Analysis of wall shear stress on the outside-in type hollow fiber membrane modules by CFD simulation (original) (raw)
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Bench Scale Testing of Next Generation Hollow Fiber Membrane Modules
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Hollow-fibre membrane module design: comparison of different curved geometries with Dean vortices
Journal of Membrane Science, 2001
The performance of several designs of curved membrane modules with Dean vortices was compared through experiments using a colloidal bentonite suspension and cellulose acetate hollow-fibre ultrafiltration (UF) membranes. The different module geometries were: straight, helically coiled, twisted and sinusoidal, or meander-shaped. The experiments show a remarkable increase in mass transfer in curved modules as compared to conventional straight ones. Comparisons were made for modules equipped with the same hollow fibres and the same Dean number (De) for a given Reynolds number (Re). At the same Dean number, all the curved geometries gave the same limiting permeate flux. A mass transfer correlation relating limiting UF flux with the mean wall shear stress has been obtained.
Journal of Membrane Science, 2010
The aim of this study was to analyze the influence of hollow fiber module design, specially packing density, and filtration operating mode on the filtration performance. In order to perform this analysis, a model based on the finite element method was used to simulate numerically the flow and filtration velocity along the fiber. An annular region of fluid surrounding the fiber was considered in order to account for the packing density˚of the module. The originality of this approach lies in the study of fiber density effect on the hydrodynamic conditions, both for inside/out (IO) and outside/in (OI) filtration modes. The numerical simulations of fluid flow have shown a modification of the axial filtration velocity profile with packing density. When the density of fibers was high, filtration took place preferentially in the bottom of the fiber. In contrast, when the packing density was low, permeate flow was higher at the top of the fiber, i.e. the filtration module. Two experimental hollow fiber modules with two packing densities were tested and showed good agreement with the numerical data. These results underline the variations of filtration velocity along the fiber that will allow some predictions on fouling deposit to be done.
MODELING OF HOLLOW FIBER TRANSVERSE FLOW MODULES USING CFD
This work was conducted in collaboration with GKSS Forschungszentrum and TU-Wien (Vienna University of Technology), in order to find the optimal configuration of a hollow-fiber membrane module with the application of computational fluid dynamics. This module is used in a humidification /dehumidification system. The simulated hollow-fiber module is composed of five frames with the fibers placed perpendicular to the main flow direction. Different geometries were compared for different parameters such as fluid dynamics, pressure drop and mass transfer. In order to simulate the mass transfer, an analogy between heat and mass transfer was used. One of the most important issues of this research was mesh generation, involving, as main problems, the quality and the achievement of acceptable number of cells. Realizable k-ε model modeling turbulence and second order discretization scheme for pressure were used, in order to obtain the most accurate results. The optimized parameters were veloci...
The impact of baffle orientation on the performance of the hollow fiber membrane
DESALINATION AND WATER TREATMENT, 2017
In this work, a new design of baffle is suggested in order to investigate the potential enhancement of mass and heat transfer fluxes in a hollow fiber membrane distillation module using Computational Fluid Dynamic (CFD) analysis. The number of baffle, gap height and the packing density are investigated in order to maintain the trade-off between the enhancement of mass flux and the pressure drop increase across baffles. The CFD simulation is performed in order to predict local mass fluxes, the temperature polarization coefficient (TPC), as well as the thermal efficiency of the hollow fiber membrane distillation at different design parameters. The CFD simulation results showed that the membrane module of 1.25-diameter pitch (50% packing density), eight baffle supports per unit length and at 0.075 mm gap is a good compromise between performance enhancement and pressure drop across baffles. The numerical results indicated that by adding baffles to hollow fiber membrane distillation, the mass flux is enhanced by 25% higher than that of the original module design. This is due to a reduction in thermal boundary layer resistance and increase in mass-transfer coefficient of the membrane distillation. The TPC of the module with a baffle is 16% higher than that of the module without a baffle. This increase is mainly due to the presence of turbulence flow as a result of improved hydrodynamic process. Accordingly, the thermal efficiency also increases by 16% due to enhancement made in both mass flux and TPC. However, the downside of adding baffles is relatively higher pumping power in the order of 20% higher than traditional module.
Journal of Membrane Science, 2016
The use of gas permeable membranes for bubbleless aeration is of increasing interest due to the energy savings it affords in wastewater treatment applications. However, flow maldistributions are a major factor in the impedance of mass transfer efficiency. In this study, the effect of module configuration on the hydrodynamic conditions and gas transfer properties of various submerged hollow fibre bundles was investigated. Flow patterns and velocity profiles within fibre bundles were predicted numerically using computational fluid dynamics (CFD) and the model was validated by tracer-response experiments. In addition, the effect of fibre spacing and bundle size on the aeration rate of various modules was evaluated experimentally. Previous studies typically base performance evaluations on the liquid inlet velocity or an average velocity, an approach which neglects the effect of geometric features within modules. The use of validated CFD simulations provides more detailed information for performance assessment. It was shown that specific oxygen transfer rates declines significantly with increasing numbers of fibres in a bundle. However, the same trend was not observed when the fibre spacing is increased. A correlation was proposed for the prediction of the overall mass transfer coefficient utilizing the local velocity values obtained from the validated CFD model.
Analysis on a vibration character of hollow fiber membrane bundle in MBR
Maejo International Journal of Energy and Environmental Communication
We have focused on membrane vibration in MBR to find an effective design for the reduction of membrane fouling. In the previous study, we developed a direct measurement method for membrane vibration of a hollow fiber membrane (HFM) using an accelerometer (ACM). In this study, we studied on vibration characters on an HFM bundle in a practical membrane module in MBR using the ACMs in a large transparent water tank. Three ACMs were attached at the middle (P1), top (P2) and bottom (P3) position along a center line in the HFM bundle in which air was supplied from a diffuser below the membrane module with different aeration rates from 0 to 250 L/min. The acceleration of membrane vibration time series for the X-axis direction (left-right displacement) and Z-axis direction (back-front displacement) was recorded at three positions. The average vibration amplitudes of the acceleration along both directions at each position were increased as the aeration rate was increased. The HFM bundle show...
Proceedings of the Water Environment Federation, 2010
The main drawback of MBR systems is the fouling of the membrane, which is decrease and/or prevented through gas sparging. However, gas sparging practices are based on rules of thumb or a trial-and-error approaches which are tedious, very time-consuming and do not necessarily provide optimal fouling control. Therefore, dedicated experiments are needed to fully understand the hydrodynamics of this two-phase flow. This work focus on the validation of extensive experiments using a pilot-scale hollow fiber GE-Zenon submerged MBR against computational fluid dynamics (CFD). It was found that the order of magnitude from the CFD model is similar compared to experimental data in magnitude based on the shear intensity contours and the overall average. However, some differences in the distribution and magnitude of shear intensity throughout the pilot-scale submerged MBR system were observed. Cumulative frequencies were considered to compare the CFD results and the experimental data. It was found that below the 50 th percentile, the CFD and experimental data was similar (error less than 8 %). At higher shear intensity, the differenced between the simulation and the experimental data increase up to 17 %. These were likely due to the approximations made in developing the CFD model (i.e. rigid membrane modules, no water-air air flow through the fibers). Although further improvements are needed to use the CFD model for optimization, the results from the present study are promising.
2015
An important consideration during product development is the sustainability level of a product. Thus, several tools and methods have been developed to assess product sustainability. However, most of current tools focus only on the environmental element without considering two important sustainability elements such economic and social elements. Other tools are limited to the cradle-to-gate system boundary, which covers two phases of the product life cycle from raw material extraction to the end of the manufacturing stage. Users need to understand the mathematical calculations and tools needed to achieve this purpose. Hence, this paper developed a comprehensive method for assessing the sustainability of product development considering all sustainability elements from cradle-to-grave. A graphical user interface (GUI) was developed for ease of use from the structured methodology. The developed GUI was embedded with the fuzzy logic calculation under the Matlab GUI platform with codes and...