Liquid Flow Patterns and Maldistribution on Large Trays

2 Liquid flow patterns and maldistribution on large trays 

Most popular theoretical models (such as the AlChE and the Chan and Fair models, Sec. 7.2.1) postulate that liquid crosses the tray in plug flow (Fig. 7.7a) with superimposed backmixing, and that vapor is perfectly mixed. Increasing tray diameter promotes liquid plug flow and suppresses backmixing. This should enhance efficiency in large-diameter columns, but such enhancement has not been observed (147,148). Liquid maldistribution is the common explanation to the observation. 

Liquid flow patterns. Liquid entering a single-pass tray flows in a diverging channel until reaching the tray centerline, then in a converging channel as the outlet weir is approached. The liquid has little incentive to move sideways and follow the curved walls of the column. Instead, it seeks the shortest path from inlet to outlet, and channels through the tray center (Fig. 7.75). This leaves stagnant zones near the curved walls on the side. 

Liquid plug flow produces a horizontal (i.e., flat) flow profile (Fig. 7.7a), Channeling produces a U-shaped flow profile (Fig, 7.8a). The liquid moves fast at the tray center and slow near the walls. Wide stagnant zones, a steep U shape, and liquid recirculation in the stagnant zones (Fig. 7.35) signify a highly channeled flow profile. The 

Higher gas flow rates flatten the U shape, narrow the stagnant regions, and reduce liquid recirculation in the stagnant regions 

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