Answer to Question #2500 in Molecular Physics | Thermodynamics for sana

Question

Cooling fins on motor engines are rough and painted gray or black why?

Answer 1

Radiated heat is a direct function of surface area. Rough surfaces have more surface area for a given object size than smoothly polished surfaces. They are better passive radiators. Considering the color, we should recall& black body radiation theory. Black is the best absorber of radiation and also the best emitter.