Setting up Automatic Transmission Coolers

**1JZ-Rolla** · 25-11-2009, 07:49 PM

One for the thermal management gurus and general tech heads out there:

I already have one transmission cooler (B&M Supercooler) mounted underneath my car, with an air-dam to force some air through the core while the car is moving (air-dam not fitted in this picture):

Its perfect for drags, hillclimbs, etc, but suffers heatsoak on anything longer than 5 or so laps at circuits like Wakefield Park.

I think one of the main limitations is that its getting 'dirty' air, i.e: air that has already potentially passed through intercooler, radiator, etc, and is generally turbulent under the car itself.

My plan is to fit a second cooler in series, with a reasonably thin core to shed heat quickly with clean airflow at the front of the car.

Question is, which cooler should be first in line out of the gearbox, the one under the car (less efficient), or the one at the front? What would be the pros and cons of each?

Thanks in advance
Phil

**brett_celicacoupe** · 25-11-2009, 11:05 PM

the results will be the same if the air temperature entering both the HXs (heat exchanger) are the same regardless of connection configuration.

i had a look and its a bit complex to get accurate results from (by varying inlet temp to one HX). what i do think is that once your moving along pretty quick (say over 40) the air temp and the HX under the car will be the same as the HX at the front of the car.

i wouldnt be suprised if there is nearly no airflow through the HX under the car above 40 due to the type of flow (turbulent).

also by saying this, even if the inlet air temp to the HX under the car is quite hotter, the slow flow of air will negate any "reheating".

you think your HX under the car is good but its probably the heat capacity of the oil taking in all the heat

cp of oil is about 2000J/kg.K

to raise 7 litres of oil by 40deg is about 560kJ

to do that in 1 second you need 560kW of power

or nearly 10kW to do it in 1 minute

what im saying here is for hillclimbs and drags, most of the energy will be taken up by the fluid itself compared to heat transfer through that HX under your car

**1JZ-Rolla** · 25-11-2009, 11:13 PM

That's my point exactly brett, the B&M cooler is unable to do its job under the car because of dirty and/or turbulent airflow. Its not efficient in that position for that reason, regardless of how good a design the core may be.

Yes, ~8 litres of oil is definitely doing the work on the short-course stuff to absorb the heat, but once heatsoaked, I need something to shed heat quickly & efficiently, hence front mounted in clean undisturbed air.

So if we ignore air temperature hitting the two cores for a moment, and assume they are the same as you mention, then there should be no difference in the end fluid temperature regardless of the order that the oil flows through the cores? Does volume of air not affect the equation?

Cheers
Phil

**brett_celicacoupe** · 25-11-2009, 11:51 PM

too painful to prove! an easy assumption is to say the cooler under your car wont do much compared to the other

for heat transfer,

q = m . cp . deltaT

q is heat transfer (W)
m is mass flow rate of fluid
cp is heat capacity of the fluid
delta T is temp difference, inlet-outlet of 1 fluid

this equation holds true for the cold and hot fluid (neglecting other conduction and radiation)

im sure you can see how this relationship works