Effects of spacer geometry on pressure drop, mass transfer, mixing behavior, and residence time distribution

Net-type turbulence promoters or grids, so-called spacers, play an important role in membrane systems referring to problems of mass transfer, homogenizing and mixing behavior. In spiral wound modules and electrodialysis stacks spacers have several functions as supporting nets (stabilisators) and as turbulence promoters to increase mass transfer rates and reduce fouling layers. Spacers show a number of geometric and fluid-dynamic parameters like, e.g., the distance between two grid rods (wavelength), the inclination angle of the grid rods and the Reynolds number. The effects of these parameters on the local flow and mass transport phenomena in narrow rectangular ducts including different spacers are investigated in gas flows in a wind tunnel. For this purpose spacers were enlarged geometrically similar and a fundamental study of the geometric parameters, based on the results of Schock [1], led to a new definition of the hydraulic diameter of spacers.