knudsen numbers
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2021 ◽  
Vol 2094 (2) ◽  
pp. 022078
Author(s):  
Vladimir N Belov ◽  
Evgeny G Mayasov ◽  
Elena A Pervushkina ◽  
Aleksey A Statuev ◽  
Viacheslav B Trukhmanov

Abstract A moment method for solving the linearized kinetic Boltzmann equation for arbitrary Knudsen numbers is presented. The isothermal flow of a rarefied gas around a cylindrical surface (the limiting cylindrical Couette problem) is investigated. The moments of the collision integral are calculated for the hard sphere model. The moment of resistance force acting per unit length of the surface, the profile of the gas flow velocity in the transient regime, and the gas velocity on the surface are calculated.


2021 ◽  
Author(s):  
Satoshi Taguchi ◽  
Tetsuro Tsuji

Abstract The thermal edge flow is a gas flow typically induced near a sharp edge (or a tip) of a uniformly heated flat plate. This flow has potential applicability as a nonmechanical flow controller in microelectromechanical systems (MEMS). However, it has a shortcoming: the thermal edge flows from each edge cancel out, resulting in no net flow. In this study, to circumvent this difficulty, the use of a U-shaped body is proposed and is examined numerically. More specifically, a rarefied gas flow over an array of U-shaped bodies, periodically arranged in a straight channel, is investigated using the direct simulation Monte-Carlo (DSMC) method. The U-shaped bodies are kept at a uniform temperature different from that of the channel. Two types of U-shaped bodies are considered, namely, a square-U shape and a round-U shape. It is demonstrated that a steady one-way flow is induced in the channel for both types. The mass flow rate is obtained for a wide range of the Knudsen numbers, i.e., the ratio of the molecular mean free path to the characteristic size of the U-shape body. For the square-U type, the direction of the overall mass flow is in the same direction for the entire range of the Knudsen numbers investigated. For the round-U type, the direction of the total mass flux is reversed when the Knudsen number is moderate or larger. This reversal of the mass flow rate is attributed to a kind of thermal edge flow induced over the curved part of the round-U-shaped body, which overwhelms the thermal edge flow induced near the tip. The force acting on each of the bodies is also investigated.


Author(s):  
Mostafa Zakeri ◽  
Ehsan Roohi

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.


2021 ◽  
Vol 91 (3) ◽  
pp. 395
Author(s):  
Т.Р. Аманбаев

The influence of the processes of deposition and coagulation of particles, caused by Brownian diffusion, on the parameters of aerosols flowing in the tube is studied. The problem is considered in a two-dimensional formulation taking into account the inhomogeneous velocity profile of the medium across the tube. At different Knudsen numbers, the distributions of the concentration and radius of clusters (formed due to particle coagulation) along the longitudinal and transverse directions were obtained by the numerical finite difference method. It was found that moving along the channel, the clusters reach the final (limiting) size. The influence of the governing parameters on the distribution of dispersed characteristics of the mixture inside the tube and on the limiting size of clusters is discussed.


2021 ◽  
Vol 33 (1) ◽  
pp. 012106
Author(s):  
V. M. Zhdanov ◽  
V. A. Zaznoba ◽  
A. A. Stepanenko

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Vahid Shariati ◽  
Mohammad Hassan Ahmadian ◽  
Ehsan Roohi

AbstractThe impetus of the current research is to use the direct simulation Monte Carlo (DSMC) algorithm to investigate fluid behaviour and gas transport in porous microchannels. Here, we demonstrate DSMC’s capability to simulate porous media up to 40% porosity. In this study, the porous geometry is generated by a random distribution of circular obstacles through the microchannel with no interpenetration between the obstacles. The influence of the morphology along with rarefaction and gas type on the apparent permeability is investigated. Moreover, the effects of porosity, solid particle’s diameter and specific surface area are considered. Our results demonstrate that although decreasing porosity intensifies tortuosity in the flow field, the tortuosity reduces at higher Knudsen numbers due to slip flow at solid boundaries. In addition, our study on two different gas species showed that the gas type affects slippage and apparent gas permeability. Finally, comparing different apparent permeability models showed that Beskok and Karniadakis model is valid only up to the early transition regime and at higher Knudsen numbers, the current data matches those models that take Knudsen diffusion into account as well.


AIAA Journal ◽  
2019 ◽  
Vol 57 (8) ◽  
pp. 3501-3505
Author(s):  
Ruihua Zhang ◽  
Shiying Cai ◽  
Chunpei Cai ◽  
Jun Li
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