The CFD simulations in spacer-filled membrane modules reveal complex fluid structure in diamond-type spacers as flow directional changes are seen due to inclined spacer filaments. Despite this complex fluid behavior the flow remains steady for the Reynolds number considered in this study. However, the flow in a parallel-type spacer earlier thought to be less complicated has shown three dimensionality as well as time dependency. Due to this transient nature, the flow becomes asymmetric with flapping motion. The eddies appear immediately behind the transverse filaments, grow in size and finally dissipate in the center of the filaments. The flow unsteadiness also causes the shear and mass transfer rates to vary in time and major fluctuations are seen in the center of the spacer filaments which may be useful in the periodic removal of foulants from membrane surfaces, thus improving the process efficiency.

Computational fluid dynamics (CFD) simulations are carried out to examine the effect of geometricparameters of Tesla valve on flow patterns, pressure drop and flow diodicity. In forward flow, the flow is relatively smooth with less flow resistance. The low velocity regions are present at the entrance to the curved section and at thejunction of the curved section and the exit channel, where flow separation takes place. In reverse flow, the flow is quite irregular, and major recirculation zones are observed in the bottom branch, in addition to the top-curved and exit sections. The simulations with small time steps show that the flow is steady when the flow takes place in the forwarddirection. The flow is mostly transient; however, when the fluid flows in the reverse direction, particularly at higher Reynolds numbers. The effect of geometric parameters such as the angles subtended by the curved section (with thehorizontal) shows that optimal values of these angles exist. For a certain range of angles, diodicity is greater than 2.The effect of multi-staging of the Tesla valve is studied, and it is found that the flow unsteadiness and overall diodicity increase with the number of stages.