Transient heat transfer in a rarefied binary gas mixture confined between parallel plates due to a sudden small change of wall temperatures

Transient behavior of the heat transfer through binary gas mixture, confined between two infinite parallel plates, caused by the sudden change of the plates’ temperatures, is studied for two monoatomic gas mixtures: Ne–Ar and He–Ar. The walls’ temperature changes are considered small compared to the equilibrium temperature of the system, so the McCormack kinetic model is used for the numerical simulations. The time evolution of the main macroscopic parameter is investigated for various species concentrations and for different gas rarefactions ranging from near the free molecular to slip flow regime. It is found that the mixture heat flux takes several characteristic times, which is defined by the distance between the plates over the most probable molecular speed, to achieve its new equilibrium state. This time of the steady state flow establishment depends strongly on the gas rarefaction, mixture nature and composition

Thermal transpiration flow

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Thermal transpiration is the macroscopic movement of rarefied gas induced by a temperature gradient. The gas moves from the lower to the higher temperature zone. An original method is proposed here to measure the mean macroscopic movement of gas in the case of a long circular cross-section glass microtube on to which a gradient of temperature is applied. The mass flow rate and the thermo-molecular pressure difference have been measured by monitoring the absolute pressure evolution in time at both ends of the capillary using high-speed response pressure gauges. Two gases Nitrogen and Helium are studied and three different temperature differences of 50, 60 and 70 Celsius degrees are applied to the tube. The analysed gas rarefaction conditions vary from transitional to slip regime.The European Community’s Seventh Framework Program (FP7/2007-2013 under grant agreement no 215504

Gas permeability in rarefied flow conditions for characterization of mineral membrane support

International audienceGas Permeability Measurement Technique (GPMT) has the advantage of being a non-destructive method, which is efficient in characterizing filtration membranes. Ceramic filtration membranes consist of successive layers of micro (support) to nano size (skin) pores. When gas flows through such a small scale structure, the molecular mean free path becomes comparable to the pore size. The Slip flow model, validated to describe the gas transport properties under rarefied flow conditions in a microchannel, is extended to porous media. The porous structure is modeled as a cluster of several identical cylindrical channels

Sublimation and deposition in gaseous mixtures

The sublimation and deposition behaviors of the Helium-Argon mixture is analyzed numerically in the temperature range where Helium is only in gaseous state while Argon can sublimate and deposit on its own solid phase. The McCormack model is implemented to model the Boltzmann collision term. Three kinds of potential are used for simulation of the intermolecular collisions: Hard Sphere, Lennard-Jones potential, and ab initio. The matrices of the kinetic coefficients have been obtained for different values of the rarefaction parameters and molar fraction of non-sublimating gas. The influence of the intermolecular potential on the kinetic coefficients as well as on the gas macroscopic profiles has been analyzed. © 2020 Elsevier LtdThe work of A. Polikarpov was financially supported by the Ministry of Science and Higher Education of the Russian Federation, the research project no. FEUZ-2020-0057. I. Graur would like to acknowledge the financial support provided by the European Union network program H2020, MIGRATE project under Grant Agreement No. 643095. F. Sharipov acknowledges the Brazilian Agency CNPq for the support of his research, grant 304831/2018-2

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

Lack of self-averaging in neutral evolution of proteins

We simulate neutral evolution of proteins imposing conservation of the thermodynamic stability of the native state in the framework of an effective model of folding thermodynamics. This procedure generates evolutionary trajectories in sequence space which share two universal features for all of the examined proteins. First, the number of neutral mutations fluctuates broadly from one sequence to another, leading to a non-Poissonian substitution process. Second, the number of neutral mutations displays strong correlations along the trajectory, thus causing the breakdown of self-averaging of the resulting evolutionary substitution process.Comment: 4 pages, 2 figure

Kinetic simulation of the non-equilibrium effects at the liquid-vapor interface

Phase change phenomena at microscale is important for novel cooling microsystems with intensive evaporation, so the development of reliable models and simulations are challenging. The vapor behaviors near its condensed phase are simulated using the non-linear S-model kinetic equation. The pressure and temperature jumps obtained numerically are in good agreement with the analytical expressions derived from the appropriate Onsager-Casimir reciprocity relations. The results of the evaporation flux are close to those given by the Hertz-Knudsen-Schrage formula, only when the values of the pressure and temperature at the upper boundary of the Knudsen layer are used. Comparison with recently measured temperature jumps are provided and disagreement with some experiments are discussed. © 2019 Elsevier Lt