Feed Spacer Geometry Research Articles

Performance analysis of cross-flow forward osmosis membrane modules with mesh feed spacer using three-dimensional computational fluid dynamics simulations

This study presents a three-dimensional computational fluid dynamics (CFD) model to characterize the effect of mesh feed spacer's geometry on the performance of cross-flow forward osmosis (FO) membranes. The performance of FO membranes against various spacer's geometrical parameters are investigated in terms of permeate water flux, reverse solute flux, concentrative external concentration polarization (CECP) on the membrane, mass transfer coefficient, and longitudinal pressure drop of the feed channel. Also, the membrane support layer is explicitly modeled as a porous medium; the relation between the internal and external concentration polarization phenomena, under different spacer's geometrical variables, is exhibited for different porosities. Our results reveal that the feed spacer's geometrical parameters affect the performance of FO membranes by influencing the volume of the low-circulation or dead zones, and the shear rate on the membrane active layer. The CECP modulus is mainly dominated by the reverse solute flux and the volume of the dead zone on the membrane, while the mass transfer coefficient and the longitudinal pressure drop are more impacted by the exerted shear stress on the membrane. Furthermore, the results of our model demonstrates that the reduction of internal concentration polarization results in an increase in CECP and a magnified impact of the spacer's geometry on the CECP modulus.

Performance Assessment of SWRO Spiral-Wound Membrane Modules with Different Feed Spacer Dimensions

Reverse osmosis is the leading process in seawater desalination. However, it is still an energy intensive technology. Feed spacer geometry design is a key factor in reverse osmosis spiral wound membrane module performance. Correlations obtained from experimental work and computational fluid dynamics modeling were used in a computational tool to simulate the impact of different feed spacer geometries in seawater reverse osmosis spiral wound membrane modules with different permeability coefficients in pressure vessels with 6, 7 and 8 elements. The aim of this work was to carry out a comparative analysis of the effect of different feed spacer geometries in combination with the water and solute permeability coefficients on seawater reverse osmosis spiral wound membrane modules performance. The results showed a higher impact of feed spacer geometries in the membrane with the highest production (highest water permeability coefficient). It was also found that the impact of feed spacer geometry increased with the number of spiral wound membrane modules in series in the pressure vessel. Installation of different feed spacer geometries in reverse osmosis membranes depending on the operating conditions could improve the performance of seawater reverse osmosis systems in terms of energy consumption and permeate quality.

3D CFD study of the effect of multi-layer spacers on membrane performance under steady flow

Multi-layer feed channel spacers have shown superior mass transfer enhancement than conventional dual-layer spacers used in reverse osmosis (RO) spiral wound membrane modules. However, mass transfer indicators do not directly address the economic advantages of multi-layer spacers. To allow for a direct economic comparison of spacer designs, a simplified multi-scale techno-economic model is proposed which can provide useful cost trends. A total of 8 feed spacer geometries with different attack angles (α = 0–60°) and filament sizes (df/hch = 0.4–0.6) are first investigated using 3D-CFD. Multi-layer spacers typically increase both Sherwood number (~12%) and friction factor (~140%). The techno-economic model is then used to assess the impact of these changes on the total processing cost for RO. The latter analysis found that larger pressure drops associated with multi-layer spacers in long channels have little impact on total water processing cost for RO, with multi-layer spacers showing lower total processing costs (by 2–4%) than the dual-layer spacer for both seawater and brackish water RO. Novel spacer designs should therefore emphasise flux enhancement. The importance of including energy recovery for a more accurate economic analysis is highlighted, especially for systems with low recovery ratio.

Feed Spacer Geometries and Permeability Coefficients. Effect on the Performance in BWRO Spriral-Wound Membrane Modules

Reverse osmosis (RO) is the most widely used technology to desalinate brackish water and seawater. Significant efforts have been made in recent decades to improve RO efficiency. Feed spacer geometry design is a very important factor in RO membrane performance. In this work, correlations based on computational fluid dynamics and experimental work were applied in an algorithm to simulate the effect of different feed spacer geometries in full-scale brackish water reverse osmosis (BWRO) membranes with different permeability coefficients. The aim of this work was to evaluate the impact of feed spacers in conjunction with the permeability coefficients on membrane performance. The results showed a greater impact of feed spacer geometries in the membrane with the highest water permeability coefficient (A). Studying only one single element in a series, variations due to feed spacer geometries were observed in specific energy consumption ( S E C ) and permeate concentration ( C p ) of about 6.83% and 10.42%, respectively. Allowing the rolling of commercial membranes with different feed spacer geometries depending on the operating conditions could optimize the RO process.

Biofouling removal in spiral-wound nanofiltration elements using two-phase flow cleaning

Biofouling has detrimental effects on the feed channel pressure drop and the permeate flux in high-pressure membrane processes such as NF and RO. Two-phase flow cleaning is a chemical-free technique that is able to remove such biofilms. This paper presents a study into the effects of the gas/liquid ratio, feed spacer geometry, applied pressure and liquid velocity on the efficiency of two-phase flow cleaning in spiral-wound nanofiltration elements. A high-speed camera, optical coherence tomography and scanning electron microscopy were used to study biofouling and its removal. Our results show that two conditions must be met to ensure that a sufficiently high shear force is applied to biofilms on membrane and spacer surfaces. A good bubble distribution in the channel is the first requirement. While it is mainly the structure of the feed spacer that controls bubble flow and bubble size, a minimum gas/liquid ratio of 0.5 is necessary to achieve a good bubble distribution. The second condition is the use of a sufficiently high liquid velocity during cleaning. The bubble velocity was found to be 3.5–5.5 times as high as the used liquid velocity, and responsible for a marked improvement in the flux recovery.

Biofouling in spiral wound membrane systems: Three-dimensional CFD model based evaluation of experimental data

A three-dimensional (3D) computational model describing fluid dynamics and biofouling of feed channels of spiral wound reverse osmosis and nanofiltration membrane systems was developed based on results from practice and experimental studies. In the model simulations the same feed spacer geometry as applied in practice and the experimental studies was used. The 3D mathematical model showed the same trends for (i) feed channel pressure drop, (ii) biomass accumulation, (iii) velocity distribution profile, resulting in regions of low and high liquid flow velocity also named channeling. The numerical model predicted a dominant biomass growth on the feed spacer, consistent with direct in situ observations on biofouling of spiral wound membrane modules and monitors using Magnetic Resonance Imaging (MRI). The model confirms experimental results that feed spacer fouling is more important than membrane fouling. The paper shows that mathematical modeling techniques have evolved to a stage that they can be used hand-in-hand with experiments to understand the processes involved in membrane fouling.