Fan Noise Reduction 1

[edison123]

Have a 1500 RPM, 1500 HP motor with shaft mounted external centrifugal fan cooling the motor (with embedded tubes around the stator periphery). The fan is mounted before the coupling with suction from the coupling end and delivery through the embedded tubes.

The operator near the motor is objecting to the noise level - created by the above fan - which was recorded at 93 dB.

I am proposing to use a 5 mm sheet metal hood with an inch thick soft rubber lining inside, around and over the fan suction area.

Will this work ?

Any other ideas ?

*Even inside a hard-boiled egg, there is a golden heart!!!*

 

[ozmosis]

It is sometimes possible for the motor manufacturer to have available axial type fans (single direction) to reduce fan noise. Might be worth asking.

93dB is about what you would expect for such a size of motor.

Or, ear defenders for the operator?

 

[edison123]

Thanks sed2. That's exactly I told the client about the expected noise level and usage of ear protection. Apparently, the management is bowing to the union pressure (which is apparently against ear protection) and wants to attenuate the noise level.

The problem started because the previous motor (which failed) running in the same location had ducted cooling wiht no fans at all which resulted in quieter running.

No axial fans be fixed since the motor is tube ventilated with the tubes embedded around the stator periphery.

So, I am trying my stunt.

*Even inside a hard-boiled egg, there is a golden heart!!!*

 

[dpc]

Some type of enclosure around the fan/motor is the most likely solution, although this obviously makes any maintenance more work.

A search for "industrial soundproofing" or "industrial noise reduction" will turn up some engineered options. You'll need some frequency spectrum data for the noise to optimize the solution. Just be thankful it isn't 3000 rpm.

http://www.acousticalsolutions.com/applications/industrial.asp

 

[MikeHalloran]

Yacht engine rooms are often lined with a sandwich comprising a sheet of finely perforated metal on the noisy side, some acoustically absorbent core (which may be fibrous felt or possibly honeycomb), and an impervious metal sheet on the quiet side. I think the stuff is sold commercially.

If the noise is particularly strong at one frequency, that would suggest an aero interaction between the fan blade tips and the tube edges. In that case the spectrum could be spread out a bit by staggering the fan blade tips or the tube edges or both, just a little, so that interaction noises don't constructively reinforce each other. Sort of like tire tread patterns are unevenly spaced.



Mike Halloran
Pembroke Pines, FL, USA

 

[edison123]

Thx dpc and mike.

Our trial is planned for this week-end. Will come back here hopefully with good news.



*Even inside a hard-boiled egg, there is a golden heart!!!*

 

[aolalde]

A pair of low noise blowers with independent motor-fan could be adapted to provide at least the same airflow through the cooling pipes. Then the original fan could be removed. Probably you need to measure the flow and pressure of air. That is frequently made for DC machines and variable speed motors.

 

[ScottyUK]

Multiple smaller blowers could incorporate a level of redundancy to allow continued operation in the event of a failure. Not as robust as the original shaft-driven fan which is obviously available if the motor is available, but better than adding a single point failure mode to the system.


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I don't have an attitude problem. You have a perception problem...

 

[edison123]

Thx alex and scotty.

Since this motor has cooler tubes around the stator outer periphery, fixing externally driven fans is not an option.

I am going to try my above method this sunday and am keeping the fingers crossed.

*Even inside a hard-boiled egg, there is a golden heart!!!*

 

[raisinbran]

This may not be practical in your situation, but noise reduction is one of the benefits of using water cooled motors. We use them quite often in the underground mining industry. If you have a process nearby that requires water, maybe it is something you can look at.

If you cannot use water, have someone do a sound level spectrum analysis to determine what frequency or frequencies are causing most of the noise. That information may better help you determine what type(s) of sound absorbing materials will provide the most benefit. Just like anything else, not all sound absorbing materials are created equal. There are companies that specialize in noise reduction strategies, and that may be the most economic road to hoe.

Good luck,
Raisinbran

 

[edison123]

The feedback.

The noise level at about 1 ft of the motor came down from 102 dB to 95 dB with the enclosure.

But it came down from 87 dB to only 85 dB at the operator end, which is about 12 ft away.

The background noise (without the motor running) was 80 dB.

Advised to use ear mufflers.

*Even inside a hard-boiled egg, there is a golden heart!!!*

 

[sslobodan]

Let us not search for solution that is good when you replace expensive fan (no one will pay for it)!

In my company we have technical person designing sound silencers for outgoing air on our projects. I remember when I was talking about them he explained about the every noise level is created by some part moving and that silencer is created to suppress some frequencies but to suppress them all he would need very big silencer and that it is expensive so he suppresses only main noise. Now you can try many things but the noise is expectable on such fans, and the problem is usually sound level regulations that consider sound outside the facility. I don't know how does the fan chamber look like (and if you have one) but you can try applying some house noise suppressing materials rather than metal sheath, either on fan chamber or on operator room. metal pases vibration, so there are better solutions because your prime concern is to lover the noise inside, metal is used in silencers to withstand air pressure when you are trying to protect outside world from your noise....