Would a Centrifugal Fan Be Better for Moving Air Through a Small Hose?

[SentinelAeon]

I have a plastic box and i am trying to move as much air through it as i can. I use a small garden hose to connect the box with some wall mounted fan (see the image attached). Given the small diameter of hose (2cm) and big fan (9.2cm) i am wondering if it would be better to use a smaller fan. Also, i am using axial fan intended for high flow and low static pressure (image of both fans in the attachment). Would in this case it be better to use a centrifugal fan intended for lower flow but higher static pressure ? Any data on this subject would be great, even links, so i can figure out the optimal setup given the small diameter of the hose.

edit: I found a video that explains the issue i am having and offers some results. But i am still interested in hearing your opinion.

 

[Baluncore]

Would in this case it be better to use a centrifugal fan intended for lower flow but higher static pressure ?

Definitely YES.

It takes pressure to push air through a hose. The large area fan is designed to operate with very low pressure and high volume.

A centrifugal blower will develop pressure until the flow reaches the operating point on the pressure-flow diagram for that blower design and RPM.

Google images for "pressure-flow diagrams" that come with different centrifugal blowers.

Alternatively, there is a third option. A positive displacement pump would move a set volume of compressed air at whatever pressure was required for it to move, or it would burst the air receiver or hose, or blow the over-pressure safety valve.

 

[SentinelAeon]

I installed a centrifugal blower and will start the test soon and will report the findings. Its a small blower fan, similar to what was used on older graphic cards. So while i verified that it is really good at blowing through a small diameter hose, i am now wondering whether it will be able to beat 2x 92mm axial fans, considering that its a mere 45mm blower fan. But i can always get a bigger one, or just use 2 or 3 of them. Or use higher speed since its considerably more silent. Those 92mm fans are like 0.6A each and when you constrain them by connecting a small hose to them, they become incredibly loud.

Btw this blower fan has 2 intake sides. Right now i only used 1 side and covered the other side. In future i will try to set it up in a way that it uses both sides, but when checking by hand, it certanly didnt feel like covering 1 side resulted in 50% less airflow. Maybe 25%.

 

[Baluncore]

Those 92mm fans are like 0.6A each and when you constrain them by connecting a small hose to them, they become incredibly loud.

Because there is too little airflow for that fan design, the blades are stalled, and the resulting inefficient turbulence is making the noise. You may sometimes notice that when stalled, the fan will spin faster, and use less power.

Btw this blower fan has 2 intake sides. Right now i only used 1 side and covered the other side. In future i will try to set it up in a way that it uses both sides, but when checking by hand, it certanly didnt feel like covering 1 side resulted in 50% less airflow. Maybe 25%.

That is to be expected, since the airflow is limited by the narrow hose outlet much more than by the fan inlet.
To get the greatest flow, open both inlet sides to the centrifugal blower.

Flow will be optimum when there is a taper, or a horn, between the blower and the inlet to the hose. Airflow there must be smooth without step changes in the airflow section, direction, or air velocity.

 

[jrmichler]

So while i verified that it is really good at blowing through a small diameter hose, i am now wondering whether it will be able to beat 2x 92mm axial fans, considering that its a mere 45mm blower fan.

If your blower does not move enough air, here's how to look for a better blower. Or you can use this method to see why that little centrifugal blower moves more air through the hose than the larger axial fan.

You predict the effect of any other fan or blower by comparing the fan curves. The figure below is from the datasheet of a randomly chosen 51mm by 51mm by 15mm centrifugal blower. The three black curves are for three different operating RPM.

The red curve represents a possible system curve. The system curve is the relation between pressure and flow rate for the system. Your system is the hose and the connections to the blower and the box. The actual flow rate is where the system curve intersects the fan curve. You can find that point by drilling a small hole at the fan discharge and connecting a water manometer (search the term). A water manometer is simply a piece of clear plastic tubing and a ruler. The system curve is a quadratic curve that starts at 0, 0.