Single-Pass Sieve Trays with Crossflow

12-1 SINGLE-PASS SIEVE TRAYS WITH CROSSFLOW 

The single-pass sieve tray with crossflow appears to be the most widely used type of tray today. In a tray of this type, the vapor passes upward through the perforations (or valves) and then through the liquid on the tray. The liquid flows down through the column and enters each plate by flowing under the downcomer weir. Then the liquid flows across the plate and over the outlet weir and into the downcomer to the plate below as shown in Fig. 12-3. In order for the liquid to flow across each plate in succession as it passes down through the column, a liquid head in each downcomer is required as depicted in Fig. 12-3. 

As the vapor passes through the liquid, a froth or foam is formed as depicted in Fig. 12-3. At the outlet weir and in the downcomer, the vapor disengages itself by the formation of vapor bubbles. To overcome the frictional forces encountered by the vapor as it passes through each stage in succession, a pressure driving force is required. (Note in Fig. 12-3, P2 P4.) 

Other types of plates consist of those in which the liquid makes more than one pass and those in which counterflow of the vapor and liquid through the same perforations is employed. 

(12-1) the change in kinetic energy from point (1) to point (2) was taken to be negligible. The frictional losses, Ff, consist of the head lost by the liquid in flowing down the downcomer which is taken to be negligible, the head lost by flowing under the downcomer weir, and the head lost in flowing across the plate. 

---

Figure 12-3 A graphical display of the meaning of the symbols used in the fluid dynamic analysis of a single-pass sieve tray with crossflow.

Example 12-1 This example is based on the results of a design calculation given by Leibson et al.12 For the following single-pass sieve tray with crossflow ... 

---