What is the difference in CFM, at a given static pressure, between a CPU fan and a Squirrel Cage Blower fan when moving air through ductwork?

Question

I have a Delta ASB0912L DC Brushless fan. PDF here.

In the datasheet it says,

RPM 3800
CFM 67.80 
IN H2O 0.302

On the blower, squirrel cage fan, Dayton from Grainger, found here (Rectangular Permanent Split Capacitor OEM Specialty Blower, Flange: Yes, Wheel Dia: 3", 115VAC)

It says,

RPM 3010
CFM @ 0.200-In. SP78
CFM @ 0.300-In. SP74

I want to exhaust fumes from a spray booth. I know there are many articles and plans online. I am trying to understand the math here.

It seems intuitive to me the Grainger fan is more powerful and will remove more air than the CPU fan. But the math makes no sense to me.

On the CPU fan it has .302 for Static Pressure and .3 for the Grainger and the CFM is pretty close.

I am moving air through 6' of ductwork, 4" in diameter, and neither tell me what CFM means in this context.

Given a 2'Lx2'Wx2'H spray box. Again, I'm not asking for plans. I can get that already. I only want to understand what these numbers mean and the spray box application gives the question context.

Why doesn't the CPU fan move almost as much as the Blower based on the specifications? Also, is the Delta IN H20 given static pressure or is that something else?

Answer 1

1. Why doesn't the CPU fan move almost as much as the Blower based on the specifications?

It is because of the working principle of fan and blower. The fan takes the air axially(axis of rotation) and pushing it in the axial direction. But the Blower works like a centrifugal compressor in which axial inlet and radial/tangential outlet are present. Fundamentally, due to the pressure reactions, the centrifugal pump/turbines are more efficient than the axial pump/turbines. That is what you are seeing as the data in the sheets.

2. Also, is the Delta IN H20 given static pressure or is that something else?

Both are in the units of inches of water column.