mm) held perpendicular to the flow. For inlet conditions of 1 atm and 298 K, the blowout velocity is 61 m/s when the equivalence ratio is unity. The recirculation zone behind the rod is six diameters long. Estimate the turbulent thermal diffusivity, . How does this value compare with the molecular thermal diffusivity, a? (Use air properties for a.)