The effect of superficial gas velocity on wavy films and its use in enhancing the performance of falling film reactors

Abstract

Mass transfer in co-current downward annular flow depends on the amount of liquid carried by the waves. The thickness of this portion of the liquid film increases with the superficial gas velocity up to about 20-25 m s-1 for two-phase air/water flow. The maximum apparent friction factors observed in air-water annular flow also appear at superficial air velocities about 20-25 m s-1. Organic compounds, like fatty alcohols and alkylbenzenes, show a maximum apparent friction factor at lower superficial gas velocities. The gas velocity at which a maximum friction factor occurs is dependent on the surface tension, appearing at lower gas velocities for liquids with lower surface tensions. Progressive increases of the superficial gas velocity can be used to graduate the mass transfer along a falling film device.