Re: temp flap, sheer glee

["Robert Myers" <rmyers@inetone.net>]

Phil,

It seems to me that you're picking over nits.  Low temperature for a given
pressure equates with a higher charge density.  Now are you cooling the
pressurized air to lower its temperature or to increase its density?  It's
six of one and half dozen of the other.

I'm sure you are familiar with the old ideal gas law equation, PV=nRT.  For
a given pressure and volume, n (the number of moles of gas is inversely
proportional to the temperature (degrees K).  You lower the temperature to
increase the number of moles of air in the charge.  (Yes, I realize that
air is not an ideal gas, but this equation serves at least as a good
approximation of reality at relatively low pressures such as we are talking
about here.)

Since the turbo does, in effect, a nearly adiabatic compression of the air
the temperature of the air is raised during compression to well above
ambient temps.  This allows a simple device such as a heat exchanger to be
used to lower the temperature below what would otherwise be experienced at
the throttlebody inlet.

Your statement and Mike's statement are both correct.  It's just a matter
of viewpoint and semantics.

At 03:30 PM 5/21/97 GMT, you wrote:
>In message <9705211333.AA16731@nj2.n-jcenter.com> Mike Arman writes:
>
>> Purpose of intercooler (turbo cars) is to reduce temp of pressurised air
>> coming from pressure/inlet side of turbo - same reason. When the turbo
>> presurises the air on its way to the cylinders, the air heats up. Sometimes
>> quite a bit. Need to get the temp back down to reasonable levels, hence
heat
>> exchanger.
>
>Not really.  The purpose of the intercooler is to increase the density of
the 
>air.  The fact that the turbo's compression has increased the temperature
over 
>ambient is exploited by the intercooler, which contributes as much (or
more, in 
>the case of the Sport) to increasing the air mass per unit volume entering
the 
>engine as the turbo does.
>
>--
> Phil Payne
> phil@sievers.com
> Committee Member, UK Audi [ur-]quattro Owners Club
>
>
___
   Bob
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