Condensation rates for a binary vapor mixture (adapted from Taylor and Krishna (1993))

Condensation rates for a binary vapor mixture (adapted from Taylor and Krishna (1993)). Here we apply Eq. (10.22) to the condensation of a binary mixture of ethylene dichloride (A) and toluene (B) for the following conditions. Vapor-phase composition: yA0 = 0.4 Liquid-phase composition at the start of condensation xA = 0.325 Interface equilibrium relation: y = 2x/(1 + 1.14x) Vapor-phase mass transfer coefficient under low-flux condition 0.054 m/s Pressure 101.325 kPa; temperature 400 K Assume that the fluxes are proportional to the liquid composition, i.e., the composition of the first drop is fixed by the relative rates of condensation. This fixes the determinacy condition as xA = NA/ N

Use this condition in the relation for NA given by Eq. (10.22). Rearrange the equation and show that the total mass flux of condensation is given by Nt = lnxAL − yAδ xAL − yA0 (10.92) Use the numerical values given and verify that NA = 0.47 and NB = 0.98 in the units of mol/m2 ·s. Note that in practice the condensation rate is determined not only by the rate of mass transfer but also by the rate at which heat can be removed from the vapor. Hence this is a coupled problem in heat and mass transfer. The example above provides the solution to the mass-transport part of the overall problem.