# Thermodynamics cycle with liquid and gas

1. Oct 14, 2012

### Gh778

I'm trying to find why this thermodynamics cycle is not possible but I don't find. The only problem for me is at step 3, the gas can't become a liquid but why ?

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2. Oct 15, 2012

### Gh778

nobody for help me ?

3. Oct 15, 2012

### TheDragon

What about the heating of the cylinder at step 2? Maybe that's where the Energy comes from. If it does than you will not have any problem.
didn't you say that it's an insulated system? If it is, how does the atmosphere heats it? If it's not, energy can move from the system to the atmosphere.

4. Oct 15, 2012

### Gh778

The system is isolated except heating from atmosphere. The heating from atmosphere give energy to gas and liquid at step 2. But like that, the system recover energy from only one source of heating, this break the 2Â° law of thermodynamics and it's not possible.

My questions is: Is it possible to have a liquid from 2 gas with different temperature for the transformation in liquid (butane and propane for example) ? Is it possible to step 3 to exist ?

5. Oct 16, 2012

### Staff: Mentor

6. Oct 17, 2012

### Gh778

I'm not sure because the expansion of gas reduce temperature of 2 gas, if this temperature is below the temperature of liquefaction of gas G2, why this gas don't become a liquid because it has always a pressure from G1 gas ? The expansion of 2 gas can continue in the time G2 become a liquid, because G2 will give energy to G1 during the time of liquefaction. For example, with G1=nitrogen and G2=butane.

Last edited: Oct 17, 2012
7. Oct 17, 2012

### Staff: Mentor

If the gas cooled and compressed itself to where it started, the conservation of energy balance wouldn't work out. Compression and expansion are reversible only if there is no heat transfer or net work out.

I suggest getting a thermodynamics textbook and start learning how these processes work rather than just guessing. Or at least read the wiki page on this.

8. Oct 20, 2012

### Gh778

Could you explain a little more, I don't understand ?

For me: if the valve give works at step 3, G1 and G2 lost temperature, when G2 start to become a liquid it give energy at G1 gas, this energy can be recover from valve. When G2 is liquid: stop to recover energy form valve. But the reality is how ?