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Developing a Hybrid Continuum-Molecular Method to Analyze Binary Gas Mixing and Separation Processes

Sabouri, Moslem | 2018

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 50997 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Darbandi, Masoud
  7. Abstract:
  8. The co-existance of rarefied and near-continuum flow regimes is widelyencountered in analyzing the multiscale flow problems, e.g., micro-and nanoflows. Previous investigations have revealed that the continuum-based simulation methods would suffer from the lack of accuracy to predict the rarefied flow regimes. On the other hand, the molecular simulation methods are not computationally efficient in simulating the near-continuum flow regimes. Therefore, the use of hybrid simulation methods has been recommended as a serious alternative to simulate the multiscale flow problems. These methods apply the molecular methods in solving the rarefied flow regions and the continuum methods in solving the near-continuum flow regions. The present work is devoted to developing a hybrid continuum-molecular simulation method to analyze the gas mixing and separation flows in domains with dual characteristics of rarefied and near-continuum flow regions. To achieve this, suitable continuum and molecular solvers are developed separately to analyze the gas mixture flows. The developed continuum and molecular solvers use the finite volume and the direct simulation Monte Carlo (DSMC) methods, respectively. After developing these individual solvers, they are used to study different problems in the fields of binary gas mixing and gas mixture separation. Comparing the results of these two solvers with each other, the physical validity of continuum solver is ensured in near-continuum flow regimes. Then, the shortcomings of continuum solver are shown in simulating highly rarefied flows. The results of these studies indicate that there are considerable effects of local flow rarefaction on weakening of the molecular diffusion and degrading the validity of linear constituitive laws. Combining the two individual continuum and molecular solvers, a hybrid continuum-molecular solver is suitably developed within an apaptive two-way state-based coupling algorithm. Using this hybrid solver, some known gas mixing and gas mixture separation problems are simulated to evaluate the accuracy and computational efficieny of the developed hybrid solver. The achieved results indicate that choosing appropriate numerical parameters; such as the continuum breakdown criterion and the algorithm of particle injection at the interface of two solvers, the computational cost can be reduced effectively while the accuracy of solution is preserved suitably
  9. Keywords:
  10. Hybrid Methods ; Finite Volume Method ; Molecular Simulation ; Gas Mixing ; Gases Separation ; Direct Simulation Monte Carlo (DSMC)Method ; Micro and Nano Flow

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