Effect of Tube-to-Pellet Diameter Ratio on Turbulent Hydrodynamics in Packed Beds: A Magnetic Resonance Velocity Imaging Study

The hydrodynamics in packed reactors strongly influences reactor performance. However, limited experimental techniques are capable of non-invasively measuring the velocity field in optically opaque packed beds at the turbulent flow conditions of commercial relevance. Here, compressed sensing magnetic resonance velocity imaging has been applied to investigate the hydrodynamics of turbulent flow through narrow packed beds of hollow cylindrical catalyst support pellets as a function of the tube-to-pellet diameter ratio, \(N\), for \(N=\) 2.3, 3.7, and 4.8. 3D images of time-averaged velocity for the gas flow through the beds were acquired at constant Reynolds number, \(R{e}_{\mathrm{p}}=\) 2500, at a spatial resolution of 0.70 mm (\(\tt x\)) \(\times\) 0.70 mm (\(\tt y\)) \(\times\) 1.0 mm (\(\tt z\)). The resulting flow images give insight into the bed and pellet scale hydrodynamics, which were systematically compared as a function of \(N\). Some changes in hydrodynamics with \(N\) were observed. Namely, the near-wall hydrodynamics changed with \(N\), with the \(N=\) 4.8 bed showing higher velocity at the wall compared to the \(N=\) 2.3 and \(N=\) 3.7 beds. Further, in the \(N=\) 3.7 bed, channels of high velocity, termed flow lanes, were found 1.3 particle diameters from the wall, possibly due to the bed structure in this particular bed. At the pellet scale, the hydrodynamics were found to be independent of \(N\). The results reported here demonstrate the capability of magnetic resonance velocity imaging for studying turbulent flows in packed beds, and they provide fundamental insight into the effect of \(N\) on the hydrodynamics.