Non-classical thermal physics in force-driven micro-channel gas flows

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.The fundamental physics of non-classical thermal characteristics in micro-channel gas flows is investigated on the basis of non-Fourier law embedded in moment equations derived from the kinetic Boltzmann equation. First, the effects of the force-stress coupling term on thermal behavior are examined in both Navier non-Fourier and non-Navier non-Fourier laws. It is shown that the ultimate source behind the non-monotonic temperature distribution is the force-stress coupling term in the constitutive equation of heat flux, irrespective of the constitutive equations of viscous stress, classical or non-classical. Second, the thermal characteristics such as the temperature and heat flux distributions for various Knudsen numbers are investigated in order to understand the complex interaction between the force and the rarefaction effects. It is shown that the central temperature reaches minimum in whole flow field after a critical Knudsen number in case of non-Navier non-Fourier law. Lastly, it is demonstrated that the force-stress coupling term in the non-Fourier law is solely responsible for the so-called Knudsen minimum of mass flow rate in the force-driven compressible Poiseuille gas flow, which is against intuition obtained from classical theory and indicates a dominant role of non-classical thermal physics in gas flow far from thermal nonequilibrium

Temperature distribution in the force-driven poiseuille gas flow by molecular dynamics

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.The thermal behavior of the force-driven compressible Poiseuille gas flow is studied by molecular dynamics (MD) simulation method. This type of flow situation occurs in the cooling system of MEMS/NEMS devices and hence the properties of Poiseuille gas flow become significant, especially the thermal behavior. The peculiar behavior of the force-driven Poiseuille gas flow, local minimum at the center in the temperature profile, is investigated in detail. Emphasis is placed on variations of the temperature distribution for different Knudsen numbers. Previously, the central temperature minimum and other flow peculiarities have been described by a non-classical non-Fourier theory based on nonlinear coupled constitutive relations. The main goal of this study is to investigate the thermal behavior of the force-driven Poiseuille gas flow using molecular dynamics simulations and to compare the results with that of non-classical non-Fourier theory. The MD results in general show agreement with the data from the non-classical hydrodynamic theory, which confirms the validity of MD method in analyzing the micro/nano gas flows including thermal behaviors

Positive thyroid transcription factor 1 staining strongly correlates with survival of patients with adenocarcinoma of the lung

This study investigated the relation between positive thyroid transcription factor 1 (TTF1) staining and survival of patients affected by primary adenocarcinoma (ADC) of the lung. Pathological tissue from consecutive ADC patients was collected from 2002 to 2004. The anti-TTF1 antibody (8G7G3/1, dilution of 1/200) was used. Thyroid transcription factor 1 staining was assessed for each tumour as positive or negative. Probability of survival was estimated by Kaplan–Meier and difference tested by log-rank test. A Cox's regression multivariate analysis was carried out. In all, 106 patients were studied (66% male, 69% PS0–1, 83% with stage III or IV). Tumours expressed positive TTF1 staining in 66% of cases. Multivariate analysis demonstrated an independent lower risk of death for patients whose tumour expresses positive TTF1 staining (HR=0.51, 95% CI 0.30–0.85; P=0.01) and higher grade of differentiation (HR=0.40, 95% CI 0.24–0.68; P=0.001). In conclusion, positive TTF1 staining strongly and independently correlates with survival of patients with primary ADC of the lung

Review of vortex methods for rotor aerodynamics and wake dynamics

Electric vertical take-off and landing (eVTOL) aircraft with multiple lifting rotors or prop- rotors have received significant attention in recent years due to their great potential for next-generation urban air mobility (UAM). Numerical models have been developed and validated as predictive tools to analyze rotor aerodynamics and wake dynamics. Among various numerical approaches, the vortex method is one of the most suit- able because it can provide accurate solutions with an affordable computational cost and can represent vorticity fields downstream without numerical dissipation error. This paper presents a brief review of the progress of vortex methods, along with their principles, advantages, and shortcomings. Applications of the vortex methods for modeling the rotor aerodynamics and wake dynamics are also described. However, the vortex methods suffer from the problem that it cannot deal with the nonlinear aerody- namic characteristics associated with the viscous effects and the flow behaviors in the post-stall regime. To overcome the intrinsic drawbacks of the vortex methods, recent progress in a numerical method proposed by the authors is introduced, and model validation against experimental data is discussed in detail. The validation works show that nonlinear vortex lattice method (NVLM) coupled with vortex particle method (VPM) can predict the unsteady aerodynamic forces and complex evolution of the rotor wake

Velocity slip in microscale cylindrical Couette flow : The Langmuir model

The velocity slip on the solid surfaces of microscale cylindrical Couette flow is investigated using the Langmuir adsorption model for the gas-surface molecular interaction. The accommodation coefficient in the Maxwell model, which is a free parameter based on the concept of diffusive reflection, is replaced by a physical parameter of heat adsorption in the Langmuir model. The phenomenon of velocity inversion is then clearly explained by introducing a velocity polar on the hodograph plane. It is also shown that the quantity used to determine the momentum slip in a concentric cylindrical geometry should be based upon the angular velocity, not the velocity itself. Finally, and despite their totally independent considerations of the gas-surface molecular interaction, the Maxwell and Langmuir slip models are shown to be in qualitative agreement with direct simulation Monte Carlo data in capturing the general features of the flow field

Computational Confirmation of AN Abnormal Mach Reflection Wave Configuration

For the Mach reflection (MR) of symmetric shock waves of opposite families, only the wave configuration of an overall Mach reflection (oMR) consisting of two direct Mach reflections (DiMR+DiMR) is theoretically admissible. For asymmetric shock waves, an oMR composed of a DiMR and an inverse Mach reflection (InMR) is possible if the two slip layers assemble a converging-diverging stream tube, while an oMR including two inverse Mach reflections (InMR+InMR) is absolutely impossible. In this paper, an overall Mach reflection configuration with double inverse MR patterns is computationally confirmed using the computational fluid dynamics technique. The aerodynamic mechanism behind such an abnormal wave pattern is illustrated. Classical two- and three-shock theories are also applied for the theoretical analysis. (C) 2009 American Institute of Physics. [DOI:10.1063/1.3073006

NUMERICAL ANALYSIS OF THE FLOWFIELD IN A SUPERSONIC COIL WITH AN INTERLEAVED JET CONFIGURATION AND ITS EFFECT ON THE GAIN DISTRIBUTION

In a supersonic chemical oxygen-iodine laser (COIL) operating without primary buffer gas, the features of flowfield have significant effects on the Laser efficiency and beam quality. In this paper three-dimensional, multi-species, chemically reactive CFD technology was used to study the flowfield in mixing nozzle implemented with a supersonic interleaving jet configuration. The features of the flowfield as well as its effect on the spatial distribution of small signal gain were analyzed