Heat and mass transfer of binary distillation in a vertical wetted-wall column

Abstract

In this study, we investigated the effects of partial condensation on the heat and mass transfer rates during ethanol–water binary distillation based on a laminar boundary layer theory applied to a wetted-wall column, as well as the characteristics of the boundary layer behavior on the vapor phase. The thickness of the thermal and concentration boundary layers were shown to decrease with an increase in partial condensation, whereas the heat and mass transfer rates were demonstrated to increase. The results of this study show that the dimensionless rates considered for the convective fluxes Sh/(1+αM) and Nu/(1+αH) can be determined through a combined application of the laminar boundary layer theory and function g(β) of a partial condensation ratio β (mole basis), where β is linearly proportional to υs/u∞ (dimensionless velocity), which is a term for the boundary condition at a vapor–liquid interface. A numerical analysis of the experiment data show that both Sh/(1+αM) and Nu/(1+αH) are approximately proportional to the Reynolds number (Re), and not to Re1/2, as is generally the case, under the condition υs=0. Therefore, we established the functional relationship g(β′)=0.4288–0.2844eβ″, i.e., the exponential function of β′, which was converted into a mass basis. The modified boundary layer theory was found to be completely self-consistent.