Calculating mechanical efficiancy of an axial fan

In summary, we are trying to improve the efficiency of a fan for an engineering project. However, we first need to figure out what the efficiency of the fan is now. We tried to calculate velocity based on cfm, but it didn't work. We then tried to measure static pressure, but that didn't work either. The best way for us to calculate the efficiency of the fan is to "pipe" the fan output into a turbine that creates electricity, but that approach has its own risks.
  • #1
physicsdude17
11
0
We are trying to improve the efficiency of a fan for an engineering project. However, we first need to figure out what the efficiency of the fan is now.

Since we know how many watts the fans motor is using at each setting, we figured we could just find how much power is in the air the fan is moving using P=1/2(rho)A(v^3), however this didn't work(maybe we're just all really bad at math?). It could be because we tried to calculate velocity based on cfm.

What is the best way for us to calculate the efficiency of the fan? We know how much power the motor is using and how many cfm of air it is moving. Thank you
 
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  • #2
The kinetic energy of the air is not the only energy: that equation doesn't capture the pressure energy of the air. A simple thumb-rule equation which you can derive from the definition of work (w=f*d) is HP= SP*CFM/(6356*eff)

...Where SP is the total static pressure generated by the fan.
 
  • #3
Efficiency is pretty vague. Unfortunately that "can" mean different things to different people. At my work, we have a script that will spit out three different efficiency numbers for a turbine stage. Some are based on work, some torque, some whatever whatever.

The important thing is to find a parameter or something you feel important to performance and make sure you just keep using the same definition.
 
  • #4
How can we measure the static pressure of the fan?

What is another way we could go about doing this project. Basically, we have to make the fan do more work using the same power or the same work using less power.

Thanks
 
  • #5
If you could "pipe" the fan output into a turbine that creates electricity, you could measure the drop in voltage to determine an efficiency. Of course, you would need the efficiency of the downstream turbine.

Conversely, don't be stuck on this idea of an efficiency. The purpose of a fan is to move air, so measure airflow.
 
  • #6
The simplest way of increasing a fan's efficiency is to polish the blades.
ASME PTC 11 will tell you how to test axial flow fans.
 

What is mechanical efficiency?

Mechanical efficiency refers to the ratio of the output power of a machine to the input power, expressed as a percentage. In the case of an axial fan, it is the ratio of the fan's power output (in the form of airflow) to the power input (in the form of electricity).

How is mechanical efficiency calculated for an axial fan?

Mechanical efficiency is calculated by dividing the fan's power output (in watts) by the power input (in watts) and multiplying by 100 to get a percentage. This can be expressed as: Efficiency = (Power output / Power input) * 100%

What factors affect the mechanical efficiency of an axial fan?

There are several factors that can affect the mechanical efficiency of an axial fan, including the design and size of the fan, the speed at which it operates, the angle of the fan blades, and the condition of the fan (such as wear and tear or build-up of debris).

Can the mechanical efficiency of an axial fan be improved?

Yes, the mechanical efficiency of an axial fan can be improved by optimizing the fan's design and reducing any sources of resistance or friction. Regular maintenance and cleaning of the fan can also help improve its efficiency.

Why is calculating mechanical efficiency important for an axial fan?

Calculating mechanical efficiency is important as it allows for the evaluation of the fan's performance and can help identify any areas for improvement. It also helps determine the energy efficiency of the fan, which can have an impact on operating costs and environmental sustainability.

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