ICNMM2006-96118 MASS FLOW RATE MEASUREMENTS IN NITROGEN FLOWS

ABSTRACT The NOMENCLATURE k λ coefficient depending on the molecular interaction model m mass of the gas in the outlet tank s standard deviation u streamwise velocity D diameter of the tube Kn Knudsen number L length of the tube P pressure Q m mass flow rate P ratio P in /P out

Experimental and numerical investigation of an axisymmetric supersonic jet

21 pages, 10 figures, 2 tables.A comprehensive study of a steady axisymmetric supersonic jet of CO2, including experiment, theory, and numerical calculation, is presented. The experimental part, based on high-sensitivity Raman spectroscopy mapping, provides absolute density and rotational temperature maps covering the significant regions of the jet: the zone of silence, barrel shock, Mach disk, and subsonic region beyond the Mach disk. The interpretation is based on the quasi-gasdynamic (QGD) system of equations, and its generalization (QGDR) considering the translational–rotational breakdown of thermal equilibrium. QGD and QGDR systems of equations are solved numerically in terms of a finite-difference algorithm with the steady state attained as the limit of a time-evolving process. Numerical results show a good global agreement with experiment, and provide information on those quantities not measured in the experiment, like velocity field, Mach numbers, and pressures. According to the calculation the subsonic part of the jet, downstream of the Mach disk, encloses a low-velocity recirculation vortex ring.This research was supported by the Spanish Dirección General de Investigación Científica y Enseñanza Superior (DGICYES), Research Projects PB94{1526 and PB97{1203, and by the Fund for Fundamental Investigations of the Russian Academy of Sciences N 98-01-00155.Peer reviewe

Numerical modelling of rarefied gas flow through a slit at arbitrary pressure ratio based on the kinetic equation

A rarefied gas flow through a thin slit at an arbitrary gas pressure ratio is calculated on the basis of the kinetic model equations (BGK and S-model) applying the discrete velocity method. The calculations are carried out for the whole range of the gas rarefaction from the free-molecular regime to the hydrodynamic one. Numerical data on the flow rate and distributions of density, bulk velocity and temperature are reported. Comparisons of the present results with those based on the direct simulation Monte Carlo method and on the linearized BGK kinetic equation are performed. The conditions of applicability of the linearized theory are discussed. © 2011 Springer Basel AG

A study of shock waves in expanding flows on the basis of spectroscopic experiments and quasi-gasdynamic equations

32 pages, 14 figures, 3 tables, 2 appendix.A comprehensive numerical and experimental study of normal shock waves in hypersonic axisymmetric jets of N2 is presented. The numerical interpretation is based on the quasi-gasdynamic (QGD) approach, and its generalization (QGDR) for the breakdown of rotational–translational equilibrium. The experimental part, based on diagnostics by high-sensitivity Raman spectroscopy, provides absolute density and rotational temperatures along the expansion axis, including the wake beyond the shock. These quantities are used as a reference for the numerical work. The limits of applicability of the QGD approach in terms of the local Knudsen number, the influence of the computational grid on the numerical solution, the breakdown of rotation–translation equilibrium, and the possible formation of a recirculation vortex immediately downstream from the normal shock wave are the main topics considered.This work was supported by the Russian Foundation for Basic Research, grant N 01-01-00061, and by the Spanish DGESIC (MEC), research project PB97-1203.Peer reviewe

The temperature and pressure jumps at the vapor-liquid interface: Application to a two-phase cooling system

International audienceThe temperature and pressure jump boundary conditions at the liquid-vapor interfaces, obtained from the kinetic theory, are implemented for the numerical simulation of two-surfaces problem of evaporation and condensation. For a small temperature difference between two interfaces the system of the Navier-Stokes equations (NS) together with the energy conservation equation and the linear approximation of these equations with the same jump boundary conditions are considered in the vapor phase. The numerical and analytical solutions are compared with that obtained previously from the linearized kinetic equation. The analytical temperature profiles derived from the both linearized systems are very close to each other, while the temperature distribution obtained from the full NS and energy equations has an absolutely different character. The velocity and pressure in the vapor phase are found to be constant, though the full NS and energy equations solution gives abrupt change of velocity near the condensation interface. The inverse temperature gradient phenomenon occurs for the considered small temperature difference. The solution in the vapor phase is then applied to a coupled two-phase system problem, which can be realized in a heat-transfer device combining the principles of both thermal conductivity and phase transition. The coupled two-sided (liquid and vapor) model with jump boundary conditions proposed here allows us to estimate the values of the evaporative mass flux and the heat flux, which can be removed from a heat source. (C) 2014 Elsevier Ltd. All rights reserved

Experimental and numerical investigation of an axisymmetric supersonic jet

21 pages, 10 figures, 2 tables.A comprehensive study of a steady axisymmetric supersonic jet of CO2, including experiment, theory, and numerical calculation, is presented. The experimental part, based on high-sensitivity Raman spectroscopy mapping, provides absolute density and rotational temperature maps covering the significant regions of the jet: the zone of silence, barrel shock, Mach disk, and subsonic region beyond the Mach disk. The interpretation is based on the quasi-gasdynamic (QGD) system of equations, and its generalization (QGDR) considering the translational–rotational breakdown of thermal equilibrium. QGD and QGDR systems of equations are solved numerically in terms of a finite-difference algorithm with the steady state attained as the limit of a time-evolving process. Numerical results show a good global agreement with experiment, and provide information on those quantities not measured in the experiment, like velocity field, Mach numbers, and pressures. According to the calculation the subsonic part of the jet, downstream of the Mach disk, encloses a low-velocity recirculation vortex ring.This research was supported by the Spanish Dirección General de Investigación Científica y Enseñanza Superior (DGICYES), Research Projects PB94{1526 and PB97{1203, and by the Fund for Fundamental Investigations of the Russian Academy of Sciences N 98-01-00155.Peer reviewe

COMPARISON OF NUMERICAL RESULTS OF MOLECULAR DYNAMICS SIMULATIONS AND S-MODEL KINETIC EQUATIONS FOR EVAPORATION AND CONDENSATION OF ARGON

International audienceThe applicability of the S-model kinetic equation for simulation of evaporation and condensation phenomena is investigated by comparing its results for Argon with those of Molecular Dynamics (MD). The steady-state evaporation and condensation between two liquid Argon layers, kept at different but constant temperatures, is simulated. The temperature ratio between the hot/cold Argon layers is fixed at T1 /T2 = 1.045 and the rarefaction parameter is equal to δ = 7.9, which corresponds to the beginning of transitional flow regime. The macroscopic profiles of temperature and heat flux in vapor between the liquid layers are depicted. Both methods predict an inverted temperature profile. The agreement between the methods depends on the evaporation/condensation coefficients and the temperature at the liquid boundaries. Therefore, it is important to obtain the evaporation/condensation coefficients and the positions of the liquid boundaries accurately

NUMERICAL COMPARISON BETWEEN S-MODEL KINETIC EQUATION AND MOLECULAR DYNAMICS SIMULATIONS FOR HEAT TRANSFER THROUGH ARGON VAPOR

International audienceDuring the last decades, the miniaturization of electrical devices has grown considerably. Because of this, the heat transfer density within those devices has increased. Therefore, the need of advanced microscale cooling systems has become important. These systems need to be more energy efficient, i.e. to evacuate higher heat fluxes than the existing cooling systems [6]. This can be achieved by new generation two-phase flow evaporative systems. Within these systems, a liquid evaporates through a nanopores membrane. The latent heat of vaporization is the dominant mode of heat transfer and the nanopores geometry generates the requisite capillary pressure to drive the liquid flow to the heat source. It is important to understand the evaporation and condensation process as well as the corresponding vapor flow behaviors for the development of these two-phase cooling systems. The first step is to focus on the liquid-vapor phase and to be able to capture any non-equilibrium effects, e.g. temperature and pressure jumps at the liquid-vapor interface by performing Molecular Dynamics (MD) simulations. However, MD simulations become computationally expensive when simulating one or multiple nanopores. Therefore, it is inevitable to use different methods such as the S-model kinetic equation [1]. This model is less computationally demanding, but its applicability needs to be investigated by comparing its results with those of the MD simulation

Ecoulements gazeux isothermes dans les microcanaux : Profils des grandeurs physiques et débits de masse

Les microsystèmes d’analyse intégrés, ou µTAS (Micro Total Analysis Systèmes), permettent d’améliorer considérablement la détection de cancers dès les premiers stades d’apparition. En effet, ils interviennent au niveau moléculaire au lieu d’attendre que la maladie ne se manifeste sous forme de tumeurs détectables. Ils offrent également un bien meilleur rendement que les techniques courantes de laboratoire. Ce papier présente le développement d’un microsystème fluidique d’analyse intégré pour la détection et la surveillance génétique de cancer. Des micro-réacteurs fluidiques, placés dans des écoulements liquides d’un macro-dispositif, représentent l’aspect novateur du système développé. Le haut rendement est obtenu par la combinaison de micro-réacteurs évoluant périodiquement en parallèle. Cette approche permet de relever le challenge technologique qu’induit la rencontre des mondes macroscopiques et microscopiques. Parce que les réacteurs sont immergés dans un milieu liquide, la contamination du dispositif et le risque associé à de faux résultats sont minimisés. Ce papier présente une vue d’ensemble sur la génération de micro-gouttes présentées comme les micro-réacteurs, le mélange à micro-échelle de ceux-ci, l’amplification d’ADN par un système fluidique basé sur la PCR et la détection utilisant des techniques optiques

THE POSITION OF THE LIQUID AND VAPOR BOUNDARIES AND ITS INFLUENCE ON THE EVAPORATION/CONDENSATION COEFFICIENTS

International audienceThermal management of electronics has become important due to the miniaturization of electronic devices during the last decades. This has increased the heat transfer density within those devices and need to be compensated by the development of an advanced microscale cooling system[1]. A potential solution is the two-phase flow evaporative cooling system. Within these systems, a liquid evaporates through a nanopores membrane with the latent heat of vaporization to be the dominant mode of heat transfer. The nanopores geometry generates the requisite capillary pressure to drive the liquid flow to the heat source. This system consist of muliple flow regimes. The heat transfer within the ridges and liquid can be considered in the continuum regime whereas the evaporation from the nanopores membrane should be considered in the transition/free molecular regime. Therefore, a multiscale modeling approach has to be developed. The evaporation process and its vapor flow from the nanopores will be described by kinetic models / DSMC and Molecular Dynamics (MD) simulations. The first approach in construction this multiscale modeling setupis the validation of the kinetic model, which is the S-model kinetic equation [2] and its kinetic boundary conditions (KBC)