The Effect of Washcoat Thickness and Average Damkohler Number on Conversion

[samanjalilian]

We have to run the code and extract the effect of washcoat thickness and average Damkohler number on conversion. First, we can assume that phi_I and phi_II are equal to zero (non-hierarchical structure in both macroscale and microscale). In the future, we can add micropores and macropores to the problem and analyze their effect.

[samanjalilian]

These are some results of the simulation. Conversion vs average Damkohler number is shown for different washcoat thicknesses. The upper figure is for low volumetric flow rate and the lower one is for high volumetric flow rate. We should have a discussion about their trend. What is your opinion @masoodmoghaddam ?

[masoodmoghaddam]

In high volumetric flow rates, by increasing the average pore damkohler number, conversion of the reactor increases until reaching a maximum limit. This limit is where the diffusion limitation is dominants and the process is diffusion limited and no more improvement will observed by increasing the average pore damkohler number.

[masoodmoghaddam]

Also, In high volumetric flow rates, by increasing the washcoat thickness, diffusion limitations increase in the washcoat at all domkohler numbers. Consequently, conversion of the reactor decreases.

[masoodmoghaddam]

But It seems that in low volumetric flow rates, by increasing the washcoat thickness, conversion of the reactor increases. What is your idea about that @samanjalilian ?

[samanjalilian]

As we know, increasing the washcoat thickness has two opposing effects. First, increases the velocity in the channel, and second, improves the internal surface area. Velocity increase can reduce the conversion (since the reactant has little time to diffuse into the washcoat) and improving the internal surface area can increase the conversion. I think In low volumetric flow rates, since the velocity in the channel is critically low, increasing the thickness does not increase the velocity too much. So, Its positive effect (increasing the internal surface area) overcomes its negative effect (velocity increase), I think that's why by increasing the washcoat thickness the conversion is improved.

[masoodmoghaddam]

Repeating the simulation with constant flow velocity will be useful here

[samanjalilian]

Yes, I am working on it. We should have a discussion on the low volumetric flow rate trend at high Damkohler numbers (diffusion limit). Why despite being in diffusion limit area, (meaning that reactant is completely consumed in the first layer of the washcoat) increasing the thickness increases the conversion?

[samanjalilian]

Repeating the simulation with constant flow velocity will be useful here

I will open an issue for this. We have to compare the results of constant velocity and constant volumetric flow rate boundary conditions.

[samanjalilian]

Thank you @masoodmoghaddam . There is something wrong with these figures. By checking the paraview, it seems that in the new version of OpenPNM, the front and back sides have changed. This somehow affected the interconnecting throats. I revised the code and changed the sides of the geometry based on OpenPNM V 2.8.2. Now it should work correctly.

[samanjalilian]

After a little bit of struggling with the code, this trend is extracted. It shows conversion vs volumetric flow rate for different Damkohler numbers.