An Aid to Thought
Over at “wattupwiththat”, a commenter opined some time ago:
I remember when I was a kid playing with a bicycle pump that compressing a gas heats it up. Is it possible that some of the high surface temps on Venus are because of that pressure?
Why not have a cold beer to help think that one through?
The same principle worked to warm the air flowing out of the mountains in Colorado.
Some I suspect that as atmosphere moves up / down cooling and warming takes place from expansion and compression just as it does on earth. Although, I suspect that venus is warm/hot becuase of the abudnance of greenhouse gasses and proximity to the sun.
The main thing I was critiquing was the notion that the Pv = nRT at time of compression has much if anything to do with the value of T some millions or billions of years later. The fact that the CO2 in a beer had to be pressurized at some point doesn’t mean the beer can never thereafter be cold.
Quite right. I got your point. Mine was to acknowledge that localized adiabatic heating of the atmosphere is likely ongoing on Venus similar to the Earth. But that such a process was a result of a more dominant weather system on Venus driven by solar radiation, as on Earth. And that a dose of greenhouse gas heat trapping exacerbates Venus’ plight.
But of course, you already know this.
But what if (starting at room temperature and pressure) you were compressing hydrogen or helium?
There’s nothing special about hydrogen or helium with respect to change in temperature with change in pressure.
When I get a SCUBA tank filled, air is pressurized to a bit over 3000 PSI. The tank gets noticeably warm. Most places put tanks being filled in a water bath, which is far more effective at distributing heat from the tank than air. But either way you go, the tank of pressurized air doesn’t remain at a high temperature; it eventually equilibrates with ambient temperature. The internal pressure is still at 3000 PSI, but there’s no persistent temperature increase due to the fact that it is under high pressure.