Vapor, distribution

Vapor Distribution Relatively large shell inlet nozzles, which may be used in condensers under low pressure or vacuum, require provision for uniform vapor distribution. 

Where only about 5% or less of the liquid dow iiflow is to be withdrawn from the column, a special collector box can be installed within the packed bed. This box can remove small quantities of intermediate boiling components that otherwise w ould accumulate in a sufficient quantity to interfere with the fractionation operation. Such a collector box must be designed very carefully to avoid interference with the vapor distribution above it or... 

Inadequate vapor distribution to packed bed. Poor separation. Design omission. 

For most trays, liquid flows across an active area of the tray and then into a downcomer to the next tray below, etc. Inlet and/or outlet weirs control the liquid distribution across the tray. Vapor flows up the tower and passes through the tray active area, bubbling up through (and thus contacting) the liquid flowing across the tray. The vapor distribution... 

Liquid distribution in a packed bed is a function of the internal vapoi/liquid traffic, the type of packing employed, and the quality of the liquid distributors mounted above the packed bed. Vapor distribution is controlled by the internal vapor/liquid traffic, by the type of packing employed, and by the quality of the vapor distributors located below the packed beds. 

Figure 8-103. Effect of liquid gradient on vapor distribution with 0.5 vapor distribution ratio. Used by permission, Bolies, W. L., Pet. Processing, Feb. thru May (1956).

Cv, from Figure 8-113 = estimated h. Vapor distribution ratio ... 

Ov Crall, the careful design of a distributor for liquid in the top of a packed tower, and for the redistribution of liquid flowing dow n multi-section packing in the tower, is essential to good consistent tower performance. However, the liquid flow is not alone, the uniformity of vapor distribution is likewise essential, because non-uniform vapor distribution can cause non-uniform liquid downflow. Then, there is the selection of the packing itself and its characteristics and requirements/sensitivity to the uniform distribution of the liquid and vapor. As earlier emphasized, the level of the distributor tray or trough can be critical to the consistent uniform liquid distribution. 

For commercial towers with good liquid/vapor distribution Norton [96] recommends standard designs use HETP ralues 13% above the system base HETP. If the system under consideration does not meet the physical properties limit, either use a conservative estimate or use actual plant or published data for the system. For comparison of HETP values for selected packings see Strigle and Rukovena [94], Figure 9-28. 

Uniformity of liquid (vapor) distribution increases packing performance efficiency. 

Podgorny, I. A., A. M. Vogelmann, and V. Ramanathan, Effects of Cloud Shape and Water Vapor Distribution on Solar Absorption in the Near Infrared, Geophys. Res. Lett, 25, 1899-1902 (1998). 

Figure 7.4 shows a modern, narrow-trough, liquid collector-vapor distributor chimney tray. While the initial vapor distribution through a packed bed is not quite so critical or difficult as the liquid distribution, it is still important. 

A properly designed valve or sieve tray will act as a vapor redistributor. Thus, poor initial vapor distribution will only lessen the efficiency of the bottom tray. But if a packed-bed vapor distributor does not work properly, vapor channeling will be promoted through the entire bed. 

The need for a proper vapor distributor, to achieve proper initial vapor distribution... 

Figure 7.17. Effect of salt content of water on vapor distribution of toluene. Successive equilibration of toluene (equal starting concentrations) between helium and water of differing salt content.

Thermodynamic predictions of the solid-phase composition have been very successful for the growth by MOCVD of group III-V compound semiconductors (e.g., InAs Sb and GaAs SbJ even though the gas-phase reactions are far from equilibrium (88-91). The procedure is also useful for estimating solid-vapor distribution coefficients of group II-VI compound semiconductors (e.g., Cd Hg e and ZnSe SJ grown by MOCVD (92). In the analysis, the gas phase is considered to be an ideal mixture, that is... 

Cycle development parameters include temperature, airflow rate, humidity, liquid peroxide concentration, liquid peroxide delivery rate, peroxide vapor delivery temperature, and peroxide vapor half-life. Temperature distribution qualification involves the use of temperature sensors located throughout the sterilant delivery line and throughout the enclosure. Vapor distribution qualification uses... 

Pilot-scale tests by Fan et al. [IChemE Symp. Ser. 142,899 (1997)] compared vapor distribution and entrainment from sparger, vapor... 

Based on the above-mentioned assumptions, the mass, momentum and energy balance equations for the gas and the dispersed phases in two-dimensional, two-phase flow were developed [14], In order to solve the mass, momentum and energy balance equations, several complimentary equations, definitions and empirical correlations were required. These were presented by [14], In order to obtain the water vapor distribution the gas phase the water vapor diffusion equation was added. During the second drying period, the model assumed that the particle consists of a dry crust surrounding a wet core. Hence, the particle is characterized by two temperatures i.e., the particle s crust and core temperatures. Furthermore, it was assumed that the heat transfer from the particle s cmst to the gas phase is equal to that transferred from the wet core to the gas phase i.e., heat and mass cannot be accumulated in the particle cmst, since all the heat and the mass is transferred by diffusion through the cmst from the wet core to the surrounding gas. Based on this assumption, additional heat balance equation was written. 

Special considerations In multipass trays. In a multipass tray, vapor distribution between the passes is largely determined by the hole area, while liquid distribution is largely a function of the weir height and length. If the geometry of the passes is perfectly identical, the distribution of vapor and liquid is the same for each pass, and tray efficiency is uniform. This is readily achievable in two-pass trays, where the design of each pass is identical to the other, but not so when a... 

MOC in Fig. 8.16d is difficult and leaves a lot of room for subjectivity. Further, MOC determination is sensitive to the accuracy of efficiency measurements—factors such aa liquid and vapor distribution, sampling procedure, end effects at the top and bottom of the packings, and the availability of a large number of efficiency points near the MOC, where conditions may not be steady-state. For instance, for one set of published experimental data reported by Eckert and Walter (61), MOC increased by about 10 percent due to reducing packed height from 10 to 5 ft-... 

Vapor flow through packings tends to be uniform if the initial liq uid and vapor distributions to the packings are uniform (15,66). 

Vapor distribution can be troublesome, especially in large-diameter columns. This type of maldistribution is best tackled at the source by paying attention to the vapor inlet arrangements. Common commercial vapor distributor designs are discussed elsewhere (23,40,152). 

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