If removing the highest amount heat per unit of air flow is the criteria; then thick radiators with close fin spacing and slow air flow is the way to go.  When you add the other criteria of fixed dynamic head (pressure), area constraints, drag, and weight; and maybe a few others; that is no longer the case.

 

Parametric studies using fairly sophisticated analytical models that I have seen suggests that for our aircraft applications the optimum lies somewhere in the 2-3” thickness range.  And this of course will depend on some configuration variables.  This is also for an optimally designed radiator.  A optimally designed AC evaporator may be a bit different because it is designed for a different fluid. 

 

Al

 

Couldn't agree more, Al.  Since the NASCAR radiators average 3" thick and they operate in the general speed range we do, 2-3" sounds good to me. 3.6" thick work for the evaporator cores, but I would say that dynamic pressure is a bit lacking for that thickness on climbout at slower airspeeds. 

 

As I mentioned, dynamic pressure (or lack thereof) would certainly be a major factor in determining optimum thickness for a particualr regime of flight as would pressure recovery in the duct, heat exchanger parameters such as fin spacing, fin configuration, etc, etc.

 

 

So like most other decisions, cooling decisions force a series of compromises.

 

Ed