Delhi Shower: Black or White Paint?

[Jabordnick]

Back when I was a youngling, I was down in Delhi, tobacco picking. Our shower consisted of a 50 gallon drum with a faucet and showerhead sitting in the greenhouse. We painted the outside of it black to collect the heat and painted the inside white to radiate it. In retrospect I'm thinking we should have painted both the outside and inside black. I'm just wondering which would have been more efficient?

 

[mathman]

Off hand I think the inside color wouldn't matter, since the heat transfer from the drum to the water would be primarily by conduction.

 

[sophiecentaur]

Black and black would maximise absorption on the outside and radiation on the inside. But, in this instance, mathman gives the correct practical answer.

It could be an advantage to have any parts of the tank which are never in the Sun painted white to reduce losses, if that's a relevant worry in Delhi. It could be relevant here in the chilly UK.