Yingsong Zheng | University of Victoria (original) (raw)

Papers by Yingsong Zheng

Research paper thumbnail of Scaled Navier-Stokes-Fourier Equations for Gas Flow and Heat Transfer Phenomena in Micro- and Nanosystems

ASME 4th International Conference on Nanochannels, Microchannels, and Minichannels, Parts A and B, 2006

Scaled Navier-Stokes-Fourier Equations for Gas Flow and Heat Transfer Phenomena in Micro-and Nano... more Scaled Navier-Stokes-Fourier Equations for Gas Flow and Heat Transfer Phenomena in Micro-and Nanosystems. [ASME Conference Proceedings 2006, 369 (2006)]. Yingsong Zheng, Jason M. Reese, Thomas J. Scanlon, Duncan A. Lockerby. Abstract. ...

Research paper thumbnail of Ellipsoidal statistical Bhatnagar–Gross–Krook model with velocity-dependent collision frequency

Physics of Fluids, 2005

In this paper, an ellipsoidal statistical ͑ES͒ Bhatnagar-Gross-Krook ͑BGK͒-type kinetic model wit... more In this paper, an ellipsoidal statistical ͑ES͒ Bhatnagar-Gross-Krook ͑BGK͒-type kinetic model with velocity-dependent collision frequency is proposed and further numerically tested for one-dimensional shock waves and planar Couette flow at steady state for hard sphere molecules. In this new kinetic model, a physically meaningful expression for the velocity-dependent collision frequency derived from the Boltzmann equation is used, while the important properties for a kinetic model are retained at the same time. This kinetic model can be simplified to the classical ES-BGK model and the BGK model with velocity-dependent collision frequency for suitable choices of parameters. The H theorem for this new kinetic model has so far been proven only for small Knudsen numbers. The numerical method used here for kinetic models is based on Mieussens's discrete velocity model ͓L. Mieussens, J. Comput. Phys. 162, 429 ͑2000͔͒. Computational results from the kinetic models ͑including the BGK model, the ES-BGK model, the BGK model with velocity-dependent collision frequency, and this new kinetic model͒ are compared to results obtained from the direct simulation Monte Carlo ͑DSMC͒ method. It is found that results obtained from this new kinetic model lie in between results from the ES-BGK model and results from the BGK model with velocity-dependent collision frequency. For one-dimensional shock waves, results from this new kinetic model fit best with results from the DSMC, while for planar Couette flow, the classical ES-BGK model is suggested.

Research paper thumbnail of Modified Model for Effective Thermal Conductivity of Nanofluids Containing Carbon Nanotubes

Journal of Thermophysics and Heat Transfer, 2007

Research paper thumbnail of Nanomaterials for Efficiently Lowering the Freezing Point of Anti-Freeze Coolants

Journal of Nanoscience and Nanotechnology, 2007

In this paper, we report, for the first time, the effect of the lowered freezing point in a 50% w... more In this paper, we report, for the first time, the effect of the lowered freezing point in a 50% water/50% anti-freeze coolant (PAC) or 50% water/50% ethylene glycol (EG) solution by the addition of carbon nanotubes and other particles. The experimental results indicated that the nano materials are much more efficient (hundreds fold) in lowering the freezing point than the regular ionic materials (e.g., NaCl). The possible explanation for this interesting phenomenon is the colligative property of fluid and relative small size of nano material. It is quite certain that the carbon nanotubes and metal oxide nano particles could be a wonderful candidate for the nano coolant application because they could not only increase the thermal conductivity, but also efficiently lower the freezing point of traditional coolants.

Research paper thumbnail of Comparing macroscopic continuum models for rarefied gas dynamics: A new test method

Journal of Computational Physics, 2006

We propose a new test method for investigating which macroscopic continuum models, among the many... more We propose a new test method for investigating which macroscopic continuum models, among the many existing models, give the best description of rarefied gas flows over a range of Knudsen numbers. The merits of our method are: no boundary conditions for the continuum models are needed, no coupled governing equations are solved, while the Knudsen layer is still considered. This distinguishes our proposed test method from other existing techniques (such as stability analysis in time and space, computations of sound speed and dispersion, and the shock wave structure problem). Our method relies on accurate, essentially noise-free, solutions of the basic microscopic kinetic equation, e.g. the Boltzmann equation or a kinetic model equation; in this paper, the BGK model and the ES-BGK model equations are considered.

Research paper thumbnail of Computing the near-wall region in gas micro-and nanofluidics: critical Knudsen layer phenomena

Journal of Computational …, 2007

In order to capture critical near-wall phenomena in gas micro-and nanoflows within conventional C... more In order to capture critical near-wall phenomena in gas micro-and nanoflows within conventional CFD codes, we present scaled Navier-Stokes-Fourier (NSF) constitutive relations. Our scaling is mathematically equivalent to applying an 'effective' viscosity to the original constitutive relations. An expression for this 'effective' transport coefficient is obtained from the half-space Kramer's flow problem. The advantage of our model over the traditional NSF equations is that the non-equilibrium flow near to the wall (the momentum Knudsen layer) can be described. Its advantage over higher-order hydrodynamic models for gas micro-and nanoflows is that the boundary conditions remain the same as required for the traditional NSF equations, so modifications to current CFD codes (provided they are already capable of modelling slip at solid surfaces) would be minimal. As an application example, we apply our model to the isothermal problem of a micro-sphere moving through a gas: we show that our model gives excellent results in the Knudsen number range Kn 0.1 and acceptable results up to Kn ≈ 0.25. This is much better than the traditional NSF model with non-scaled constitutive relations.

Research paper thumbnail of Scaled Navier-Stokes-Fourier Equations for Gas Flow and Heat Transfer Phenomena in Micro- and Nanosystems

ASME 4th International Conference on Nanochannels, Microchannels, and Minichannels, Parts A and B, 2006

Scaled Navier-Stokes-Fourier Equations for Gas Flow and Heat Transfer Phenomena in Micro-and Nano... more Scaled Navier-Stokes-Fourier Equations for Gas Flow and Heat Transfer Phenomena in Micro-and Nanosystems. [ASME Conference Proceedings 2006, 369 (2006)]. Yingsong Zheng, Jason M. Reese, Thomas J. Scanlon, Duncan A. Lockerby. Abstract. ...

Research paper thumbnail of Ellipsoidal statistical Bhatnagar–Gross–Krook model with velocity-dependent collision frequency

Physics of Fluids, 2005

In this paper, an ellipsoidal statistical ͑ES͒ Bhatnagar-Gross-Krook ͑BGK͒-type kinetic model wit... more In this paper, an ellipsoidal statistical ͑ES͒ Bhatnagar-Gross-Krook ͑BGK͒-type kinetic model with velocity-dependent collision frequency is proposed and further numerically tested for one-dimensional shock waves and planar Couette flow at steady state for hard sphere molecules. In this new kinetic model, a physically meaningful expression for the velocity-dependent collision frequency derived from the Boltzmann equation is used, while the important properties for a kinetic model are retained at the same time. This kinetic model can be simplified to the classical ES-BGK model and the BGK model with velocity-dependent collision frequency for suitable choices of parameters. The H theorem for this new kinetic model has so far been proven only for small Knudsen numbers. The numerical method used here for kinetic models is based on Mieussens's discrete velocity model ͓L. Mieussens, J. Comput. Phys. 162, 429 ͑2000͔͒. Computational results from the kinetic models ͑including the BGK model, the ES-BGK model, the BGK model with velocity-dependent collision frequency, and this new kinetic model͒ are compared to results obtained from the direct simulation Monte Carlo ͑DSMC͒ method. It is found that results obtained from this new kinetic model lie in between results from the ES-BGK model and results from the BGK model with velocity-dependent collision frequency. For one-dimensional shock waves, results from this new kinetic model fit best with results from the DSMC, while for planar Couette flow, the classical ES-BGK model is suggested.

Research paper thumbnail of Modified Model for Effective Thermal Conductivity of Nanofluids Containing Carbon Nanotubes

Journal of Thermophysics and Heat Transfer, 2007

Research paper thumbnail of Nanomaterials for Efficiently Lowering the Freezing Point of Anti-Freeze Coolants

Journal of Nanoscience and Nanotechnology, 2007

In this paper, we report, for the first time, the effect of the lowered freezing point in a 50% w... more In this paper, we report, for the first time, the effect of the lowered freezing point in a 50% water/50% anti-freeze coolant (PAC) or 50% water/50% ethylene glycol (EG) solution by the addition of carbon nanotubes and other particles. The experimental results indicated that the nano materials are much more efficient (hundreds fold) in lowering the freezing point than the regular ionic materials (e.g., NaCl). The possible explanation for this interesting phenomenon is the colligative property of fluid and relative small size of nano material. It is quite certain that the carbon nanotubes and metal oxide nano particles could be a wonderful candidate for the nano coolant application because they could not only increase the thermal conductivity, but also efficiently lower the freezing point of traditional coolants.

Research paper thumbnail of Comparing macroscopic continuum models for rarefied gas dynamics: A new test method

Journal of Computational Physics, 2006

We propose a new test method for investigating which macroscopic continuum models, among the many... more We propose a new test method for investigating which macroscopic continuum models, among the many existing models, give the best description of rarefied gas flows over a range of Knudsen numbers. The merits of our method are: no boundary conditions for the continuum models are needed, no coupled governing equations are solved, while the Knudsen layer is still considered. This distinguishes our proposed test method from other existing techniques (such as stability analysis in time and space, computations of sound speed and dispersion, and the shock wave structure problem). Our method relies on accurate, essentially noise-free, solutions of the basic microscopic kinetic equation, e.g. the Boltzmann equation or a kinetic model equation; in this paper, the BGK model and the ES-BGK model equations are considered.

Research paper thumbnail of Computing the near-wall region in gas micro-and nanofluidics: critical Knudsen layer phenomena

Journal of Computational …, 2007

In order to capture critical near-wall phenomena in gas micro-and nanoflows within conventional C... more In order to capture critical near-wall phenomena in gas micro-and nanoflows within conventional CFD codes, we present scaled Navier-Stokes-Fourier (NSF) constitutive relations. Our scaling is mathematically equivalent to applying an 'effective' viscosity to the original constitutive relations. An expression for this 'effective' transport coefficient is obtained from the half-space Kramer's flow problem. The advantage of our model over the traditional NSF equations is that the non-equilibrium flow near to the wall (the momentum Knudsen layer) can be described. Its advantage over higher-order hydrodynamic models for gas micro-and nanoflows is that the boundary conditions remain the same as required for the traditional NSF equations, so modifications to current CFD codes (provided they are already capable of modelling slip at solid surfaces) would be minimal. As an application example, we apply our model to the isothermal problem of a micro-sphere moving through a gas: we show that our model gives excellent results in the Knudsen number range Kn 0.1 and acceptable results up to Kn ≈ 0.25. This is much better than the traditional NSF model with non-scaled constitutive relations.