[keithw]

If you want to find if the painted heat shield improves heat transfer you should measure the tube inside rather than the heat shield. Isn't the purpose of a heat shield to keep the heat in and be cooler on the outside?

So, how does a heat shield work? The heat from the tube is primarily radiated as IR with some visible light. That energy strikes the inside of the heat shield. Some is reflected back toward the tube and some is absorbed and heats the shield. If the inside is shiny then more will be reflected and less absorbed. If flat black then more will be absorbed and less reflected. The absorbed heat will warm the heat shield. That heat will be reradiated from the inside and outside evenly if the surface is the same and perhaps unevenly if the surfaces are different. So, the heat radiated by the outside of the heat shield is the heat put out by the tube minus the amount reflected back toward the tube minus the amount reradiated back toward the tube. On top of this some heat is conducted to the chasis and some is removed by convection of the air.

It is actually a bit more complicated than that but thermodynamics are really not my thing.

keithw