Lattice Boltzmann Simulation of Rarefied Gas Flow Along Moving Rigid Objects in Micro-Cavities

2015 ◽  
Author(s):  
Weilin Yang ◽  
Hongxia Li ◽  
TieJun Zhang ◽  
Ibrahim M. Elfadel
Keyword(s):  
Free Path ◽  
Lattice Boltzmann ◽  
Path Length ◽  
Gas Flow ◽  
Rarefied Gas ◽  
Free Path Length ◽  
Mean Free Path ◽  
Fluid Simulation ◽  
Transition Flow ◽  
Rarefied Gas Flow

Rarefied gas flow plays an important role in the design and performance analysis of micro-electro-mechanical systems (MEMS) under high-vacuum conditions. The rarefaction can be evaluated by the Knudsen number (Kn), which is the ratio of the molecular mean free path length and the characteristic length. In micro systems, the rarefied gas flow usually stays in the slip- and transition-flow regions (10−3 < Kn < 10), and may even go into the free molecular flow region (Kn > 10). As a result, conventional design tools based on continuum Navier-Stokes equation solvers are not applicable to analyzing rarefaction phenomena in MEMS under vacuum conditions. In this paper, we investigate the rarefied gas flow by using the lattice Boltzmann method (LBM), which is suitable for mesoscopic fluid simulation. The gas pressure determines the mean free path length and Kn, which further influences the relaxation time in the collision procedure of LBM. Here, we focus on the problem of squeezed film damping caused by an oscillating rigid object in a cavity. We propose an improved LBM with an immersed boundary approach, where an adjustable force term is used to quantify the interaction between the moving object and adjacent fluid, and further determines the slip velocity. With the proposed approach, the rarefied gas flow in MEMS with squeezed film damping is characterized. Different factors that affect the damping coefficient, such as pressure of gas and frequency of oscillation, are investigated in our simulation studies.

Imaging of Metal/Semiconductor Interface by Ballistic-Electron-Emission Microscopy (Beem)

1992 ◽  
Vol 295 ◽  
Author(s):  
E. Y. Lee ◽  
B. R. Turnew ◽  
J. R. Jimenez ◽  
L. J. Schowalter
Keyword(s):  
Free Path ◽  
Spatial Resolution ◽  
Electron Emission ◽  
Path Length ◽  
Free Path Length ◽  
Mean Free Path ◽  
Ballistic Electron Emission Microscopy ◽  
Semiconductor Interface ◽  
Ballistic Electron ◽  
Emission Microscopy

AbstractStudies in ballistic-electron-emission spectroscopy (BEES) have enabled precise energy measurements of Schottky barrier heights with excellent spatial resolution and, more recently, it was shown that even scattering at the metal/semiconductor interface affects the BEES spectrum [1]. Monte Carlo simulations have been done to predict the spatial resolution of ballistic-electron-emission microscopy (BEEM) [2]. In this paper, we will discuss the experimental spatial resolution of BEEM, and we will also give some of our BEES results for Au/Si and for Au/PtSi/Si. Our experimental BEEM studies indicate that, for Au/Si, hot electron transport is diffusive rather than ballistic, because the inelastic mean free path length (∼100 nm) is much larger than the elastic mean free path length (∼10 nm). This is in agreement with existing theories and with the literature on the internal photoemission method of studying the transport. Even in this diffusive regime, the spatial resolution of BEEM is still expected to be very good, being on the order of 10 nm [2]. Our preliminary work on PtSi shows that it has an attenuation length of 4 nm, which differs significantly from that of Au.

A STUDY ON PENETRATION DEPTH OF POLARIZATION IMAGING

2010 ◽  
Vol 03 (03) ◽  
pp. 177-181 ◽  
Author(s):  
RAN LIAO ◽  
NAN ZENG ◽  
DONGZHI LI ◽  
TIANLIANG YUN ◽  
YONGHONG HE ◽  
...  
Keyword(s):  
Penetration Depth ◽  
Free Path ◽  
Path Length ◽  
Free Path Length ◽  
Mean Free Path ◽  
Optical Measurements ◽  
Degree Of Polarization ◽  
Polarization Imaging ◽  
Optical Clearing ◽  
Different Response

Optical clearing improves the penetration depth of optical measurements in turbid tissues. Polarization imaging has been demonstrated as a potentially promising tool for detecting cancers in superficial tissues, but its limited depth of detection is a major obstacle to the effective application in clinical diagnosis. In the present paper, detection depths of two polarization imaging methods, i.e., rotating linear polarization imaging (RLPI) and degree of polarization imaging (DOPI), are examined quantitatively using both experiments and Monte Carlo simulations. The results show that the contrast curves of RLPI and DOPI are different. The characteristic depth of DOPI scales with transport mean free path length, and that of RLPI increases slightly with g. Both characteristic depths of RLPI and DOPI are on the order of transport mean free path length and the former is almost twice as large as the latter. It is expected that they should have different response to optical clearing process in tissues.

Mean free-path length theory of predator–prey interactions: Application to juvenile salmon migration

2005 ◽  
Vol 186 (2) ◽  
pp. 196-211 ◽  
Author(s):  
James J. Anderson ◽  
Eliezer Gurarie ◽  
Richard W. Zabel
Keyword(s):  
Free Path ◽  
Path Length ◽  
Free Path Length ◽  
Mean Free Path ◽  
Juvenile Salmon ◽  
Predator Prey

Simulation of Long Microchannel Flow in Transitional Regime Using Lattice Boltzmann Method

2010 ◽  
Author(s):  
Mohammad Normohammadzadeh ◽  
Mohammad Rahnama ◽  
Saeed Jafari ◽  
Alireza Akhgar
Keyword(s):  
Free Path ◽  
Lattice Boltzmann ◽  
Flow Simulation ◽  
Mean Free Path ◽  
Lattice Boltzmann Model ◽  
Microchannel Flow ◽  
Transition Flow ◽  
Good Correspondence ◽  
Flow Configuration ◽  
Transition Flow Regime

Microscale flow simulation is considered in this paper for a microchannel flow geometry. Lattice Boltzmann Model (LBM) was used as the numerical method for flow simulation, in which an effective mean free path was used in relaxation time appeared in LBM. The effective mean-free-path makes it possible to investigate flow characteristics in transition flow regime, for which Knudsen number varies from 0.1 to 10. Such implementation does not change the computational efficiency of LBM significantly. Results are obtained for flow configuration in a long microchannel. The slip velocity was predicted in this flow configuration with good accuracy. Good correspondence with Direct Simulation Monte Carlo (DSMC) method was observed.

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