Comparison of 3-D and 2-D DSMC Heat Transfer Calculations of Low-Speed Short Microchannel Flows

Zhen, Chaw-En; Hong, Zuu‐Chang; Lin, Ya-Ju; Hong, Nien-Tzu

doi:10.1080/10407780601149888

Cited by 25 publications

(5 citation statements)

References 19 publications

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“…The ratio of the total length L to the width of the channel H sets to 13.5 while the solid surfaces of the channel extend to infinity in the direction perpendicular to the x-y plane, so the problem is effectively two-dimensional. 5,[40][41][42] Due to the fact that the material of silicon, which is commonly used for micron-sized devices, is a good heat conductor, the gas flow in the micro-channel could be considered isothermal. 13 In this work, the gas flow is driven by the pressure difference between the inlet/outlet of the channel and we are interested in the influence of bend on the MFR at various Knudsen numbers.…”

Section: Formulation Of the Problemmentioning

confidence: 99%

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Rarefaction throttling effect: Influence of the bend in micro-channel gaseous flow

Liu

Tang

et al. 2018

Physics of Fluids

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Micro-bends are frequently encountered in micro-electro-mechanical systems (MEMS) as a basic unit of complex geometry. It is essential for a deep understanding of the rarefied gas flow through bent channel. In this paper, a two-dimensional pressure-driven gas flow in a micro-channel with two bends is investigated by solving the Bhatnagar-Gross-Krook kinetic equation via the discrete velocity method in the slip and transition flow regimes. The results show that the mass flow rate (MFR) through the bent channel is slightly higher than that in the straight channel in the slip flow regime but drops significantly as the Knudsen number increases further. It is demonstrated that the increase of MFR is not due to the rarefaction effect but to the increase in cross-section of the bent corners. As the rarefaction effect becomes more prominent, the low-velocity zones at the corners expand and the gas flow is "squeezed" into the inner corner. The narrowed flow section is similar to the throttling effect caused by the valve, and both the changes in MFRs and the pressure distribution also confirm this effect. The classical Knudsen minimum changes due to this "rarefaction throttling effect". The Knudsen number at which the minimum MFR occurs gradually increases with the bend angle, and finally disappears in the transition flow regime. In addition, the onset of rarefaction throttling effect shifts to a smaller Knudsen number with a lower tangential momentum accommodation coefficient.

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Section: Formulation Of the Problemmentioning

confidence: 99%

“…It should be noted that, even though we carefully selected the aspect ratio of the bent channel / 13.5 LH  in the two-dimensional simulations according to the previous literature [5,40,41]…”

Section: The Enhancement and Reduction Of Mfr At Different Knudsenmentioning

confidence: 99%

Rarefaction throttling effect: Influence of the bend in micro-channel gaseous flow

Liu

Tang

et al. 2018

Physics of Fluids

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“…The length of the channel (L) is twenty times larger than its inlet height (i.e., L = 20 × H i = 8 × 10 −6 m). The problem is assumed to be two-dimensional, which is a valid assumption for channels with considerably large depths [43,49]. The molecular properties of gaseous nitrogen are summarised in Table 1, where d p is molecular diameter, m p is molecular mass, ω is the viscosity-temperature index, T ref is the reference temperature in the viscositytemperature relation, and µ 0 is the viscosity at the reference temperature.…”

Section: Problem Descriptionmentioning

confidence: 99%

Pressure-Driven Nitrogen Flow in Divergent Microchannels with Isothermal Walls

2021

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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.

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“…The problem is assumed to be two-dimensional, which is a valid assumption for channels with considerably large depths [43,49]. The molecular properties of gaseous nitrogen are summarised in Table 1, where d p is molecular diameter, m p molecular mass, ω the viscosity-temperature index, T ref the reference temperature in the viscosity-temperature relation, and µ 0 the viscosity at the reference temperature.…”

Section: Problem Descriptionmentioning

confidence: 99%

Pressure-driven Nitrogen Flow in Divergent Microchannels with Isothermal Walls

Ebrahimi,

Shahabi,

Roohi

2021

Preprint

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Gas flow and heat transfer in confined geometries at micro and nano scales differ considerably from those at macro-scales, mainly due to nonequilibrium effects such as velocity slip and temperature jump. The nonequilibrium effects enhance 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 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.

show abstract

Comparison of 3-D and 2-D DSMC Heat Transfer Calculations of Low-Speed Short Microchannel Flows

Cited by 25 publications

References 19 publications

Rarefaction throttling effect: Influence of the bend in micro-channel gaseous flow

Rarefaction throttling effect: Influence of the bend in micro-channel gaseous flow

Pressure-Driven Nitrogen Flow in Divergent Microchannels with Isothermal Walls

Pressure-driven Nitrogen Flow in Divergent Microchannels with Isothermal Walls

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