EFFECT OF VISCOSITY ON HYDRODYNAMIC PROPERTIES OF PULSING FLOW IN TRICKLE BEDS

New data on pulsing flow onset, properties of pulses (frequency, celerity, length), liquid holdup and pressure drop are presented for aqueous glycerol solutions of viscosity 6.7 and 20.2 mPa s and compared with similar measurements from an air-water (1.0 mPas) system. With the exception of viscosity, all other physical properties of the liquid phase are kept constant and fairly close to those of water, thus allowing a direct assessment of the effect of viscosity. Pulse formation and propagation with viscous liquids is examined on the basis of time records from a conductance type technique. A striking effect due to increased liquid viscosity is the reduction of the pulsing flow regime; in particular, the pulsing-to-bubbling transition boundary is shifted towards higher gas flow rates. Pulse frequency and celerity appear to decrease only slightly with increasing liquid viscosity, whereas the two-phase pressure gradient increases significantly. Liquid holdup also tends to increase with viscosity. Moreover, holdup with viscous liquids tends to increase significantly with the liquid flow rate, whereas an insignificant effect is found for water. A new correlation for estimating liquid holdup is proposed, and a simple model for predicting pulsing flow characteristics is modified in order to take account of the aforementioned effects.