# Gas-Solid Reaction Modeling with Random Pore Model. Pdepe: Spatial discretization has failed. Discretization supports only parabolic and elliptic equations, with flux term involving spatial derivative.

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VINCENZO MAIELLO on 15 Sep 2020
Edited: VINCENZO MAIELLO on 8 Oct 2020
Hello everyone,
I am studying the reaction's kinetics of calcium oxide with carbon dioxide through the Random Pore Model of Bhatia and Perlmutter. You can find the equations and code attached that I am trying to solve with the pdepe but it appears the error "Error using pdepe (line 293) Spatial discretization has failed. Discretization supports only parabolic and elliptic equations, with flux term involving spatial derivative".
Is there anyone who could tell me why I have this kind of error in the code and how to fix it?
clc,clear
%% RPM
% Properties
global phi zeta beta psi eps0 cb ceq s0 ks Sh
R=41e-6; %[m]
cb=1.95e-5; %[kmol m^-3]
ks=0.559e-5; %[m^4 kmol^-1 s^-1]
ceq=1.93e-3; %[kmol m^-3]
s0=42e6; %[m^-1]
psi=1.52; %[-]
zeta=2.10; %[-]
eps0=0.47; %[-]
beta=8120; %[-]
phi=45.46; %[-]
Sh=4.48; %[-]
%Axes
rmesh=linspace(0,R,100);
etamesh=rmesh/R; %eta
tspan=linspace(-1523,0,100);%tetac
%% Solver
m=2;
sol=pdepe(m,@pdefun,@icfun,@bcfun,etamesh,tspan);
cstar=sol(:,:,1);
xcao=sol(:,:,2);
%% Plots
surf(etamesh,tspan,sol,'edgecolor','none')
xlabel('xcao [-]')
ylabel('deltatetac [-]')
zlabel('c* [-]')
% Pdefun
function [c,f,s] = pdefun(x,t,u,dudx)
global phi zeta beta psi eps0 cb ceq s0 ks Sh
cs=u(1);
xcao=u(2);
c=[-phi^2 1]';
f=[1-((zeta-1)*(1-eps0)/eps0)*xcao 0]'.*dudx;
s=[0 -(cs*(1-xcao)*(1-psi*log(1-xcao)^(0.5)))/(1+((beta*zeta)/(psi)*(1-psi*log(1-xcao))^(0.5)-1))]';
end
% Bcfun
function [pl,ql,pr,qr] = bcfun(xl,ul,xr,ur,t)
global phi zeta beta psi eps0 cb ceq s0 ks Sh
pl = [0 0]';
ql = [1 1]';
pr=[0 0]';
qr =[0 0]' ;
end
% Icfun
function u0 = icfun(x)
global phi zeta beta psi eps0 cb ceq s0 ks Sh
u0 =[-ceq/(cb-ceq) 0]';
end

Bill Greene on 15 Sep 2020
Your right-end boundary conditions are invalid.
Possibly you want:
pr=[ur(1)-1 0]';
qr =[0 1]' ;
VINCENZO MAIELLO on 8 Oct 2020
Edited: VINCENZO MAIELLO on 8 Oct 2020
Good evening,
I used your example to solve the system and the next step is to perform a parameter estimation using lsqnonlin (PDE system,datas and code are attached) and I have the error "Unable to perform assignment because the size of the left side is 2-by-1 and the size of the right side is 2-by-10''
Do you have an idea of how I can fix the problem?