I need help to solve this partial differential equation.
∂C/∂t=D((∂^2 C)/(∂r^2 )), boundary conditions, C = Co a t r = a(t)
C = 0 at r = b(t)
Initial Conditions, C = Co at t = 0

Here C= concentration of diffusion substance, t=time, r= radious of sphere, D= diffusion constant

This a hollow sphere a(t)<r<b(t) and the boundaries are not fixed and changed with time.

I've solved the problem with fixed boundaries. Right now I've been struggling with moving/variable boundaries