Further realities of droplet burning

A number of phenomena excluded by the assumptions given in Section 3.3.2 can modify the burning rate of a droplet. These phenomena often are too complex to be included in accurate theoretical burning-rate analyses and necessitate semiempirical methods in deriving burning-rate formulas. The most important of these additional phenomena will now be considered. 

If iUs of interest to account for the difference between and 7], then equation (A-23) may be employed with p representing the partial pressure of the fuel vapor, Xpj times the specified hydrostatic pressure the mole fraction Xp i may be obtained from equation (1-12)—namely, Xpj == F, i il F—where W is the average molecular weight (T If/)] and Yp I is given by equation (64). The. value of 7] obtained in this manner is a wet-bulb temperature somewhat below 7J,. 

For suspended or free droplets that are not initially at the boiling point, there is a contribution to Q given by (f)nrfp Ci(dTJdt)/m, where 7  

The correction to K just cited remains consistent with the d-square law for the total burning time. If radiant transfer from the flame or from hot 

If Le 1, then a formulation on the basis of coupling functions is less convenient. Equations (1-31), (1-32) and (1-33) become good starting equations for an analysis, especially if the flame-sheet approximation is adopted, since then the flux fractions remain constant on each side of the 

To write simple formulas it is useful to define v = (vp Wp/vg Wo)io, oo the product of the stoichiometric mass ratio of fuel to oxidizer with the oxidizer mass fraction at infinity. Then equation (62) for the flame-standoff ratio becomes 

is given by equation (64). The. value of Tj obtained in this manner is a wet-bulb temperature somewhat below T.  

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