Rounded downcomer outlets

When downcomer backup is critical, pressure drop of liquid leaving the downcomer is sometimes minimized by using a rounded downcomer outlet lip (Fig. 6.19). This is done infrequently, and usually only with highly foaming systems. 

K is reduced from 0.6 to 0.3 by using the rounded downcomer outlet. To obtain this feature from the tray vendor, you need to specify a "Full Radius Downcomer Outlet." This will lower the liquid level in the downcomer by an inch or so. If you re limited by downcomer backup, this would provide about an extra 5 percent of capacity. No great improvement. But it doesn t cost very much either. 

Figure 6.19 Downcomers with rounded outlet lips.

---