VFD for the air blower

[HilaryE]

Dear All,

I need to provide a source of the airflow to my experiments. The range of air velocities that I need is 2m/s to 20m/s. A source of airflow (I think it will be an air blower) will need to be powerful enough to overcome some significant resistances, given to the airflow by physical obstacles (therefore, fans may not be suitable for my experiments).

I think about purchase of this device

https://www.amazon.com/Professional-Blower-Extraction-220Volt-Europe/dp/B06ZYYTV9W

This device has adjustment of the airflow velocity, but for some experiments, I will need pretty low velocities (beyond a regular spec of this or similar devices). Therefore, I am looking for ways of extra adjustment of such blower speed.

I came across the VFD (Variable Frequency Drive).
- I wonder whether control of the linked blower by VFD will work in order to get velocities as low as 2m/s.
- I also wonder whether application of VFD is the most optimum solution for reduction of air blower speed.

Any advice and help on this would be much appreciated.

Thank you.
Regards.

 

[jraef]

I’m no mechanical engineer, but you are looking for a specific velocity (2m/s), that blower is rated for a specific volume (4.5 m³/min). Have you determined if that volume is sufficient to provide your needed velocity? Using a quick on-line calculator, that volume, through the (probable, but unstated) 50mm nozzle, will result in a Terminal velocity of around 13m/sec, short of your desired 20m/s. A narrower aperture would increase the air velocity, but likely decrease the volume. You don’t state your needed volume nor the aperture you can live with for whatever you are doing here. Those are necessary aspects of picking a blower.

As to your question, that blower states the motor speed as being 16,000RPM, so that means it is undoubtedly a type of single phase motor called a “universal motor” that is a kind of DC motor that runs on AC, because that is what you would need to attain that rotational speed. So a “VFD” would not work for this (nor would most VFDs work on any single phase motor). However one advantage of a universal motor is that they respond to simple voltage control, so if this does not already have that, you could add it externally. But I would ask the mfr before subjecting it to that, they seem to go into a lot of detail about the voltage supply.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[FacEngrPE]

I am a mechanical engineer, Jraef's answer is correct. Universal motors are often applied to light weight household appliances and power tools because the motors torque curve matches the requirements of a blower load quite well, and the result is a very light weight assembly. Speed is very controllable with a voltage adjustment, and running for extended periods at low speed is unlikely to result in over heating. Depending on tour requirements and budget, you could look at the range of corded leaf blowers, they are all relatively inexpensive, compared to the cost of a VFD, 3 phase motor, and the associated air moving hardware.

The particular blower you cite

https://www.bosch-professional.com/kw/en/products/gbl-800-e-06019804P0

requires 800 W. This power requirement is within the capabilities of ceiling fan speed controllers (these control speed by adjusting fan input voltage), so less then $40, keep it simple.

Fred

 

[mparenteau]

One other thing to consider...I don't know how a 2 m/s velocity compares to motor rpm, but motors have an operable range where they are able to self cool. Operation below the speed range can cause excess heating and prolonged operation can burn up the motor.

Mike

 

[FacEngrPE]

Motor operable range is less of an issue when driving a blower. At low speed, the blower will demand very little shaft torque, so the motor current will also be low.
The experimental service described is most likely going to be intermittent.

A continuous service solution is completely valid (3 phase motor, industrial blower, vfd), it will cost 10X or so with respect to the Bosch blower and a simple control.

I would likely bead off some airflow, or expand the experiment area (either will change the velocity), before I would use the continuous service solution.

Fred