Transport mechanisms in porous fins

Lotus-type fins are a class of porous metal foam having high aerothermal performance. We investigate the flow and scalar transport through a set of such fins by means of MRI-based velocimetry and concentration measurements. For compatibility with the measurement technique, magnified 3D-printed replicas are utilized, with water-based solutions as the working fluid. The choice of geometric parameters (fin spacing and thickness, porosity, and hole diameter) is based on previous thermal studies. The Reynolds number based on the mean pore diameter and inner velocity ranges from Re=80 to 3800. The velocity and vorticity fields show the formation of elongated jets, which impact on the successive fin, producing interacting wall-jets and eventually streamwise swirling motion. The random hole distribution causes the time mean streamlines to meander in a random-walk manner. The mechanical dispersion associated with this is evaluated using the 3D velocity data. Overall the flow measurements suggest that a change in regime occurs around Re=290, and we hypothesize that this coincides with the inception of unsteady/turbulent motion. This is supported by the measurements of concentration of an isokinetic nonbuoyant plume of scalar injected upstream of the stack of fins. The diffusion of scalar away from the injection point is significantly faster for Re>290.