BTU Output of Centrifuges

[2Hart]

Does anyone know how I can measure or caculate the BTU output of a few centrifuges that we have in our labs. Apparently, if the output is above 10% of the other equipment I will ahve to do a room mapping.

 

[davidbeach]

All of the electric power into the centrifuge will become heat out. All of the heat out will go into the room unless there are piped or ducted cooling systems connected to the centrifuge.

 

[analogkid2digitalman]

David- will it all become heat out? If power in is 100% converted to heat, what energy is left to create motion?

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[geekEE]

Yes, energy is put into creating motion, but then the motion all gets turned back into heat through friction.

 

[2Hart]

I agree the motion all gets turned back to heat, however some of the heat will heat the product in the centrifuge, some will be dispated by the rotor, some will be absorbed by the material so not all the heat will escape out of the centrifuge.

 

[dpc]

Actually, even energy that goes into heating the product or absorbed by anything else eventually gets rejected back into the room, unless you do something to prevent that from happening.

 

[jraef]

If the product goes out of the room, the heat it carries goes with it. But in a lab environment these are not likely production centrifuges, probably sampling. In that case it's likely the samples stay in the lab long enough to return to "room temperature" so you would have to consider it (the heat energy) staying. If you are talking medical vials or something small like that, they won't retain enough heat to worry about and will give it up rapidly anyway, so assume it is all still in the room.

If the samples are of large quantity AND immediately removed however, then you would have to somehow determine how much heat transferred into them, maybe just a simple little differential measurement.

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[peebee]

There's one other big heat sink on many many centrifuges, and that sink is usually located outside of the centrifuge room: the breaking resistor on the VFD controller. If you have one of those, then the large majority of the electrical input power will be burnt off by the resistor and exhausted outside the room. In that event, the BTU output of the centrifuge will only be the running-load power input into the motor -- NOT the starting energy. You'd only need to account for frictional losses, not the kinetic energy. The frictional losses should be much much less than the kinetic energy.

If you just have an on-off switch though, and a mechanical brake, then all the above is true, every bit of power you send to your motor will be converted to heat in the room with a 100% efficacy.

 

[peebee]

....sorry, braking resistor. Too bad you can't edit these posts.....

 

[geekEE]

Hmm...you make a good point peebee. I guess it would depend on what kind of centrifuge the original poster was talking about. I was assuming he was talking about a small tabletop centrifuge rather than a large industrial centrifuge. If 2Hart is still reading this, giving us a little more detail might be helpful.

 

[2Hart]

Thanks for all the info. I am actually talking about tabletop centrifuges. One of the manufacturer's has gotten back to me about the BTU output and says it is about 1200 BTUs for their unit.

 

[itsmoked]

1200 x 0.0002928 = 0.35kWHr

Do these units have a nameplate that sez: 120V @ 2A or 300W or ?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[2Hart]

The nameplate says 110 - 127v with an amperage rating of 5.0 amps. However when I ran the unit and took measurements of voltage and current we got 117.1 volts and a current reading of 2.9 amps at maximum speed and no samples inside.

 

[peebee]

2.9x117 = 340W = 1160BTUh sounds like a winner

 

[2Hart]

The manufacturers must be using the same formula and acounting for some error, so it looks like my problem is solved. Thanks for everyones help on the matter.