Paul,

That thicker radiators seem to have disappointing performance appears to me to

have more to do with the plenum than radiator - like the P-51 had quite thick

radiators, but also a very good plenum.  As Ed pointed out a couple of days ago,

the pressure drop across a thick radiator is not nearly as much higher than the

drop across a thin radiator as one would expect.  

 

We need to be careful about comparing “thick” and “thin” because it is very dependant on rad core design.  A more open matrix can be thicker for the same pressure drop; but will have a lower heat transfer per unit of volume.  Always a tradeoff.  As I recall, the P-51 had a much more open matrix than current high performance racing radiators.  It had some sort of hexagonal fin arrangement – don’t know the details.

 

Certainly the plenum design is important, but we have to work within certain constraints. We have fixed amount of dynamic head available, and we have to achieve a certain volumetric flow rate to remove the heat with a relatively limited temperature difference; all within some space constraints.  And a small area, thick rad is working against the plenum pressure recovery ratio because getting the higher pressure recovery requires a bigger expansion ratio in the plenum.

 

The pool of experience and analysis suggests certain ranges that we should work within.  I’ve expressed my conclusions on that before; and I didn’t just pull them out of the air.  Not that it really matters; but I do have an MS degree in engineering, and years of space nuclear power system design.  That doesn’t mean you can’t go outside those ranges, but recognize the risk, and do your testing before you try to go fly.

 

Al