# Levitate a ball. Fans and blowers. HELP, WHICH USE.

#### Alvaro

Hi, I have a question about fans and fluid mechanics.

I need to use a fan for my carreer final proyect and im not sure what kind of fan use here. ( i have doubts about wich fan to use, high airflow fans or high static pressure fans).

My project consist in levitate a ball(or any aerodynamic object) by air , the ball will be in a tube and the fan will woks with out dust or big particles( clear air ). (Then i will use a close loop control but this is other matter).

There are fans that priorize air flow vs static pressure , and my question is wich type of fan i need to use here . ( I can use axial fans or centrifugal blowers).

The goal here is move a ""heavy"" object (the ball) so which kind of fan will you use ?[/B]

(I know that i need to use bernuilli equation to know the pressure aply to the ball(and the drag equation later), but i dont know if i need high air speed/air flow or static ourtput pressure).

Thanks and kind regards.

#### Woody

I think the drag must come first.
Once you have the coefficient of drag, and the mass of the ball, and the size of the ball, you can work out the flow rate you require.
Once you know the flow rate you require, you can then find out what sort of fan you will require to provide this flow rate over the ball.

As a starting point I just googled "drag of a sphere" and found: <drag of a sphere>

You will not achieve ideal flow, that is just theoretical.
You will not want oscillating unsteady, because then the ball will move from side to side with the oscillating flow.

Note that for a sphere the reference length in the Reynolds number equation will be the diameter.

#### oz93666

Generally speaking axial fans are for pushing high volumes of air at low pressure ..

Centrifugal blowers create greater pressure , but lower flow rate ...

For your task a Centrifugal Blower is probably the best ... but this is not a hard and fast rule , for example model airplane flyers sometimes use electric ducted fans ...

These are fairly cheap, axial , extremely powerful ,and compact, use brushless motors , running on low voltage DC ... a number of these in parallel would certainly work.... or if the ball is no heavier than about 500gm just one fan. They come in many sizes (see eBay). The advantage to this type is you have complete control over the air flow by varying the current .... This is not the case for most centrifugal fans.

But the normal form of axial fan like this computer fan would be no good ....

ANY type of centrifugal fan will be OK ...

I would think about what you will do with the fans when the project is over and dismantled , let this have some bearing on your choice .

As is often the case not enough information has been provided to give a good answer .... Is this 'heavy' ball 100 gms or 100Kgms and how big is the tube????

Last edited:
1 person

#### Alvaro

The ball will be something close to a tenis ball. ( close because i will print the object with my 3d printer, to use diferent aerodinamic shapes).
The mass will be betwen 40-80 grames and the duct will have a diameter of 7 cm.

I tried with a computer fan with this featuresthe fan : EC8025M12X )

DC FAN 8025 ? EVERCOOL

I can see that it has 25 CFM and 0.08 Inch H2O pressure.

With this features i couldnt even levitate a paper ball ( i test it, bit depressing)

So i must asum that i need higher static pressure innstead of CFMs ?
(Maybe i need only to use more powerfull fans, but i prefer to understand which features i need to priorize higger, because maybe only is a question of output pressure)

I find this blower as a replace to the fanthe blower: EC9733H12X-B) EC 9733 SERIES ? EVERCOOL 20 CFM and 0.41 Inch H2O pressure.

I have less airflow but better pressure.

#### Alvaro

Ball features:
40-80 grames
7 cm diameter.

Duct features:
8 cm diameter
60-80 cm lenght.

I tried with this pc fan(from a old PC), and im not even close: The fan: EC8025M12X
25 CFM and 0.08 Inch H2O pressure.

With this features i couldnt even levitate a paper ball ( i test it, bit depressing)
So i must asum that i need higher static pressure innstead of CFMs ?

(Maybe i need only to use more powerfull fans, but i prefer to understand which features i need to priorize higger, because maybe only is a question of output pressure)
I find this blower as a replace to the fanthe blower: EC9733H12X-B)

EC 9733 SERIES ? EVERCOOL
20 CFM and 0.41 Inch H2O pressure.

I have less airflow but better pressure.

#### Alvaro

Generally speaking axial fans are for pushing high volumes of air at low pressure ..

Centrifugal blowers create greater pressure , but lower flow rate ...

For your task a Centrifugal Blower is probably the best ... but this is not a hard and fast rule , for example model airplane flyers sometimes use electric ducted fans ...

These are fairly cheap, axial , extremely powerful ,and compact, use brushless motors , running on low voltage DC ... a number of these in parallel would certainly work.... or if the ball is no heavier than about 500gm just one fan. They come in many sizes (see eBay). The advantage to this type is you have complete control over the air flow by varying the current .... This is not the case for most centrifugal fans.

But the normal form of axial fan like this computer fan would be no good ....

ANY type of centrifugal fan will be OK ...

I would think about what you will do with the fans when the project is over and dismantled , let this have some bearing on your choice .

As is often the case not enough information has been provided to give a good answer .... Is this 'heavy' ball 100 gms or 100Kgms and how big is the tube????

Ball features:
40-80 grames
7 cm diameter.

Duct features:
8 cm diameter
60-80 cm lenght.

I tried with this pc fan(from a old PC), and im not even close: The fan: EC8025M12X
25 CFM and 0.08 Inch H2O pressure.

With this features i couldnt even levitate a paper ball ( i test it, bit depressing)
So i must asum that i need higher static pressure innstead of CFMs ?

(Maybe i need only to use more powerfull fans, but i prefer to understand which features i need to priorize higger, because maybe only is a question of output pressure)
I find this blower as a replace to the fanthe blower: EC9733H12X-B)

EC 9733 SERIES ? EVERCOOL
20 CFM and 0.41 Inch H2O pressure.

I have less airflow but better pressure.