Calculating the required fan size and cfm.

[Uridan]

hi,

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 :)
Regards
Uridan

 

[russ_watters]

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.

 

[sir-pinski]

Hi Uridan,

Calculating the required fan size and CFM (cubic feet per minute) for your wind tunnel project will involve some basic fluid mechanics principles. First, you will need to determine the required air velocity to achieve the 10m/s winds for terminal velocity of the ball. This can be calculated using the formula V = √(2gh), where V is the velocity, g is the gravitational constant (9.8 m/s²), and h is the height of the tunnel (50cm in this case). This gives us a required air velocity of approximately 3.13 m/s.

Next, you will need to calculate the cross-sectional area of the tunnel. This can be done by using the formula A = πr², where A is the area, and r is the radius of the tunnel (13cm for the upper diameter, 11cm for the mid diameter, and 9cm for the lower diameter). This gives us a total cross-sectional area of approximately 850 cm².

To determine the required CFM, we can use the formula Q = AV, where Q is the flow rate (in cubic feet per minute), A is the area (in square feet), and V is the velocity (in feet per minute). Converting our values to feet, we get a required flow rate of approximately 146 CFM. This is the minimum flow rate needed to achieve the required air velocity in the wind tunnel.

As for fan size and number of blades, it will depend on the specific fan you choose to use. You will need to consider the fan's CFM rating, static pressure capabilities, and efficiency. It would be best to consult with a professional or do some research on different fan options to determine the best fit for your project.

In terms of having multiple fans in case of failure, it is a good idea to have a backup system in place. However, keep in mind that adding more fans may also increase the overall airflow and potentially affect the accuracy of the control system. It may be beneficial to have a backup fan with a lower CFM rating to maintain consistency in the airflow.

I hope this helps you in your project. Good luck!

Best regards,