1. 
   downcomer
   a pipe through which flow is downward.
   Found op http://www.encyclo.co.uk/visitor-contributions.php
   
   
2. 
   Downcomer
   Down'com`er noun A pipe to conduct something downwards; specif.: (a) (Iron Manuf.) A pipe for leading the hot gases from the top of a blast furnace downward to the regenerators, boilers, etc. (b) (Steam Engin.) In some water-...
   Found op http://www.encyclo.co.uk/webster/D/116
   
   
3. 
   Downcomer
   • (n.) A pipe to conduct something downwards; • (n.) A pipe for leading the hot gases from the top of a blast furnace downward to the regenerators, boilers, etc. • (n.) In some water-tube boilers, a tube larger in diameter than the water tubes to conduct the water from each top drum t...
   Found op http://thinkexist.com/dictionary/meaning/downcomer/
   
   
4. 
   Downcomer
   large external pipes in many water-tube boilers, carrying unheated cold water from the steam drum down to the water drum as part of the circulation path.
   Found op http://en.wikipedia.org/wiki/Glossary_of_boiler_terms
   
   
5. 
   downcomer
   1) A pipe through which flow is downward
   Found op http://www.mijnwoordenboek.nl/EN/crossword-dictionary/downcomer/1
   
   

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