You can’t really talk about
radiator thickness without also including the variables of the core matrix;
fin density, tube spacing, thicknesses, etc. Fin density is one of the
most important.
The attached chart shows
radiator cooling drag as a function of thickness for some different sizes
(area). Note that in this case the curves have a minimum point, an
optimum; that occurs somewhere in the vicinity of 3” thick. Also note
that it is for staggered fins at a fin density of 8 fins/inch. Typical
auto radiators, and many used in racing, have densities of 14 – 16 fins/inch
that are not staggered. Higher fin density shifts these curves to the
left, so for 14 fins/inch (not staggered) the optimum may be more like 2 1/2”
thick. For configuration reasons, NASCAR and other racers may find that
using a thicker radiator with lower fin density is more advantageous.
This may also be true for aircraft use. IIRC, the WW II liquid cooled
airplanes had rads 6-10” thick with a rather open matrix.
The chart is also for 220 kts at
15,000 ft.; a little beyond where we generally go. However; I believe
slower trades off for lower (higher density) so the optimums MAY stay in about
the same place. Anyway, the idea is to give a feeling for how these
things trade off. Putting this together with what seems to work well is that
for the automotive type rad, somewhere around 2 ˝” thickness is good.
Check the fin density of the evaporator cores. I haven’t; but I think
they have a more open core making the roughly 3” thickness more
suitable.
Al