my cyclone is makin me hot....

[Michael W. Clark]

I come back to this reference a lot:

http://en.wikipedia.org/wiki/First_l...thermodynamics

One key in this is how you define the 'system' boundaries (its a different problem if talking about the entire shop to the outside, vs just the DC system, vs just a DC 'closet'). We got all wrapped up in this once before, and Im not sure its very productive to continue to beat it.

The original poster was asking about heat coming out of the closet, where the DC motor/blower/cyclone was housed. My guess is that warm air coming out of this closet (and into the shop) is heated primarily by the motor/blower inefficiencies.

Carl, I agree. It does depend on the boundry. My comment to the OP, was that it is expected that the motor will heat the space based on its inefficiencies. Especially a small DC closet. My concern is the assumption that 5HP worth of heat is being added to the shop. There is a fundamental difference between energy, work, and heat, however they are related by the 1st Law of Thermo.

If you draw the boundary around the shop and the shop is insulated (no temperature interchange between it and the surroundings), then the energy put in, electrically, increases the energy in the shop (system).

If you draw the boundry around the motor, elctrical energy in, heat out (inefficiency), and shaft work out.

If you draw the boundry around the air in the shop, the fan puts energy into the air (system) and the system energy increases, and I think we all agree on that? The question is whether this energy increase is all heat or part heat and part work. Heat causes a temperature difference, work causes something to happen. If you assume all heat, then that would ignore the kinetic/potential energy of the air movement.

Mike

[Michael W. Clark]

Alan,
Air at the pressures in most DC systems is considered incompressible. In fact, we are under negative pressure for most of the system, which actually expandes the air. We can account for the change in air density based on the SP, but it is very small at these pressures, especially for argument's sake.

The compressor is a different animal and the air is considered a compressed gas. It approximately follows the ideal gas laws where P is proportional to VxT (P=pressure, V=Volume, T=Temperaure). If you increase the pressure, the volume goes down, but the temperature goes up. Yes, it is difficult (at best) to hang on to an outlet pipe from an air compressor. Mine gets so hot, I can feel the heat with my hand a few inches away.

Not sure on the cyclone thing unless it is because you were dead-heading the fan and not moving any air. Theoretically, more energy would go to heat the air, since no KE is being generated? You would also be pulling lower amps because you weren't moving any air.

Mike

[Alan Bienlein]

Yes when the cyclone got extremely warm to the touch I was dead heading it. I was checking for leaks around the system and yes I do understand that the amp draw is lower with the blast gates closed. I also know that the air coming out from the filters of my cyclone is noticeably warmer which is what the OP is asking about.

I also know the warming is less with at least 2 blast gates open.

[Carl Beckett]

If you are putting energy into the system, and it is carried away by the airstream, the more air flow the 'cooler' it will feel ( for the same energy in ). So low air flow would be high temperature difference to dissipate the energy

High air flow would dissipate the same energy with lower temp difference. Maybe this is why with blast gates open it is ' cooler' ?

But it Also suggests that the heat generated is not friction or 'work' done by the air flow in the pipes. Maybe just blower viscous or bearing losses....or again heat conducted through the motor mounting.

[Carl Beckett]

Carl, I agree. It does depend on the boundry. My comment to the OP, was that it is expected that the motor will heat the space based on its inefficiencies. Especially a small DC closet. My concern is the assumption that 5HP worth of heat is being added to the shop. There is a fundamental difference between energy, work, and heat, however they are related by the 1st Law of Thermo.

If you draw the boundary around the shop and the shop is insulated (no temperature interchange between it and the surroundings), then the energy put in, electrically, increases the energy in the shop (system).

If you draw the boundry around the motor, elctrical energy in, heat out (inefficiency), and shaft work out.

If you draw the boundry around the air in the shop, the fan puts energy into the air (system) and the system energy increases, and I think we all agree on that? The question is whether this energy increase is all heat or part heat and part work. Heat causes a temperature difference, work causes something to happen. If you assume all heat, then that would ignore the kinetic/potential energy of the air movement.

Mike

So if discussing the effect of shop heating, all electrical energy into the system converts to heat??

[Michael W. Clark]

So if discussing the effect of shop heating, all electrical energy into the system converts to heat??

Carl, I'm assuming this is directed at me, but not sure I understand what you are asking?

Theoretically, yes. But, it would depend on how efficient the device is at converting electrical energy to heat. Is it forced convection heat? If so, then part of the energy goes to power the fan.

[Carl Beckett]

If you draw the boundary around the shop and the shop is insulated (no temperature interchange between it and the surroundings), then the energy put in, electrically, increases the energy in the shop (system).

Michael, yes. Your post was correct as I understand it.

So I was simply restating what you were posting. If the boundary condition is the shop environment - insulated and no loss - then all electrical that goes in increases energy in the shop. (ie: heat) - because there is no energy transfer (heat or state change of matter or otherwise) across the boundary.

This is my understanding of how the first law of Thermodynamics works.

[Ole Anderson]

Do you run your cyclone continuously for 5-6 hours or only when you need it? Running a 5 hp cyclone to use it as an air cleaner is very inefficient when you can do the same thing with a 1/4 hp ambient air cleaner. Not saying you do, but I have heard of those who do.

Jeff seems to have dropped out of this turned-thermodynamics discussion, but I am still curious how long he runs his 5 hp DC system such that it is warming up his shop. Do any of you notice the same heating effect, and if so do you leave your DC running for long periods of time.

[David Kumm]

I run a 7.5 motor and about 2000 cfm at 6000+ fpm through my pipes. The motor is in the attic so I avoid that gain but the outlet pipe also is in the attic so I pick up some from that. If I leave the Dc on for 1/2 hr or more I notice a few degree increase. My shop is air conditioned but spotty and 2000 sq ft with 10' ceilings so I've always attributed the heat gain to the effect of circulating the warmer air at the ceiling and mixing the warm and cool spots. The Temp seems to even out and doesn't continue to rise. Dave

[Carl Beckett]

Jeff seems to have dropped out of this turned-thermodynamics discussion, but I am still curious how long he runs his 5 hp DC system such that it is warming up his shop. Do any of you notice the same heating effect, and if so do you leave your DC running for long periods of time.

My apologies.

[John Lanciani]

Jeff seems to have dropped out of this turned-thermodynamics discussion, but I am still curious how long he runs his 5 hp DC system such that it is warming up his shop. Do any of you notice the same heating effect, and if so do you leave your DC running for long periods of time.

Yes. Running my 3 hp cyclone and 3 hp drum sander will raise the temp in my well insulated 25' x 25' shop 4-5 degrees in 1 hour. Running the DC with another machine for an hour or more continuously is not unusual for me, either. Nice in the winter, not so much in the summer. A 5k BTU air conditioner won't keep up in the hot months.

[Ryan Brucks]

If you put a 100w lightbulb in one box, a 100w fan in another box, and a 100w heater in yet a third box, all three boxes would rise in temperature by the same amount if they started the same and were left closed for the same amount of time. The boxes don't care what kind of device is in them. They only care how much energy went into the cloesd system.

A watt is a watt is a watt is a watt.

[Ole Anderson]

My apologies.

You are apologizing for...?

[Dan Friedrichs]

No it does not. Explain how moving 75 lbs/min (1000 CFM at standard density) requires no power. If you add 5hp worth of heat to the energy required to move the air, you are creating energy. There are other forms of energy besides heat, energy takes different forms.

You cannot "create" energy.

From a physics perspective, if you move something, you don't actually do work on it (unless you raise it, to increase its potential energy). It does require energy to move things, because of friction. If you had a box on a frictionless table, it would take no energy to push it around the table. Likewise, if air could flow without friction against itself or other objects, it would require no energy to move air. But since there is friction, whatever energy goes into your blower is used to overcome friction losses (and, thus, is turned into heat). Some of the energy becomes kinetic energy in the moving air stream, which is then also eventually turned into heat once that moving air hits something (which absorbs the kinetic energy and turns it into heat).

As Ryan said, a watt is a watt is a watt. It all goes to heat, eventually. And if you assume that there is some insulation in the OP's shop's walls, a reasonable conclusion is that the full amount of energy drawn by his dust collector does get turned into heat in his shop.

[Carl Beckett]

must........... be ............. strong........... and .......... resist ................ urge............ to .... reply



Maybe we should start a new thread titled DC physics?

The goal would be to get more of us on the same page and talking the same language, so that we dont propagate confusion and ill advise to the community. Not to mention OVERWHELMING a relatively innocent question.

Im sure I can learn a lot from everyone here, and always enjoy a good free body diagram.....