How to calculate pressure thrust created by a fan?

In summary, when calculating the pressure thrust or negative pressure created by a fan, the fan specifications such as size and CFM can be used. To determine the pressure drop caused by a fan in a cabinet, a manometer or U-form tube filled with water can be used to measure the vacuum in mm of water column. If only CFM is available, it can be converted into velocity pressure using geometry and Bernoulli's equation can then be used to convert velocity into force.
  • #1
adilsyyed
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If I know fan specifications like the size, CFM etc. How can I calculate the pressure thrust or negative pressure it creates.

I am using a fan in an opening of the cabinet that pushes air outside the cabinet. And I need to know how much pressure drop it will cause on the suction side. It will be very small I guess but worth calculating.
 
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  • #2
It is easier to measure. If you do not have a manometer, make a U-form one (transparent pipe may suit it) filled with water. Difference in water levels will show the vacuum in the box in mm of water column the fan can achieve.
 
  • #3
[static] Pressure is typically part of the specs, but if all you have is CFM, then the static pressure is probably near zero. So just use geometry to convert cfm into fpm, then use bernoulli's equation to convert velocity into velocity pressure, then geometry again to convert velocity pressure into force.
 

1. How do I calculate the pressure thrust created by a fan?

To calculate the pressure thrust created by a fan, you will need to know the fan's air flow rate, the fan's exit velocity, and the density of air. You can then use the formula P = ρ*A*V^2, where P is the pressure thrust, ρ is the air density, A is the fan's exit area, and V is the fan's exit velocity. This will give you the pressure thrust in Newtons (N).

2. What is the difference between pressure thrust and static thrust?

Pressure thrust is the force generated by a fan due to the pressure difference between the inlet and outlet. Static thrust, on the other hand, is the force generated by a fan due to the acceleration of air through the fan. Pressure thrust is typically smaller than static thrust, as it only takes into account the pressure difference and not the velocity of the air.

3. How does the shape of a fan affect the pressure thrust?

The shape of a fan can affect the pressure thrust in several ways. A fan with a larger exit area will typically produce more pressure thrust, as it allows for more air to be expelled. Additionally, the angle and curvature of the fan blades can also impact the pressure thrust, as they affect the direction and velocity of the air flow.

4. Is there a maximum pressure thrust that can be achieved by a fan?

Yes, there is a theoretical maximum pressure thrust that can be achieved by a fan. This is known as the Betz limit, which states that the maximum pressure thrust a fan can generate is 16/27 times the density of air times the fan's exit area times the exit velocity squared. In practice, however, it is difficult for fans to achieve this maximum due to factors such as friction and turbulence.

5. What are some common units for measuring pressure thrust?

Pressure thrust can be measured in several different units, including newtons (N), pounds of force (lbf), and kilogram-force (kgf). In some cases, it may also be expressed in terms of pressure, such as pounds per square inch (psi) or pascals (Pa). It is important to check the units being used in any calculations to ensure they are consistent.

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