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The gas flow characteristics in lid-driven cavities are influenced by several factors, such as the cavity geometry, gas properties, and boundary conditions. In this study, the physics of heat and gas flow in cylindrical lid-driven cavities with various cross sections, including fully or partially rounded edges, is investigated through numerical simulations using the direct simulation Monte Carlo (DSMC) and the discrete unified gas kinetic scheme (DUGKS) methods. The thermal and fluid flow fields are systematically studied for both constant and oscillatory lid velocities, for various degrees of gas rarefaction ranging from the slip to the free-molecular regimes. The impact of expansion cooling and viscous dissipation on the thermal and flow fields, as well as the occurrence of counter-gradient heat transfer (also known as anti-Fourier heat transfer) under non-equilibrium conditions, is explained based on the results obtained from numerical simulations. Furthermore, the influence of the incomplete tangential accommodation coefficient on the thermal and fluid flow fields is discussed. A comparison is made between the thermal and fluid flow fields predicted in cylindrical cavities and those in square-shaped cavities. The present work contributes to the advancement of micro-/nano-electromechanical systems by providing valuable insight into rarefied gas flow and heat transfer in lid-driven cavities. [ABSTRACT FROM AUTHOR]

The motivation of the current paper is to provide a detailed review of crucial topics in micro- and nanoscale gas flows, i.e., velocity slip and temperature jump phenomena and their modeling, Knudsen minimum, and thermally-driven flows with application in Knudsen pumps. Non-equilibrium gas flows at the micro and nano scales exhibit peculiarities different from the intuition of macroscopic continuum fluid dynamics and heat transfer. Rarefied gas flows experience unique features such as slip and jump boundary effects , Knudsen paradox , pumping effect , , anti-Fourier heat transfer , thermal critical Knudsen number , and rarefied gas shock polars. This paper reviews the latest advancements and investigations on the gas–surface velocity and temperature inequalities, named velocity slip and temperature jump , in rarefied gas flows. Thermodynamic non-equilibrium effects are localized in the Knudsen layer within a width of a few gas mean free path near the surfaces. These particular features result in inequalities between the velocity and temperature of the gas concerning the surface. Experimental investigations of the slip and jump conditions from the first observation to the recent studies are reviewed. Next, a comprehensive review of the different categories of velocity slip models from the Maxwell model up to the recently developed models will be performed. For the first time, all the current models on the viscosity of rarefied gas are classified and compared in the present paper. Progress in the derivation of the models describing the temperature jump of rarefied gas over a solid surface will be performed. Next, a unique behavior of rarefied gas named the Knudsen paradox or Knudsen minimum is introduced and reviewed based on the different viewpoints. Different possible reasons for the origin of the Knudsen paradox phenomena are reviewed. A complete set of experimental and numerical works which detected the Knudsen paradox feature will be historically reviewed. Then, the closed-form relations obtained from the numerical simulations and experimental measurements indicating and predicting the occurrence of the Knudsen paradox phenomenon are reviewed and compared. The end section of this paper focuses on deemed physical and real-world applications of the rarefied flows at small scales utilizing thermally driven gas flows, i.e., the pumping effect of the rarefied gas. The pumping effect of the rarefied gas under temperature gradient leads to the Knudsen pump or Knudsen compressor concept. The main advantage over macro-scale pumps is that these sorts of pumps do not suffer from reduced life cycles due to various modes of mechanical failure because they do not have any rotating and moving parts. Moreover, the pumps mentioned above could find applications in gas chromatography, spectroscopy, moving gases on a chip, forced convection cooling, and micro-nano scale actuators. Different classes of thermally-induced flows with their origins are proposed and discussed, containing the recently detected thermally-driven flows. Based on that, a critical and comprehensive review of the different types and configurations of Knudsen pumps will be presented in detail. The newest published research containing new designs of Knudsen pumps has been considered in this review. Different numerical techniques developed or employed to simulate Knudsen pumps will be extensively reviewed. Besides, all published experimental investigations on Knudsen pumps will be reviewed and classified. Overall, this review will provide insights into the emerging physical science and engineering application of micro- and nanoscale gas flows. [ABSTRACT FROM AUTHOR]

The direct simulation Monte Carlo (DSMC) method, which is a probabilistic particle-based gas kinetic simulation approach, is employed in the present work to describe the physics of rarefied gas flow in super nanoporous materials (also known as mesoporous). The simulations are performed for different material porosities ( 0.5 ≤ ϕ ≤ 0.9 ), Knudsen numbers ( 0.05 ≤ Kn ≤ 1.0 ), and thermal boundary conditions (constant wall temperature and constant wall heat flux) at an inlet-to-outlet pressure ratio of 2. The present computational model captures the structure of heat and fluid flow in porous materials with various pore morphologies under rarefied gas flow regime and is applied to evaluate hydraulic tortuosity, permeability, and skin friction factor of gas (argon) flow in super nanoporous materials. The skin friction factors and permeabilities obtained from the present DSMC simulations are compared with the theoretical and numerical models available in the literature. The results show that the ratio of apparent to intrinsic permeability, hydraulic tortuosity, and skin friction factor increase with decreasing the material porosity. The hydraulic tortuosity and skin friction factor decrease with increasing the Knudsen number, leading to an increase in the apparent permeability. The results also show that the skin friction factor and apparent permeability increase with increasing the wall heat flux at a specific Knudsen number. [ABSTRACT FROM AUTHOR]

The impetus of the this study is to investigate flow and thermal field in rarefied gas flows inside a trapezoidal micro/nano-cavity using the direct simulation Monte Carlo (DSMC) technique. The investigation covers the hydrodynamic properties and thermal behavior of the flow. The selected Knudsen numbers for this study are arranged in the slip and transition regimes. The results show the center of the vortex location moves by variation in the Knudsen numbers. Also, as the Knudsen number increases, the non-dimensional shear stress increases, but the distribution deviates from a symmetrical profile. The cold to hot transfer, which is in contrast with the conventional Fourier law, is observed. We show that the heat transfer is affected by the second derivative of the velocity. By increasing the Knudsen number, the transferred heat through the walls decreases, but the contraction/expansion effects on the temperature in the corner of the cavity become higher. [ABSTRACT FROM AUTHOR]

We provide the first direct calculation of the Knudsen layer (KL) thickness in rarefied gas flows based on the ballistic molecular motions in the direct simulation Monte Carlo simulations. Calculations reproduce a linear relation between the KL thickness and the mean free path (MFP) of the gas, which agrees with the classical gas kinetic theory statement. The ratio of the KL thickness and MFP is only a function of the gas molecular model at slight flow gradients. However, high flow gradient and high surface curvature effects destroy the linear relation between the KL thickness and MFP. [ABSTRACT FROM AUTHOR]

Well-known polars in classical shock wave theory, that is, flow deflection angle-shock angle (θ-β), hodograph (u*,v*), and pressure deflection (θ-P*) diagrams, are investigated for the rarefied gas flows using a recently proposed shock wave detection technique by Akhlaghi and coworkers. The agreement between the obtained polars with the analytical relations in classical shock wave theory has been shown in the continuum limit for the cases of supersonic flow over the wedge and cylinder geometries. Investigations are performed using the RGS2D direct simulation Monte Carlo solver for supersonic gas flows over a circular cylinder at continuum limit and Kn = 10−4, 10−3, 0.01, 0.03, 0.07, and 0.10. Two species of nitrogen and argon at various Mach numbers of 1.5, 3.0, and 10.0 are considered. The shock polars are investigated along bow shock waves in front of the cylinder. The results indicate that rarefaction significantly affects the shock polars. As Knudsen number increases, shock angle, maximum flow deflection angle, and aft shock pressure increase. However, velocity components after the shock wave decrease as the flow becomes more rarefied. These effects are stronger for θ-β polar under the weak shock condition. Meanwhile, they are stronger for θ-P* and hodograph polars in strong shock situations. [ABSTRACT FROM AUTHOR]

Gas flow and heat transfer in confined geometries at micro-and nanoscales differ considerably from those at macro-scales, mainly due to nonequilibrium effects such as velocity slip and temperature jump. Nonequilibrium effects increase with a decrease in the characteristic length-scale of the fluid flow or the gas density, leading to the failure of the standard Navier–Stokes–Fourier (NSF) equations in predicting thermal and fluid flow fields. The direct simulation Monte Carlo (DSMC) method is employed in the present work to investigate pressure-driven nitrogen flow in divergent microchannels with various divergence angles and isothermal walls. The thermal fields obtained from numerical simulations are analysed for different inlet-to-outlet pressure ratios ( 1.5 ≤ Π ≤ 2.5 ), tangential momentum accommodation coefficients, and Knudsen numbers ( 0.05 ≤ Kn ≤ 12.5 ), covering slip to free-molecular rarefaction regimes. The thermal field in the microchannel is predicted, heat-lines are visualised, and the physics of heat transfer in the microchannel is discussed. Due to the rarefaction effects, the direction of heat flow is largely opposite to that of the mass flow. However, the interplay between thermal and pressure gradients, which are affected by geometrical configurations of the microchannel and the applied boundary conditions, determines the net heat flow direction. Additionally, the occurrence of thermal separation and cold-to-hot heat transfer (also known as anti-Fourier heat transfer) in divergent microchannels is explained. [ABSTRACT FROM AUTHOR]

In this paper we numerically evaluate the recently developed Aoki et al. slip and jump conditions in high-speed rarefied gas flows for the first time. These slip and jump conditions are developed to be employed with the Navier–Stokes–Fourier equations. They were derived based on the Boltzmann equation with the first order Chapman–Enskog solution, and the analysis of the Knudsen layer. Four aerodynamic configurations are selected for a comprehensive evaluation of these conditions such as sharp-leading-edge flat plate, vertical plate, wedge and circular cylinder in cross-flow with the Knudsen number varying from 0.004 to 0.07, and argon as the working gas. The simulation results using the Aoki et al. boundary conditions show suitable agreement with the DSMC data for slip velocity and surface gas temperature. The accuracy of these boundary conditions is superior to the conventional Maxwell, Smoluchowski and Le boundary conditions. [ABSTRACT FROM AUTHOR]

A new efficient direct simulation Monte Carlo (DSMC) method is proposed for the simulation of microporous media based on the dusty gas model (DGM). Instead of simulating gas flow through a microporous medium with a complex geometry of micropores that mimics the physical pore morphology, the DGM-DSMC method replaces it with the gas flow through a system of randomly distributed motionless virtual particles with simple spherical shapes confined in the considered domain. In addition, the interactions of gas molecules with the porous particles are simulated stochastically. For the aim of our study, the DGM is implemented in Bird's two-dimensional DSMC code. The obtained results for the average velocity of gas flow through microscale porous media with given porosity are verified for different pressure gradients with those reported in the literature where porous particles are modeled physically in the domain. Thereafter, the effective parameters in porous media such as porosity, particle diameter, and rarefaction on flow behavior including velocity profile, apparent gas permeability, and mass flow rate are investigated. A comparison with the results predicted by the Open source Field Operation and Manipulation (OpenFOAM) software suggests that the employed DGM-DSMC is more accurate in highly porous media and its computational cost is considerably low. [ABSTRACT FROM AUTHOR]

Rarefied gas flows in nano-scale isosceles triangular cavities with a motion away from the square corner are considered over a wide range of flow rarefactions regimes, i.e., 0.01 ≤ Kn ≤ 10, using the direct simulation Monte Carlo (DSMC) method. We put emphasis to the rarefaction effects on the vortical behaviors and heat transfer patterns of rarefied monatomic and diatomic gases. We show that the primary vortices appearing in the triangular cavity are Moffat-type vortices, which disappear as velocity slip increases over the walls. However, an additional vortex is observed at Kn > 1 on the inclined wall attributable to the balance of the thermally driven flows from the cold to the hot region and flow induced by the primary vortex. We also report variations in the effective length scale of the fluid circulation with the Knudsen number. Our investigations specify that the competition between the Fourier term and shear stress gradient component of the heat flux constitutive relation results in the cold-to-hot transfer in triangular cavities. Also, heat flux patterns predicted by the asymptotic theory of the Boltzmann equation for the weakly non-linear flow and by the linearized form of the Regularized 13 moments (R13) equations are compared with the DSMC solution suitably at low Knudsen number regimes. [ABSTRACT FROM AUTHOR]

A detailed study on thermally driven flows through divergent micro/nanochannels is presented. Rarefied gas flow behavior and thermal mass flow rate were investigated with different divergence angles ranging between 0 and 7 at two aspect ratios () using particle-based direct simulation Monte-Carlo (DSMC) method. We compare our DSMC solutions for normalized thermal mass flow rate with the numerical solution of the Boltzmann-Krook-Walender (BKW) model and Bhatnagar-Gross-Krook (BGK) model and asymptotic theory over a wide range of Knudsen number in the transition regime. The flow field properties including Mach number, pressure, overall temperature and magnitude of shear stress are examined in detail. Based on our analysis, we observed an approximately constant velocity and pressure distribution at a microchannel with a small opening angle. Our results also demonstrate that the heat lines from weakly nonlinear form of Sone constitutive law and DSMC show good agreement at low Knudsen numbers. Moreover, we show that the effect of divergence angle is influential in increasing normalized thermal mass flow rate at early transition regime. [ABSTRACT FROM AUTHOR]

In this study we use the direct simulation Monte Carlo (DSMC) to elaborate on the heat transfer patterns in the pressure-driven rarefied flow through micro/nanochannels. Finite length planar micro/nanochannels are considered using with symmetrical wall heat flux boundary conditions, and the gas flow is considered to be in slip and transition regimes. When considering zero-conductive or cooled walls, the DSMC solution predicts a possibility of the anti-Fourier heat transfer, i.e., the transfer of heat from cold-to-hot regions of the flow field. It turns out that the competition between the contributions of temperature gradient and pressure gradient (shear stress) in the heat flux results in three different heat transfer regimes. The regimes consist of complete hot-to-cold heat transfer regime, the entire anti-Fourier regime, and localized anti-Fourier regime. While the heat flux due to the shear stress is directed from the outlet towards the inlet, the Fourier term is strongly influenced by viscous slip heating, which then acts as a heat source, and contributes to patterns of heat flux on the fluid layer adjacent to the walls. Furthermore, the heat flux regimes for complete or localized cold-to-hot transfer are classified according to the magnitude of the normalized heat flux and the Knudsen number. Additionally, effects of heat flux condition on the mass flow rate are discussed. [ABSTRACT FROM AUTHOR]

The present work is related to the study of the nitrogen gas flow through diverging micro/nano-channels. The direct simulation Monte-Carlo (DSMC) method has been used to study the flow. The Simplified Bernoulli Trials (SBT) collision scheme has been employed to reduce the computational costs and required amounts of the computer resources. The effects of various divergence angles on flow and thermal fields have been studied for different Knudsen numbers in late-slip and early-transition regimes. The inlet-to-outlet pressure ratio has been set to 2.5 for micro/nano-channels with a uniform constant wall temperature. By analyzing the numerical results no flow separation has been found due to slip at the wall which is different than flow behavior in continuum regime. The results indicate that the viscous component has a relatively large contribution in the overall pressure drop and flow behavior. It observed that for low divergence angles the effects of pressure forces dominate the effects of shear stress and divergence angle and cause the flow to accelerate along the channel while by increasing the divergence angle and therefore the effects of flow expansion, the flow decelerates along the channel. The mass flow rate through channel increases by increasing the divergence angle. Cold-to-hot heat transfer has been observed in diverging micro/nano-channels. In order to investigate the thermal behavior in diverging micro/nano-channels, the results have been compared to weakly non-linear constitutive laws derived from Boltzmann's equation. [ABSTRACT FROM AUTHOR]

The accuracy of numerical simulations of rarefied gas flows, in particular the Navier-Stokes-Fourier (N–S–F) equations, depends on the employed surface boundary conditions. In the literature, the combination of the second-order slip/jump conditions has primarily been used for either the Burnett or the BGK Burnett equations for hypersonic gas flows. In this work, we suggest the second-order temperature jump condition in a new form. The second-order slip/jump conditions are implemented in the framework of OpenFOAM to employ with the N–S–F equations for low-speed nanoscale and hypersonic rarefied gas flows. We investigate both the first and second-order slip/jump boundary conditions for low speed rarefied gas flow in the pressure-driven backward facing step nanochannel as well as hypersonic gas flows over the flat plate and past a circular cylinder in cross-flow. Simulation results show that the combination of the second-order slip/jump (in new form) conditions predicts better surface properties than those of the first-order slip/jump conditions for all cases studied by comparing the Burnett and DSMC data. Especially, the N–S–F simulation results of the second-order slip/jump (in new form) conditions of the cylinder case can capture the Burnett data at Kn = 0.1, while those of the first-order conditions do not. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the effects of convective heat transfer on the argon gas flow through micro/nanochannels subject to uniform wall heat flux (UWH) boundary condition using the direct simulation Monte Carlo (DSMC) method. Both the hot wall (qwall > 0) and the cold wall (qwall < 0) cases are considered. We consider the effect of wall heat flux on the centerline pressure, velocity profile and mass flow rate through the channel in the slip regime. The effects of rarefaction, property variations and compressibility are considered. We show that UWH boundary condition leads to the thermal transpiration. Our investigations showed that this thermal transpiration enhances the heat transfer rate at the walls in the case of hot walls and decreases it where the walls are being cooled. We also show that the deviation of the centerline pressure distribution from the linear distribution depends on the direction of the wall heat flux. [ABSTRACT FROM AUTHOR]

In the current work, the effect of shear work due to the velocity slip on the non-equilibrium heat transfer in a pressure driven micro/nanochannel is evaluated under the constant wall heat flux boundary condition. As our simulation tool, the DSMC method is employed. Implementation of the wall heat flux in the DSMC method is performed using the “modified Iterative” technique. We investigate the effects of rarefaction, property variations and compressibility. The numerical results show that shear stress on the walls significantly affects all aspects of the flow behavior and heat transfer through micro/nanochannels such as heat flux rates. We also analyze the counter-gradient heat flow (cold to hot heat transfer) phenomenon appearing at the cooling conditions. It is observed that viscous dissipation affects the heat flux applied to the walls and may overcome the wall heat flux, i.e., in the case of low cooling wall heat flux condition, shear work may completely heat the flow field. Nusselt number singularity is also discussed. [ABSTRACT FROM AUTHOR]

The present work uses the direct simulation Monte Carlo (DSMC) method to investigate thermally-driven rarefied flow induced by the partially heated diamond in a channel. Two types of flows are generated in the medium: the radiometric flow induced from the middle tip of the diamond with various temperatures on its side and the rightward thermal edge flow induced by the temperature difference between the diamond and the medium. The accommodation coefficients of the top and bottom borders were considered, and it is observed that the thermal edge flow is weakened if we set the top and bottom channels' walls as specular. In this work, we studied the influence of the geometrical parameters and operating conditions on the rarefied gas flow under specular conditions of the top and bottom walls. This includes the sizes of the diamond, the working pressure represented by the Knudsen number (Kn), and the temperature difference. The results show that varying the accommodation coefficients of channel walls affect the velocity field and results in the generation of vortices behind the diamond in the channel. We show that the drag force of the diamond is proportional to the temperature difference and increases slightly with the increase of Kn. [ABSTRACT FROM AUTHOR]

Rarefied gas flow through micro/nano electro mechanical systems does not perform exactly as that in macro-scale devices. The main goal of this study was to investigate mixed subsonic-supersonic flows in micro/nano channels and to provide physical descriptions on their behaviours. We use DSMC method as a reliable numerical tool to extend our simulation because it provides accurate solution for the Boltzmann equations over the entire range of rarefied flow regime or Knudsen numbers. As is known, the appearance of oblique/normal shocks at the inlet of a channel adds to the complexity of internal flow field analyses. We found some very unique physical aspects of micro/nano flows including mixed supersonic-subsonic flow regimes in constant area ducts and the attenuation of emitted shocks, which are attributed to the strong viscous forces and dominant rarefaction effects at micro/nano scales. [ABSTRACT FROM AUTHOR]

In this paper, we study mass flow rate of rarefied gas flow through micro/nanoscale channels under simultaneous thermal and pressure gradients using the direct simulation Monte Carlo (DSMC) method. We first compare our DSMC solutions for mass flow rate of pure temperature-driven flow with those of Boltzmann-Krook-Walender equation and Bhatnagar-Gross-Krook solutions. Then, we focus on pressure-temperature-driven flows. The effects of different parameters such as flow rarefaction, channel pressure ratio, wall temperature gradient and flow bulk temperature on the thermal mass flow rate of the pressure-temperature-driven flow are examined. Based on our analysis, we propose a correlated relation that expresses normalized mass flow rate increment due to thermal creep as a function of flow rarefaction, normalized wall temperature gradient and pressure ratio over a wide range of Knudsen number. We examine our predictive relation by simulation of pressure-driven flows under uniform wall heat flux (UWH) boundary condition. Walls under UWH condition have non-uniform temperature distribution, that is, thermal creep effects exist. Our investigation shows that developed analytical relation could predict mass flow rate of rarefied pressure-driven gas flows under UWH condition at early transition regime, that is, up to Knudsen numbers of 0.5. [ABSTRACT FROM AUTHOR]

SUMMARY We extend a hybrid DSMC/Navier-Stokes (NS) approach to unify the DSMC and the NS simulators in one framework capable of solving the mixed non-equilibrium and near-equilibrium flow regions efficiently. Furthermore, we use a one-way state-based coupling (Dirichlet-Dirichlet boundary-condition coupling) to transfer the required information from the continuum region to the rarefied one. The current hybrid DSMC-NS frame is applied to the hypersonic flows over nanoflat plate and microcylinder cases. The achieved solutions are compared with the pure DSMC and NS solutions. The results show that the current hybrid approach predicts the surface heat transfer rate and shear stress magnitudes very accurately. Some important conclusions can be drawn from this study. For example, although the shock wave region would be a non-equilibrium region, it is not necessary to use a pure DSMC simulator to solve it entirely. This is important when the researchers wish to predict the surface properties such as velocity slip, temperature jump, wall heat flux rate, and friction drag magnitudes accurately. Our investigation showed that our hybrid solution time would be at least 40% (for the flat plate) and 35% (for the cylinder) of the time that must be spent by a pure DSMC solver to attain the same accuracy.Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this study the direct-simulation Monte Carlo (DSMC) method is utilized to investigate thermal characteristics of micro- or nanocavity flow. The rarefied cavity flow shows unconventional behaviors which cannot be predicted by the Fourier law, the constitutive relation for the continuum heat transfer. Our analysis in this study confirms some recent observations and shows that the gaseous flow near the top-left corner of the cavity is in a strong nonequilibrium state even within the early slip regime, Kn = 0.005. As we obtained slip velocity and temperature jump on the driven lid of the cavity, we reported meaningful discrepancies between the direct and macroscopic sampling of rarefied flow properties in the DSMC method due to existence of nonequilibrium effects in the corners of cavity. The existence of unconventional nonequilibrium heat transfer mechanisms in the middle of slip regime, Kn = 0.05, results in the appearance of cold-to-hot heat transfer in the microcavity. In the current study we demonstrate that existence of such unconventional heat transfer is strongly dependent on the Reynolds number and it vanishes in the large values of the lid velocity. As we compared DSMC solution with the results of regularized 13 moments (R13) equations, we showed that the thermal characteristic of the microcavity obtained by the R13 method coincides with the DSMC prediction. Our investigation also includes the analysis of molecular entropy in the microcavity to explain the heat transfer mechanism with the aid of the second law of thermodynamics. To this aim, we obtained the two-dimensional velocity distribution functions to report the molecular-based entropy distribution, and show that the cold-to-hot heat transfer in the cavity is well in accordance with the second law of thermodynamics and takes place in the direction of increasing entropy. At the end we introduce the entropy density for the rarefied flow and show that it can accurately illustrate departure from the equilibrium state. [ABSTRACT FROM AUTHOR]

In this article, a new hybrid approach combining Fokker Planck (FP) and Direct Simulation Monte Carlo (DSMC) is introduced. The FP approach, which is an approximation of the Boltzmann equation, has been recently introduced for modeling rarefied gas flows. Compared to standard molecular methods like DSMC, it has a lower computational cost. However, the FP model may provide erroneous results in modeling some flow features, including vortex region and shock waves. The DSMC approach is accurate enough; yet, it has a high computational cost, especially at low Knudsen/low Mach number conditions. The purpose of this article is to suggest an optimized hybrid algorithm to benefit from high-speed modeling and sufficient accuracy simultaneously. We show a modified form of the gradient length Knudsen number, i.e., Kn GL /Kn, must be considered to define the range of accuracy of the FP method. We used Kn GL /Kn as a parameter for switching between DSMC and FP. The cavity flow and the nozzle flow are considered for the investigation of the proposed hybrid algorithm. The dependence of the accuracy and computational cost on Kn GL /Kn is reported. The results demonstrate that the optimized Kn GL /Kn is between 3 and 4, which gives suitable computational cost and acceptable accuracy. • Report on the evaluation of a hybrid Fokker-Plank-DSMC approach to treat micro-cavity and micro-nozzle flows. • Using a novel criterion for switching between Fokker-Plank and DSMC solvers. • A thorough study of the numerical efficiency of the hybrid scheme at various Kn and back pressure magnitudes. [ABSTRACT FROM AUTHOR]

Current work investigates the effect of thermal creep on the behavior of rarefied gas flow through micro/nanochannels using the direct simulation Monte Carlo method. Thermal creep effects are studied on velocity profiles, streamwise velocity and pressure, and thermal mass flow rate. The strength of thermal creep is examined at different Knudsen number, channel pressure ratio, and bulk temperature. The thermal mass flow rate variation is investigated over a wide range of flow rarefaction from the slip to free molecular regime. [ABSTRACT FROM AUTHOR]