| 摘要 |
The heater has an inner fire box with a horizontal axis and smoke tubes, and a flame return box containing one or more toroid or halfring tubes between the outlet of the combustion gases from the fire box and their entry into the tube bundles and connected to the heater housing on the water side above and below the fire box. If the heater produces hot or super-heated water in a closed circuit the water return is situated in the axis of the tube or tubes connecting the toroid or half-ring elements in the lower part of a flame return housing or the fire box.
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