radiator design - Topic

I highly recommend obtaining a thermodynamics textbook and going through, at the very least, the heat exchanger segment. Any first year engineering thermodynamics class will cover these in much greater detail than possible on a forum.

But, in a nutshell, you need to know the mass flow rates of the air and the coolant (trickier for coolant, as it varies with RPM,) the specific heats of both, temperatures of both, heat transfer coefficients (depending on the method you want to use)

The calculation of the actual heat rejection isn't the difficult part, a couple thermocouples can tell you that. The part where the real decisions come in:

What do you want your system volume to be? System volume provides a "buffer" increasing the total heat capacity of the cooling system. This buffer can be sized to a specific amount of running time - say, an autocross lap - before the system reaches an overheat state. Water is also heavy.

Are you getting good airflow? You may rely on a fan for idle cooling only, or also utilize one for augmenting at-speed cooling. Do you use one or two or 12 radiators, and where do you put them to ensure you get the airflow your calculations say you need? What kind of pressure ratio do you need to get proper airflow through your radiator?

What impact does fan distance or a fan shroud have on heat rejection at low speed? At high speed?

What measures will you implement for air/steam control? A swirl pot? Vent lines? Header tank?

I would start with Carroll Smith - I think it's Design to Win that covers basic cooling system design.

Then hit the engineering texts. Once you understand the quantities and effects at work in a heat exchanger (aka "radiator," which isn't technically correct) you can start looking at OEM radiators to get an idea for scale.

What size radiators do OEM's use? Are these still acceptable solutions in a race environment? What compromises do FSAE teams make that will limit the effectiveness of a stock cooling system (race conditions, poor airflow, high idle/restricted conditions.)

This is the stage where you make yourself a list of questions - what do you NEED to make it work. After that, you can start answering the questions and making design decisions.

I encourage new teams to start with a stock system, then, money and time permitting, go to a more specialized system. The OEM components are available very cheaply compared to custom components - and as long as you can show that they are sufficient for your needs and design intent and understand the data that supports your claim, the judges will back you up.

Wesley
OU Sooner Racing Team Alum '09

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