Axial Blower

Any ducted fan can "suck" air if the opening is not fully blocked. Too much restriction may cause motor overheating, due to reduced air flow.

PC power supply fans are ducted.

Thank you lyn for your "hyper quick" answer.I don't know if there is room to compare axial fan to a blower, but I did it, and I found that a partialy blocked blower will supply air the same as total open one.This isn't the case with an axial fan!The question is if the gap between the fan blades tips and the duct is the main factor for air losses in blocked fan.

The clearance is part of it and so is the blade design. Blowers have much closer clearances that fans.

Depending on how much velocity you need a ducted fan such as was pictured in #1 probably won't work. But it will continue to move some air.

I'm getting the picture that the OP is trying to move air from a partial vacuum.This centrifugal blower approaches the best you can do for that application. Next step is multistage then positive displacement. No clue what volume/time and suction static operating is wanted.

The 'muffin' or axial type design, can't produce much suction static, as the blades stall.

I think you may be correct.

The flow is dependent on the pressure difference across the restriction. If you have atmospheric pressure on one side and a total vacuum on the other, that is only about 1 bar or 14.5 psi pressure difference. There is no way to 'suck' more than that. As others have mentioned, a centrifugal design may get closer to maximum than an axial fan.

If that isn't enough flow then you must either reduce the restriction or use a blower (or even a positive displacement pump) to provide positive pressure on the intake side of the restriction.

You have not stated whether the ducts are on discharge or both sides or whether the blockage is constant or periodic.

Assuming only discharge- your best choice is a vaneaxial fan- can handle pressure up to 7 inches WC (some higher).

If the blockage is periodic- no problem, just SLIGHTLY reduced flow during blockage. If it is permanent, and the fan cannot be moved a little down stream, build some type of "flattened" oval around it to streamline flow as well as possible and add 1/2 inch WC to rating of fan.

If ducted on both sides, or just inlet, essentially the same solution but built into the duct.

When you build the streamline baffle, make it two piece with joint above and below the obstruction.

Vaneaxial fans are available as belt-drive with motor out of airstream, so cooling is no problem.

There is no such thing as "suck" in physics, only "blow". If you have a fan inlet that is being partially blocked, then you need to increase the pressure on the other side of the blockage to increase the "suck" on the inlet of the fan. To do this, you must blow more air at the blockage side of the system.

"Suck" is only a force in banking "science". There it is known as "interest, fees, and demand".

not QUITE correct. "Suck" in this concept is actually just a lower absolute pressure than on the other side of the restriction.

IF the pressure is not low enough to overcome the resistance to flow presented, then the flow volume will be less than desired.

Since it is likely not very easy to create another motive force to the air upstream of the disruptor, then you need to increase the magnitude of the pressure differential by lowering the absolute pressure at the fan inlet. Fans with enough total pressure capability will be able to achieve this.

A simple axial fan as shown in an earlier post will not be able to generate an adequate total pressure to overcome the obstruction restriction, where a vaneaxial fan DOES have such capacity.

By the way- when you use ANY fan to generate a lower absolute pressure sufficient to clear the obstructor restriction, you have to "size" the fan for the absolute volume of the air being moved. Increased negative pressure will cause the air to expand, although the horsepower needed to move it is still based on "standard" air- 68F/20C and 0% RH at sea level.

Well, just remember, "horror vacui".

Try as I might, failing to remember isn't likely....

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