Engineroom Fan

[Truckdriver2]

It was required to replace a previously centrifugal engineroom supply fan with an axial flow fan. The new fan may be oversized to some extent. The headroom over the fan is poor. The damper therefore strikes an angle of about 45 degrees to the fan intake. Also the inlet vent is angled at 45 degrees upwards. The air entering the fan is therefore, I believe, quite turbulent.

The fan is producing an unacceptable level of noise. A VSD was fitted to try out different RPM. At lower RPM the fan noise is considerably less but the fan develops a considerable singing noise.

It is not immediately feasible to reposition the fan in order to develop better flow characteristics. The way I see it the noise has to be accepted but silenced.

The inlet duct is large, say 2.5 meters by 2.5 meters but there is little space thickness wise to fit a silencer.

Can anyone suggest a company or product that may be fitted to silence this noise or any other method to reduce the noise?

 

[MikeHalloran]

Can you just space the fan farther from the damper, or whatever is the nearest obstruction in the air path? I'm guessing that some of the noise comes from aero interaction between moving fan blades and stationary ... something.





Mike Halloran
Pembroke Pines, FL, USA

 

[pauljohn]

Removing obstacles from before and after the fan would probably help.

If the fan is oversized you simply might be trying to push too much air into the engineroom. If the noise stops when you open doors and hatches then slowing the fan down would be more appropriate. IMO the engine room should be slightly pressurized at max cruising revs.

Can't think what the singing noise is. Can you remove the fan from the duct and run it in the open to see if the fan itself is faulty?

 

[powerjunx]

I wonder how this audible sound seems to be singing but i think more probably a "whistling" as it speeds up.
I bet, since the equipment was oversized that somehow triggers to blow more air volume with a greater force, this would be at the forefront of the fan where a loosen duct works tend to block air flow, the latter would create notoriuos whistling sound. You may try to set the speed exactly as the old fan produces the same capacity, else you may secure proper fastening of duct works.



"Whenever you are asked if you can do a job, tell them, certainly I can! Then get busy and find out how to do it." Theodore Roosevelt.

 

[seatrendgokhan]

Truckdriver2,

In our vessels we always face that problem and we solve it as follows;

a round ventilation channel bolted on top of the fan. the outer shell of the channel must be of thin galvanized CS plate with aproximately 5 mm holes all over it and inner shell of the channel is the same. the gap between inner and outer shell will be filled with heat insulation material (glasswool is acceptable). The height of the channel would be the same as the fan's hieght.

BR
Gokhan

GOKHAN
Naval Arc.& Marine Eng.

 

[aquatica]

In other words Gokhal mentioned a sort of 'silencer'. It is not uncommon to see silencers in high velocity exhaust systems but they have a different design but similar principle. Dimensions and flow rate would have helped me in giving you a better engineering solution!