burgermeister

This is somewhat of a continuation of a previous thread about fan cooling that had morphed into oil cooling.
https://rennlist.com/forums/993-foru...3-6-motor.html

The car in question uses a 993 3.6, stock, in a kit car chassis. Oil temperature on track is a problem. I instrumented the car and can measure oil and air temperatures at the cooler inlet & outlet, as well as airflow through the cooler.

Taking a decent bit of data on road, and extrapolating to 230F oil temps (which I easily achieve on track), the cooler (7 x 22 x 2.5" core) is good for 11-13KW of cooling - this is inline with what Setrab publishes for similar sized coolers. So far, so good.

I tried a number of things to increase airflow through the cooler, none of which did anything significant. So increasing airflow is not going to happen.

Then I found a website that does crossflow heat exchanger calculations.
https://checalc.com/solved/heat_exch_analysis.html

Using the on-road data and measuring the oil cooler, I came up with Area = 2 m^2, and Heat Transfer Coefficient U = 100. Oil flow was guessed at.1 or .2 kg/s - still running on the thermostat, with most of the oil not passing through the cooler.

Measured air flow at 70MPH (average track speed at short regional tracks) is 42 MPH in the duct (60in^2 area), giving .72 m^3/s air flow, or .8 kg/s.

Based on other threads, oil pump capacity is 65 l/min, presumably at redline, thus flow at 5000RPM (average on track engine speed) looks like it should be .9 l / s --> .825 kg/s.

Typing all this in I get 12KW of heat transfer, pretty darn close to the back of the envelope calculations from road data. So, possibly a valid model. I reduced air flow in the screenshot below - not much effect on heat transfer.



Key is that the air coming out of the oil cooler only gains about 30F in temperature with .8kg/s of air flow. Adding air flow does not increase the heat transfer appreciably - it mostly makes the exit air cooler. This suggests that adding air flow may not be the solution, which is handy as I cannot seem to add airflow anyway.

I have no space for another cooler - except behind the first cooler! I reduced the airflow through the cooler by 25% to account for additional resistance from an added cooler (already done in the above screenshot). Heat transfer is not changed much, air exit temp is now the shown +40F.

Sticking the exit parameters into the same website, I get this:


Another 7.5kW of heat transfer. That's not bad! It's like another 60% of a full sized oil cooler, and I can package it!

And if I run the oil through the downstream cooler first, the whole package will become a reverse flow / cross flow hybrid heat exchanger, which should be a little better than what the model predicted.

Any thoughts on this? Anyone every try it?

wallyman424

You are doing a great job analyzing the data to correct your situation. I agree that you need either to replace your cooler with a better one or add another cooler. Probably the easiest plumbing wise is to add it downstream. The best part is you have all the probes in place to validate your improvements.

k722070

interesting idea of stacking coolers.
will probably work even with no gap between coolers.
during construction of the system have the current cooler cleaned or flow tested.
it might be the fins are clogged inside or out.

e9stibi

Added a GT Oil Cooler from Carneval and the car runs much cooler on the track, even in Texas summer heat. It is in sandwich with the AC fan and the DIY instructions were good. The kit comes with everything you need, except for the resistors that you want to replace while the bumper is off. The only regret is that I should have done it sooner because it is so effective.

k722070

looked at the picture of the oil cooler, can't you just install a larger fan?
stock fan covers the entire cooler.
and I think you'd want the fans mounted on the back of the cooler similar to stock.
fit a fan that fill the entire duct work and sucks the air through.