For a uniform cloud of $70\backslash$mu m char particles flowing in a stream of hot,

isothermal gas; for $5\%,10\%,$ and $20\%$ excess air determine $($a$)$ the particle

burnout time based on $99\%$ burnout and $($b$)$ plot the particle mass divided by

the initial particle mass as a function of time. Use an effective char kinetic

rate constant of $0\mathrm{.}5$ gO$2/($cm$2$ s $$ atmO$2),$ a char density of $0\mathrm{.}8$ g$/$cm$3,$ and an initial oxygen pressure of $0\mathrm{.}1$ atm.