Noise, Heat and Power

[drawoh]

I am mounting in a sealed cabinet, a scanner that draws about 600W. I have been assuming that all of this is given off as heat. When the thing runs, it makes a great deal of audible noise. The device feels only slightly warm to the touch. We are guessing that much of the power is being converted to noise. Can I subtract this from the heat load, or does all this stuff become heat?

--
JHG

 

[EdStainless]

It all eventually becomes heat.
600W of noise, is this 120db like a jack hammer?

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[IRstuff]

Unless the loads are known to be purely resistive, not all the 600W might be actual power.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[LittleInch]

Is 600W a peak load only for a short period - i.e. when it is running?

how do you know what it draws?

what sort of scanner makes a noise that loud??

Anyway power to sound is quite low for items as opposed to sound systems, but even 50W would be very loud

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[drawoh]

Thanks.

I don't have a gut feel for decibels. If we are standing next to it, we cannot talk in normal conversational tones. At steady state, it draws 3A at 120VAC. It is a prism scanner that runs at fairly high speed.

--
JHG

 

[IRstuff]

Loudness, particularly in confined spaces, may be misleading. A few watts in a closet would probably be quite deafening. Note that even then, the conversion efficiency is rather poor:

http://www.sengpielaudio.com/calculator-efficiency.htm

says that speakers, which are designed to make sound, only have about 2% conversion efficiency; that means that 98% if the power is still lost in electrical heat.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529

 

[MintJulep]

You know, but perhaps have forgotten, that temperature and heat are different things. A slightly warm big thing and a really hot small thing can reject the same heat.

Consider that 100W is on the powerful end of home stereo equipment, and respectable adults rarely turn the volume past 4 or 5.

Noise is mechanical vibration moving air molecules around. It all becomes heat eventually.

 

[SomptingGuy]

Sound power is nowhere near as high as many people seem to think when they describe losses. The reference used is 1e-12W. To get a single Watt of sound power would require quite a large source.

Steve

 

[LittleInch]

Also 3 A at 120v is closer to 300 - 350 W of power...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[EdStainless]

I wonder how much of the sound is resonance?
350W isn't bad. As long as the unit is tightly bonded the cabinet you can use it as the heat dissipation device.

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P.E. Metallurgy, Plymouth Tube

 

[drawoh]

EdStainless,

I would guess that there is no resonance, yet. The mirror pumps air in pulses, which is just about the dictionary definition of sound. It will be installed in a sealed, sheet metal box. There will not be a good thermal contact between the scanner and the box. Heat will be dumped into the internal air, through internal heat exchangers, through the wall of the box and through external heat exchangers. Any energy that escapes the box as sound will not have to be dumped as heat, at least until someone takes a sledge hammer to everything.

There may be enough happening around the system that no one will notice the racket, but I don't want to count on it.

If we put sound dampening inside the box, it appears we will keep heat inside too.

--
JHG

 

[EdStainless]

There are enclosure coolers, either just heat exchangers that let you keep the box sealed or actual sir conditioners. These are fairly standards items.

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P.E. Metallurgy, Plymouth Tube

 

[gruntguru]

. . and you can ventilate an (insulated) box to remove heat while keeping most of the sound in by using acoustically lined ducts.

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