# MATLAB: Solve 1-D interfacial mass transfer using pdepe

mass transferpdepe

Hi Everyone,
I am trying to use pdepe to solve a diffusion problem and Im having issues trying to set my left side boundary condition.
`` dP=0.04; %thickness polymer layer [cm] d=100; %times in days [d] tt=d*86400; %time in seconds [s] x = linspace(0,dP,5);  t = linspace(0,tt,100);  m = 0; sol = pdepe(m,@equa,@IC,@BC,x,t); u =sol(:,:,1)  function [c,f,s,algo] = equa(x,t,u,DuDx) ∂Cp/∂t=D*∂/∂x(∂Cp/∂x) c = 1; f = D*DuDx; s = 0; end   function u0 = IC(x) u0 = Cpo;  %Initial  concentration[microg/cm^3]  end function [pl,ql,pr,qr] = BC(xl,ul,xr,ur,t) pl =0; ql =1; pr =h*((ur/K)-Cinf); qr =D; end   the first boundary condition (0,t)  ∂Cp/∂x=0   the second boundary condition (x,t)  h*(Cp/K-Cinf)+D*∂Cp/∂x=0``
Rigth now looks like it is working using Cinf as a constant but actually Cinf should change and increase with time (accumulation).
``Cinf=A/V*integral(∂Cp/∂x (t) dt, 0,t)I really dont know how to solve it this way Could someone please guide me?``

First of all one error in your actual code:
h*(Cp/K-Cinf)+D^2*∂Cp/∂x=0
Concerning your question about Cinf there are two ways to solve this problem: