Reverse osmosis separation processes are often performed using spiral wound mem- brane modules. Spacer meshes are placed between adjacent membrane layers to prevent them from coming into contact. Spacers promote mixing and increase mass transfer by disrupting fluid flow in the channel, and can reduce the chance of concen- tration polarization in the membrane. In this thesis a simplified membrane module configuration consisting of a straight channel with an array of centred cylindrical spacers is analyzed using direct numerical simulation. The purpose of the study is to gain a better understanding of the fluid flow and mass transfer in the channel, and to determine if any phenomena are periodic.

Solutes with Schmidt numbers of 1, 3, and 5 are examined for Reynolds numbers of 100, 300, and 500 (based on the cylinder diameter and bulk velocity when there is no blockage). Flow and concentration fields were analyzed for their impact on effects such as the vortex shedding, velocity spectra, pressure drop, shear rate, and mass transfer. Vortices are shed along the top and bottom of the cylinders, and their convection downstream has significant impacts on the local shear stress at the wall. As the Reynolds number increases, the local peak of the shear rate fluctuates, indicating that the flow is not periodic.

The concentration field becomes more dilute with an increase in both Reynolds and Schmidt numbers. The location of the local maxima and minima is dependent on the nature of vortex shedding. Mass transfer enhancement is strongly related to shear stresses and improved with increasing Reynolds number and Schmidt num- ber. The spatial distribution of the Sherwood number does not indicate a periodic concentration field for a Reynolds number above 100.

The scope of the work was limited by a need for computing resources in excess of what was available. Future work should include gaining additional data points for the proposed correlations by varying the Reynolds and Schmidt numbers. Additional configurations should be considered, such as an array of cylinders with an off-centre location, and an array of cylinders that follow a ”zig-zag” pattern.