Total Evaporative Heating Surface
The (total) evaporative heating surface is the sum of two components:
The direct heating surface, the surface of the lining of the firebox that directly receives radiant heat from the fire. In the central left hand section of the picture below, the visible parts of this surface consist of copper plates.
The indirect heating surface, the surface of the boiler firetubes carrying the hot gases from the fire to the smokebox through the water in the boiler. In the central section of the picture below, the firetubes are of polished brass. Those on the far right of the boiler barrel have been cut, leaving only a short length at the end.
© 2005 J.D.H. Smith
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