convert shaft-torque to heatflow?

I have the shaft torque... what I need is a half horsepower of heatflow at 300 F.

I'm having visions of paddles inside of an insulated tank full of gear oil. Bet it would work just fine. But it smells a bit klugey.

Any more *elegant* way to do it?

Reply to
alanh_27
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Torque is in units of energy, heat flow in units of energy/second. You can't convert them.

hvacrmedic

Reply to
RP

That's exactly what I wanted to suggest. Mechanical energy can easily be (directly) converted to thermal by friction. The paddle solution is what is used in brakes for engine test stands, just with the intent to put some load onto the motor.

Nick

Reply to
Nick Müller

Yes, but torque can't be converted to thermal energy. Nor is there such a thing as heat flow at 300F. That's gibberish. I assume he means heat flow from a fluid held at an equilibrium temperature of 300F. In this case, the Btuh generated at a given torque from a given motor will depend upon the angular velocity of the shaft. This will in turn correspond to a specific resistance to rotation. Thus for measurable temperature rise of the fluid in the shortest time period, it's best to use a small arm radius and higher angular velocity-- less fluid will be required to provide the same back pressure and thus the same torque. The sensible heat requirement will be lower with lower fluid mass. How he is going to provide 300F is another matter. He'll have to do some heavy calculations or by trial and error adjust the flow of heat removing media and/or insulation value of the tank.

hvacrmedic

Reply to
RP

even if the termology is wrong (and it is), what he wanted was clear.

Nick

Reply to
Nick Müller

It isn't clear how he's going to do it given that he doesn't even know what the hell he's saying, so it's moot anyway :) OTOH, yes, I could gather that he wanted to heat some fluid by friction.

hvacrmedic

Reply to
RP

If you only accept stricly scientific asked questions, you also might have used some inductive logic to restucture and resolve the question - by the one solution the OP has given - as a challenge.

Nick

Reply to
Nick Müller

What challenge? This effect dates way back to the very discovery of heat/energy equivalence. It is the very experiment that was used to demonstrate it. Neither was deciphering his message a challenge, the real challenge is on his part, to learn basic thermodynamics which is covered in most every seventh grade physical science class. Now if he's

*in* seventh grade then he doesn't need to be spamming the sci. groups.

hvacrmedic

Reply to
RP

It's so absolutely clear that in the three posts I so far see you've made, exactly how many answer the OP's question?

---------- Ed Ruf Lifetime AMA# 344007 ( snipped-for-privacy@EdwardG.Ruf.com)

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Reply to
Ed Ruf

Say Tau, in inch-pounds.

rpm = 63000HP/Tau. For instance, 0.5 HP and Tau = 105 in-lb makes 300 rpm.

Use a pump?

Nick

Reply to
nicksanspam

Exactly the first one, if you take the efford to read. My other exactly two were about RP's useless bashing. Exactly this posting is about your challenge in reading answers and remembering names over exactly 4 postings.

exact enough?

Anyhow, EOT Nick

Reply to
Nick Müller

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)

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Reply to
Ed Ruf

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

Reply to
Rick

Some MODERN dynos are water pumps. But the original Prony brake was just a friction brake. For a few horsepower or less, a drum brake would work fine. Modern brakes, either disk or drum, can dissipate hundreds of hp for a short while.

While some modern dynos use water pumps, others use generators. A generator takes approximately as much power to turn it as the electrical power delivered. One can turn a generator with the shaft, run the heat into power resistors. Since power resistors can get pricy, light bulbs are a cheap substitute. A modern generator should be able to take a horsepower indefinitely. So load up the generator with a dozen headlight bulbs or so- that will generate oddles of heat. This has the advantage of moving the heat away from the generating location by a few feet of (very heavy) wire.

Reply to
Don Stauffer

If all you need is 1/2 HP of heat flow, a more elegant solution would be a 372-watt (1/2 HP) electric heater. The equilibrium temperature will be determined by insulation -- or by throttling the heat flow when (if) 300F is reached.

If you have a source of given constant torque , unusual though that might be, then other posters have said how to find the speed at which your torque source produces 1/2 HP. You then need to size your tank and paddles so it runs at this speed (with given gear oil or other viscous medium) when driven by your available torque, thus converting the mechanical power to heat. Again, steady-state temp will depend on insulation.

An easier solution might be a small hydraulic pump. You could then throttle the flow with a valve to set the speed for given torque to dissipate 1/2 HP. The heat would be liberated downstream from the valve, heating the incompressable fluid. That presumes that the pump can handle 300F operating temp.

Reply to
Don Foreman

Seemed clear enough to me, though perhaps not stated in textbook fashion: he has a known torque, wants to use this torque to get

1/2HP (372 watts) of heat flow at an operating temp of 300F. Variables he has to work with are therefore speed, insulation and the nature of the dissipator.

If he knew all of the answers, he wouldn't have had the question!

Reply to
Don Foreman

"RP" wrote: Torque is in units of energy, heat flow in units of energy/second. You can't convert them. ^^^^^^^^^^^^^^^ If you're going to adopt a superior attitude, and criticize the OP, at least try to get it right. Torque is NOT in units of energy. Lb-ft and ft-lbs are not the same. I'll leave it to you to figure out what I am talking about.

Reply to
Leo Lichtman

You mean axial/radial pumps. Not piston pumps. They exist for a long time. At least before WW II. Schenck is one of the producers.

ACK

This is a good solution, if the OP is willing to buy a generator (scrap yard).

The elegant thing with the "paddle pump"*) is, that it is the most direct way. Also, they can be easily regulated by controlling the amount of liquid in the pump body.

*) we (Germany) call them water-whirl-brakes, I don't know your terminus technicus.

Nick

Reply to
Nick Müller

What about Newton Meters?? or Meter Newtons?? I think I will have another Fig newton :-)

On the serious side, the paddle wheel thing... Seems to me that when dealing with fluid dynamics, there is no heat unless there is friction.......but I could be wrong

Reply to
Noon-Air

True. But "lb-ft-radians" *is* a unit of energy and the radians, being unitless, could have been neglected, as in most rotary calculations. In other words, turning a shaft with a torque of 1 lb-ft, through an angle of one radian, does 1 ft-lb of work.

But I know what you meant, Leo. I'm just being pedantic.

Don Kansas City

Reply to
Don A. Gilmore

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