Heat Transfer in a Locomotive Type Boiler

<...available text books for detailed information...>

→ "Fundamentals of Heat, Mass and Momentum Transfer", by Welty, Wicks & Wilson.

You do realise that the firebox extends from the front of the cab to the front of the engine?

in between the actual firebox and the smoke stack at the front, you have heat runner tubes of varying sizes distributed through the liquid to be heated, running axially to the boiler, this improves the heat transfer from the "fire" to the water inside the pressure vessel.

The steam from the pistons is taken by pipes to a position under the smoke stack, and the escaping steam blows up and out the stack acting as a venturi to assist in sucking the heat through the heater tubes.

So, in essence, the firebox wall isn't just a box at 1 end of the boiler, it is incorporated in the tubes.

In some cases, the steam take off on the top of the boiler is also taken through the firebox "hot" area to increase the heat (energy) that the steam is carrying.

http://www.nrel.gov/docs/fy06osti/39309.pdf

http://crtd.asme.org/eew/boilertube.pdf

http://www.toodoc.com/prevention-of-boiler-tube-failure-pdf.html

http://www.gewater.com/handbook/boiler_water_systems/fig12-2.jsp