Calculating Fan Size: Not Driven by Motor

In summary, to lower a 150kg mass 20m to the ground using a fan to dissipate energy, the fan will need to be powered by 1471.5W.
  • #1
al_garnett
9
0
Hey, I'm trying to find a fan that will dissipate 1471.5W. The fan is going to be driven via a belt connected to a driving spool and not driven by an electric motor.

How do i go about calculating the required fan size?

Is there anywhere i can look at fan specifications for fans that are not driven by an electric motor?

Thanks
 
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  • #2
Does it have to be exactly 1471.5W or would 1472W be fine? Or 1471.499W?

There are many variables besides fan size (diameter), like the number of blades and their pitch, that determine the energy used.
The energy used by the fan at a particular speed depends on how much it changes the speed of the fluid that it is expected to push about (and losses).
You could have a look at electric fan specs and use the blades off one that is closest - either buy them or use them as a starting point for your design.
 
  • #3
Simon Bridge said:
Does it have to be exactly 1471.5W or would 1472W be fine? Or 1471.499W?

There are many variables besides fan size (diameter), like the number of blades and their pitch, that determine the energy used.
The energy used by the fan at a particular speed depends on how much it changes the speed of the fluid that it is expected to push about (and losses).
You could have a look at electric fan specs and use the blades off one that is closest - either buy them or use them as a starting point for your design.

Im essentially lowering a 150kg mass 20m to the ground by using the fan to dissipate energy.
The mass will be attached to a rope that is wrapped around a spool.
As the mass descends the rope will be pulled from the spool causing it to rotate. The spool will then drive the fan via a belt.
The mass has a gravitational potential energy of 29,340J, calculated using E=mgh.
Subsequently, by setting the time required for the descent, 20 seconds, and using the equation Power=E/time I find the power input to the fan 1471.5W.
Basically i need to find a suitable fan to dissipate this amount of energy so that the mass will descend at 1m/s.
If anyone could help it would be greatly appreciated.
 
  • #4
Airflow times pressure (divided by efficiency) equals power...just make sure you have the units right.
 
  • #5
You should look at a drawing of the chime mechanism of a mechanical clock, they use a contraption rather like a paddle wheel from an early steamship to slow down the striking weight, it should be easier to "tune", I don't think that this approach will give you a particularly repeatable result, simple things like air pressure will effect the result.
 
  • #6
Im with jobrag - experiment with a paddlewheel.
You can also slow the fall by having it lift another weight.
 

1. How do I determine the appropriate fan size for a specific space?

When calculating fan size, you need to consider the volume of the space and the air changes per hour (ACH) required. To determine the volume, measure the length, width, and height of the space and multiply them together. Then, determine the ACH needed based on the type of space (e.g. residential, commercial, industrial) and the desired air quality. Finally, use a fan selection chart or calculator to find the appropriate fan size for your specific needs.

2. What is the relationship between fan size and airflow?

The size of a fan is directly related to the amount of airflow it can produce. This is because larger fans have larger blades, which can move more air with each rotation. However, there are other factors that can affect airflow, such as the design and speed of the fan. It is important to consider all these factors when selecting a fan size for a specific application.

3. Can I use a larger fan to increase airflow?

While a larger fan can generally produce more airflow, it is not always the most efficient solution. Using a fan that is too large for a space can result in excessive energy consumption and noise levels. It is important to select a fan size that is appropriate for the specific needs of the space to ensure optimal performance and energy efficiency.

4. How do I calculate the required horsepower for a fan?

The horsepower (HP) of a fan is determined by the fan size, rotational speed, and air density. You can use a formula to calculate the required HP for a fan, or use a fan selection software that takes into account all the necessary variables. It is important to select a fan with the appropriate HP to ensure it can handle the required airflow without overworking the motor.

5. Are there any safety considerations when selecting a fan size?

Yes, safety is an important factor to consider when selecting a fan size. It is crucial to ensure that the fan is not too large for the space, as this can create excessive air velocity and potentially cause harm to individuals or damage to equipment. It is also important to follow all safety guidelines and regulations when installing and operating a fan to prevent any accidents.

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