Liquid throw

The liquid throw is the horizontal distance travelled by the liquid stream flowing over the downcomer weir. It is only an important consideration in the design of multiple-pass plates. Bolles (1963) gives a method for estimating the liquid throw. 

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Liquid throw over weir...60% downflow width, maximum... 

Liquid throw The horizontal distance traveled by the liquid after flowing over a weir. 

Criteria for determining downcomer area are described below. The author recommends that the downcomer area be set large enough to satisfy all of these criteria except for liquid throw over the weir. 

Liquid throw. Liquid throw (or jump) over the weir is the horizontal distance the liquid travels from the outlet weir before reaching the main body of liquid in the downcomer (Fig. 6.15). 

In early designs, downcomer width was set so that the liquid throw over the weir does not reach the column wall (48, 73, 88, 172, 257, 371). The purpose of this practice was to provide a pathway for vapor disengaged in the downcomer to the tray above. Design criteria for adequate liquid throw are presented in the literature (48, 73, 88, 172, 257,371). Since then, it has been demonstrated (396-398) that even at very low liquid flow rates and wide downcomers, the liquid throw hits the column wall, and that the above criteria were ineffective. These criteria were based on clear liquid, while the downcomer liquid is aerated, and therefore travels longer horizontal distances. 

Thomas et al. (396-398) observed that even when the liquid velocity exceeded the design criterion, the downcomer inlet was not completely closed. They pointed out that it may even be advantageous for the aerated liquid to hit the column wall, as it assists in breaking up the froth, thus reducing the quantity of vapor entering the downcomer. On this basis, liquid throw over the weir is not considered a limiting factor (246, 371, 396-398), and is normally omitted from downcomer sizing calculations. 

Antijump baffles (Fig. 6.16) are often installed in the center and off-center downcomers of multipass trays in order to avoid a phenomenon similar to liquid throw (Sec. 6.16). Here the concern is that liquid jumping across the center downcomer, from one side to another, may cause excessive localized liquid buildup near the tray outlet, which may lead to premature flooding. Simulator tests (144) showed that antijump baffles can enhance tray capacity by as much as 25 percent in some instances. 

In early designs, criteria for including emtjjump baffles were based on the liquid throw over the weir (48, 73, 88, 371). More recent publi-... 

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