Study of Flow Characteristics of Gas Mixtures in a Rectangular Knudsen Pump

Zhang, Zhijun; Wang, Xiaowei; Zhao, Lili; Zhang, Shiwei; Zhao, Fan

doi:10.3390/mi10020079

Cited by 22 publications

(31 citation statements)

References 57 publications

(75 reference statements)

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“…DSMC is a highly-efficient method to solve the Boltzmann equation [ 40 , 41 ]. Moreover, the DSMC method has been widely used in the research of rarefied gas flow induced by temperature field [ 42 , 43 , 44 ] and low-pressure gas actuators based on Knudsen force [ 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ].…”

Section: Numerical Approachmentioning

confidence: 99%

Impact of Improved Design on Knudsen Force for Micro Gas Sensor

Wang

Zhang

et al. 2020

Micromachines

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Knudsen force generated by thermally driven gas flow in a microscale structure has been used for gas detection and has shown immeasurable potential in the field of microelectromechanical system (MEMS) gas sensors due to its novel sensing characteristics. In this article, the performances of three kinds of Knudsen force gas sensors with improved isosceles triangular shuttle arm structures were studied. In the first design, the top side and right side lengths were equal; in the second, the top side and bottom side lengths were equal; and for the third, the bottom side and right side lengths were equal. A detailed investigation including gas flow, thermal characteristics, Knudsen force, and coupling effects between the shuttle-heater pairs was conducted using the direct simulation Monte Carlo (DSMC) method and the main mechanisms for gas flow presented were almost the same in this work. However, the second design returned the highest Knudsen force performance. The value increased by 42.9% (P = 387 Pa) compared to the Knudsen force of the original square shuttle arm. The results also demonstrate that the coupling effects become weak toward the right with an increase in the number of shuttle-heater pairs.

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Section: Numerical Approachmentioning

confidence: 99%

Impact of Improved Design on Knudsen Force for Micro Gas Sensor

Wang

Zhang

et al. 2020

Micromachines

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“…The studied configuration is composed of a series of alternately connected narrow and wide channels in serial cascades [ 18 , 31 ]. It is up-down symmetrical with a black dot-dashed line, thus only the upper half of the configuration is presented, as shown in Figure 1 .…”

Section: Problem Statementmentioning

confidence: 99%

“…It is well-known that in order to accurately simulate the molecular collision process to obtain a reliable macroscopic quantity, the use of a more physically realistic collision model is crucial. In previous research on the Knudsen pump, the hard sphere (HS) model [ 19 ] and variable hard sphere (VHS) model [ 20 , 21 , 22 , 23 , 24 , 31 ] are two common molecular models for particle simulations. In fact, the HS model has disadvantages of constant collision cross-section and unrealistic scattering law [ 32 ].…”

Section: Introductionmentioning

confidence: 99%

Numerical Investigation into the Flow Characteristics of Gas Mixtures in Knudsen Pump with Variable Soft Sphere Model

Wang

Han

et al. 2020

Micromachines

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In Knudsen pumps with geometric configuration of rectangle, gas flows are induced by temperature gradients along channel walls. In this paper, the direct simulation Monte Carlo (DSMC) method is used to investigate numerically the flow characteristics of H2–N2 mixtures in the Knudsen pump. The variable soft sphere (VSS) model is applied to depict molecular diffusion in the gas mixtures, and the results obtained are compared with those calculated from a variable hard sphere (VHS) model. It is demonstrated that pressure is crucial to affecting the variation of gas flow pattern, but the gas concentration in H2–N2 mixtures and the collision model do not change the flow pattern significantly. On the other hand, the velocity of H2 is larger than that of N2. The velocities of H2 and N2 increase if the concentration of H2 rises in the gas mixtures. The results of velocity and mass flow rate obtained from VSS and VHS models are different. Finally, a linear relation between the decrease of mass flow rate and the increase of H2 concentration is proposed to predict the mass flow rate in H2–N2 mixtures.

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“…, where ̅ = �8 � �� ⁄ is the mean thermal velocity, and ξΔt is the time step parameter. Based on equations above, the mesh size results to be 47080 cells (see Fig.1 (b)), while the time step was set to 4x10 -9 s corresponding to the condition ξΔt ≤ 0.2, in accordance with typical DSMC requirements [18]. The methodology in DSMC computation has been previously validated based on experiments performed in [19] on a tronco-conical axisymmetric micronozzle.…”

Section: �̅mentioning

confidence: 99%

Comparison of numerical predictions of the supersonic expansion inside micronozzles of micro–resistojets

2019

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The present work provides a numerical investigation of the supersonic flow inside a planar micronozzle configuration under different gas rarefaction conditions. Two different propellants have been considered, namely water vapor and nitrogen, which relate to their use in VLMs (the former) and cold gas microthrusters (the latter), respectively. Furthermore, two different numerical approaches have been used due to the different gas rarefaction regime, i.e. the typical continuum Navier–Stokes with partial slip assumption at walls and the particle–based Direct Simulation Monte Carlo (DSMC) technique. As a result, under high–pressure operating conditions, both water and nitrogen flows supersonically expanded into the micronozzle without chocking in combination with a linear growth of the boundary layer on walls. However, when low–pressure operating condition are imposed and a molecular regime is established inside the micronozzle, a very rapid expansion occurred close to the nozzle exit in combination with a strong chocking of the flow and a micronozzle quality reduction of about 40%. Furthermore, water exhibited specific higher specific impulse than nitrogen above 60%.

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Study of Flow Characteristics of Gas Mixtures in a Rectangular Knudsen Pump

Cited by 22 publications

References 57 publications

Impact of Improved Design on Knudsen Force for Micro Gas Sensor

Impact of Improved Design on Knudsen Force for Micro Gas Sensor

Numerical Investigation into the Flow Characteristics of Gas Mixtures in Knudsen Pump with Variable Soft Sphere Model

Comparison of numerical predictions of the supersonic expansion inside micronozzles of micro–resistojets

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