Study on the effects of spacer geometry in membrane feed channels using three-dimensional computational flow modeling

Shakaib, M.; Hasani, S. M. F.; Mahmood, M.

doi:10.1016/j.memsci.2007.03.010

Cited by 97 publications

(61 citation statements)

References 18 publications

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“…On the other hand, many works have been devoted to the CFD modeling of spacer-filled channels designed for other processes, such as: reverse osmosis, membrane distillation, ultra-filtration, etc. [6][7][8][9][10][11][12][13]. In accordance with these studies, the presence of the spacer significantly influences the fluid flow inside the channel in terms of pressure drops, concentration polarization, distribution of vortexes, recirculation zones, and shear stress.…”

Section: Introductionsupporting

confidence: 68%

CFD analysis of the fluid flow behavior in a reverse electrodialysis stack

Gurreri¹,

Tamburini²,

Cipollina³

et al. 2012

Desalination and Water Treatment

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Salinity Gradient Power by Reverse Electrodialysis (SGP-RE) technology allows the production of electricity from the different chemical potentials of two differently concentrated salty solutions flowing in alternate channels suitably separated by selective ion exchange membranes. In SGP-RE, as well as in conventional ElectroDialysis (ED) technology, the process performance dramatically depends on the stack geometry and the internal fluid dynamics conditions: optimizing the system geometry in order to guarantee lower pressure drops (DP) and uniform flow rates distribution within the channels is a topic of primary importance. Although literature studies on Computational Fluid Dynamics (CFD) analysis and optimization of spacer-filled channels have been recently increasing in number and range of applications, only a few efforts have been focused on the analysis of the overall performance of the process. In particular, the proper attention should be devoted to verify whether the spacer geometry optimization really represents the main factor affecting the overall process performance. In the present work, realized within the EU-FP7 funded REAPower project, CFD simulations were carried out in order to assess the effects of different parameters on the global process efficiency, such as the choice of spacer material and morphology, and the optimization of feed and blowdown distribution systems. Spacer material and morphology can affect the fluid dynamics inside each channel. In particular, the appropriate choice of net spacer material can influence the slip/no-slip condition of the flow on the spacer wires, thus significantly affecting the channel fluid dynamics in terms of pressure drops. A Unit Cell approach was adopted to investigate the effect of the different choices on the fluid flow along the channel. Also, the possibility of choosing a porous medium to substitute the net spacer was theoretically addressed. Such investigation focused on the porosity and the fiber radius required to respect the process constrains of pressure drops and mechanical stability. On the other hand, the overall pressure drops of a SGP-RE or ED stack can be considered as resulting from different contributions: the pressure drop relevant to the feed distributor, the pressure drop inside the channel, and the pressure drop in the discharging collector. The choice of the optimal stack geometry is, therefore, strongly related to the need of both minimizing each of the above terms and obtaining the most uniform feed streams distribution among the stack channels. In order to investigate such aspects, simulations were performed on a simplified ideal planar stack with either 50 spacer-less or 50 spacer-filled channels. The effect of the distribution/collector channel *Corresponding author. (2012) 390-403 Octoberthickness and geometry on single-channel flow rates and overall pressure drops in the system was analyzed and a significant influence of distributor layout and size on the overall process performance was found.

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Section: Introductionsupporting

confidence: 68%

CFD analysis of the fluid flow behavior in a reverse electrodialysis stack

Gurreri¹,

Tamburini²,

Cipollina³

et al. 2012

Desalination and Water Treatment

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“…In the partially woven configuration, one set of filaments remains straight, with each strand being in contact with the top and bottom plane alternatingly, while the other set is woven through the gaps between the first set of filaments [30]. The middle layer configuration is built based on the 'Parallel spacer' [2,40] and 'Middle layer spacer' [31] in the literature. The filaments are arranged in a similar manner to those in the nonwoven configuration, but one set of straight filaments has a smaller diameter and pierces through the other set of filaments whose diameter is the same as the channel height.…”

Section: Feed Spacer Geometrymentioning

confidence: 99%

“…Other types of spacers that have been considered in 3D CFD models include 'Parallel spacer' [2,40] and 'Middle layer spacer' [31], both consisting of thick filaments with a diameter equivalent to the channel height and thinner filaments piercing through the thick ones. However, 3D models of woven spacers with realistic spacer geometries are lacking.…”

Section: Introductionmentioning

confidence: 99%

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

Adjiman

2017

Journal of Membrane Science

126

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Feed spacers are used in spiral wound reverse osmosis (RO) membrane modules to keep the membrane sheets apart as well as to enhance mixing. They are beneficial to membrane performance but at the expense of additional pressure loss. In this study, four types of feed spacer configurations are investigated, with a total of 20 geometric variations based on commercially available spacers and selected filament angles. The impact of feed spacer design on membrane performance is investigated by means of three-dimensional (3D) computational fluid dynamics (CFD) simulations, where the solution-diffusion model is employed for water and solute transport through RO membranes.Numerical simulation results show that, for the operating and geometric conditions examined, fully woven spacers outperform other spacer configurations in mitigating concentration polarisation (CP).When designed with a mesh angle of 60º, fully woven spacers also deliver the highest water flux, although the associated pressure drops are slightly higher than their nonwoven counterparts. Middle layer geometries with a mesh angle of 30º produce the lowest water flux. On the other hand, spacers with a mesh angle of 90º show the lowest pressure drop among all the filament arrangements examined. Furthermore, the computational model presented here can also be used to predict membrane performance for a given feed spacer type and geometry.

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“…On the other hand, even at very low Reynolds numbers, the flow patterns in these channels may be very complex and characterized by very small structures, thus requiring very fine meshes to be properly simulated. The Unit Cell approach is the generally adopted solution to reliably simulate these channels [19,30,31,[33][34][35]39,41,42,[48][49][50]. The Unit Cell represents the repeating unit of the whole periodic domain which is typically investigated in CFD studies.…”

Section: Unit Cell Approachmentioning

confidence: 99%

“…Many CFD studies were performed by simulating the periodic domain of the spacer-filled channel (for more details, see section 3.1). Both commercially available spacers [29] and non-commercially available spacers [ [30][31][32][33][34][35] were simulated. In these works, various geometrical parameters of spacers made by overlapping two series of cylindrical filaments were investigated: angle between crossing filaments, filament spacing, filament size, and flow attack angle.…”

Section: Introductionmentioning

confidence: 99%

Pressure drop at low Reynolds numbers in woven-spacer-filled channels for membrane processes: CFD prediction and experimental validation

Gurreri

Tamburini

Cipollina

et al. 2017

DWt

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a b s t r a c tThe energy consumption due to pumping power is a crucial issue in membrane processes. Spacers provide mechanical stability and promote mixing, yet increasing pressure drop. Woven spacers and their behaviour at low Reynolds numbers are less studied in the literature. Nevertheless, they are typical of some membrane technologies, as reverse electrodialysis (RED). RED is a promising technology for electric power generation by the chemical potential difference of two salt solutions within a stack equipped by selective ion-exchange membranes. The mechanical energy required for pumping the feed solutions, can dramatically reduce the net power output. In this work computational fluid dynamics (CFD) simulations of spacer-filled channels at low Reynolds numbers were carried out in parallel with an experimental campaign focused on the collection of data for model validation. Woven spacers 280-480 μm thick were investigated at the flow rates typical of RED channels. The construction of the computational domain was based on measurements made by optical microscopy and micrometer. Fully developed flow conditions were assumed, thus, periodic boundary conditions were adopted (unit cell approach). The experiments were carried out in a flow cell with one channel. Pressure drops were measured with and without the spacer, in order to quantify the effect of inlet-outlet channel and identify the distributed pressure drops due to the woven nets. Experimental results showed that the distributed pressure drop along the spacer-filled channel for the cases investigated is around 40% of the overall pressure loss. The significant contribution of the manifolds is due to the relatively high velocity of the fluid entering and leaving the channel in radial direction in the inlet and outlet holes, as in the RED stacks commonly used. However, an improved geometry of the distribution and collection system can easily result in a significant reduction of hydraulic loss in this part of the stack. Therefore, the optimization of the spacer geometry is crucial. In this regard, a good agreement between CFD results and experimental data on hydraulic loss along the channel was found, thus confirming that a simple CFD model (as the one presented in this work) can be a powerful and cheap tool, able to efficiently evaluate the pressure drops within spacer-filled channels of any customised geometry.

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Study on the effects of spacer geometry in membrane feed channels using three-dimensional computational flow modeling

Cited by 97 publications

References 18 publications

CFD analysis of the fluid flow behavior in a reverse electrodialysis stack

CFD analysis of the fluid flow behavior in a reverse electrodialysis stack

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

Pressure drop at low Reynolds numbers in woven-spacer-filled channels for membrane processes: CFD prediction and experimental validation

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