To model a biphasic stirred tank reactor, intrinsic reaction kinetics and interfacial area are required. In this study, reactor modeling for n-butyraldehyde aldol condensation was investigated under industrially relevent conditions. The interfacial area in the reactor was directly measured using a borescope system under appropriate temperature, NaOH concentration and rpm conditions. To estimate the interfacial area, a semiempirical correlation was developed, which provides good estimates within +/- 15% error. The reactor model based on two-film theory was developed, combining the interfacial area and intrinsic reaction kinetics reported in our prior work. The model was verified by reaction experiments in the range 0.05-1.9 M NaOH, 80-130 degrees C, and 600-1000 rpm. The prediction errors using the interfacial area from direct measurements and the correlation were +/- 8% and +/- 15%, respectively, suggesting that the model accuracy may be improved with better interfacial area estimation. (c) 2015 American Institute of Chemical Engineers AIChE J, 61: 2228-2239, 2015