The large energy consumption of membrane desalination process has encouraged researchers to explore different spacer designs using Computational Fluid Dynamics (CFD) for maximizing permeate per unit of energy consumed. In previous studies of zigzag spacer designs, the filaments are modeled as circular cross sections in a two-dimensional geometry under the assumption that the flow is oriented normal to the filaments. In this work, we consider the 45° orientation of the flow towards the three-dimensional zigzag spacer unit, which projects the circular cross section of the filament as elliptical in a simplified twodimensional domain. OpenFOAM was used to simulate the mass transfer enhancement in a reverse-osmosis desalination unit employing spiral wound membranes lined with zigzag spacer filaments. Properties that impact the concentration polarization and hence permeate flux were analyzed in the domain with elliptical filaments as well as a domain with circular filaments to draw suitable comparisons. The range of variation in characteristic parameters across the domain between the two different configurations is determined. It was concluded that ignoring the elliptical projection of circular filaments to the flow direction, can introduce significant margin of error in the estimation of mass transfer coefficient.
In regions with limited potable water availability, membrane desalination is being employed to filter water using a pressure-driven approach. Because of the high energy consumption required to produce the pressure differential needed for this method, researchers have been trying different geometric designs of spacer filaments to enhance the amount of permeate flux in terms of energy utilization. The purpose of spacer filaments is to support membranes structurally and induce turbulent mixing in spiral wound membrane desalination. In this paper, the improvement of mass transfer in desalination driven by reverse osmosis has been studied using Computational Fluid Dynamics (CFD) with the introduction of spiral wound membranes that are lined with spacer filaments in a zig-zag formation having alternating diameters for strands. The fluid flow characteristics for a 2-dimensional geometric model were resolved using the open-source program OpenFOAM by changing the Reynolds number to just before the inception of instabilities. Ratios of alternate strand diameters were also varied between one and two. Based on a detailed analysis of velocity contours, pressure distribution, wall shear stresses, and steady-state vortex systems, the research findings offer guidance for employing alternating strand design in zig-zag formation for optimum mass transfer and minimal pressure drop when accounting for concentration polarization.
Membrane desalination is a pressure driven process which is being employed on a large scale in areas which do not have an easy access to fresh water resources. The large energy consumption of this process has encouraged researchers to explore the different spacer designs for maximizing permeate per unit of energy consumed. Computational fluid fynamics (CFD) was used to simulate the mass transfer enhancement in a reverse-osmosis desalination unit employing spiral wound membranes lined with zigzag spacer filaments of alternating diameters. Finite Volume based open source software OpenFoam was used to resolve the flow properties in a two-dimensional model by varying the Reynolds number until the onset of instability. Diamters of alternate strands were varied between ratios of 1, 1.5 and 2. The research provides guidelines based on comprehensive data set of velocity contours, pressure distribution, wall shear stresses and steady state vortex systems for using alternating strand design in zigzag configuration for maximum mass transfer and least pressure drop taking into account the concentration polarization.
This paper discusses the results of a study regarding the impact of using Project-Based Learning (PBL) to enhance the understanding of the concepts related to Pipe Network Analysis, a subtopic of Fluid Mechanics, studied by students enrolled in a mechanical engineering degree. It has been frequently reported by students and professors alike, that a lecture-only approach is not effective in terms of helping students grasp the fundamentals of a subject, nor does it help students in actual problem solving where different variables have to be catered to, which may have been ignored in a conventional lecture. Therefore, in this study, a more open-ended, complex project-based approach was used in addition to the lectures on the subject of Pipe Network Analysis. The project required students to design a pipe network for a scaled setup based on specified fluid flow and pressure head requirements at different nodes. An experimental setup that implemented these pipe networks was also developed in order to validate the theoretical results. The students’ grades and their documented responses were used as the criterion for compiling and analyzing the results. We also describe how we incorporated PBL into the classrooms in order to improve the learning experience, and evaluate the efficacy of the proposed method. The overall results show that the students were proactively engaged in the PBL activity, linking their knowledge to the real world, which ultimately led to improved concept development.
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