I've seen models of this set up before but never really understood what they were trying to show. The picture is of the front of a steam locomotive with its front open. This space opens into the chimney above. Smoke goes up the chimney,not steam, but I'd been left with the impression that steam was coming through the pipes shown. In fact, very hot air and smoke particles from the firebox are coming through. There is water behind the white wall in the top picture. The arrangement means that thermal energy is applied to the tank of water over a much larger surface area and so the process is more efficient. Water boils and steam builds up at the top. Then the two substantial pipes that come from the middle top and go down each side actually carry the steam down to the pistons.
https://www.explainthatstuff.com/steamengines.html
