Hydrodynamics of Multiphase Reactors

Multiphase reactors enable simultaneous interaction of gas, liquid and often solid phases to drive chemical transformations at industrial scale. The hydrodynamics of these systems govern mass and heat transfer, mixing patterns and pressure drop, all of which critically influence conversion, selectivity and safety. Central parameters include void fraction, which quantifies the volumetric proportion of each phase; wetting efficiency, which describes the extent of liquid contact with solid catalysts; and interfacial area, which controls rates of gas–liquid and liquid–solid exchange. Flow regimes span from dispersed bubbles through trickle and pulse flows to fluidised beds, each exhibiting distinct mixing and transport characteristics. Empirical correlations have long been employed for design, yet modern research integrates pore-scale simulation, computational fluid dynamics (CFD) and advanced imaging to resolve local velocities, phase distributions and capillary effects. Such approaches offer predictive insight for scale-up, reactor optimisation and process intensification. Applications range from petrochemical hydrogenation in trickle beds to wastewater treatment in aerated packed towers, and to emerging uses in biofuel production and microgravity processing. By coupling rigorous experiments with multiscale modelling, researchers are developing robust frameworks for the reliable operation of multiphase reactors under diverse conditions and novel geometries.

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Dynamic multiscale modelling of trickle bed reactors has advanced through frameworks that solve coupled mass and energy balances across gas, liquid and solid phases. A notable case study of arabinose oxidation demonstrated how catalyst particle shape and reactor length strongly affect conversion and temperature profiles, offering a general methodology applicable to a wide array of heterogeneous reactions. In the realm of process intensification, researchers have turned to periodic open cellular structures (POCS) manufactured by additive techniques. Comparative studies of strut-based and novel sheet-based POCS revealed up to a five-fold increase in volumetric mass transfer coefficient relative to conventional random packing, while maintaining manageable two-phase pressure drops. These findings point towards versatile reactor internals that can be tailored to specific mass transfer demands. On a more fundamental level, experiments aboard the International Space Station have shed light on gas–liquid flow regimes in packed beds under microgravity. Four distinct patterns—from dispersed bubbles to gas continuous flow—were characterised by pressure gradient measurements, revealing significant hysteresis and demonstrating the dominant role of capillary forces at low velocities. The pressure-drop correlations derived for each regime provide baseline data for refining terrestrial and space-based reactor designs.

Hydrodynamics of Multiphase Reactors publication trend

The graph below shows the total number of articles in hydrodynamics of multiphase reactors across all publications each year (not limited to Nature Index journals).

Technical terms

Void fraction: The fraction of reactor volume occupied by a particular phase, typically gas or liquid, important for estimating residence time and flow distribution.

Mass transfer coefficient: A measure of the rate at which species move between phases per unit interfacial area, central to reaction kinetics in multiphase systems.

Wetting efficiency: The proportion of solid catalyst surface effectively covered by liquid, which influences liquid–solid mass transfer and catalyst utilisation.

Pressure drop: The loss of fluid pressure along a reactor due to frictional and interfacial resistance, affecting pumping requirements and flow regime transitions.

Periodic open cellular structure (POCS): A regular, porous framework produced by additive manufacturing to enhance mass transfer and tailor flow paths in packed reactors.

Flow regime: A characteristic pattern of phase distribution and motion (e.g. bubbly, trickle, pulse) that dictates mixing, transport and reaction performance.

References

1. Dynamic modelling of trickle bed reactor: Case study of arabinose oxidation. Powder Technology (2023).
2. Conceptual study on the intensification of gas–liquid mass transfer in trickle bed reactors by the application of strut-based and novel sheet-based periodic open cellular structures (POCS). Chemical Engineering and Processing - Process Intensification (2024).
3. The international space station packed bed reactor experiment: capillary effects in gas-liquid two-phase flows. npj Microgravity (2023).