(618be) Mixing Distribution Pattern In a Glass Packed Bed As a Function of Hydrophobic/Hydrophilic Surface Treatment

In many petrochemical and biological processes packed beds play an important role increasing the efficiency of the separation or reaction mechanisms. Besides the geometry, distribution and pellets size, interfacial characteristics of the packing are critical. This study evaluates the effect that hydrophobic/hydrophilic properties of the packing have in the flow pattern distribution when a dyed drop impacts a water saturated glass bed. To produce hydrophilic surfaces, glass spheres of 0.5 mm diameter were cleaned with a HCl (30%)-Methanol (1:1 v/v) by ultrasonication to activate silanol functional groups followed by an ethanol washing in order to eliminate organic contaminants. On the other hand, hydrophobic surfaces were obtained carrying out the process mentioned hereinbefore, followed by a silanization reaction with thrimethylclorosilane as the active compound. Subsequently, surface properties were characterized by angle contact measurements. A Petri dish of 11.0 cm diameter was randomly packed with a monolayer of treated spheres and flow evolution was monitored after the release of the dyed drop from 1.0 cm above the surface. Image data was collected with a 30 fps digital video camera and analyzed with a custom designed image processing software. Dyed flow  intensity, flow front velocity and flow distribution were measured at several angle orientations in order to determine pattern symmetry and to obtain diffusion parameters. The results indicated that dyed fluid diffuses at very high rates with a star-shape pattern for the hydrophilic packing, whereas for the hydrophobic case the distribution is completely different, obtaining a highly circular front which evolves 600 times slower. The study analyzes the obtained data in terms of convection/diffusion models and discusses the surface interaction mechanisms.