For equal volumes of each, a cold air parcel has more matter in it than a hot air parcel.Release this Atwoods machine from rest, and the cold air parcel sinks, pulling downward on the rope, and the pulley re-directs the rope tension to pull upward on the hot air parcel.......
The REASON that hot air rises and cold air sinks can be explained by the force of buoyancy. You can, if you want to, alternatively explain it by molecular speeds in the kinetic molecular theory of gasses.
I choose the buoyancy answer. Think of every individual volume unit of gas as being an object hanging from an inextensible massless rope across an ideal pulley. For equal volumes of each, a cold air parcel has more matter in it than a hot air parcel. Release this "Atwood's machine" from rest, and the cold air parcel sinks, pulling downward on the rope, and the pulley re-directs the rope tension to pull upward on the hot air parcel. So you see, hot air rises and cold air sinks.
Of course, there isn't actually any real rope, but there analogously speaking can be. The tension in the rope is best understood as the force of buoyancy. It really is more of a compressive force in nature, so if you want, invert the imaginary Atwood machine and put the pulley on the floor.
http://en.wikipedia.org/wiki/Buoyancy#Be…
Simply put: yes.
Hot air has more excited molecules and are spaced further apart than cold air. So, within a volume of space, regardless of the space (test tube, air-conditioned room, atmosphere). There is less mass in warm air than cool air, so warm air is less affected by gravity and cooler air is "heavier". Without other forces - warm air rises - cool air "sinks".
Most people think that air conditioners lower the temperature in their homes simply by pumping cool air in. What's really happening is the warm air from your house is being removed and cycled back in as cooler air. This cycle continues until your thermostat reaches the desired temperature.
Actually it is a kind of Refrigerator but without the outer case.
This is how the evaporation cycle in an air conditioner works (See How Refrigerators Work for complete details on this cycle):
The compressor compresses cool Freon gas, causing it to become hot, high-pressure Freon gas.
This hot gas runs through a set of coils so it can dissipate its heat, and it condenses into a liquid.
The Freon liquid runs through an expansion valve, and in the process it evaporates to become cold, low-pressure Freon gas.
This cold gas runs through a set of coils that allow the gas to absorb heat and cool down the air inside the building.
I think its just like a Carnot engine.
And all this necessarily requires you to put your air conditioner at a sufficient height.
