Quoting the article with interspersed comments:
- Let's condider 100psia
- Actually state of the art is more like 4000psia or even 5000psia.
compressed air is a very paradoxical substance. It is often imagined as a reservoir of potential energy. Actually, absolutely all (excluding effects of non-ideal behavior) of the energy added to air by the compression process is rejected as heat if the temperature of the air is held constant.
- This requires cooling by an inter cooler and an aftercooler
- Of course. That's what "if the temperature of the air is held constant" means.
When the air is permitted to expand, it cools and produces much less work than was used to compress it. However, if the temperature of the air is held constant while the air expands, the heat energy which was rejected during compression is re-absorbed
- Where is this source of heat??
- It is part of the heat engine. When both fuel and compressed air are expended by a mobile engine, there is no theoretical restriction on the fraction of chemical energy in the fuel which can be converted to work, because the engine does not operate in a closed cycle. This could lead to more efficient use of fuel if compressed air is produced efficiently in a large stationary plant.
and used to produce the same amount of work as went into the compression.
- Is it to be assumed that the compression and expansion processes are VERY VERY SLOW so that the temperatures can equalize with the atmospheric surruounings?
- The larger the temperature difference between the surroundings and the processes, the faster heat flows. It is not necessary to have very slow heat flow, but you have to use the realized temperatures as the hot and cold source/sink temperatures in thermodynamic calculations. The hot source temperature is the temperature of the hot process gas, not the temperature of the external hot source, and so for the cold source.
- --NotSCar 2006-09-14 20:24:11
- --Archimerged 04:44, 23 September 2006 (UTC)