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Calculating the required fan size and cfm.

  1. Dec 13, 2009 #1

    I am an electronic engineer student and I am doing a study on control systems that can be used to control a ball's height in a vertical wind tunnel.

    I have a problem in calculating the fans needed (as in size and number of blades) and the amount of cfm that the fans need to produce. The wind tunnel specs are:

    Upper diameter: 26cm
    mid diameter: 22 cm
    lower diameter: 18cm
    Tunnel height: 50cm

    the ball that needs to be lifted requires 10m/s winds for terminal velocity.

    I don't know that much about flow rates and fluid mechanics that is why I am asking :shy:.

    My plan is to make a number of fans at the top of the wind tunnel so if one of the fans fail, the other fans will compensate to keep the ball at the pre set height.

    Thanks, any help would be appreciated :)
  2. jcsd
  3. Dec 13, 2009 #2


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    Staff: Mentor

    Welcome to PF.

    If you have the dimensions (how big is the ball, though, and where will you be holding it?) and the required velocity, you can calculate the flow rate with simple geometry (cross sectional area times velocity). Obviously, you have some units to convert...

    For fan selection, you have a fair amount of velocity there, which means a fair amount of pressure so I'm not sure an axial (bladed) fan will do. You may need a centrifugal fan. Once you have the airflow, though, start looking for fan curves of available fans and you'll start to get an idea of how real fans perform.
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