[rtapan12]

Hello friends;
I am new this forum. I had few quarries about modeling the pressure drop in packed columns
1) In darcy and ergun equations, what exactly mean the superficial velocity. In gas phase system, the pressure and velocity are related to each other. velocity is different at the inlet and exit of the column. if I use these different velocities the darcy and ergun constants are different. which is the right velocity to use in the model(ergun or darcy)? any suggestions.
2) what happens to the darcy or ergun constants, if the particle size is 70 micron and tude to particle diameter ratio is >150. Will the clustering of micron sized particles will effect the constants? we observed very high values(>>greater than 5000 instead of 150). Is this possible? Suggestions please!

Best Regards,
tapan

[eugenedakin]

Hello rtapan12,

This is an exciting and difficult area of chemistry/mechanics/geology.

Superficial velocity is the hypothetical velocity if the porosity were 100% (which it never is). Yes, pressure and velocity are related to each other. Changing the velocity (with the same differential pressure) will assume the packed column has more or less porosity. As an example, a constant packed column with a porosity of 2 Darcy will have material (gas or liquid) move slower (given a same pressure and everything else being equal - which it never is equal) than the same constant packed column with a lower porosity (lets say 0.2 Darcy).

I am guessing that your question #2 may relate to the ideal packing theory (IPT). Having different sized particles will lower the overall porosity of the packed column. This will lower the efficiency of fluid/gas flow, and will increase the pressure differential for a constant volume of material.

I hope this helps,

Eugene