Firing into a industrial boiler

ricphysic

Which transfers more heat inside a water tube boiler furnace. The flame entering the boiler, or the combustion gases generated by the flame from a combustion chamber located outside the boiler?

Assume the flame is not impinging any water tube.

Would appreciate any and all feedback…with a brief explanation. Or perhaps you know of a better website where this question could be posted...or reference manual?

Thank you.

clem

The "flame" is just the light caused by the combustion gases.