Hydrodynamics of gas–liquid micro-fixed beds – Measurement approaches and technical challenges

Despite many areas that are open to investigation in the hydrodynamic study of micro-fixed bed reactors, conducting research in this field is mostly hampered by a number of experimental challenges that have made many attempts ineffectual. This work provides a summary of the technical challenges, problems and misconstrues one might encounter in performing hydrodynamic experiments on micro-fixed bed reactors. Some of these issues will be pointed out upon comparing classical residence time distribution (RTD) measurements through electrical conductivity probes at micro-fixed bed scale with near-wall RTD obtained via visualizations of dye-tracer elution and monitoring the changes in gray level intensity of the images. Laterally-averaged gray level intensity at both upstream and downstream extremities of the wall regions of interest acted as inlet and outlet curves for the Aris method. The major outcome of this work was experimental confirmation of theoretically predicted maximum liquid velocity in the high porosity zone close to the wall. Finally, the experimental results on pressure drop and liquid holdup obtained upon following the right experimental protocols are presented.