The influence of the reactor pressure on the liquid hold-up in the trickle-flow regime and on the transition between trickle-flow and pulse-flow has been investigated in a trickle-flow column operating up to 6.0 MPa with water, and nitrogen or helium as the gas phase. The effect of the gas velocity and gas density on the hold-up has been explained by means of the modified Galileo number Ga{1+ΔP/(ρlgL)}. At the transition between trickle- and pulse-flow the liquid hold-up is - for a given value of the superficial gas velocity - nearly the same at each gas density. Therefore, at elevated gas densities the transition occurs at higher liquid throughputs. From a comparison of the experiments with water-nitrogen and water-helium it has been concluded that at an equal gas density - for given values of vl and vg - the hydrodynamic behaviour is the same.
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