My CMX extrusion is 0.69 lbs/FT. It measures 3” wide with 0.375” sides. A foot of it has 81” sq in surface area, fins of course are only on 1 side. The cooler I would make would be a 24” double pass cooler which is 8 ft of extrusion. That would have 648” sq in of surface area and weigh 5.52 lbs.
The round heat exchanger material is 3” diameter which would be 113” of surface area per foot. (2) 12” heat exchangers would only have 226” sq in of surface area but they are double pass so I don’t know how you would take that into account.
I don’t think you would need the same surface area as the flat extrusion because the round will hold more coolant.
A 1 FT piece of CMX extrusion holds 5 oz of water. 8 FT cooler would hold only 40 ounces, that’s only 0.312 gallons of coolant.
(2) 12” round heat exchangers should hold 0.72 gallons of coolant.
So the big question is what’s more affective at cooling?
The round heat exchanger has cooling fins all the way around the outside and inside which the flat extrusion does not.
To add to this, a 12” piece of 1x.058 tube holds about 4.5 oz of water and each one of my 1” frame tubes is 4 ft so just my frame tubes alone(not including the one below the motor which isn’t used if T-stat is open) hold 36 ounces which is 0.28 gallons.