Visualization of the packing structure of packed beds with micron-sized particles using confocal microscopy to estimate their pressure drop

• Packed beds with fluorescent-labelled, micron-sized particles were fabricated. • The pressure drop of the fabricated packed beds was experimentally measured. • Deviations between the measured and Kozeny-Carman pressure drop were found. • The 3D particle coordinates of the packed beds were obtained by confocal microcopy. • The pressure drop deviations were reproduced by CFD using the coordinates. The pressure drop is a critical parameter of micro packed-bed reactors because it determines operating conditions such as the pumping power for practical uses. Here, we use confocal microscopy to examine the packing structure of packed beds with micron-sized particles (<2 μm in diameter) to investigate the effect of the packing structure on the pressure drop. The pressure drop of packed beds was experimentally measured. Distinct gaps between the measured pressure drop and the Kozeny-Carman equation were found, indicating that the pressure drop of micron-sized particles cannot be simply predicted using well-established equations. Packing structures of the packed beds were visualized in 3D via confocal microscopy by employing fluorescent-labelled silica particles as the packed particles. It is worth emphasizing that no conventional techniques have achieved visualizing the packing structures of packed beds with such small particles so far. The pore size distribution could qualitatively explain the difference in pressure drop of beds containing a single type of particles. By employing the 3D particle coordinates, the difference between the pressure drop of (mixed) packed-bed reactors with micron-sized particles and the Kozeny-Carman prediction could be reproduced via 3D computational fluid dynamics using the finite-element method. This concludes that visualizing the structure of a packed bed using confocal microscopy enables prediction of the pressure drop and will contribute to designing micro packed-bed reactors with low pressure drop.