Showing papers on "Knudsen number published in 2015"
TL;DR: It is found that most of the values of correction factor fall in the slip and transition regime, with no Darcy flow regime observed, indicating Knudsen diffusion always plays a role on shale gas transport mechanisms in the reconstructed shales.
Abstract: Porous structures of shales are reconstructed using the markov chain monte carlo (MCMC) method based on scanning electron microscopy (SEM) images of shale samples from Sichuan Basin, China. Characterization analysis of the reconstructed shales is performed, including porosity, pore size distribution, specific surface area and pore connectivity. The lattice Boltzmann method (LBM) is adopted to simulate fluid flow and Knudsen diffusion within the reconstructed shales. Simulation results reveal that the tortuosity of the shales is much higher than that commonly employed in the Bruggeman equation, and such high tortuosity leads to extremely low intrinsic permeability. Correction of the intrinsic permeability is performed based on the dusty gas model (DGM) by considering the contribution of Knudsen diffusion to the total flow flux, resulting in apparent permeability. The correction factor over a range of Knudsen number and pressure is estimated and compared with empirical correlations in the literature. For the wide pressure range investigated, the correction factor is always greater than 1, indicating Knudsen diffusion always plays a role on shale gas transport mechanisms in the reconstructed shales. Specifically, we found that most of the values of correction factor fall in the slip and transition regime, with no Darcy flow regime observed.
282 citations
TL;DR: Comparisons with the results of direct simulation Monte Carlo (DSMC) and other benchmark data demonstrate that the DUGKS is a reliable and efficient method for multiscale flow problems.
Abstract: This paper is a continuation of our work on the development of multiscale numerical scheme from low-speed isothermal flow to compressible flows at high Mach numbers. In our earlier work [Z. L. Guo et al., Phys. Rev. E 88, 033305 (2013)], a discrete unified gas kinetic scheme (DUGKS) was developed for low-speed flows in which the Mach number is small so that the flow is nearly incompressible. In the current work, we extend the scheme to compressible flows with the inclusion of thermal effect and shock discontinuity based on the gas kinetic Shakhov model. This method is an explicit finite-volume scheme with the coupling of particle transport and collision in the flux evaluation at a cell interface. As a result, the time step of the method is not limited by the particle collision time. With the variation of the ratio between the time step and particle collision time, the scheme is an asymptotic preserving (AP) method, where both the Chapman-Enskog expansion for the Navier-Stokes solution in the continuum regime and the free transport mechanism in the rarefied limit can be precisely recovered with a second-order accuracy in both space and time. The DUGKS is an idealized multiscale method for all Knudsen number flow simulations. A number of numerical tests, including the shock structure problem, the Sod tube problem in a whole range of degree of rarefaction, and the two-dimensional Riemann problem in both continuum and rarefied regimes, are performed to validate the scheme. Comparisons with the results of direct simulation Monte Carlo (DSMC) and other benchmark data demonstrate that the DUGKS is a reliable and efficient method for multiscale flow problems.
203 citations
TL;DR: In this paper, a new mathematical model has been constructed to characterize gas flow in nano-pores, based on the advection-diffusion model, and a comprehensive coefficient for characterizing the flow process was proposed.
153 citations
TL;DR: The method is assessed for flow across parallel plates and three-dimensional flows in porous media, showing excellent agreement of the mass flow with analytical and numerical solutions of the Boltzmann equation across the full range of Knudsen numbers.
Abstract: We present a lattice Boltzmann realization of Grad's extended hydrodynamic approach to nonequilibrium flows. This is achieved by using higher-order isotropic lattices coupled with a higher-order regularization procedure. The method is assessed for flow across parallel plates and three-dimensional flows in porous media, showing excellent agreement of the mass flow with analytical and numerical solutions of the Boltzmann equation across the full range of Knudsen numbers, from the hydrodynamic regime to ballistic motion.
99 citations
TL;DR: Simulations performed in a heterogeneous porous medium with components of different porosity and permeability indicate that Klinkenberg's effect plays a significant role on fluid flow in low-permeability porous media, and it is more pronounced as the Knudsen number increases.
Abstract: Gas slippage occurs when the mean free path of the gas molecules is in the order of the characteristic pore size of a porous medium. This phenomenon leads to Klinkenberg's effect where the measured permeability of a gas (apparent permeability) is higher than that of the liquid (intrinsic permeability). A generalized lattice Boltzmann model is proposed for flow through porous media that includes Klinkenberg's effect, which is based on the model of Guo et al. [Phys. Rev. E 65, 046308 (2002)]. The second-order Beskok and Karniadakis-Civan's correlation [A. Beskok and G. Karniadakis, Microscale Thermophys. Eng. 3, 43 (1999) and F. Civan, Transp. Porous Med. 82, 375 (2010)] is adopted to calculate the apparent permeability based on intrinsic permeability and the Knudsen number. Fluid flow between two parallel plates filled with porous media is simulated to validate the model. Simulations performed in a heterogeneous porous medium with components of different porosity and permeability indicate that Klinkenberg's effect plays a significant role on fluid flow in low-permeability porous media, and it is more pronounced as the Knudsen number increases. Fluid flow in a shale matrix with and without fractures is also studied, and it is found that the fractures greatly enhance the fluid flow and Klinkenberg's effect leads to higher global permeability of the shale matrix.
98 citations
TL;DR: The feasibility of simulating methane transport characteristics in the organic nano-pores of shale through the Lattice Boltzmann method and results show that at small Knudsen number, LBM results agree well with Poiseuille's law, and flow rate (flow capacity) is proportional to the square of the pore scale.
Abstract: Permeability is a key parameter for investigating the flow ability of sedimentary rocks. The conventional model for calculating permeability is derived from Darcy's law, which is valid only for continuum flow in porous rocks. We discussed the feasibility of simulating methane transport characteristics in the organic nano-pores of shale through the Lattice Boltzmann method (LBM). As a first attempt, the effects of high Knudsen number and the associated slip flow are considered, whereas the effect of adsorption in the capillary tube is left for future work. Simulation results show that at small Knudsen number, LBM results agree well with Poiseuille's law, and flow rate (flow capacity) is proportional to the square of the pore scale. At higher Knudsen numbers, the relaxation time needs to be corrected. In addition, velocity increases as the slip effect causes non negligible velocities on the pore wall, thereby enhancing the flow rate inside the pore, i.e., the permeability. Therefore, the LBM simulation of gas flow characteristics in organic nano-pores provides an effective way of evaluating the permeability of gas-bearing shale.
81 citations
TL;DR: The growth and structure of particles undergoing agglomeration are investigated from the free molecular to the continuum regime by discrete element modeling (DEM) and the resulting SPSD is in excellent agreement with that obtained by DEM.
Abstract: Agglomeration occurs in environmental and industrial processes, especially at low temperatures where particle sintering or coalescence is rather slow. Here, the growth and structure of particles undergoing agglomeration (coagulation in the absence of coalescence, condensation, or surface growth) are investigated from the free molecular to the continuum regime by discrete element modeling (DEM). Particles coagulating in the free molecular regime follow ballistic trajectories described by an event-driven method, whereas in the near-continuum (gas-slip) and continuum regimes, Langevin dynamics describe their diffusive motion. Agglomerates containing about 10-30 primary particles, on the average, attain their asymptotic fractal dimension, D(f), of 1.91 or 1.78 by ballistic or diffusion-limited cluster-cluster agglomeration, corresponding to coagulation in the free molecular or continuum regimes, respectively. A correlation is proposed for the asymptotic evolution of agglomerate D(f) as a function of the average number of constituent primary particles, n(p). Agglomerates exhibit considerably broader self-preserving size distribution (SPSD) by coagulation than spherical particles: the number-based geometric standard deviations of the SPSD agglomerate radius of gyration in the free molecular and continuum regimes are 2.27 and 1.95, respectively, compared to ∼1.45 for spheres. In the transition regime, agglomerates exhibit a quasi-SPSD whose geometric standard deviation passes through a minimum at Knudsen number Kn ≈ 0.2. In contrast, the asymptotic D(f) shifts linearly from 1.91 in the free molecular regime to 1.78 in the continuum regime. Population balance models using the radius of gyration as collision radius underestimate (up to about 80%) the small tail of the SPSD and slightly overpredict the overall agglomerate coagulation rate, as they do not account for cluster interpenetration during coagulation. In the continuum regime, when a recently developed agglomeration rate is used in population balance equations, the resulting SPSD is in excellent agreement with that obtained by DEM.
79 citations
TL;DR: In this paper, a new proof of existence and exponential decay for solutions close to a global equilibrium, with explicit regularity bounds and rates of convergence, were derived in the Navier-Stokes perturbative setting on the torus.
68 citations
TL;DR: In this article, a pore-scale model based on the lattice Boltzmann method developed in a previous study is used to predict the Knudsen diffusivity and permeability of the reconstructed organic matter.
65 citations
TL;DR: In this paper, the authors present high-order gas-kinetic unified algorithms (GKUAs) for rarefied gas flow computations in phase space, which combine the discrete velocity ordinate method in velocity space and the compact highorder finite-difference schemes in physical space.
61 citations
TL;DR: A fast spectral method for binary mixtures of monatomic gases that has a computational cost O and is accurate and effective in simulating highly rarefied gas flows, i.e. it captures the discontinuities and fine structures in the velocity distribution functions.
TL;DR: In this article, a finite element analysis (FEA) of transient ballistic-diffusive phonon heat transport in a two-dimensional domain using a commercial package (COMSOL Multiphysics) was reported.
TL;DR: In this paper, the non-reactive elastic Boltzmann equation for multicomponent gaseous mixtures was considered and it was shown that well prepared initial conditions lead to solutions satisfying the Maxwell-Stefan diffusion equations in the vanishing Mach and Knudsen numbers limit.
Abstract: We consider the non-reactive elastic Boltzmann equation for multicomponent gaseous mixtures We deduce, under the standard diffusive scaling, that well prepared initial conditions lead to solutions satisfying the Maxwell-Stefan diffusion equations in the vanishing Mach and Knudsen numbers limit
TL;DR: In this paper, heat flow along two-dimensional strips as a function of the Knudsen number is examined in two different versions of heat-transport equations with non-local terms, with or without heat slip flow.
Abstract: Heat flow along two-dimensional strips as a function of the Knudsen number is examined in two different versions of heat-transport equations with non-local terms, with or without heat slip flow. In...
TL;DR: In this article, the authors investigated the nonlinear vibration and instability of a fluid conveying smart composite microtube made of polyvinylidene fluoride (PVDF) based on the modified couple stress theory and Timoshenko beam model.
Abstract: Electro-thermo-mechanical nonlinear vibration and instability of a fluid conveying smart composite microtube made of polyvinylidene fluoride (PVDF) are investigated in this article based on the modified couple stress theory and Timoshenko beam model. The composite matrix is reinforced by double-walled boron nitride nanotubes (BNNTs). Mechanical, electrical, and thermal characteristics of equivalent composite are determined based on micromechanical model. The surrounded elastic medium is taken into account using Winkler and Pasternak models. Considering the small-size effects and slip boundary conditions of microflow through Knudsen number and applying Hamilton's principle, the coupled differential equations, containing displacement and electric potential terms, are obtained. The differential quadrature method is applied to discretize the coupled governing equations and boundary conditions, which are then solved to obtain the nonlinear frequency and critical fluid velocity of the fluid-conveying microtube. The detailed parametric study is conducted, focusing on the combined effects of the Knudsen number, nonlocal parameter, BNNT volume percent, temperature change, elastic medium, and aspect ratio on the nonlinear frequency and critical fluid velocity. Results indicate that the natural frequency and the critical fluid velocity of the smart composite microtube increase with increasing the small-scale parameter. POLYM. COMPOS., 36:1314–1324, 2015. © 2014 Society of Plastics Engineers
TL;DR: In this paper, the performance of a microelectromechanical in-plane Knudsen radiometric actuator, a self-contained device having thermal force generation, sensing, and tuning mechanisms integrated onto the same platform, is evaluated in terms of a non-dimensional force coefficient.
Abstract: The generation of forces and moments on structures immersed in rarefied non-isothermal gas flows has received limited practical implementation since first being discovered over a century ago. The formation of significant thermal stresses requires both large thermal gradients and characteristic dimensions which are comparable to the gas molecular mean free path. For macroscopic geometries, this necessitates impractically high temperatures and very low pressures. At the microscale, however, these conditions are easily achieved, allowing the effects to be exploited, namely, for gas-property sensing and microstructure actuation. In this letter, we introduce and experimentally evaluate performance of a microelectromechanical in-plane Knudsen radiometric actuator, a self-contained device having Knudsen thermal force generation, sensing, and tuning mechanisms integrated onto the same platform. Sensitivity to ambient pressure, temperature gradient, as well as gas composition is demonstrated. Results are presented in terms of a non-dimensional force coefficient, allowing measurements to be directly compared to the previous experimental and computational data on out-of-plane cantilevered configurations.
TL;DR: In this article, the diffusion characteristics of nanoscale gas flow in a shale gas reservoir were investigated and the measured properties have been used to determine a diffusion coefficient by classification standard of gas flow regime.
TL;DR: In this article, the nonlinear vibration in a coupled system of Boron-Nitride nano-tube reinforced composite (BNNTRC) micro-tubes conveying viscous fluid is studied.
TL;DR: In this article, the Ellipsoidal Statistical model (ES-model) and the Shakhov model (S- model) were constructed to correct the Prandtl number of the original BGK model through the modification of stress and heat flux.
Abstract: The Ellipsoidal Statistical model (ES-model) and the Shakhov model (S- model) were constructed to correct the Prandtl number of the original BGK model through the modification of stress and heat flux. With the introduction of a new pa- rameter to combine the ES-model and S-model, a generalized kinetic model can be developed. This new model can give the correct Navier-Stokes equations in the con- tinuum flow regime. Through the adjustment of the new parameter, it provides abun- dant dynamic effect beyond the ES-model and S-model. Changing the free parameter, the physical performance of the new model has been tested numerically. The unified gas kinetic scheme (UGKS) is employed for the study of the new model. In transition flow regime, many physical problems, i.e., the shock structure and micro-flows, have been studied using the generalized model. With a careful choice of the free parameter, good results can be achieved for most test cases. Due to the property of the Boltz- mann collision integral, the new parameter in the generalized kinetic model cannot be fully determined. It depends on the specific problem. Generally speaking, the S- model predicts more accurate numerical solutions in most test cases presented in this paper than the ES-model, while ES-model performs better in the cases where the flow is mostly driven by temperature gradient, such as a channel flow with large boundary temperature variation at high Knudsen number. AMS subject classifications: 65M10, 78A48
TL;DR: In this paper, a smoothed-particle hydrodynamics (SPH) method was proposed for the solution of one-dimensional heat conduction problem within a nanoscale thin slab for Knudsen numbers of 0.1 and 1 under the effect of Dual-Phase-Lag (DPL) model.
TL;DR: In this paper, it was shown that non-equilibrium effects in the gas can account for this behaviour, with ambient pressure reductions increasing the gas' mean free path and hence the Knudsen number.
Abstract: Recent experiments on coating flows and liquid drop impact both demonstrate that wetting failures caused by air entrainment can be suppressed by reducing the ambient gas pressure. Here, it is shown that non-equilibrium effects in the gas can account for this behaviour, with ambient pressure reductions increasing the gas' mean free path and hence the Knudsen number $Kn$. These effects first manifest themselves through Maxwell slip at the gas' boundaries so that for sufficiently small $Kn$ they can be incorporated into a continuum model for dynamic wetting flows. The resulting mathematical model contains flow structures on the nano-, micro- and milli-metre scales and is implemented into a computational platform developed specifically for such multiscale phenomena. The coating flow geometry is used to show that for a fixed gas-liquid-solid system (a) the increased Maxwell slip at reduced pressures can substantially delay air entrainment, i.e. increase the `maximum speed of wetting', (b) unbounded maximum speeds are obtained as the pressure is reduced only when slip at the gas-liquid interface is allowed for and (c) the observed behaviour can be rationalised by studying the dynamics of the gas film in front of the moving contact line. A direct comparison to experimental results obtained in the dip-coating process shows that the model recovers most trends but does not accurately predict some of the high viscosity data at reduced pressures. This discrepancy occurs because the gas flow enters the `transition regime', so that more complex descriptions of its non-equilibrium nature are required. Finally, by collapsing onto a master curve experimental data obtained for drop impact in a reduced pressure gas, it is shown that the same physical mechanisms are also likely to govern splash suppression phenomena.
TL;DR: In this paper, a three-dimensional numerical study of gaseous slip flow through diverging microchannel was performed for nitrogen gas flowing through microchannel with different divergence angles (4°, 8°, 12° and 16°), hydraulic diameters (118, 147 and 177μm) and lengths (10, 20 and 30mm).
TL;DR: In this paper, the Simplified Bernoulli trials (SBT) collision algorithm was used in place of the conventional No-Time-Counter (No-Counter) scheme in the direct simulation Monte Carlo (DSMC) method, thus reducing the required particle number.
TL;DR: In this article, the pore geometry in the catalyst layer was simplified into a bundle of tubes whose diameters can be derived from pore-size distribution of the focused ion beam (FIB) images.
TL;DR: In this article, it was shown that increased Maxwell slip at reduced pressures can substantially delay air entrainment, and unbounded maximum speeds are obtained, as the pressure is reduced only when slip at the gas-liquid interface is allowed for, and the observed behaviour can be rationalised by studying the dynamics of the gas film in front of the moving contact line.
Abstract: Recent experiments on coating flows and liquid drop impact both demonstrate that wetting failures caused by air entrainment can be suppressed by reducing the ambient gas pressure. Here, it is shown that non-equilibrium effects in the gas can account for this behaviour, with ambient pressure reductions increasing the mean free path of the gas and hence the Knudsen number Kn. These effects first manifest themselves through Maxwell slip at the boundaries of the gas, so that for sufficiently small Kn they can be incorporated into a continuum model for dynamic wetting flows. The resulting mathematical model contains flow structures on the nano-, micro- and millimetre scales and is implemented into a computational platform developed specifically for such multiscale phenomena. The coating flow geometry is used to show that for a fixed gas–liquid–solid system (a) the increased Maxwell slip at reduced pressures can substantially delay air entrainment, i.e. increase the ‘maximum speed of wetting’, (b) unbounded maximum speeds are obtained, as the pressure is reduced only when slip at the gas–liquid interface is allowed for, and (c) the observed behaviour can be rationalised by studying the dynamics of the gas film in front of the moving contact line. A direct comparison with experimental results obtained from a dip-coating process shows that the model recovers most trends but does not accurately predict some of the high viscosity data at reduced pressures. This discrepancy occurs because the gas flow enters the ‘transition regime’, so that more complex descriptions of its non-equilibrium nature are required. Finally, by collapsing onto a master curve experimental data obtained for drop impact in a reduced pressure gas, it is shown that the same physical mechanisms are also likely to govern splash suppression phenomena.
01 Dec 2015
TL;DR: In this article, the effects of the suction/injection, mixed convection, the Knudsen number, Prandtl number and the radius ratio on the MPA hydrodynamic and thermal behaviors were investigated.
Abstract: This work analyzes the behaviors of fully developed mixed convection flow of an incompressible and viscous fluid in a vertical micro-porous-annulus (MPA) taking into account the velocity slip and temperature jump at the outer surface of inner porous cylinder and inner surface of outer porous cylinder. The present study explores the effects of the suction/injection, mixed convection, the Knudsen number, Prandtl number and the radius ratio on the MPA hydrodynamic and thermal behaviours. It is interesting to remark that as suction/injection on the MPA increases, the fluid velocity and temperature is enhanced. In addition, the rate of heat transfer at outer surface of inner porous cylinder decrease with increase in Knudsen number for suction at the inner porous cylinder and simultaneous injection at the outer porous cylinder while the result is just contrast at inner surface of outer porous cylinder.
TL;DR: Rosenberg et al. as mentioned in this paper assessed the significance and nature of ion kinetic effects in D3He-filled, shock-driven inertial confinement fusion implosions through measurements of fusion burn profiles.
Abstract: The significance and nature of ion kinetic effects in D3He-filled, shock-driven inertial confinement fusion implosions are assessed through measurements of fusion burn profiles Over this series of experiments, the ratio of ion-ion mean free path to minimum shell radius (the Knudsen number, NK) was varied from 03 to 9 in order to probe hydrodynamic-like to strongly kinetic plasma conditions; as the Knudsen number increased, hydrodynamic models increasingly failed to match measured yields, while an empirically-tuned, first-step model of ion kinetic effects better captured the observed yield trends [Rosenberg et al, Phys Rev Lett 112, 185001 (2014)] Here, spatially resolved measurements of the fusion burn are used to examine kinetic ion transport effects in greater detail, adding an additional dimension of understanding that goes beyond zero-dimensional integrated quantities to one-dimensional profiles In agreement with the previous findings, a comparison of measured and simulated burn profiles shows that models including ion transport effects are able to better match the experimental results In implosions characterized by large Knudsen numbers (NK ∼ 3), the fusion burn profiles predicted by hydrodynamics simulations that exclude ion mean free path effects are peaked far from the origin, in stark disagreement with the experimentally observed profiles, which are centrally peaked In contrast, a hydrodynamics simulation that includes a model of ion diffusion is able to qualitatively match the measured profile shapes Therefore, ion diffusion or diffusion-like processes are identified as a plausible explanation of the observed trends, though further refinement of the models is needed for a more complete and quantitative understanding of ion kinetic effects
TL;DR: In this article, the nonlinear vibration response of coupled viscoelastic carbon nanotubes (CNTs) conveying viscous fluid is investigated based on nonlocal and modified couple stress theories.
Abstract: Nonlinear vibration response of coupled viscoelastic carbon nanotubes (CNTs) conveying viscous fluid is investigated based on nonlocal and modified couple stress theories. The CNTs are placed in a uniform two-dimensional (2D) magnetic field and modeled by a Timoshenko beam. The effect of slip boundary condition is considered in the Navier–Stokes relations based on the Knudsen number correction factor. The higher-order governing equations of motion are derived based on the energy method and Hamilton’s principle where the differential quadrature (DQ) approach is applied to obtain the nonlinear frequency of coupled system. A detailed parametric study is conducted, focusing on the combined effects of 2D magnetic field, Visco-Pasternak foundation, Knudsen number, surface effect, velocity of conveying viscous fluid, and different theories. Also, the Galerkin method is applied to compare our linear results to those that are obtained by the DQ approach. The results of this article could be useful in designing and manufacturing of double nano-/micromechanical systems that are usually used in advanced biomechanics and optics.
TL;DR: A comprehensive mathematical model that incorporates all known mechanisms for simulating gas flow in shale strata is presented and shows that adsorption and gas viscosity change will have a great impact on gas production.
Abstract: Gas transport in unconventional shale strata is a multi-mechanism-coupling process that is different from the process observed in conventional reservoirs. In micro fractures which are inborn or induced by hydraulic stimulation, viscous flow dominates. And gas surface diffusion and gas desorption should be further considered in organic nano pores. Also, the Klinkenberg effect should be considered when dealing with the gas transport problem. In addition, following two factors can play significant roles under certain circumstances but have not received enough attention in previous models. During pressure depletion, gas viscosity will change with Knudsen number; and pore radius will increase when the adsorption gas desorbs from the pore wall. In this paper, a comprehensive mathematical model that incorporates all known mechanisms for simulating gas flow in shale strata is presented. The objective of this study was to provide a more accurate reservoir model for simulation based on the flow mechanisms in the pore scale and formation geometry. Complex mechanisms, including viscous flow, Knudsen diffusion, slip flow, and desorption, are optionally integrated into different continua in the model. Sensitivity analysis was conducted to evaluate the effect of different mechanisms on the gas production. The results showed that adsorption and gas viscosity change will have a great impact on gas production. Ignoring one of following scenarios, such as adsorption, gas permeability change, gas viscosity change, or pore radius change, will underestimate gas production.
TL;DR: In this article, the authors focus on the isothermal rarefied gas flow through long channels with longitudinally varying cross section and apply two approaches, an analytical one and a numerical one that is based on the solution of the linearized S-model, both allowing them to predict the mass flow rate in diverging and converging flow directions for arbitrary pressure gradients.
Abstract: Moderately rarefied gas flows are clearly distinguished from viscous flow in the continuum regime and from free molecular flow at high rarefaction. Being of relevance for various technical applications, the understanding of such flow processes is crucial for considerable enhancement in micro electromechanical systems (MEMS) and vacuum techniques. In this work, we focus on the isothermal rarefied gas flow through long channels with longitudinally varying cross section. We apply two approaches, an analytical one and a numerical one that is based on the solution of the linearized S-model, both allowing us to predict the mass flow rate in diverging and converging flow directions for arbitrary pressure gradients. Both approaches are validated by CO2, N2 and Ar permeation experiments on tapered microchannels manufactured by means of micromilling. The local Knudsen numbers ranged from 0.0471 to 0.2263. All the numerical and analytical results are in good agreement to the experimental data and show that the mass flow rate is significantly higher when the duct is perfused in converging direction. The understanding of the physical phenomenon of this gas flow diode effect might pave the way for novel components in MEMS such as static one-way valves.