Number of overall transfer units

Equation 55 is a tigoious expression for the number of overall transfer units for equimolar counterdiffusion, in distillation columns, for instance. 

Number of transfer units based on phase 2, Number of overall transfer units based on phase 1, Number of overall transfer units based on phase 2,... 

The height and number of overall transfer units are defined as H0g and Nog by ... 

The number of overall transfer units was estimated for this system using three different empirical methods. The results were as follows ... 

Once Lhe vapor- and liquid-phase transfer units have been determined, they are combined to obtain the number of overall transfer units (vapor concentration basis) by Eq. (5.9-19). Finally, the leeal, or polar, efficiency is computed ... 

The additional subscript M has been added to emphasize the fact that the number of overall transfer units computed by Eq. (13-35) may differ slightly from the number computed by use of Eq. (13-34). The difference results from the fact that over any one stage of a distillation column, the slope of the equilibrium line generally changes, which gives rise to more than one possible choice for m as demonstrated in the last section of Sec. 13-2. 

Also, it follows from Eq. (13-34) that the number of overall transfer units may be expressed in terms of the number of gas-phase and liquid-phase units as follows... 

Then, it follows from Eqs. (13-46) and (13-48) that one should be able to predict the modified Murphree plate efficiency on the basis of the total number of overall transfer units, namely,... 

Comparison of the Murphree efficiency [Eq. (13-59)] with the modified Murphree efficiency [(13-48) and (13-49)] shows that the Murphree efficiency depends on riOGMi [Eq. (13-59)] while the modified Murphree efficiency depends on n OGi [Eq. (13-49)]. The number of overall transfer units riOGi and n 0Gui for the two efficiencies depend on the same set of transfer units (riGi and n Li) and are the same except that the quantity yfK. /yf appears in riOGi in the same position that mi appears in riOGMi. 

For dilute mixtures and when Henry s law applies, prove that the number of overall transfer units for cocurrent gas absorption in packed towers is given by... 

Schmidt number, /pD Number of overall transfer units... 

The authors [32] took into account the axial dispersion in both phases through the number of overall transfer units (NTUs), which consists both of the number of true transfer units determined by the interfacial transfer rate and the number of dispersion units. The column was divided into sections in which temperatures and thermal properties of both phases were approximately constant. 

The boundary conditions were represented by Danckwerts equations [40]. The authors used the experimental results for axial dispersion from their previous investigations [29,30]. The differential equations were solved using several well-known approximations, which relate the number of overall transfer units with the number of true transfer units, as well as with the axial dispersion and with the extraction factor. 

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