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Modifications were made to the Packed Bed Reactor Experiment (PBRE) and flown on the International Space Station as PBRE-2 to eliminate external pressure oscillations at higher liquid flow rates and the packing diameter was reduced to increase the pressure gradient for lower flows. It is found that gas hold-up is a function of bed history at low liquid and gas flow rates whereas higher gas hold-up and pressure gradients are observed for the test conditions following a liquid only pre-flow compared to the test conditions following a gas only pre-flow period. Over the range of flow rates tested, the capillary force is the dominant contributor to the pressure gradient, which is found to be linear with the superficial liquid velocity but is a much weaker function of the superficial gas velocity and varies inversely with the particle diameter.

Experimental results on pressure drop and flow patterns for gas–liquid flow through packed beds obtained in the International Space Station with two types of packing are presented and analyzed. It is found that the pressure drop depends on the packing wettability in the viscous–capillary (V–C) regime and this dependence is compared with previously published results developed using short duration low‐gravity aircraft tests. Within the V–C regime, the capillary contribution is the dominant force contributing to the pressure drop for the wetting case (glass) versus the viscous contribution dominating for the non‐wetting case (Teflon). Outside of the V–C regime, it is also found that hysteresis effects that are often strong in normal gravity gas–liquid flows are greatly diminished in microgravity and pressure drop is nearly independent of packing wettability. A flow pattern transition map from bubble to pulse flow is also compared with the earlier aircraft data.

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SignificanceGas-liquid up-flow in a packed bed is studied experimentally in the limit of zero flow rate.Two patterns of bubble behavior are detected based on the magnitude of the Bond number (Bo). The gas hold-up of the bed is found to be nonmonotonic with a maximum around Bo of unity. The bubble to particle diameter ratio is found to scale inversely with Bo. K E Y W O R D SBond number, bubble size, hold-up, packed bed, particle size