Effects of permeability on the flow past porous spheres at moderate Reynolds number: A PIV experimental study

Porous particles are commonly used in chemical industries and the existence of porous structures as well as porous-fluid interfaces can essentially affect flow characteristics of porous particles, which is crucial for controlling multiphase flow processes and improving energy efficiency. Herein, a particle image velocimetry (PIV) experimental study was conducted to investigate the effects of permeability and Reynolds number (Re) on the flow characteristics of porous particles. For any given Darcy numbers Da at the range of 0 similar to 1.28 x 10(-3), the wake lengths behind porous spheres are approximately linear to log(10)Re. When Da >= 4.90x10(-5), evidences suggest that wake lengths behind porous spheres exhibit substantial enlargement as compared to their solid counterparts owing to the heightened push effect exerted by penetration flows. Furthermore, a trough in the profile of wake lengths behind porous spheres was found for Da of 5x10(-6)similar to 2x10(-5) and Re of 400 similar to 1200, which is induced by the combined influence of permeability and surface roughness of porous spheres. An empirical correlation of wake length L=f(Re,Da) was proposed with a clear physical meaning and a good prediction accuracy MRE=8.18 %.