Simulation of the Flow around Spacer Filaments between Narrow Channel Walls. 1. Hydrodynamics

Abstract

Insights into the effect of spacer filaments in membrane systems on the flow pattern were obtained using a computational fluid dynamics code. The flow patterns were examined for a single filament adjacent to the wall and centered in the channel and for three different spacer configurations, the cavity, zigzag, and submerged spacers, with variations in both the mesh length and filament diameter for Reynolds numbers ranging from 90 to 768. Large recirculation regions were formed behind the filaments, and the flow around the filament increased the shear stress on the wall. For an identical Reynolds number and filament diameter, a single filament adjacent to a membrane wall produced a larger recirculation region than a single filament in the center of the channel. For the cavity and submerged spacers, above a critical Reynolds number or mesh length, the recirculation regions between sequential filaments influenced each other and merged to form one large recirculation region between sequential filaments. In contrast, the zigzag spacer forced the channel flow into a zigzag pattern, which caused the recirculation region to reattach to the wall.

Entrance length effects on Graetz number scaling in laminar duct flows with periodic obstructions: Transport number correlations for spacer-filled membrane channel flows

“…D h = 2H, in agreement with the definition of the hydraulic diameter for infinite parallel plates without obstacles [2]. Note that various other definitions for the hydraulic diameter in channel flows with obstacles exist, e.g., based on the diameter of the obstacle [28] or based on the free passage (area or volume) [29,30]. The Prandtl number describes the ratio between viscous diffusion and thermal diffusion…”

Fluid dynamics of spacer filled rectangular and curvilinear channels

“…Furthermore, studies of fine flow structures in small independent cells and their impact on neighboring cells has not been reported in details. Recently, Koutsou et al [14] reported a 2D flow simulation in a rectangular channel in the presence of cylindrical turbulence promoters similar to a case reported by Schwinge et al [8,9]. They concluded that more realistic 3D simulations are needed for optimization of spacers.…”

“…They also reported 2D flow visualization and pressure drop. Schwinge et al [8,9] reported two-dimensional CFD studies on hydrodynamics, mass transfer enhancement and estimation of foulant deposits in spacer filled channels. The flow characteristics were examined for arrangements of individual filaments in three different configurations namely zigzag, cavity and submerged with variation in mesh length and filament diameters.…”

The effect of feed spacer geometry on membrane performance and concentration polarisation based on 3D CFD simulations

“…Secondly, the flow is assumed to be laminar and steady. Although this assumption is justifiable for the relatively low Reynolds number examined here, flow in a narrow spacer-filled channel can become unsteady and transitional at high inlet velocities [10,[44][45]. Thirdly, physical properties of the fluid are assumed to be constant and the adopted diffusion coefficient corresponds to a relatively low temperature range.…”