Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 55, Number 16
Sunday–Tuesday, November 21–23, 2010; Long Beach, California
Session RC: Rarefied Gases and Direct Simulation Monte Carlo |
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Chair: Veronica Eliasson, University of Southern California Room: Long Beach Convention Center 102A |
Tuesday, November 23, 2010 3:05PM - 3:18PM |
RC.00001: Measures of Thermal Transpiration Flow Marcos Rojas, Irina Graur, Pierre Perrier Thermal transpiration is the macroscopic movement of gas-particles induced by a temperature gradient. The gas-particles move from the lower to the higher temperature zone. The main aim of the present work is to measure experimentally the flow created by thermal transpiration in a tube heated at its outlet. The experimental system is composed by a circular cross section micro-tube and two reservoirs settled respectively at the inlet and outlet of the capillary. The reservoirs are coupled to two high-speed response time capacitance diaphragm gauges which monitor the pressure variation in time. By monitoring the pressure variation in time is possible to measure the macroscopic movement of gas-particles along the tube: by thermal transpiration gas-particles move from the cold to the hot region of the tube increasing the hot-side reservoir absolute pressure; while a drop of pressure is registered in the cold-side reservoir. The experiments are conducted for three different gases, Argon, Helium and Nitrogen, in a pressure range from $0.1$ to $10$ \textit{torr} and for three different temperature differences: $\Delta T=30,\,40,\,50$ degrees. The gas rarefaction conditions go from transitional to slip regime. [Preview Abstract] |
Tuesday, November 23, 2010 3:18PM - 3:31PM |
RC.00002: Plane Poiseuille Flow of a Rarefied Gas in the Presence of a Strong Gravitation Toshiyuki Doi Poiseuille flow of a rarefied gas between two horizontal planes in the presence of a strong gravitation is considered, where the gravity is so strong that the path of a molecule is curved considerably as it ascends or descends the distance of the planes. The gas behavior is studied based on the Boltzmann equation. An asymptotic analysis for a slow variation in the longitudinal direction is carried out and the problem is reduced to a spatially one dimensional problem, as was in the Poiseuille flow problem in the absence of the gravitation. The mass flow rate as well as the macroscopic variables is obtained for a wide range of the mean free path of the gas and the gravity. A numerical analysis of a two dimensional problem is also carried out and the result of the asymptotic analysis is verified. [Preview Abstract] |
Tuesday, November 23, 2010 3:31PM - 3:44PM |
RC.00003: Surface Effects on Nanoscale Gas Flows Ali Beskok, Murat Barisik 3D MD simulations of linear Couette flow of argon gas confined within nano-scale channels are performed in the slip, transition and free molecular flow regimes. The velocity and density profiles show deviations from the kinetic theory based predictions in the near wall region that typically extends three molecular diameters (s) from each surface. Utilizing the Irwin-Kirkwood theorem, stress tensor components for argon gas confined in nano-channels are investigated. Outside the 3s region, three normal stress components are identical, and equal to pressure predicted using the ideal gas law, while the shear stress is a constant. Within the 3s region, the normal stresses become anisotropic and the shear stress shows deviations from its bulk value due to the surface virial effects. Utilizing the kinetic theory and MD predicted shear stress values, the tangential momentum accommodation coefficient for argon gas interacting with FCC structured walls (100) plane facing the fluid is calculated to be 0.75; this value is independent of the Knudsen number. Results show emergence of the 3s region as an additional characteristic length scale in nano-confined gas flows. [Preview Abstract] |
Tuesday, November 23, 2010 3:44PM - 3:57PM |
RC.00004: High Knudsen Number Fluid Flow at Near-Standard Temperature and Pressure Conditions using Precision Nanochannels Subhra Datta, A.T. Conlisk, William H. Fissell, Shuvo Roy, Jeff Majestrelli Gas flows over a wide range of Knudsen numbers ($\sim$0.5-10) are studied using silicon nanochannel arrays with slit-shaped pores that range from micrometer to sub-10nm scales. The flows are generated under conditions of room temperature and near-atmospheric pressure ($\sim$22$^{\circ}$C and $\sim$101-115 kPa) and span the continuum flow, continuum-slip flow, transition flow and free-molecular flow regimes. The measured flow rates of helium, argon and carbon dioxide are in good agreement with the Unified Slip Model(USM) proposed by Beskok and Karniadakis (Beskok A., Karniadakis G.E., Nanoscale and Microscale Thermophysical Engineering 3 (1999), no. 1, 43-77). The measured volumetric gas flow rates agree well with calculations based on the USM up to a Knudsen number of about Kn $\sim$ 4, well into the transition regime; above this value the agreement for much of the data is qualitative and at very large Knudsen numbers the data is in the free molecular regime as expected. [Preview Abstract] |
Tuesday, November 23, 2010 3:57PM - 4:10PM |
RC.00005: Energy accommodation of gas molecules with free-standing vertically aligned single-walled carbon nanotube arrays Ikuya Kinefuchi, Kizen Ryu, Kei Ishikawa, Junichiro Shiomi, Shu Takagi, Shigeo Maruyama, Yoichiro Matsumoto The scattering process of gas molecules on vertically aligned single-walled carbon nanotubes (VA-SWNTs) was investigated by molecular beam technique. The measurement was performed for the free-standing samples, which enabled us to evaluate the scattering process of gas molecules on VA-SWNT films themselves in detail without the presence of substrates. The scattered molecules are divided into three components: reflected molecules, diffusively transmitted molecules, and directly transmitted molecules without interaction with SWNTs. Even for the film as thin as 0.1 $\mu$m, the incident molecules are found to be well accommodated to the surface temperature. This result suggests that, regardless of film thickness, most molecules have enough number of collisions with SWNTs for efficient energy transfer at the randomly oriented layer at the topmost of the films. [Preview Abstract] |
Tuesday, November 23, 2010 4:10PM - 4:23PM |
RC.00006: Numerical Analysis on Energy Accommodation Process of Gas Molecules on Carbon Nanotube Film Jumpei Kawasaki, Ikuya Kinefuchi, Shu Takagi, Yoichiro Matsumoto Because of its large specific surface areas due to its nanoscale structure, film made up with carbon nanotubes (CNTs) is expected to be used as one of the applications for trapping gas molecules and enhancing heat exchange. The relationship between the diffusive movement of gas molecules inside the film and the energy accommodation process, however, has not been clarified yet. In this study, we introduced numerical simulation to analyze the energy accommodation process of gas molecules on CNT film. The film was modeled by piling up cylinders representing CNT bundles. Different scattering models between a CNT and a gas molecule were used to investigate the scattering angle distributions, number of collisions, and intrusion depths of gas molecules that were reflected by and transmitted through the film. The results of calculations well reproduced experimental results. We confirmed that although energy exchange of each collision between single CNT and a gas molecule is small, randomly oriented structure of CNT film induced diffusive movement of gas molecules inside the film, which leads to high accommodation between the film and gas molecules. [Preview Abstract] |
Tuesday, November 23, 2010 4:23PM - 4:36PM |
RC.00007: Nonlinear and coupling effects on the gaseous Knudsen layer near the solid surface Rho Shin Myong The Knudsen layer (also known as the kinetic boundary layer) found in the region of a gas flow very close to the solid surfaces plays a critical role in modeling the rarefied and micro-scale gas flows. Although the Knudsen layer has been investigated extensively using kinetic theory in the past, capturing it within the continuum framework, which may provide distinct advantages in terms of computational efficiency, remains a daunting task. In particular, the exact underlying mechanisms behind abnormal behaviors in the Knudsen layer (smaller velocity slip and shear stress, nonlinear velocity profile, velocity gradient singularity, non-zero tangential heat flux) are not understood fully. In this work, those questions associated with the nonlinear and coupling effects in shear stresses and heat fluxes are investigated on the basis of the phenomenological nonlinear coupled constitutive relation (NCCR) and gas-surface molecular interaction model. [Preview Abstract] |
Tuesday, November 23, 2010 4:36PM - 4:49PM |
RC.00008: The reality of diffuse volume transport Howard Brenner Whereas mass flow in a continuum is necessarily accompanied by a concomitant volume flow, the converse is not true. That is, volume can be transported independently of mass. In particular, volume can be transported by purely molecular or diffuse action. For example, volume unaccompanied by mass can flow through a fluid that is completely at rest (and hence for which there is no mass flow) provided that density gradients exist. This occurs, for example, during steady-state heat conduction in quiescent isobaric liquids and gases, wherein the density varies locally with the temperature. Equally striking is the fact that volume can be transported through solid walls impermeable to matter. This talk is devoted to analyzing a gedanken experiment permitting these phenomena to be directly visualized, and hence providing undisputable evidence that diffuse volume transport is a real physical phenomenon relevant to continuum fluid mechanics. [Preview Abstract] |
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