# As close to perpetual motion as we might ever get.

1. Aug 19, 2010

### WhatIfMachine

I am here today to propose a "perpetual" device. it doesnt make energy, its perpetual in the sense that more energy (specificly electricity) is recieved that the amount used. Have your heard of the Dyson bladeless fan? well ill post a link for you to read, but ill put all the basic information you need to know here with my proposal that works with the laws of physics.

The Dyson fan isnt really bladeless, inside the pedestal there is indeed a fan. "A motor rotates nine asymmetrically-aligned blades to pull air into the device. According to Dyson, these blades can pull in up to 5.28 gallons (about 20 liters) of air per second. " The air then proceeds to flow out of a ramp inside the circle. But thats not what you feel when the fluid flow of wind blows. You feel more than the 20 liters because

"It boils down to physics. While it's true that the atmosphere is gaseous, gases obey the physical laws of fluid dynamics. As air flows through the slits in the tube and out through the front of the fan, air behind the fan is drawn through the tube as well. This is called inducement. The flowing air pushed by the motor induces the air behind the fan to follow.

Air surrounding the edges of the fan will also begin to flow in the direction of the breeze. This process is called entrainment. Through inducement and entrainment, Dyson claims the Air Multiplier increases the output of airflow by 15 times the amount it takes in through the pedestal's motor."

Meaning 1/15 of the normal amount of electricity used in normal fans can influence the same breeze. So what if this fan was facing a wind turbine? (miniature of course, unless the fan where to be enlarged for this purpose) Couldn't it make more electricity than used?

2. Aug 19, 2010

### Staff: Mentor

No. Airflow energy comes from a combination of pressure and flow rate. The Dyson blower is very high pressure and very low flow. The induced air is high flow and virtually no pressure. The net result is a fan that is LESS energy efficient than a typical fan due to the losses involved in the high pressure/velocity flow.

3. Aug 19, 2010

### WhatIfMachine

but doesnt inducement and entrainment cause both the area and preasure to increase? If the fan is putting out about 15 times as much as as it takes in, that means that either the flow or preasure is increased, either way the turbine spins more than it would without the multplication.

Last edited: Aug 19, 2010
4. Aug 19, 2010

### cjl

Not exactly. It's true that the flow rate is vastly increased, but the pressure drops off. The end result is a high-volume, low-pressure flow that actually contains less energy than the initial low-volume, high-pressure flow.

5. Aug 19, 2010

### WhatIfMachine

hm, well I think it was a good thought. Maybe if I wait long enough someone will come up with a reason for it to work and an arguement will insue, but so far it seems I picked out a dud idea.

6. Aug 19, 2010

Dud ideas are the easiest to pick out, unfortunately.

7. Aug 19, 2010

### WhatIfMachine

haha, aint that the truth? of course I guess its my fault for thinking I of all people could make the closest thing to perpetual motion as will probably ever be made.

8. Aug 19, 2010

### alxm

Sorry, but it was an abysmal thought. A machine which puts out more energy than it consumes (when the whole system is viewed) is considered a perpetuum mobile.

Energy is conserved. It cannot be created out of nothing.

9. Aug 19, 2010

### WhatIfMachine

um, the dyson fan isnt perpetual :P and the plan as a whole isnt perpetual, it just gets more electricity than used.

Last edited: Aug 20, 2010
10. Aug 19, 2010

### alxm

http://en.wikipedia.org/wiki/Perpetual_motion" [Broken]

You can't get more energy than you consume. The difference has to come from somewhere, because energy is conserved. This is the first law of thermodynamics.

Last edited by a moderator: May 4, 2017
11. Aug 19, 2010

### Staff: Mentor

It is a very common misunderstanding of people looking for perpetual motion to not know what "perpetual motion" means. And though you may not like it, conservation of energy has been exquisitely well proven, so the equations that describe how things like induction/the Venturi effect work all use conservation of energy as the framework on which the equations are built. Ie, the Bernoulli equation is a conservation of energy statement that can be used to relate high pressure, low velocity flow with high velocity, low pressure flow.

12. Aug 20, 2010

### WhatIfMachine

it was a typo, the dyson machine isnt perpetual, I dont mean the device as a whole is perpetual, I mean if you replace the word "energy" with "electricity" then its (not really) perpetual in the since that it puts out more energy that it consumes.

we might not be able to achieve perpetual motion, but that doesnt mean we cant build devices that put our more of a specific type of energy than it takes in. My dyson proposal gets it extra energy from inducement and entrainment, but im no expert in... well anything really so, as cjl said, "...the flow rate is vastly increased, but the pressure drops off." could be a possibility and I accept that.

13. Aug 20, 2010

### Staff: Mentor

You're not getting it: what you are saying is practically word for word the definition of a perpetual motion machine.

14. Aug 20, 2010

### WhatIfMachine

I dont think you get it, thats my point. thus the title of this thread, "As close to perpetual motion as we might ever get."

I know perpetual motion is impossible, as you cannot create or destroy energy, but this isnt creating anything. it mearly puts out more ELECTRICITY that is consumes. If I just said energy, yes that would be perpetual, but no, the idea of the device is to put out more electricity.

15. Aug 20, 2010

### Q_Goest

The Dyson fan apparantly uses the same principal as eductors (sometimes called jet pumps or ejectors). They take a high pressure fluid, accelerate it, then use the kinetic energy of the flow stream to entrain additional fluid. So the energy put into accelerating the motive stream is transfered to the air that is being entrained. The primary difference between the Dyson fan and an eductor is the eductor entrains air inside the device whereas the Dyson fan entrains air outside the device. Otherwise, the basic principal is the same.
http://en.wikipedia.org/wiki/Eductor-jet_pump

If you looked at the overall isentropic efficiency of such a device, you'd find they are typically lower than a device that accelerates all the fluid without entrainment. That's because the compression of the motive air already results in losses, and additional losses occur due to the turbulence between the motive flow and entrained flow. So although it *sounds* like the Dyson fan is more efficient than a conventional fan, the overall process is likely much less efficient than a conventional fan.

16. Aug 20, 2010

### WhatIfMachine

ah well, I guess there is nothing left to do but let the thread die. Thank you everyone for the detailed explinations

17. Aug 20, 2010

### cjl

Since the only kind of energy that the dyson fan consumes is electrical, it would be a perpetual motion machine if it was able to put out more electrical energy (through any mechanism) than it consumes. This is because if you managed to hook up a generator in such a way as to generate more energy than the fan consumes, you could hook the fan up to its own output, which could then run perpetually (ignoring things like the motor burning out) without any outside input of energy.

18. Aug 20, 2010

### Xtensity

Not perpetually... but for a very long time perhaps. Some energy is lost through kinetic friction...simply with air particles touching other physical constructs(such as the fan frame)

19. Aug 20, 2010

### cjl

If it genuinely put out more electrical energy than it took in, it would run perpetually. You're right that in reality, there are losses, but they would cause the output power to be less than the input.

20. Aug 20, 2010

### RonL

If one can really flex their thinking, it is the same as a steam or air jet ejector, instead of a high pressure moving out of a small orifice at the center, this device changes size of the orifice and pressure of the air.