Pressure drop hydraulic tray

The sum of the dry tray pressure drop (APdry) plus the hydraulic tray pressure drop (APhyd) equals the total tray pressure drop (AP, ) ... 

When the dry tray pressure drop is significantly less than the hydraulic tray pressure drop, then the tray will start to leak or weep, and tray efficiency will be adversely affected. 

The hydraulic tray pressure drop on tray 2 increases, due to increased liquid level. 

The actual height of fluid overflowing the weir is quite a bit greater than we calculate with this formula. The reason is that the fluid overflowing the weir is not clear liquid, but aerated liquid—that is, foam. The fluid on the tray deck, below the top of the weir, is also foam. This reduces the effective weight of the liquid on the tray due to aeration. To summarize, the weight of liquid on the tray, called the hydraulic tray pressure drop, is... 

Once the weight of liquid on one portion— the lowest area—of a tray deck exceeds the dry tray pressure drop, the hydraulic balance of the entire tray is ruined. Vapor flow through the low area of the tray deck ceases. The aeration of the liquid retained by the weir on the low area of the tray deck stops, and hence the hydraulic tray pressure drop increases even more. As shown in Fig. 4.3, the liquid now drains largely... 

---