Total tray pressure drop

Although Sutherland did not obtain an equation for total tray pressure drop, correlation at this time indicates that it follows the effective head concept of Hughmark. This is a limited evaluation because the data available did not indicate any clear liquid heights over about 0.75 in. 

Uneven vapor flow bubbling-up through the tray deck will promote vapor-liquid channeling. This sort of channeling accounts for many trays that fail to fractionate up to expectations. To understand the cause of this channeling, we will have to quantify total tray pressure drop. 

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

An increase in reflux rate, assuming that the reboiler is on automatic temperature control, increases both the tray weir loading and the vapor velocity through the tray deck. This increases both the total tray pressure drop and the height of liquid in the tray s downcomer. Increasing reflux rates, with the reboiler on automatic temperature control, then will always push the tray closer to, or even beyond, the point of incipient flood. 

The total tray pressure drop HDC2 (inches of liquid) is calculated with preceding factors installed in Eq. (3.60). 

Residual pressure drop, i.e., total tray pressure drop less diy pressure drop less dear liquid height, in of liquid. 

Calculate the total tray pressure drop. The total tray pressure drop is the dry tray pressure drop plus the height of the liquid on the tray deck. Aeration is assumed to reduce the tray liquid density to 40% of the nonaerated liquid density. 

Multichordal downcomers can increase weir length (Fig. 6). Fig. 6 shows a combined multichordal and stepped downcomer. The increased weir length decreases the liquid crest height over the weir. This decreases total tray pressure drop. The stepping is a variation of a sloped downcomer. The step increases the downcomer inlet area with a minimum decrease in tray active area. 

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