[Fwd: [M] [M} IC Thermodynamics]- Part 3

[Joe Boucher]

I have some more design thoughts on the SVO/TC Intercooler.  Allan
Slocam was
kind enough to provide me with a couple of papers that Ford submitted to
the
SAE back in the mid 80's.  One of them makes a SWAG statement that 70%
intercooler effectiveness was assumed.  The other one states that "The
final
intercooler design resulted in a unit that showed the lowest induction
temperatures during WOT acceleration and the fastest recovery to
stabilized
temperatures".

Basically my thoughts are "What a crock!"  Ford intended for the
intercooler
to work in a surge mode.  Now, I know that doesn't come as shock to any
of us
performance minded 2.3 Turbo owners.  However, I have continued my work
on
modeling the thermodynamic performance of the TC/SVO IC's and , indeed,
I
can't see any way for it to work short of being a thermal mass.

One of the major issues is the amount of air flow to the unit.  On an
87-88
TC, the hood scoop openings are approximately 1" x 5" and there are 2 of
them.
This gives about 10 square inches of opening.  If we base this on a car
going
45 mph or 66 ft/sec then with no entrance or duct work losses, the max
air
flow through the IC is only 275 cfm.

This is important because of cross flow correction to the LMTD.  This
may also
be difficult to explain.  If you refer to my post on October 19, I
calculated
inlet and outlet air temps for both sides of the unit assuming discharge

manifold air was cooled to 120F.  (One unfortunate problem with doing
heat
exchanger design by the methods of 20 years ago is that you have to
assume
temps and then back calculate to see if you can get there,-- Its called
an
iterative solution).

My October 19 post used 500cfm air flow to the IC and got a corrected
Log Mean
Temperature Difference of 61.36F.  Redoing that for an outside air flow
of 275
cfm generates some very different answers.

Compressor side:

Inlet Temp = 302F   T1
Exit Temp  = 120F   T2

Air Side

Inlet Temp = 80F   t1
Exit temp  = 260F  t2

LMTD = ((T1-t2)-(T2-t1))/ln((T1-t2)/(T2-t1))

T1-t2 =42
T2-t1 =40
t2-t1 =180
T1-t1 =222

LMTD = (42-40)/ln(42/40) = 41F

Correcting for unmixed crossflow
S= (t2-t1)/(T1-t1) = .81
R= (T1-T2)/(t2-t1) = 1.01
The correction curves in figure 16.17 in Process Heat Transfer By Donald

Kearns don't have this point on the charts.  The charts only go down to
a .6
correction factor and the curves go vertical as they approach this
point.  The
correction factor probably is in the neighborhood of .3.  That would
give us
an LMTD of 12.3F.

I know, Can I say that in English?  Gonna Be tough.

With that driving temperature difference, and CFM flowrate, the
intercooler
would have to be about the size of the engine compartment.  The assumed
heat
rejection is too high for 275 cfm air side flow.  We need to choose a
different operating point.

To make a long story short, I think that the TC/SVO IC with 275 cfm air
flow
will only cool the intake charge to approximately 200F on an 80F day.
Remember, that is based on 18 psi boost and 20.24 lb/min air flow.  The
saving
grace is the thermal mass of the intercooler.  If we assume a thermal
mass of
5lbs, then the temperature of the unit will increase by approximately
70F
during a 7 second 0-60 run.  The air flow to the unit will only allow it
to
recover from a 0-60 burst over several minutes.

I am not showing the calculations for heat transfer coefficients because
they
occupy several pages and I doubt that very many people have the
background to
understand them.  They are also heavily based on charts and curves in my
heat
exchanger design books.  Email me privately if you want them.

I'm really not saying anything new here.  The TC/SVO IC is in a horrible
place
for cooling of an air to air unit.  No amount of ducting or fans can
change
the performance of the unit appreciably.  Please, no flames saying that
everyone already know this.  I took on this project to do an Engineering

evaluation of the stock TC intercooler versus a front mounted air to air

versus a liquid to air.  I'm still working on the others.

Obviuosly, an Air to Air unit MUST be placed where it can get good air
flow.

Obviously, the liquid to air rejection unit must be placed where it can
get
EVEN MORE air flow.

More to come later.

Don