CONDENSATION OF MIXED VAPORS AND THERMODYNAMICS

A literal interface between thermodynamics and transport phenomena occ urs in the steady-state condensation/vaporization of mixed vapors/liqu ids in wetted-wall towers. Unfortunately, several prominent transport texts assume that the ratio of molar fluxes is the same as the corresp onding ratio of mole fractions at the interface for the phase being fo rmed. This is shown to be true only at particular vertical positions c orresponding to the first drop of condensate. The thermodynamics of th e condensation/vaporization of mixtures is reviewed to understand why the ratio of pure-component fluxes at the interface differs from that of corresponding equilibrium mole fractions. The dynamics of steady-st ate condensation in wetted-wall towers is also developed based on the film theory of Colburn and Drew. the temperature/composition diagram i s used to trace both transport phenomena and thermodynamic variables a t various tower heights. The Ackermann factor is corrected allowing mo re general use of the design equations when the vapor is nonideal. The usual neglect of liquid-film resistance to heat transfer is examined. Numerical calculations show an unusual rise in the interfacial temper ature in a parallel flow tower immediately below the onset of condensa tion. Possible and impossible sets of temperature and composition prof iles are described.