Air con?
Saw this interesting idea on facebook, electricity free air conditioning. The idea is that putting plastic bottles into a window will cause the air to cool down. Sounds reasonable, air expanding out of the bottle cools as it does work on the surroundings. The explanation given is that compressing the air makes it colder but its the other way round, when air is compressed work is done so the temperature should increase, it will then decrease as the gas expands. So as the gas is compressed it gets hot then cools on expansion, won't the final temperature be the same? When gas is compressed into a container it gets hot, it then cools down to room temp, when released it expands cooling below room temp. What could be happening here is that the compressed air loses heat to the outside then cools below its original temp when it expands inside. For the system to work there must be some airflow but there appears to be little wind in the video, maybe convection currents draw air into the bottles.
I am always suspicious when I see these claims for zero this and energy free that, if it works does it really matter why?
The answer to that last question is of course yes :-)