Aftercooler Gains

[David Gregory]

Just to interject and comment on the idea of using a vapor-compression
system to cool the intake charge.  If this unit is intended for use on a
street car, I don't think it would be necessary to size the AC system based
upon max power output.
I've thought about this before, and i think that the way to go would be to
use a water-air intercooler and then use the AC system to cool the water
that is circulated.  This way, you could size the system that it would
maintain a give intake temp at a cruise speed of say 100 Mph (just to be a
bit ridiculous).  In order to cruise at that speed, a car is most certainly
not using all of its power (my old 93 maxima would do a rev limited 145 with
only 190 HP).  In that way you might only be sizing the AC system to support
your desired temp drop at say 100 Hp.  Then, when you did develop your max
power, you would have the capacitance of the liquid coolant to fall back
upon.
Thus the size of your AC system becomes a matter of consideration... do you
want to be able to run "full boost" for 10 min, 5 min, 1 min... 30 secs?
Also, the length of time that you can "make more hp" than you designed for
will be dependent upon the mass of the coolant.  The more coolant you have,
the longer it will take the coolant temp. to rise when running over spec.
Of course, the flip side is it will also take longer to return to acceptable
level.
I think that this idea could work with an automotive style AC compressor on
a street or even a drag car... just not on a road race car where you would
need to make full power continuously for a considerable amount of time.

Now, if you wanted to get really crazy and spend lots of money, you could
use thermoelectric devices :)

David Gregory

-----Original Message-----
From: owner-diy_efi at diy-efi.org [mailto:owner-diy_efi at diy-efi.org]On
Behalf Of Greg Hermann
Sent: Tuesday, April 17, 2001 8:23 PM
To: diy_efi at diy-efi.org
Subject: Re: Aftercooler Gains



>
>By the way, does anyone have any real AC compressor figures to examine, at
a
>variety of full load shaft speeds?

Yeah, but it would prolly go over the limit for a post! Compressor HP will
vary with suction pressure, condensing temp/pressure, compressor
displacement, and compressor speed. At "normal" AC conditions, say 35
degree suction temp and 135 degree condensing temp, you can figure ROUGHLY
1 HP compressor power per 12,000 BTUH of cooling effect. With higher
suction temps, a given displacement/rpm compressor will have a higher
"capacity" and pull more HP to drive it--because the refrigerant gas will
be more dense at the higher suction temp.

There are LOTS of variables!

Perhaps the numbers for a 200 HP compressor at 0 F suction and 110 F
condensing at 1200 rpm,using NH3 refrigerant would be of interest?? :-)

That 20 HP number wasn't too unrealistic for the conditions and load
mentioned!

Greg
>
>Your math is probably correct, don't rely upon mine at this point.

See my prio post about the math--it wasn't.
>
>Since you appear well adept with thermo crunching, what do you specifically
>think of the air/dynalene/freon hybrid intercooling system found at
>www.coolflow.com?  Would be very interested in hearing your thoughts.
>
>
>Thanks;
>Walt.
>
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