Going by those thermal conductivity numbers, and the total surface area of the radiators, and the thin-ness of the tubes and fins.
There are 54 tubes. Let's say that each is 1cm wide, 24cm long and with a wall thickness of 0.15mm
The thermal conductive resistance of the tubes works out to 0.26m^2 (cross-sectional surface area of the tubes) x 159 W/mK / 0.00015m = 274752 W/K, or basically 275000W/K
If the tubes were made out of pure copper, this increases to 665000W/K
For worst case 150W heat dissipation through the radiator, the walls of the tubes for copper vs red brass is causing a decrease of (150 / 275000) - (150 / 665000) = 0.0003C
i.e. not an awful lot. Heck, even for the ~4kW or so that a car would push through the heater-core we're still talking about a 0.01C difference between red-brass and pure copper.
Okay, so let's work in the fins as done with red-brass vs pure copper.
5 fins per cm, 54 tubes, medium fin length is 4mm (half of the angular distance between tubes). Fin thickness is 0.1mm.
Total cross-sectional surface area is 0.013m^2
Assuming an even heat spread to the halfway point along the fins between each pair of tubes, heat spreading resistance of the fins works out to around 156 * 0.013 / 0.002 = 1014W/K for red-brass, and to 2502 W/K
For a 150W heat source, this means ~0.15C for red-brass, and 0.06C for pure copper
All up, the difference for making the radiator using pure copper tubes and fins vs red-brass tubes and fins, for a ~150W heat source is less than 0.1C in terms of the added thermal resistance due to the metal used in a radiator of the size being used here.
Radiator's are about two things, air-flow and size.
The radiator's used here will work better than the DTek Pro style cores because they are larger for starters, and offer almost 2x the total fin->air surface area of the DTek Pro cores, and really, that's where the benefit is coming from, not from the use of copper over red-brass.
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