Transition to pulsing flow, holdup and pressure drop in packed columns with cocurrent gas-liquid downflow

Abstract

Trickle beds of 1 meter in length and resp. 5, 10 and 20 cm in diameter were operated in the so-called pulsing flow regime. The packing was 2.5 resp. 4 mm Raschig rings. Air was taken as the gas phase. Several liquids were used. In this contribution we describe the transition from gas-continuous to pulsing flow, the liquid holdup and the pressure drop over the column. The transition can be described by an effective Froude-number. Correlations are set up for the transition point as well as for the hold-up. Pressure drop is shown to be linearly dependent upon the pulse frequency. In a separate series of experiments the transition to pulsing flow was measured in a 5 mm capillary tube, used as a wetted wall column. It became clear, that the onset of pulsing flow in such a capillary is not determined by the same parameter as the onset of pulsing flow in a packed column.