I am trying to solve a time dependent diffusion equation of a shrinking particle sphere with radius r (at time=0, let it be r[0]).The particle has a solute concentration of 100%, and the matrix solute concentration in equilibrium is C0=Exp[-Subscript[E, v]/k/T], reached infinitely far from the particle. The solute concentration at the particle surface is Cr=Exp[2*[CapitalOmega]*[Gamma]/r/k/T]*C0 because of the capillary effect.
The essence of the problem is the boundary r is dynamically changed due to diffusion.
Use the Fick's second law:
D[c[x, t], t] - Subscript[D, 0]*Exp[-(Subscript[E, m])/k/T]/\[CapitalOmega]/\[Xi]* D[D[c[x, t], x], x] == 0
With the Boundary condition:
c[x, 0] == Exp[-Subscript[E, v]/k/T] + r[0]/x*Exp[-Subscript[E, v]/k/T] (Exp[2*\[CapitalOmega]*\[Gamma]/r[0]/k/T] - 1)
c[Infinity, t] == Exp[-Subscript[E, v]/k/T]
We can list the PDE
pde = D[c[x, t], t] -
Subscript[D, 0]*Exp[-(Subscript[E, m])/k/T]/\[CapitalOmega]/\[Xi]*
D[D[c[x, t], x], x] == 0
sol = DSolve[{pde,
c[x, 0] ==
Exp[-Subscript[E, v]/k/T] +
r[0]/x*Exp[-Subscript[E, v]/k/
T] (Exp[2*\[CapitalOmega]*\[Gamma]/r[0]/k/T] - 1),
c[Infinity, t] == Exp[-Subscript[E, v]/k/T], c[r, t] == Exp[-Subscript[E, v]/k/T]*Exp[2*\[CapitalOmega]*\[Gamma]/r/k/T]}, c[x, t], {x, t}]
The symbols beside radius, time and concentrations are just parameters with real values, If you want.
T = 373;
\[Gamma] = 6.24; \[CapitalOmega] = 0.0166;
r[0] = 10; k = 8.6173324*10^\[Minus]5; Subscript[E, m] = 0.65;
Subscript[E, v] = 0.65;
Subscript[D, 0] = 1; \[Xi] = 0.781;
However, it did not work. There is a solution if I drop the c[Infinity, t] and c[r,t] boundary, but the solution contains an extra unknown function K[1]. Where went wrong...I need some helps.
Best regards,
Jack
DSolve
solution without initial and boundary conditions, if you can, and then apply the boundary conditions to determine the unknown function. By the way, usingSubscript
variables in a problem like this is asking for difficulty. $\endgroup$DSolve
can't handle b.c. at infinity directly (at least now). $\endgroup$