Diy heatsink question

Hey all you led bad asses... I'm looking to build 2 24 inch bars with 3 watt LEDs maybe about 15 to 20 watts a piece..this might be far out but I have access to some stout u channel aluminum.. 6 inch wide by 3 inch tall and 5/16 inches thick. Could this be used to passively cool 20 watts ?

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9" long piece would do a great job to passively cool 20W. 24" would be good for up to 54W.

Sweet I was hoping you would answer.. Now I have the confidence, and extra cash, to move forward with my build. Basically I'm wanting to supplement my 3 cxa 3070 3000k. I'm thinking 660 630 and 450?? I am trying to mimick what bueno time did over at icmag a while back. Am I on the right track?

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