kind of? more like is. Tell them how it is, don't be gentle

"..axial fan, and that really has no place in ventilation systems.." is really wrong. or at least a too simplified statement

Axial fan is fine for ventilation without fine filtration. If you have a paper or fabric filter, there is a notable restriction to flow, so a centrifugal fan is very likely needed.

@@IndustrialAccessoriesCompany What about using a tube axial fan with ducting? One of the reasons I'm asking is because I'm getting ready to build an evaporative cooler for a greenhouse by forcing air through ducting (4" corrugated drain pipe) My tube axial fan is a Dayton 12" with a four fin blade with a 3/4hp motor that moves at a max of 2877rpms. (I don't know what kind of static pressure it can pull or push) It will be attached to a 20' 12"diameter culvert pipe that elbows at 45 degree into a 20' piece of 12" diameter culvert that is the manifold for about 30 - 4" drain pipes that travel about 25-30 feet to complete the air loop (without filtration). So, I have air pushing through about 200' of underground tubing. It looks like some of the evaporative coolers that are similar in build are using "inline fans, (centrifugal fan) but they don't have nearly the moving power at 12" that I am thinking the tube axial has...(am I wrong?) I'm attempting to move just under 8000cf of air in about a minute or two through ducting. The 12" inline will move 8000cf in about 5-6 minutes. Do I need to go back to the drawing board?

Hello - thank you for your question. Luis Castano's reply is: "Not all AC motors have the ability to be reversed, but most do. Reverse direction is made by simply switching wire connections. DC motors are not common in industrial applications."

The question is too broad. Depends on the type and size of fan. A way to get an idea of flow capacity is to measure the inlet diameter, calculate the inlet area and multiply by flow velocity of 3000 feet per minute.