The Experts below are selected from a list of 267 Experts worldwide ranked by ideXlab platform
Felix Sharipov - One of the best experts on this subject based on the ideXlab platform.
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influence of quantum intermolecular interaction on internal flows of Rarefied Gases
Vacuum, 2018Co-Authors: Felix SharipovAbstract:Abstract In order to model gaseous flows over the whole temperature range beginning from 1 K, the intermolecular interaction should be considered on the basis of quantum approach. Such a consideration becomes important in case of light Gases like helium and hydrogen. Recently, the direct simulation Monte Carlo (DSMC) method widely used to calculate flows of Gases has been generalized to implement the quantum approach to intermolecular collisions. To evaluate the influence of the quantum scattering on typical flows of light Gases, a benchmark problem has been solved for two helium isotopes 3He and 4He using an ab initio potential. More specifically, the flow-rate and flow-field of helium flowing through an orifice have been calculated over the temperature range from 1 K to 300 K for various values of the pressure ratio with the numerical error of 0.5%. As expected, no influence of the quantum effects on the flow-rate has been detected for the temperature 300 K. Though, the quantum approach requires less computational effort than the classical one at this temperature. For temperatures lower than 300 K, the influence of the quantum effects exceed the numerical error and reaches 41% at the temperature of 3 K. In this case, the quantum interaction is the only approach to model gas flows.
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sound propagation through a binary mixture of Rarefied Gases at arbitrary sound frequency
European Journal of Mechanics B-fluids, 2016Co-Authors: Denize Kalempa, Felix SharipovAbstract:Abstract The sound propagation through a binary mixture of Rarefied Gases in a semi-infinite space is investigated on the basis of the McCormack model to the linearized Boltzmann equation. The source of sound waves is an infinite and flat plate oscillating in the direction normal to its own plane. It is considered a fully established oscillation so that the solution of the kinetic equation depends on time harmonically. The diffuse scattering gas–surface interaction law is assumed as the boundary condition on the oscillatory plate. A realistic intermolecular potential based on experimental data for the transport coefficients of the mixture is employed in the calculations. Two mixtures of noble Gases, namely, Helium–Argon and Helium–Xenon, are considered in order to investigate the influence of the molecular mass ratio of species on the problem. A wide range of the oscillation speed parameter, defined as the ratio of intermolecular collision frequency to sound frequency, is considered. The amplitudes and phases of the macrocharacteristics of the gas flow are calculated and the results are compared to those obtained for a single gas.
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ab initio simulation of heat transfer through a mixture of Rarefied Gases
International Journal of Heat and Mass Transfer, 2014Co-Authors: Jose L Strapasson, Felix SharipovAbstract:The heat flux problem for a binary gaseous mixture confined between two parallel plates with different temperatures is studied on the basis of the direct simulation Monte Carlo method with an implementation of ab initio potential. The calculations were carried for a wide range of the gas rarefaction, for several values of the mole fraction and for two values of the temperature difference. The smaller value of the difference corresponds to the limit when the nonlinear terms are negligible, while the larger value describes a nonlinear heat transfer. The heat flux, temperature, and mole fraction distributions are presented. To study the influence of the intermolecular potential, the same simulations are carried out for the hard sphere molecular model. A relative deviation of the results based on this model from those based on the ab initio potential is analyzed. It is pointed out that the difference between the heat flux of the two potentials is about 8% and 5% for the small and large temperature differences, respectively. The temperature distribution between plates is weakly affected by the molecular potential, while the chemical composition variation is the most sensitive quantity for the considered problem. The reported results can be used as benchmark data to test model kinetic equations for gaseous mixtures.
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General approach to transient flows of Rarefied Gases through long capillaries
Vacuum, 2014Co-Authors: Felix Sharipov, Irina GraurAbstract:An approach to model a transient flow of Rarefied gas through a long capillary based on numerical data for flow rate previously obtained from the linearized and stationary kinetic equation was proposed. As an example, non-steady flow through a long circular tube connecting two reservoirs is considered. Pressures in the reservoirs and flow rates in the inlet and outlet are obtained as a function of time. It is shown that the behaviors of these quantities vary by changing the gas rarefaction from the free-molecular regime to hydrodynamic one. The typical time to reach the equilibrium state is calculated. (c) 2013 Elsevier Ltd. All rights reserved.
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general approach to transient flows of Rarefied Gases through long capillaries
Vacuum, 2014Co-Authors: Felix Sharipov, Irina GraurAbstract:Abstract An approach to model a transient flow of Rarefied gas through a long capillary based on numerical data for flow rate previously obtained from the linearized and stationary kinetic equation was proposed. As an example, non-steady flow through a long circular tube connecting two reservoirs is considered. Pressures in the reservoirs and flow rates in the inlet and outlet are obtained as a function of time. It is shown that the behaviors of these quantities vary by changing the gas rarefaction from the free-molecular regime to hydrodynamic one. The typical time to reach the equilibrium state is calculated.
Jose L Strapasson - One of the best experts on this subject based on the ideXlab platform.
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ab initio simulation of heat transfer through a mixture of Rarefied Gases
International Journal of Heat and Mass Transfer, 2014Co-Authors: Jose L Strapasson, Felix SharipovAbstract:The heat flux problem for a binary gaseous mixture confined between two parallel plates with different temperatures is studied on the basis of the direct simulation Monte Carlo method with an implementation of ab initio potential. The calculations were carried for a wide range of the gas rarefaction, for several values of the mole fraction and for two values of the temperature difference. The smaller value of the difference corresponds to the limit when the nonlinear terms are negligible, while the larger value describes a nonlinear heat transfer. The heat flux, temperature, and mole fraction distributions are presented. To study the influence of the intermolecular potential, the same simulations are carried out for the hard sphere molecular model. A relative deviation of the results based on this model from those based on the ab initio potential is analyzed. It is pointed out that the difference between the heat flux of the two potentials is about 8% and 5% for the small and large temperature differences, respectively. The temperature distribution between plates is weakly affected by the molecular potential, while the chemical composition variation is the most sensitive quantity for the considered problem. The reported results can be used as benchmark data to test model kinetic equations for gaseous mixtures.
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benchmark problems for mixtures of Rarefied Gases i couette flow
Physics of Fluids, 2013Co-Authors: Felix Sharipov, Jose L StrapassonAbstract:The planar Couette flow for gaseous mixture He–Ar is calculated by the direct simulation Monte Carlo method based on ab initio potential over the whole range of the gas rarefaction for several values of the mole fraction and for two values of the wall speed. The smaller value of the speed corresponds to the limit when the nonlinear terms are negligible, while the larger value describes a nonlinear flow. The shear stress, velocity gradient, temperature, and mole fraction profiles are presented. The reported results can be used as benchmark data to test model kinetic equations for gaseous mixtures. To study the influence of the intermolecular potential, the same simulations are carried out for the hard sphere molecular model. A relative deviation of the results based on this model from those based on the ab initio potential are analyzed. It is pointed out that the difference between the shear stresses of the two potentials for the linearized solution is within 1%, while it reaches 6% for the nonlinear cases.
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ab initio simulation of transport phenomena in Rarefied Gases
Physical Review E, 2012Co-Authors: Felix Sharipov, Jose L StrapassonAbstract:Ab initio potentials are implemented into the direct simulation Monte Carlo (DSMC) method. Such an implementation allows us to model transport phenomena in Rarefied Gases without any fitting parameter of intermolecular collisions usually extracted from experimental data. Applying the method proposed by Sharipov and Strapasson [Phys. Fluids 24, 011703 (2012)], the use of ab initio potentials in the DSMC requires the same computational efforts as the widely used potentials such as hard spheres, variable hard sphere, variable soft spheres, etc. At the same time, the ab initio potentials provide more reliable results than any other one. As an example, the transport coefficients of a binary mixture He-Ar, viz., viscosity, thermal conductivity, and thermal diffusion factor, have been calculated for several values of the mole fraction.
Henning Struchtrup - One of the best experts on this subject based on the ideXlab platform.
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poiseuille flow of moderately Rarefied Gases in annular channels
International Journal of Heat and Mass Transfer, 2012Co-Authors: Peyman Taheri, Henning StruchtrupAbstract:Abstract In this study, rarefaction effects in pressure-driven gas flows in annular micro-channels are investigated. The influence of gas rarefaction, aspect ratio of the annulus, and surface accommodation coefficient on wall friction, mass flow rate, and thermal energy flow rate is studied. For this, the linearized Navier–Stokes–Fourier (NSF) and regularized 13-moment (R13) equations are solved analytically. The results are compared to available solutions of the Boltzmann equation to highlight the advantages of the R13 over the NSF equations in describing rarefaction effects in the process. Moreover, a second-order slip boundary condition is proposed to improve the accuracy of the classical NSF equations.
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Numerical solution of the moment equations using kinetic flux-splitting schemes
2012Co-Authors: Anirudh Singh Rana, Manuel Torrilhon, Henning StruchtrupAbstract:Processes in Rarefied Gases are accurately described by the Boltzmann equation. The solution of the Boltzmann equation using direct numerical methods and direct simulation Monte Carlo methods (DSMC) is very time consuming. An alternative approach can be obtained by using moment equations, which allow the calculation of processes in the transition regime at reduced computational cost. In the current work, a finite volume method is developed for the solution of these moment equations. The numerical scheme is based on kinetic schemes, similar to those developed for the Euler and Navier-Stokes equations by Deshpande (1986), Perthame (1990), Xu et al. (2005), Le Tallec and Perlat (1998), and others.
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Resonance in Rarefied Gases
Continuum Mechanics and Thermodynamics, 2011Co-Authors: Henning StruchtrupAbstract:Dispersion and damping of ultrasound waves are a standard test for mathematical models of Rarefied gas flows. Normally, one considers waves in semi-infinite systems in relatively large distance of the source. For a more complete picture, ultrasound propagation in finite closed systems of length L is studied by means of several models for Rarefied gas flows: the Navier-Stokes-Fourier equations, Grad’s 13 moment equations, the regularized 13 moment equations, and the Burnett equations. All systems of equations are considered in simple 1-D geometry with their appropriate jump and slip boundary conditions. Damping and resonance are studied in dependence of frequency and length. For small L, all wave modes contribute to the solution.
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poiseuille flow of Rarefied Gases between concentric cylinders
ASME 2011 9th International Conference on Nanochannels Microchannels and Minichannels Volume 1, 2011Co-Authors: Peyman Taheri, Henning StruchtrupAbstract:Miniaturized devices are used currently in many engineering applications. Nonetheless, despite much progress in their fabrication, the fundamental understanding of fluid flow and heat transfer on the microscale is still not satisfactory. In this study, rarefaction effects in pressure-driven gas flows in annular microchannels are investigated. The influence of Knudsen number, aspect ratio of the annulus, and surface accommodation coefficient on wall friction, mass flow rate, and thermal energy flow rate is discussed. For this, the linearized Navier–Stokes–Fourier (NSF) and regularized 13-moment (R13) equations are solved analytically. The results are compared to available solutions of the Boltzmann equation to highlight the advantages of the R13 over the NSF equations in describing rarefaction effects in the process. Moreover, in order to improve the accuracy of the NSF system a second-order slip boundary condition is proposed.Copyright © 2011 by ASME
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rarefaction effects in thermally driven microflows
Physica A-statistical Mechanics and Its Applications, 2010Co-Authors: Peyma Taheri, Henning StruchtrupAbstract:Rarefied gas flow in a parallel-plate micro-channel is considered, where a streamwise constant temperature gradient is applied in the channel walls. An analytical approach to the problem is conducted based on linearized and semi-linearized forms of the regularized 13-moment equations (R13 equations), which are a set of macroscopic transport equations for Rarefied Gases at the super-Burnett order. Typical nonequilibrium effects at the boundary, i.e., velocity slip, temperature jump, and formation of Knudsen boundary layers are investigated. Nonlinear contributions lead to temperature, density, and normal stress profiles across the channel which are not reported elsewhere in literature.
G Spiga - One of the best experts on this subject based on the ideXlab platform.
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multi temperature hydrodynamic limit from kinetic theory in a mixture of Rarefied Gases
Acta Applicandae Mathematicae, 2012Co-Authors: Marzia Bisi, Giorgio Martalò, G SpigaAbstract:Starting from the Boltzmann kinetic equations for a mixture of gas molecules whose internal structure is described by a discrete set of internal energy levels, hydrodynamic equations at Euler level are deduced by a consistent hydrodynamic limit in the presence of a two-scale collision process. The fast process driving evolution is constituted by mechanical encounters between particles of the same species, whereas inter-species scattering proceeds at the macroscopic scale. The resulting multi-temperature and multi-velocity fluid-dynamic equations are briefly commented on, and some results in closed analytical form are given for special simplified situations like Maxwellian collision kernels, or mono-atomic hard sphere Gases.
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a kinetic ellipsoidal bgk model for a binary gas mixture
EPL, 2011Co-Authors: Maria Groppi, Stefania Monica, G SpigaAbstract:An ellipsoidal BGK model is proposed for a binary mixture of Rarefied Gases in the frame of kinetic theory. It fulfils the crucial properties of the actual Boltzmann equation (collision invariants, equilibria, entropy dissipation), and introduces a further constraint on velocity equalization of the two species. The model features two disposable relaxation parameters which can be used to fit exactly, in the continuum limit, Fick's law for diffusion velocities and Newton's law for the viscous stress in the relevant set of Navier-Stokes equations. Positivity of temperature fields is guaranteed by a physically meaningful restriction on the parameters themselves.
Jason M Reese - One of the best experts on this subject based on the ideXlab platform.
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Molecular free path distribution in Rarefied Gases
Journal of Physics D: Applied Physics, 2011Co-Authors: Nishanth Dongari, Yonghao Zhang, Jason M ReeseAbstract:We present the results of investigations into the distribution of molecular free paths in Rarefied Gases using molecular dynamics simulations. Our tests on a range of different gas densities and confinements (unbounded, single bounding wall, and parallel bounding walls) indicate that the molecules perform Lévy-type flights, irrespective of the presence of a bounding wall. The free paths most closely follow a power-law distribution. Simulations of Gases confined by planar surfaces indicate that the local molecular mean free path varies sharply close to a solid surface. These results may yield new insight into diffusive transport in Rarefied Gases, in particular, the constitutive behaviour of gas flows in micro and nanoscale devices.
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Molecular free path distribution in Rarefied Gases
Journal of Physics D: Applied Physics, 2011Co-Authors: Nishanth Dongari, Yonghao Zhang, Jason M ReeseAbstract:We present the results of investigations into the distribution of molecular free paths in Rarefied Gases using molecular dynamics simulations. Our tests on a range of different gas densities and confinements (unbounded, single bounding wall and parallel bounding walls) indicate that the molecules perform Levy-type flights, irrespective of the presence of a bounding wall. The free paths most closely follow a power-law distribution. Simulations of Gases confined by planar surfaces indicate that the local molecular mean free path varies sharply close to a solid surface. These results may yield new insight into diffusive transport in Rarefied Gases, in particular, the constitutive behaviour of gas flows in micro- and nanoscale devices.
