Investigation into the Hydrodynamics of Liquid-Solid Inclined Microfluidised Beds

Macroscale inclined and microfluidised beds hold great promise in delivering enhanced heat and mass transfer rates when compared to their vertically aligned macroscale counterparts. It is therefore reasonable to consider that a combination of the two technologies in the form of inclined microfluidised beds could offer even greater benefits with the potential to overcome the restrictions posed by low values of Reynolds numbers prevalent within microfluidics. However, this promise may at times be frustrated due to the challenges posed by the increased significance of surface forces in comparison to volumetric ones. A step towards overcoming these challenges is to understand the hydrodynamics within such a system, hence this study investigated the effects of column inclination and different particle-to-channel diameter combinations on the bed hydrodynamics. A key outcome of the study was the verification of the suitability of the Ergun equation for prediction of minimum fluidisation velocities due to small deviations between 1.01 and 1.81 times the theoretical values, for a particle-to-diameter range of 0.025 to 0.165 at inclinations between 0° and 10°. Investigation into the effect on bed expansion behaviour showed that the bed contracted with an increase in bed inclination. An unexpected observation during the bed expansion was the appearance of a secondary high voidage region and the appearance of strong circulation patterns with an increase in bed inclination. A detailed analysis of these phenomenon suggested the presence of a critical angle at 6° and 10° for the 85 µm, 4x4 mm and 165 µm, 1x1 mm bed respectively, whereby the liquid-solid back-mixing due to the modified particle trajectories resulted in the disappearance of the high voidage region.