0

I have a project where I need to generate a certain flow rate to levitate a ping pong ball using the Bernoulli principle. From some rough calculations, I found that it would take about 30 CFM through a 2" diameter hole to lift the ball.

enter image description here

The only fan I have is a big box fan (an axial fan) that can provide 2000 CFM. I tried taping a trash bag to my box fan and routing the flow to a small hole, but there was almost no flow through the hole. I think that I basically created an orifice plate, which requires a pressure difference to generate flow. Axial fans have notoriously low pressure ratios, so it's no surprise that this didn't work.

Is there any way that I could use my box fan to do what I want to do? Could I use something like a large converging nozzle on the end of my fan?

What if I wanted to supply multiple pipes with airflow to lift multiple ping pong balls? Could I use an axial fan? Or would something like a centrifugal fan be better?

nwsteg
  • 167
  • 6

1 Answers1

1

Converging ducts have been constructed for years.

Often an exercise to work out the angle needed for lowest losses, about 6 degrees iirc.

Aslo an exercise to calculate the shortest joint lines especially for welders.

Solar Mike
  • 14,798
  • 1
  • 19
  • 29
  • 1
    Even a converging duct may have too much pressure drop -- I suspect there's a way to calculate this. Before you go to much more trouble, make a cone out of paper or light cardboard that has a 2" diameter at one end and a circumference to match the fan on the other. Then tape the cone on the fan, and try it out. – TimWescott Apr 01 '22 at 20:54
  • I will try this! Any comment on the length of the cone? Would wall-friction losses (not sure if that's the right term) be significant for this application? – nwsteg Apr 02 '22 at 14:47