Transfer Units for Binary Systems

It is traditional for chemical engineers to model packed columns through the concept of transfer units (in much the same way as we used transfer units in the treatment of transfer in the froth on a tray in Sections 12.1.2 and 12.2.1). For two component systems Eq. 12.3.12 simplifies to (cf Eq. 12.1.7) 

Equation 12.3.13 is similar to the corresponding expressions for binary mass transfer in the 

Mass transfer coefficients for packed columns sometimes are expressed as the height of a transfer unit (HTU). Thus, for the vapor and liquid phases, respectively, 

The overall height of a transfer unit for a two-component system is 

The performance of a packed column is often expressed in terms of the height equivalent to a theoretical plate (HETP). The HETP is related to the height of packing by 

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