Wall proximity effects on flow over a simple membrane spacer

Spacer-filled channels are employed in membrane modules in many industrial applications where feed-flow spacers (employed to separate membrane sheets and create flow channels) tend to enhance mass transport characteristics (and possibly) mitigate fouling and concentration polarization phenomena. In this work direct numerical simulation was performed for the flow in spacer-filled channels to obtain a better understanding of fluid flow phenomena in these assemblies. Reynolds numbers of 300, 500 and 800 were considered. The effect of spacer location was also studied for three different configurations: spacer at the centre of the channel, off-centre, and attached to the wall. Instantaneous velocity fields and flow structures, such as boundary layer separation on the walls and on the cylinder, eddies on the walls, recirculation regions and vortex shedding were investigated. A Fourier analysis was carried out on the time series velocity data. Using this analysis the Strouhal number was calculated and the development of the flow towards a broader turbulent state at higher Reynolds number was captured. Other statistical characteristics such as time-averaged velocities and wall shear rates are obtained and discussed. The average pressure loss was calculated for the channels and found to be highest for spacer at the centre of the channel and lowest for spacer attached to the wall.