Murphree efficiencies

Murphree plate efficiency (Murphree, 1925), defined in terms of the vapour compositions by ... 

Point efficiency (Murphree point efficiency). If the vapour and liquid compositions are taken at a point on the plate, equation 11.64 gives the local or point efficiency, Emv. 

The best-established theoretical method for predicting is that of the AIChE (Bubble-Tray Design Manual, American Institute of Chemical Engineers, New York, 1958). It is based on the sequential prediction of point efficiency, Murphree efficiency, and overall column efficiency ... 

Liquid viscosity Chemical potential of component t in phase I Mixture mean viscosity defined in Eq. (15-180) Reference viscosity (of water) MOSCED asymmetry factor Efficiency of a batch e3q)eriment [Eq. (15-175)] Efficiency of a continuous process [Eq. (15-176)] Murphree stage efficiency Murphree stage efficiency based on dispersed phase Overall stage efficiency Solvatochromic polarity parameter... 

Two efficiency definitions are in common use for engineering design overall tray efficiency and Mur-phree tray efficiency. Murphree tray efficiency basis can be set on either the vapor phase or the liquid phase. Most literature reports data on a vapor phase... 

System Tray type Tray efficiency (Murphree) Overall... 

Specifications Vaporization plate efficiency Murphree (plate)... 

In practice, tray efficiencies (Murphree Efficiency) are used that are defined by... 

Many different measures of efficiency have been developed. Let us look at the two commonly used measures, which are the stage-based Murphree tray efficiency (Murphree, 1925) and overall efficiency. 

As mentioned previously, the number of actual plates in an absoiber is related to the number of theoietical plates by a factor known as the plate efficiency. In its simplest definition, the overall plate efficiency is defined as the ratio of theoretical to actual plates required for a given separation. For individual plates, the Murphree vapor efficiency (Murphree, 1935) more closely relates actual performance to the theoretical-plate standard. It is d ined by the following equation ... 

Typical operating data from a commercial absorber are presented in Table 5-6. Contact in this absorber is by means of perforated trays. Unfortunately, the number of trays is not specified so that tray efficiencies cannot be calculated from the data. However, since this has been shown to be a liquid-film controlled system, tray efficiencies would be expected to be quite low. Data reported from other installations have indicated tray efficiencies (Murphree vapor) to be on the order of 5% for absorption of CO2 in hot potassium carbonate solutions. 

Fig. 13.4-2. Using Murphree efficiencies. Murphree efficiencies effectively lower the solid equilibrium line to the dashed line. They do so because the vapor composition y leaving a particular stage is less than the equilibrium value y. Remember that these efficiencies may not have the same value in each stage.

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