Packed and fluidised beds in microfluidic devices offer the potential of enhanced heat and mass transfer capability at a scale where the process can be closely controlled. The knowledge of hydrodynamics of packed and fluidised beds in capillary tubes is essential for the design and optimization of such devices. This study experimentally examines the hydrodynamics of packed and fluidised beds in terms of pressure drop, bed expansion and minimum fluidisation velocity in tube sizes with inner diameters of 0.8, 1.2 and 17.1 mm. Specifically the influence of the wall on the hydrodynamic characteristics of the beds was examined by changing the tube-to-particle diameter ratio. It was found that as the tube diameter reduces the bed voidage sharply increases leading to a reduction in the pressure drop across the bed. Also a pressure drop overshoot was observed at lower tube-to-particle diameter ratios which found to be associated with contact stresses due to wall friction. (C) 2011 Elsevier B.V. All rights reserved.