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Simulation of Computational Fluid Dynamics Model of Seawater Desalination using Ion Concentration Polarization Phenomenon: Optimization and Performance Evaluation

Nasiri Avanaki, Masoud | 2025

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 58749 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Mohammadi, Ali Asghar
  7. Abstract:
  8. The depletion of freshwater resources in the world is a critical problem. Concentration polarization microfluidic desalination is a solution to solve this problem. In this study, the numerical simulation of the performance of the concentration polarization microfluidic desalination system was studied. For this purpose, an electrokinetic mathematical model was solved in COMSOL software to describe the transport of ions and their interaction with the electric field and fluid flow using the finite element method. The study of the mass transfer flux showed that the main mechanism for the formation of the concentration polarization phenomenon is the electric migration flux of sodium and chloride ions, which at high voltages leads to the formation of a type II electroosmotic current. Also, the study of the voltage-current curve showed that this system operates in three ohmic, limiting and over-limiting regimes. In the ohmic and limiting regime, the type I electroosmotic current is significant in the nanochannels, and in the over-limiting regime, the type II electroosmotic current is significant in the vicinity of the nanochannels. On the other hand, the study of the distribution of sodium ion concentration in the system showed that the formation of the ion discharge zone occurs in the ohmic regime. Also, in the limiting regime, its expansion stops, and with the formation of vortices in the overlimiting regime, the ion discharge zone expands, reducing energy consumption by 12% and increasing the salt discharge rate by 50%. Also, operating the system in the overlimiting regime reduces the selectivity index of nanochannels and reduces the lifetime of nanochannels. Further, by studying the effect of voltage on the functional parameters of the system, it was found that the most optimal state of voltage application is the state in which all voltages applied in the bifurcated microchannel (anodic) are equal to each other and greater than the voltage applied in the rectangular microchannel (cathode). Finally, using the results of studying the effect of voltage on the functional parameters of the system, the flow rate of the system was increased by using the design of a circular microfluidic system. In this section, three designs were presented, the most optimal of which is the centralized circular microfluidic system. This system, with its optimal desalination performance, and by increasing the desalination microchannels, increased the system flow rate up to 8 times the initial value
  9. Keywords:
  10. Microfluidic System ; Numerical Simulation ; Desalination ; Nano Channel ; Ion Concentration Polarization Phenomenon ; Computational Fluid Dynamics (CFD)

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