Particle packing structure in a rectangular micro-capillary

Packed beds of micro-sized particles may be used for enhancing heat and mass transfer in microfluidic devices where Reynolds numbers are small. By increasing the surface area per unit volume, such micro-packed beds can also be used to significantly enhance the functionality of such devices. As the effectiveness of a packed bed is dictated by its packing structure, it is of interest to understand this structure and how it is affected by system parameters such as the channel-to-particle ratio - this has received little attention for micro-packed beds. In the work reported here, X-ray micro-computed tomography and image analysis is used to determine the packing structure of micro-packed beds of glass particles for channel-to-particle ratios of 5.19, 5.80, 6.56 and 7.55 in a channel of D = 200 mum square cross-section. The bed-average porosity was found to be far higher than macroscale PBs, vary from approximately 67% to 60% as the channel-to-particle ratio increased, with the packing structure and porosity varying both across the bed width and along its length. The former clearly arises from the effect of the wall, whilst the latter arises from the sedimentation method used to create the packed bed.