Design and Analysis of Multiphase Gas–Liquid Distributors for Uniform Flow Distribution in Parallel Microchannels: Experiments and Phase-Field Simulations

Abstract: Numbering-up of parallel micro- and millichannels is a promising route to scale up gas-liquid microreactors, but its success depends on distributing the gas and liquid uniformly across all channels. In segmented (Taylor) flow, this is difficult because bubble splitting at each junction interacts with the hydraulic resistance of the whole distributor network, so small local asymmetries can grow into network-wide maldistribution. This thesis investigates how splitting-junction geometry, fluid properties and distributor architecture govern flow uniformity, through high-speed imaging experiments, phase-field simulations and data-driven modelling.  Among four junction geometries, a hybrid flow-focusing-with-wedge (FFW) junction gave the most uniform splitting. It eliminated bypass failure and achieved the shortest splitting time, at only a modest pressure-drop penalty relative to the plain junction. Across five gas-liquid systems, continuous-phase viscosity emerged as the dominant property: high-viscosity silicone oils gave the most stable distribution, while the low-viscosity aqueous surfactant system was the most sensitive. Among the distributor architectures that achieved reliable multi-junction splitting, the square-root width progression provided the widest high-symmetry operating window and the lowest maldistribution, whereas the 2 mm constant-width design exhibited persistent downstream non-splitting. A two-dimensional phase-field model in COMSOL Multiphysics, validated against experiments, reproduced the measured trends and revealed the pressure and velocity fields that drive splitting. A geometry-aware artificial neural network, trained on 1279 literature and in-house data points, predicted bubble lengths with R² = 0.9166 on an independent experimental dataset. Together, these findings provide practical design guidelines for passive gas-liquid distributors in scalable parallel microreactor systems.

List of Publications (included in the thesis):

1. Moorthy, B.; Gupta, K.; Rajesh, V. M. Modified Splitting Distributor for Enhanced Flow Uniformity in Parallel Microchannels: An Experimental Study on the Effect of Fluid Properties. Industrial & Engineering Chemistry Research, 2024, 63(41), 17492–17511. https://doi.org/10.1021/acs.iecr.4c01967
2. Moorthy, B.; Gupta, K.; Rajesh, V. M. Effect of Multiphase Distributors on Gas–Liquid Flow Uniformity in Parallel Micro- and Milli-Channels. Chemical Engineering Journal, 2026, 530, 173313. https://doi.org/10.1016/j.cej.2026.173313
3. Moorthy, B.; Gupta, K.; Rajesh, V. M. Numerical Study on Modified Splitting Distributor for Enhanced Flow Uniformity in Parallel Microchannels. International Journal of Computational Fluid Dynamics (under revision).

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