Downcomers are frequently mounted outside the boiler casing on a water-tube boiler for the purpose of __________.
β’ Natural circulation in water-tube boilers (how hot and cold water/steam move by density difference) β’ Role and location of downcomers versus risers in a boiler β’ Effect of temperature on water density and circulation inside the boiler
β’ Think about what you want the water inside the downcomers to be like: hotter or cooler than the water in the riser tubes? How would that affect circulation? β’ If you mount downcomers outside the hot furnace/casing, what happens to their temperature compared to tubes inside the furnace? β’ Which choice best supports a strong, continuous circulation loop between drums and tube banks?
β’ Identify the primary function of downcomers (what they carry, and between which parts of the boiler). β’ Decide whether downcomers should be hot like risers or relatively cooler to help natural circulation. β’ Eliminate options that focus mainly on maintenance or solids settling, and focus on those related to circulation and temperature differences.
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