# Recover energy from unique temperature

1. Nov 18, 2012

### Gh778

Why is not possible to use this simple cycle for recover energy from unique temperature ?

1/ (first drawing) For limited friction I think it's possible to put outside pressure of 10 nPa. The speed velocity of the cylinder is constant, I think it's possible to use small speed like 20 m/s but bigger is the speed bigger is the efficiency. The cylinder has a gas inside. If velocity is constant, this need rotational speed is changing in time but like that it's possible to prevent problem for lost kinetics energy when radius change and problem with frictions. The goal when cylinder rotating is to keep constant the kinetics energy of gas, velocity is constant not rotational speed.

2/ (Second drawing) Or for not change kinetics energy of gas, put inside cylinder an object when pressure is low at bottom. When cylinder move in translation, move out red object and recover energy.

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Last edited: Nov 18, 2012
2. Nov 18, 2012

### Staff: Mentor

The (partial) separation of the gas and/or lifting of the cylinder slows the belt.

You cannot violate energy conservation or the second law of thermodynamics with any setup, unless you discover completely new laws of physics (which will not happen in those concepts).

3. Nov 18, 2012

### Gh778

so the kinetics energy of cylinder slow down, this lost of energy is in energy of the pressure of gas, is that ?

4. Nov 18, 2012

### Staff: Mentor

You add some energy to get a pressure difference, right.

5. Nov 18, 2012

### Gh778

So in this case we can change velocity in pressure. Imagine a system like drawing, a solid move in translation at V1, a cylinder with gas inside move in translation at -V2, V2>V1. If after turn some degrees, V2 slow down to V1, we can turn the system around a circle. But the center of gravity has seen V1 and V2 at start not two same velocity, how does it work for compensate all ?

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6. Nov 18, 2012

### Staff: Mentor

7. Nov 18, 2012

### Gh778

I'm interesting about the center of gravity. The radius of gas increase in the cylinder so the centripetal forces decrease (mv²/r), the speed of cylinder decrease too, the energy is converted to pressure, so the centripetal forces decrease too. In this case, how the center of gravity don't move even a unique cylinder ?

The setup is to move to the left one solid (masse m) at V1 speed same density of gas and same repartition of density when cylinder is rotating, move to the right one cylinder with gas inside (masse m) at V2 speed. While cylinder and solid move the center of gravity don't change. Until cylinder and solid turn, in a standard setup V1=V2 at start and after, here V2>V1 at start but when rotating V1=V2.

8. Nov 18, 2012

### Staff: Mentor

No, my problem is much more basic:
What happens in the setup? Do the moving parts, after reaching the circle, somehow stick to it? Is that circle a rotating disk, with a fixed center, or completely fixed, or whatever?

If that disk is fixed to some point, you can get forces on this anchor, accelerating or moving the center of mass of your system.

mω^2r
Without a quantitative analysis of the velocity, you cannot tell.

9. Nov 18, 2012

### Gh778

yes, the circle is fixed at its center only, an arm keep cylinder when it pass near it. The circle can turn freely.