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I'm studing the gas diffusion in two cases:

1. first case: gas diffusion in 3D open space in a spheric simmetrical case

∆C(x,y,z,t)-(1/D)(∂C(x,y,z,t))/∂t=0

where:

x,y,z arbitraries

gas concentration =0 for big spheric dimensions lim┬(r→∞)〖C(r,t)〗=0

concentration C is C=C(r,t)

2. second case: gas diffusion in a open orizontal cilinder with a lenght = ∞

∆C-(1/D)∂C/∂t=0

where:

cilinder lenght = ∞

cilider simmetrical axis is given by C=C(r,z) where C=Σ of C (gas concentration), Q (gas quantity) and z is -∞<z<+∞

for t=0 C=(r,z,0)=∂(r)/πr

I just have developed the analitic solutions but my problem now is to develop the numerical solutions with MATLAB and COMSOL and I'm not so close to the softwares.

there is anybody can help me or can indicate me a MATLAB/COMSOL model to modified?

thank you in advance

mike