Tolerance downcomer area

Minimum downcomer width and minimum downcomer area. As the downcomer becomes smaller, its width decreases faster than its length, turning the downcomer into a long and narrow slot. This geometry increases the resistance to liquid downflow and to upflow of disengaging vapor. Small downcomers are also extremely sensitive to foaming, fouling, construction tolerances, and introduction of debris. Smaller weirs associated with small downcomers distort the liquid flow pattern as it approaches the weir ("weir constriction effect ), which in-... 

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