Vapor flow

Forward-feed operation is shown in Fig. 3.12a. The fresh feed is added to the first stage and fiows to the next stage in the same direction as the vapor flow. The boiling temperature decreases from stage to stage, and this arrangement is thus used when the... 

V = vapor flow rate from the separator L = liquid flow rate from the separator Zi = mole fraction of component i in the feed y = mole fraction of component i in the vapor Xi = mole fraction of component i in the liquid... 

Component Vapor flow rate flunolh ) Liquid flow rate (kmolh" )... 

The multicomponent form of the Underwood equation can be used to calculate the vapor flow at minimum reflux in each column of the sequence. The minimum vapor rate in a single column is obtained by alternate use of two equations ... 

TABLE S.4 Total Vapor Flows for the 14 Possible Sequences for the Separation of a Mixture of Alkanes... 

Rank order Total vapor flow (kmol h )... 

Solution Table 5.4 gives the total vapor flow for difierent sequences in rank order. The sequence with the lowest total vapor flow is shown in Fig. 5.4. 

Figure 5.4 The sequence with the lowest total vapor flow for Example 5.3.

In one sense, the thermospray nebulizer could be considered a pneumatic device, in which a fastflowing argon gas stream is replaced by a very rapidly vaporizing flow of solvent from the sample solution. A typical arrangement of a thermospray device is shown in Figure 19.18. 

Acetone can be handled safely if common sense precautions are taken. It should be used in a weU-ventilated area, and because of its low flash point, ignition sources should be absent. Flame will travel from an ignition source along vapor flows on floors or bench tops to the point of use. Sinks should be rinsed with water while acetone is being used to clean glassware, to prevent the accumulation of vapors. If prolonged or repeated skin contact with acetone could occur, impermeable protective equipment such as gloves and aprons should be worn. 

The upward flow of gas and Hquid in a pipe is subject to an interesting and potentially important instabiHty. As gas flow increases, Hquid holdup decreases and frictional losses rise. At low gas velocity the decrease in Hquid holdup and gravity head more than compensates for the increase in frictional losses. Thus an increase in gas velocity is accompanied by a decrease in pressure drop along the pipe, a potentially unstable situation if the flows of gas and Hquid are sensitive to the pressure drop in the pipe. Such a situation can arise in a thermosyphon reboiler, which depends on the difference in density between the Hquid and a Hquid—vapor mixture to produce circulation. The instabiHty is manifested as cycHc surging of the Hquid flow entering the boiler and of the vapor flow leaving it. 

A reactor is termed a radial or panel-bed reactor when gas or vapor flow perpendicular to a catalyst-fiHed aimulus or panel. These are used for rapid reactions to reduce stresses on the catalyst or to minimize pressure drops. Similar cross-flow configurations also are used for processing soHds moving... 

Typically, a baffle condenses a vapor flow to a Hquid in such a way that Hquid can drain off for recycle. A weU-designed and useful trap, on the other hand, catches and retains condensables such as water and the higher vapor pressure fraction of the working fluid of a pump. Although the terms baffle and trap seem to describe the same type of function, namely, to slow down but not prevent the rate at which some species of molecules pass through, traps can completely stop some molecular species (23). 

Stripping section liquid and vapor flows, because the feed is at the boiling point. 

Plate Columns. There are two general types of plates in use crossflow and counterflow. These names refer to the direction of the Hquid flow relative to the rising vapor flow. On the cross-flow plate the Hquid flows across the plate and from plate to plate via downcomers. On the counterflow plate Hquid flows downward through the same orifices used by the rising vapor. 

The term in equation 42 is called a Souders-Brown capacity parameter and is based on the tendency of the upflowing vapor to entrain Hquid with it to the plate above. The term E in equation 43 is called an E-factor. and E to be meaningful the cross-sectional area to which they apply must be specified. The capacity parameter is usually based on the total column cross section minus the area blocked for vapor flow by the downcomer(s). Eor the E-factor, typical operating ranges for sieve plate columns are... 

Internal diffusion occurs during drying when Hquid or vapor flow obeys the fundamental diffusion laws. 

Fig. 11. Two-truck tray dryer. A, air inlet duct B, air-exhaust duct with damper C, axial flow fan D, fan motor, 2—15 kW E, air heaters F, air-distribution plenum G, distribution slots and H, wheeled tmcks and trays. The arrows iadicate air and vapor flow pattern.

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