Use the separation of variables method to solve the following
problem. Consider a long, narrow
tube connecting two large, well-mixed reservoirs containing a
small concentration of N2 in another
inert gas. The tube length is L = 100 cm. To establish an
initial concentration profile in the
tube, each reservoir is held at a fixed concentration:
Reservoir 1 contains no N2 and reservoir 2 has
2 × 10−6 mol/cm3 of N2.
(a) At t = 0, the concentrations of the reservoirs are rapidly
(instantaneously) switched. Solve
for the concentration in the tube as a function of position
and time. The diffusion coefficient of N2
is D = 0.2 cm2/s.
(b) Plot the concentration c(z, t) as a function of the
position along the tube at four different
times (initial, early, intermediate, and long times). Use
software to plot enough terms of the series
solution to have a reasonable representation of the solution.
As always, be sure to clearly label
your axes.
(c) Repeat part (b), but plot the transient part of the
solution, ct(z, t).