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

New data on pulsing flow onset, properties of pulses (frequency, celer ity, length), liquid holdup and pressure drop are presented for aqueou s glycerol solutions of viscosity 6.7 and 20.2 mPas.s and compared wit h similar measurements from an air-water (1.0 mPa.s) system. With the exception of viscosity, all other physical properties of the liquid ph ase are kept constant and fairly close to those of water, thus allowin g a direct assessment of the effect of viscosity. Pulse formation and propagation with viscous liquids is examined on the basis of time reco rds from a conductance type technique. A striking effect due to increa sed liquid viscosity is the reduction of the pulsing now regime; in pa rticular, the pulsing-to-bubbling transition boundary is shifted towar ds higher gas flow rates. Pulse frequency and celerity appear to decre ase only slightly with increasing liquid viscosity, whereas the two-ph ase pressure gradient increases significantly. Liquid holdup also tend s to increase with viscosity. Moreover, holdup with viscous liquids te nds to increase significantly with the liquid flow rate, whereas an in significant effect is found for water. A new correlation for estimatin g liquid holdup is proposed, and a simple model for predicting pulsing flow characteristics is modified in order to take account of the afor ementioned effects.