Murphree vapor efficiency

Rate of Mass Transfer in Bubble Plates. The Murphree vapor efficiency, much like the height of a transfer unit in packed absorbers, characterizes the rate of mass transfer in the equipment. The value of the efficiency depends on a large number of parameters not normally known, and its prediction is therefore difficult and involved. Correlations have led to widely used empirical relationships, which can be used for rough estimates (109,110). The most fundamental approach for tray efficiency estimation, however, summarizing intensive research on this topic, may be found in reference 111. 

E = Murphree vapor efficiency, corrected for recycle of hqiiid entrainment... 

Murphree vapor efficiency forjth component on nth tray... 

Equilibrium composition of the vapor for the Murphree vaporization efficiency, component i, stage / defined by Eq. (4.20). 

For the entire plate and for gas concentrations, the Murphree vapor efficiency is usecl ... 

For an individual tray, the concept of efficiency often used is the Murphree vapor efficiency, defined as the ratio of the composition change in the vapor stream to the composition change if the vapor leaving the tray were in thermodynamic equilibrium with the liquid leaving. Thus,... 

This rate-based analysis of trayed columns gives an estimate of the number of overall gas phase mass transfer units corresponding to a given tray. The practical application of this analysis is to provide a means for estimating the tray Murphree vapor efficiency discussed in Section 14.3. 

The Murphree vapor efficiency may be estimated from Nqq, the number of overall gas phase mass transfer units (Section 14.2). For component z, the Murphree vapor efficiency is written as... 

Combined with the above equation for E, the Murphree vapor efficiency is expressed as a function of Nqq. 

In order to use the overall efficiency in a design problem, one carries out an equilibrium-stage analysis and then determines the number of actual stages as the number of equilibrium stages divided by Eo. Thus the overall efficiency concept is simple to use once Eo is known, but it is often not easy to predict reliable values of Eo-The other commonly used approach involves the concept of the Murphree vapor efficiency Em defined as ... 

The second method used is the Murphree vapor efficiency ... 

Equation (5.9-2) defines the Murphree vapor efficiency. an equivalent expression could be given in teims of liquid concentrations, but the vapor concentration basis is the one most used, and it is equivalent to its couaterpart dealing with the liquid. It should be noted thy the value or y is based on the exit concentration of the liquid and is silent ou the idea that liquid concentration can vary from point to point of the tray when liquid concentration gradients are severe, as in the case of very loug liquid flow pelhs. it is possible for the Muiphree efficiency to have a value greater than ]. 0,... 

The column operates with a reflux ratio L/D of 4 to 1. The Murphree vapor efficiency is 80%. 

Murphree postulated that the vapor between trays is well mixed, that the liquid in the down-comers is well mixed, and that the liquid on the tray is well mixed and is of the same conposition as the liquid in the downcomer leaving the tray. For the nomenclature illustrated in Figure 4-27A. the Murphree vapor efficiency is... 

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