# Need advice on how realistic these results are. Intuitively they seem way off.

Question asked by Daniel Cox on Apr 1, 2012

I am modeling the pressure distribution of air around a large fan. The fan is 10' in diameter and moves 94,000 CFM. I need to know the effect adding a large duct around the inlet of the fan would have on the pressure. If the duct causes a huge pressure drop then we can't use it.

The duct would completely enclose the inlet and extend 18'. After modeling the air flow Solidworks tells me the lowest-pressure point in the entire duct would be only 0.4 psi below atmospheric pressure. It seems to me that a fan of this size pulling air through 18' of duct would cause much lower pressure than that.

I have added some pictures of the model and results. Air enters through the rectangular inlet shown in the two pictures of the model. It exists through the opening, which I have modeled as a red disk. As you can see the pressure inside the duct is barely below atmospheric pressure. Intuitively it seems like it should be much lower. As a student with no real experience my intuitive frame of reference may not be realistic. Any thoughts?

EDIT: The length units in the attached pictures are in inches. I can't figure out how to change them to feet.

Message was edited by: Daniel Cox