Expansion or compression -- which is more energy efficient?

[T C]

where A is the area of the piston, and the differential displacement of the piston is ds=dV/A. This is the work that is used in the first law of thermodynamics, and is equal to the decrease in internal energy of the gas (for adiabatic change). It is what you are calling the total "energy consumption."

No. The gas works as it expands and the piston works by pulling atmospheric pressure outwards. The work done by the piston against the atmospheric pressure is positive here while the work done by the gas is negative. It has to be deducted from the work done by the done against the atmospheric pressure.

here is no energy consumption involved in advancing the piston for the case of a massless, frictionless piston. The work done by the gas on one side of the piston is equal in magnitude to the work done on the other side of the piston by the atmosphere and the pulling force

How can you say so? The piston is working against the atmospheric pressure and the gas inside is working on the piston. So get the net energy expenditure, we have to deduct the work done by the gas inside from the work done by the piston by working against atmospheric pressure.

 

[russ_watters]

Like all other cooling cycles, it's closed. It sucks heat from one place and dumps that into atmosphere. And there is no phase change occurring in this process.

The high pressure side of piston will face the atmosphere and there is no poking hole. The enclosed gas will remain inside the cylinder.

So, are these the processes? I really don't like guessing, but....

Gas in the cylinder starts at atmospheric pressure and room temperature.

1. Gas is adiabatically expanded and cooled. That part you at least made clear.
2. Gas absorbs heat from the room, heating it to room temperature, but remaining a lower pressure.
3. Piston compresses the gas, heating it, while heat is transferred outdoors (outdoors and indoors are at same temperature), keeping the gas at room temp (isothermal compression), and ending up at the state it started in.

Is this your cycle?

 

[Chestermiller]

No. The gas works as it expands and the piston works by pulling atmospheric pressure outwards. The work done by the piston against the atmospheric pressure is positive here while the work done by the gas is negative. It has to be deducted from the work done by the done against the atmospheric pressure.

How can you say so? The piston is working against the atmospheric pressure and the gas inside is working on the piston. So get the net energy expenditure, we have to deduct the work done by the gas inside from the work done by the piston by working against atmospheric pressure.

I totally disagree with your interpretation and stand by what I said previously. You should know that I have a lot of practical experience with thermodynamics (>60 years), so I am very confident in what I am saying.

I can help you work your way through this if you are willing to work with me. If so, I would like you to start out by writing down a Newton's law force balance on the piston that includes $P_{atm}$, $P_{gas}$, F (the external pulling force needed to move the piston), and the piston area A.

Thank you.

 

[T C]

So, are these the processes? I really don't like guessing, but....

Gas in the cylinder starts at atmospheric pressure and room temperature.

1. Gas is adiabatically expanded and cooled. That part you at least made clear.
2. Gas absorbs heat from the room, heating it to room temperature, but remaining a lower pressure.
3. Piston compresses the gas, heating it, while heat is transferred outdoors (outdoors and indoors are at same temperature), keeping the gas at room temp (isothermal compression), and ending up at the state it started in.

Is this your cycle?

That's it.

 

[T C]

I totally disagree with your interpretation and stand by what I said previously. You should know that I have a lot of practical experience with thermodynamics (>60 years), so I am very confident in what I am saying.

In the first scenario, I have calculated the net energy consumption by subtracting the work done by the gas from the energy spent by the piston i.e. (4539.38 - 2240.28) J. And now, as per you, it should be (4539.38 + 2240.28) J, right?