A model is described which may be used to simulate a packed column for countercurrent A simple model was proposed previously ( 1 4 ) to explain the large observed differences between the gas-phase mass transfer coefficients for vaporization and absorption. The model was composed of stagnant liquid pockets with holdup h, and liquid which flows rapidly over the packing corresponding to the operating holdup ha. The sum of the two holdups is ht, the total holdup. I t was then assumed that vaporization can take place from the total surface area which is proportional to ht and that absorption can take place only on the rapidly moving surface area which is proportional to h,, because the stagnant pockets become saturated and ineffective. The correlation knarap -G a p -ht was obtained and shown to represent the data. However, there are no completely stagnant pockets in a packed column, and previous dye dispersion (16) and particle velocity ( 1 3 ) studies in this series showed that the pockets have widely varying residence times from fractions of a second up to 5 to 10 min. The residence times of many pockets were found to be functions of time, probably due to the complex flow geometry above the pockets investigated. The flow was found to be laminar over the outside surfaces of rings, laminar or turbulent in pockets, and turbulent at ring junctions. Thus a wide range of conditions was found from slow moving laminar flow to rapid and complete mixing and even periodic renewal every few seconds by splashing.Most workers in the field of absorption accompanied by chemical reaction have considered only the liquid-phase mass transfer coefficient and neglected the gas-phase coefficient, particularly for systems where absorption with no reaction is liquid-phase controlled. These systems (such as (1)
