TURBULENT FORCED DIFFUSION FLAMES

A microscale, eta(beta)similar to eta/sigma(beta)(1/3), is introduced for turbulent diffusion flames, where eta and sigma(beta), respectively, are the Kolmogorov scale and the flame Schmidt number. In terms of this scale, the turbulent mass transfer integrated over a length l of a liquid fuel is shown to be M' = mu Bl/eta(beta), where mu is the dynamic viscosity and B is the transfer number, B = (Y(O infinity)Q/nu(O)M(O) - h(w))/h(fg), where Y-o is the mass fraction of oxidizer, Y-o infinity its ambient value, Q the heat release for a simple global chemical reaction, and nu(o) and M(o) the orddant stoichiometric coefficient and molecular weight, respectively, h(w), = c(p)(T-w - T-infinity), c(p) the specific heat of gas, T-w and T-infinity the fuel and ambient temperatures, respectively, and h(fg) the heat of evaporation. It is shown by the similarity between the mass and momentum transfer, M'/mu B = C-f, C-f being the drag coefficient, and that M'/mu B/(M'/mu B)(B=0) = C-f/(C-f)(B=0) = 1/(1+B)(3/4), where the subscript B = 0 for the case without boundary mass transfer. The agreement between the model and the sparse experimental data is reasonable.