RE: Intercooler explanation

["R. Cummings" <cumm@flash.net>]

Mark Quinn said:
>Actually I believe that the main reason for the "heating of the air" is the
>compression itself (anisothermal?/anisobaric? - what's the word I'm looking
>for here guys?).  Anyway, taking 1 cubic foot of air at some temperature
>and
>squishing it down to half a cubic foot (say) approx. doubles the
>temperature
>of that air (the same thermal energy has to reside in half the space).
>
You are right. The reason for the increase in air temperature after
compression is the compression itself. I think what you are refering to is
isentropic or reversible adiabatic. Isentropic means a process with no
change in entropy. Adiabatic means a process with no heat transfer. A
reversible adiabatic compression is done without any heat transfer and is
isentropic. The process is reversible, if you decompress the air it will
return to the orginal temperature and pressure. 

While compressing air in a turbo or supercharger is not exactly reversible
adiabatic since there is some inefficiency and heat transfer taking place,
it is not a bad assumption for calculation purposes. The thermodynamic
formula for compression processes is pv^n is a constant. p is pressure, v is
specific volume. n=1.3 for reversible adiabatic compression of air. The
relation to temperature for a perfect gas is pv = RT where R is the gas
constant and T is the absolute temperature.

Bob Cummings 87 Coupe GT blinking digital dash and erratic temp gauge