convert shaft-torque to heatflow?

Brian Whatcott wrote:

r.c.m added back on, because those guys actually make real metal things. You're always welcome to edit the target groups of your own Original Posts. Respectfully request that you don't edit mine?

i don't think those things were designed to shed 1272.5 BTU/hour on a continuous basis. I think they are optimized for converting bolii of shaftpower, into heat for radiation into the ambient air, intermittently. Pretty much the same difference between a golf-cart battery, and a engine-starting battery.
Anyway, I'm not looking to "shed" heat, I'm looking to "pump" it, so I can bake real things.
I think the pro's use super-heated steam, but I think my entire mooted power capacity is smaller than their calculation error-budgets....
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On 9 Jul 2005 22:07:08 -0700, in sci.engr.mech alanh snipped-for-privacy@yahoo.com wrote:

You need to provide a bit more information. You have the torque and the power, so as posted you can find the rpm. The real question is what you mean by heat flow at 300F? I would assume you intend to transfer this energy to some other system, as you just can't dump 1/2 hp ( 0.707 BTU/sec) into an insulated tank with the temp ever increasing. Knowing what you intend to do with it might influence the answer.

I would start thinking of using a positive displacement gear pump connected to your tank of gear oil discharging through a pipe with a valve to allow you to vary the pressure drop and hence dissipation rate to your needs. ---------- Ed Ruf Lifetime AMA# 344007 ( snipped-for-privacy@EdwardG.Ruf.com) http://EdwardGRuf.com
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gear
Yeah, a band heater on the outside. But since I can't find any mention of what you're trying to accomplish I don't know if that will work.
Pumps will work, but you lose heat through the plumbing and pump body. Then you have to worry about pump seals, the noise. A BS #1 pump would probably be about right but I don't recall if they're rated to 300 F
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alanh snipped-for-privacy@yahoo.com wrote:

I don't know what you mean by "heat flow"; but if you just want to turn torque (and RPM I presume) into heat, you might just use the shaft to turn a generator, and run the electrical output through a big resistor. That's the way dynamic braking systems work on the servos and spindle motors in many machine tools. Once you have a nice hot resistor, then you can collect, store, or transfer the heat any way your heart desires.
This method might be more "elegant" just because it doesn't need tanks of oil, or plumbing, hydraulics, etc. It might also be more efficient, because the heat all happens in one specific place (the resistor), instead of all over the volume of a tank. And, depending on how you collect/store/transfer the heat, it doesn't need to be lost in the plumbing.
With any method you choose, keep in mind that as you increase the load on the shaft, you'll also increase the heat generated by the source of your power. The real, total heat created by the system will be the sum of heat dissipated at the source, and at the "target". If the source-end heat is a substantial percentage of the total, then you might want to think about collecting heat on that end, too.
KG -- I'm sick of spam. The 2 in my address doesn't belong there.
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Now you're floating my boat. Might more than make up for the conversion-inefficiency of going through a conversion to electricity....

The wind driving the windmill gets hotter? Then why do they call it "chill factor"?
The river driving the micro-hydro, gets hotter?
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alanh snipped-for-privacy@yahoo.com wrote:

<laughing>
No, not so you'd notice. I was thinking about an electric motor that draws more amperage to run a load, or an engine that burns more fuel. Or a set of bicyle pedals pushed by someone who burns more calories.
I suppose there MUST be some increased pressure/friction/heat where wind or water come into contact with fan or turbine blades. There IS more work being done if the load is bigger. But you'd be hard pressed to measure or collect that kind of heat, I'm sure.
KG
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On 9 Jul 2005 22:07:08 -0700, alanh snipped-for-privacy@yahoo.com wrote:

Sure. You didn't provide enough details for specifics but I'll offer these generalities up.
Eddy current. Spin a magnet in close vicinity of a conductive metal like copper or aluminum. It will be heated by the high induced eddy currents. If you're heating a vessel then if a well can be provided on the outer surface, the rotor from a permanent magnet stepper or brushless DC motor could be spun inside the well. Regulate the heat by varying the insertion depth.
Hydraulic pump. Drive the pump from your shaft. Supply a closed loop of hydraulic oil to the pump. Provide an orifice suitable to build enough back pressure to properly load the shaft. Pressure ~~ torque input for a positive displacement pump. The oil leaving the orifice is hot. Circulate this hot oil through your process.
Permanent magnet generator and resistive heater. A small PM stepper, BLDC or DC servo motor would do. Select the immersion heater to properly load the generator.
Shear type absorber. This absorber was invented by Lockheed in the 50s to load jet engines and is the basis of most automotive engine dynamometers such as the SuperFlow brand. This absorber consists of a series of tightly fitting discs, alternately fixed and driven. The discs have holes on the same radii but in an even/odd combination so that the working fluid is accelerated by the rotating disc, slowed by the stationary disc and sheared at the interface. The working fluid is usually oil or water, although high pressure gas will work. A dense, high MW gas like SF6 would work best. Fluorocarbon refrigerants should also work well, as would air.
The load is controlled over a very wide range by varying the level of the working fluid in the absorber. In this instance, the heat would be transferred to the process via the heated fluid.
This type of absorber is very compact for the power absorbed. One capable of absorbing 400 watts might be as small as a 35mm film can. One capable of absorbing 10,000 HP is small enough for a man to hold in his arms. A rule of thumb is that with 6" discs, figure 1000 hp per disc, stacking as many as needed.
There is an SAE paper documenting the design. If this catches your attention, I can probably dig up the number. I have the paper around here somewhere.
A non-obvious version of this could be a gearbox spun at sufficient speed that the internal losses amount to the power you need. Circulate the lube oil to the process.
Heat pump. Drive a small compressor with the shaft power and set up a refrigeration cycle. This would have the advantage of a COP >1. Arrange the condenser in the process to be heated.
John
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Generator and electrical heater?

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Not enough information given to reach a conclusion. But ... if you assume a given RPM on a brake shaft, say 1000 RPM, and 6.812 pounds of cooling water either agitated at 100% efficiency or used as a perfect cooling medium on a brake:
When the brake is doing 1/2 HP of work, torque would be 2.626 ft. pounds. There is 0.001285 BTU per ft/lb. or 2043.58 BTU from 2.626 ft./lb. A BTU is the amount of heat required to raise 1 lb. of water 1 degree F. Therefore (2043.58 / 6.812 = 300) deg F temperature rise in 6.812 lbs. of water (or of course, 6.812 F temp rise in 300 lbs. of water).
Bob Swinney

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