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Micromachines
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Gas Flows in Microsystems, Volume II
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Gas Flows in Microsystems, Volume II

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "A：Physics".

Deadline for manuscript submissions: closed (30 November 2020) | Viewed by 13898

Special Issue Editors

Prof. Stéphane Colin

E-Mail Website
Guest Editor
Institut Clément Ader, Université de Toulouse, 3 rue Caroline Aigle, 31400 Toulouse, France
Interests: microfluidics; gas microflows; fluidic microsystems; microscale heat transfer
Special Issues, Collections and Topics in MDPI journals
Dr. Lucien Baldas

E-Mail Website
Guest Editor
Institut Clément Ader, Université de Toulouse, 3 rue Caroline Aigle, 31400 Toulouse, France
Interests: microfluidics; gas microflows; fluidic microsystems; particle-laden microflows
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The last two decades have witnessed a rapid development of micro-electromechanical systems (MEMS) involving gas microflows in various technical fields. Gas microflows can, for example, be observed in micro-heat exchangers designed for chemical applications or for cooling of electronic components, in fluidic micro-actuators developed for active flow control purposes, in micronozzles used for the micro-propulsion of nano- and picosats, in micro-gas chromatographs, analyzers or separators, in vacuum generators and in Knudsen micropumps, as well as in some organs-on-a-chip, such as artificial lungs. These flows are rarefied due to the small MEMS dimensions, and rarefaction can be increased by low pressure conditions. The flows relate to the slip flow, transition or free molecular regimes and can involve monatomic or polyatomic gases and gas mixtures. Hydrodynamics and heat and mass transfer are strongly impacted by rarefaction effects, and temperature-driven microflows offer new opportunities for designing original MEMS for gas pumping or separation. Accordingly, this Special Issue seeks to showcase research papers, short communications, and review articles that focus on novel theoretical and numerical models or data as well as on new experimental results and techniques for improving knowledge on heat and mass transfer in gas microflows. Papers dealing with the development of original gas MEMS are also welcome.

We look forward to receiving your submission.

Prof. Stéphane Colin
Dr. Lucien Baldas
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • gas microflows
  • rarefied flows
  • microscale heat and mass transfer in gases
  • gas MEMS
  • theoretical, experimental and numerical analysis

Related Special Issue

Published Papers (6 papers)

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Research

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21 pages, 5771 KiB  
Article
The Correctness of the Simplified Bernoulli Trial (SBT) Collision Scheme of Calculations of Two-Dimensional Flows
by Kiril Shterev
Micromachines 2021, 12(2), 127; https://doi.org/10.3390/mi12020127 - 26 Jan 2021
Cited by 3 | Viewed by 2049
Abstract
Micro-electromechanical systems (MEMS) have developed rapidly in recent years in various technical fields that have increased their interest in the Direct Simulation Monte Carlo (DSMC) method. In this paper, we present a simple representation of the DSMC collision scheme and investigate the correctness [...] Read more.
Micro-electromechanical systems (MEMS) have developed rapidly in recent years in various technical fields that have increased their interest in the Direct Simulation Monte Carlo (DSMC) method. In this paper, we present a simple representation of the DSMC collision scheme and investigate the correctness of the Simplified Bernoulli Trial (SBT) collision scheme for the calculation of two-dimensional flows. The first part of the collision scheme, which determines collision pairs, is presented following the derivation of the expression for the mean free path and using the cumulative distribution function. Approaches and conclusions based on one-dimensional flows are not always directly applicable to two- and three-dimensional flows. We investigated SBT correctness by using the two-dimensional pressure-driven gas flow of monoatomic gas as a test case. We studied the influence of shuffling of the list of particles per cell (PPC) before the collision scheme’s execution, as well as the minimal and maximal number of PPC, on the correctness of the solution. The investigation showed that shuffling and the number of PPC played an important role in the correctness of SBT. Our recommendations are straightforwardly applicable to three-dimensional flows. Finally, we considered the mixing of two gases and compared the results available in the literature. Full article
(This article belongs to the Special Issue Gas Flows in Microsystems, Volume II)
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15 pages, 4270 KiB  
Article
A Bidirectional Knudsen Pump with a 3D-Printed Thermal Management Platform
by Qisen Cheng, Yutao Qin and Yogesh B. Gianchandani
Micromachines 2021, 12(1), 58; https://doi.org/10.3390/mi12010058 - 06 Jan 2021
Cited by 7 | Viewed by 2144
Abstract
This paper reports on a bidirectional Knudsen pump (KP) with a 3D-printed thermal management platform; the pump is intended principally for microscale gas chromatography applications. Knudsen pumps utilize thermal transpiration, where non-viscous flow is created against a temperature gradient; no moving parts are [...] Read more.
This paper reports on a bidirectional Knudsen pump (KP) with a 3D-printed thermal management platform; the pump is intended principally for microscale gas chromatography applications. Knudsen pumps utilize thermal transpiration, where non-viscous flow is created against a temperature gradient; no moving parts are necessary. Here, a specialized design leverages 3D direct metal laser sintering and provides thermal management that minimizes loss from a joule heater located on the outlet side of KP, while maintaining convective cooling on the inlet side. The 3D-KP design is integrative and compact, and is specifically intended to simplify assembly. The 3D-KP pumping area is ≈1.1 cm2; with the integrated heat sink, the structure has a footprint of 64.2 × 64.2 mm2. Using mixed cellulose ester (MCE) membranes with a 25 nm average pore diameter and 525 μm total membrane thickness as the pumping media, the 3D-KP achieves a maximum flow rate of 0.39 sccm and blocking pressure of 818.2 Pa at 2 W input power. The operating temperature is 72.2 °C at ambient room temperature. In addition to MCE membranes, anodic aluminum oxide (AAO) membranes are evaluated as the pumping media; these AAO membranes can accommodate higher operating temperatures than MCE membranes. The 3D-KP with AAO membranes with 0.2 μm average pore diameter and 531 μm total membrane thickness achieves a maximum flow rate of 0.75 sccm and blocking pressure of 496.1 Pa at 9.8 W at an operating temperature of 191.2 °C. Full article
(This article belongs to the Special Issue Gas Flows in Microsystems, Volume II)
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14 pages, 7269 KiB  
Article
Numerical Study of Nanoparticle Deposition in a Gaseous Microchannel under the Influence of Various Forces
by Fubing Bao, Hanbo Hao, Zhaoqin Yin and Chengxu Tu
Micromachines 2021, 12(1), 47; https://doi.org/10.3390/mi12010047 - 01 Jan 2021
Cited by 3 | Viewed by 1901
Abstract
Nanoparticle deposition in microchannel devices inducing contaminant clogging is a serious barrier to the application of micro-electro-mechanical systems (MEMS). For micro-scale gas flow fields with a high Knudsen number (Kn) in the microchannel, gas rarefaction and velocity slip cannot be ignored. [...] Read more.
Nanoparticle deposition in microchannel devices inducing contaminant clogging is a serious barrier to the application of micro-electro-mechanical systems (MEMS). For micro-scale gas flow fields with a high Knudsen number (Kn) in the microchannel, gas rarefaction and velocity slip cannot be ignored. Furthermore, the mechanism of nanoparticle transport and deposition in the microchannel is extremely complex. In this study, the compressible gas model and a second-order slip boundary condition have been applied to the Burnett equations to solve the flow field issue in a microchannel. Drag, Brownian, and thermophoretic forces are concerned in the motion equations of particles. A series of numerical simulations for various particle sizes, flow rates, and temperature gradients have been performed. Some important features such as reasons, efficiencies, and locations of particle deposition have been explored. The results indicate that the particle deposition efficiency varies more or less under the actions of forces such as Brownian force, thermophoretic force, and drag force. Nevertheless, different forces lead to different particle motions and deposition processes. Brownian or thermophoretic force causes particles to move closer to the wall or further away from it. The drag force influence of slip boundary conditions and gas rarefaction changes the particles’ residential time in the channel. In order to find a way to decrease particle deposition on the microchannel surface, the deposition locations of different sizes of particles have been analyzed in detail under the action of thermophoretic force. Full article
(This article belongs to the Special Issue Gas Flows in Microsystems, Volume II)
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17 pages, 9294 KiB  
Article
Numerical Investigation into the Flow Characteristics of Gas Mixtures in Knudsen Pump with Variable Soft Sphere Model
by Chunlin Du, Xiaowei Wang, Feng Han, Xiaoyu Ren and Zhijun Zhang
Micromachines 2020, 11(9), 784; https://doi.org/10.3390/mi11090784 - 19 Aug 2020
Cited by 6 | Viewed by 1850
Abstract
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Gas Flows in Microsystems, Volume II)
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15 pages, 4030 KiB  
Article
Thermally Developing Flow and Heat Transfer in Elliptical Minichannels with Constant Wall Temperature
by Liangbin Su, Zhipeng Duan, Boshu He, Hao Ma and Zairan Xu
Micromachines 2019, 10(10), 713; https://doi.org/10.3390/mi10100713 - 21 Oct 2019
Cited by 6 | Viewed by 3538
Abstract
Laminar convective heat transfer of elliptical minichannels is investigated for hydrodynamically fully developed but thermal developing flow with no-slip condition. A three-dimensional numerical model is developed in different elliptical geometries with the aspect ratio varying from 0.2 to 1. The effect of Reynolds [...] Read more.
Laminar convective heat transfer of elliptical minichannels is investigated for hydrodynamically fully developed but thermal developing flow with no-slip condition. A three-dimensional numerical model is developed in different elliptical geometries with the aspect ratio varying from 0.2 to 1. The effect of Reynolds number (25 ≤ Re ≤ 2000) on the local Nusselt number is examined in detail. The results indicate that the local Nusselt number is a decreasing function of Reynolds number and it is sensitive to Reynolds number especially for Re less than 250. The effect of aspect ratio on local Nusselt number is small when compared with the effect of Reynolds number on local Nusselt number. The local Nusselt number is independent of cross-section geometry at the inlet. The maximum effect of aspect ratio on local Nusselt number arises at the transition section rather than the fully developed region. However, the non-dimensional thermal entrance length is a monotonic decreasing concave function of aspect ratio but a weak function of Reynolds number. Correlations for the local Nusselt number and the thermal developing length for elliptical channels are developed with good accuracy, which may provide guidance for design and optimization of elliptical minichannel heat sinks. Full article
(This article belongs to the Special Issue Gas Flows in Microsystems, Volume II)
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Review

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52 pages, 14972 KiB  
Review
Review of Optical Thermometry Techniques for Flows at the Microscale towards Their Applicability to Gas Microflows
by Stéphane Colin, José M. Fernández, Christine Barrot, Lucien Baldas, Slaven Bajić and Marcos Rojas-Cárdenas
Micromachines 2022, 13(11), 1819; https://doi.org/10.3390/mi13111819 - 25 Oct 2022
Cited by 1 | Viewed by 1940
Abstract
Thermometry techniques have been widely developed during the last decades to analyze thermal properties of various fluid flows. Following the increasing interest for microfluidic applications, most of these techniques have been adapted to the microscale and some new experimental approaches have emerged. In [...] Read more.
Thermometry techniques have been widely developed during the last decades to analyze thermal properties of various fluid flows. Following the increasing interest for microfluidic applications, most of these techniques have been adapted to the microscale and some new experimental approaches have emerged. In the last years, the need for a detailed experimental analysis of gaseous microflows has drastically grown due to a variety of exciting new applications. Unfortunately, thermometry is not yet well developed for analyzing gas flows at the microscale. Thus, the present review aims at analyzing the main currently available thermometry techniques adapted to microflows. Following a rapid presentation and classification of these techniques, the review is focused on optical techniques, which are the most suited for application at microscale. Their presentation is followed by a discussion about their applicability to gas microflows, especially in confined conditions, and the current challenges to be overcome are presented. A special place is dedicated to Raman and molecular tagging thermometry techniques due to their high potential and low intrusiveness. Full article
(This article belongs to the Special Issue Gas Flows in Microsystems, Volume II)
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