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Show this estimate will overpredict the mass transfer number, and therefore underpredict drag. The droplet penetration distances are larger than would be predicted by an unsteady model. Th us, the calculation is conservative in that actual trajectories will be shorter, resulting in fewer droplets escaping the incinerator unburned and less wall impingement and quenching. The Reynolds number in the drag correlations is based on free-stream density and velocity, droplet diameter, and either free-stream viscosity8 or the average of the fuel-air mixture viscosity at the surface and the free stream viscosity9. The fuel-air mixture viscosity is evaluated using an established method for multicomponent gas mixturesll . Results and Discussion One-Dimensional Multicomponent model: The one-dimensional multicomponent model provides detailed information on the ignition, burning, and extinction of blended droplets in quiescent air. Due to the absence of convection in this model, burning rates are predicted conservatively low for the purpose of hazardous waste incineration. The blended droplet in these studies is composed of 35% nonane and 65% tetrachloroethane, by volume. c o .~ (.) III u: CI) DROPLET CONCENTRATION PROFILE 0 .24 lew!a Number - 30 Time - eo Mllllaec 0.20 .. ---.• ---~--."'- - --"'----"'--.-"-------- - .- .. TIme - 120 mllllaec 0 .18 lewla Number - 1 ~ 0 .12 ~ Q) C to C o Z 0 .08 0 .04lew1is -Nu-mb-er -- 1- -_T_ime_ - ~1 20 _m_i_ll- l-.e-.c:_ __ 0 .00 +---.--....,..--....,--....,--....,----r----,-----. 0 .0 0 .125 0 .250 0 .375 0 .500 0 .825 0 .750 0 .875 1.000 Radial Distance Figure 1. Mass fraction of nonane inside blended droplet as a function of droplet radius at times 60 msec and 120 msec. By changing the Lewis number, we see the effect of species diffusion within the droplet. Le=30 is species-diffusion limited. Le=1 is distillation-limited. Figure 1 shows the effect of species diffusion inside the droplet. The mass fraction of nonane as a function of droplet radius is plotted at two different times during combustion of the TECA/nonane blended droplet. The dashed line in this figure represents the mass fraction of nonane as a function of droplet radius for a high Lewis number(Le=30), where Lewis number is defined to be the ratio of thermal to mass diffusion. The concentration profile is the same at 60 and 120 msec. Typical liquid hydrocarbon fuels have a Lewis number between ten and thirty, the range of uncertainty being almost entirely due to the difficulty of estimating species diffusion coefficients. A high Lewis number, such as Le=30, results in a significant resistance to mass diffusion and represents a diffusion-limited droplet. Results from our model show that for Le=30, the concentration of hydrocarbon fuel remains constant throughout the droplet lifetime at the initial mass fraction of 0.2. These results are consistent with previous analytical models12 . Although our model is spherically symmetric, we can simulate internal circulation in a crude fashion by varying the Lewis number of the liquid droplet. In the limit of convection dominated transport, the Lewis 4 |