Recent content by Dario56

Common method of fitting the experimental data to the model is using the least squares method. The goal is to find parameters such that sum of squares of differences between experimental and model values (objective function) are minimized. Objective function is commonly differentiable with...

Suppose there is a cylindrical (pellet) sample in the oxygen atmosphere as shown on the photo attached. Oxygen diffuses from the outside to the sample interior everywhere on the outer surface of the sample. From the photo, it can be seen that diffusion profile of oxygen is measured in the axial...

After discussing the question from the last comment, I learned that diffusion equation being the parabolic PDE does one approximation which answers my previous question. Namely, that any perturbation from equilibrium (in my case, mole flux being imposed on the boundary) is propagated with...

Suppose there is a non-stationary diffusion process in 2D rectangular plane. Component diffuses from the outside through all four faces of the plane. When I think about the simulations of the non-stationary diffusion in Matlab for example (finite difference numerical solution), I remember how...

I did, classic textbook. The start of the new paradigm in ChemE.

I think I don't have accurate picture of the diffusion process. When I think about the simulations of the non-stationary diffusion in Matlab for example (finite difference numerical solution), I remember how time change in concentration happens simultaneously at all points and concentration...

Yes, I've already understood it from your previous response and that makes more sense. I was describing what was confusing me earlier. Not often I can see this to you (as I learned a lot from our discussions here), but your assumption is incorrect. I'm a chemical engineer.

Hmm, it seems I've got some things to think about. In this problem, as it can be seen on the image provided, component diffuses through all 4 faces of the plane. I thought that concentration change in the sample centre can't change before the component coming from the plane edge arrives at that...

The sketch is provided. There is a flux across all 4 sides. Mole flux is in the opposite direction across the mutually parallel sides. It's something to include in the boundary conditions. It's true that only normal component contributes to molar flow across the boundary. The problem I had is...

I'll check it out. Thank you. Well, I think it means that the diffusion front doesn't reach the centre of the sample during the time frame of the process. Concentration gradient at that point remains zero inside the concerned time frame. If the time is long enough, diffusion front will reach...

I'm not sure I understand this. The problem is I can't find the analytical solution for the 2D diffusion for my initial and boundary conditions. Also, I realized I made a mistake earlier in boundary conditions. Here, I'll outline all initial and boundary conditions. Initial condition is the...

Yes, that's what I think also. However, diffusion profile is measured along one of the coordinates. Therefore, one of the coordinates is kept constant and diffusion is effectively modelled as 1D although 2D solution must be used. What confuses me a bit here is that the value of constant...

There is a known initial concentration of the tracer which is the same anywhere inside the sample before diffusion starts $$ c(x,y,0) = c_0 $$

Small solid sample. Diffusing species are oxide-ions created by oxygen reduction reaction on the gas/solid interphase. In that sense, it's a tracer. Boundary conditions are of Dirchlect type. Concentration of the tracer isn't directly defined at the gas/solid interphase, but its molar flux...

I have a discussion with a colleague of mine. We have a thin cuboid sample whose two dimensions are similar to each other and are both much bigger than the sample thickness. I'm doing an experiment in which the diffusion of some species is induced and its diffusion profile is measured in one of...