Unsteady heat transfer in a gas mixture

The time-dependent problem of heat transfer between two parallel plates in a binary gas mixture was investigated on the basis of numerical solution of BGK type kinetic model equation with collision integral taken in the form of McCormack model. The time evolution of the normal heat flux was simulated and time needed to reach the steady state conditions was obtained

Simulation of adsorption and desorption phenomena in a gas chromatography microcolumn

International audienceThe main goal of the present work is to optimize the micro-column for the gas chromatography analysis device, which is the device used in the real-time monitoring of atmospheric BTEX concentration for indoor environments. The BTEX group of molecules (Benzene, Toluene, Ethylbenzene and Xylenes) is, among volatile organic compounds (VOC), the most widely found in indoor air and its main sources are the cleaning products, building materials and outdoor air supply [1]. Among the BTEX compounds, Benzene is the most dangerous one, since it has been proven as a carcinogenic component [2]. The European Commission report [3] stated that the limit concentration of Benzene in an indoor environment should be 5μg/m³. Therefore, it is really important to measure the concentration of these species in indoor environments. The separation of BTEX takes place inside the micro-column is due to the adsorption and desorption phenomena. The relative rates of adsorption and desorption onto and off the stationary phase inside the chromatographic column allow chemicals in the analyzed samples to be separated and then quantified. Aiming to have a good performance of chemical detection, it is always important to have well-separated analytes in the GC column, hence designing an efficient column is crucial to the success of the microchemical detection system [4]. Usually, the micro-columns used in gas-chromatographs are silica tubes of about 150 to 300 microns in diameter and about 20 meters long [5]. These columns have a thin stationary phase layer coated onto the walls of about 1μm thick. The different adsorption and desorption rates between the species to be separated with the stationary phase will generate different interactions between them, and each species will reach the outlet of the micro-column in a distinct instant. Placed after the micro-column, another component of the gas chromatography device, called detector, is accountable for measuring the concentration of each specie in tested air sample. The final output provided by the gas chromatograph analyzed in the present work is a graph containing the concentration of the BTEX compounds species in time, called chromatogram. In a very long and narrow channel and under isothermal conditions, the pressure and density could change considerably between the inlet and outlet in the function of the applied end conditions. Therefore, the velocity of the flow in the outlet cross-section of the column is higher than the velocity nearby the inlet. Consequently, even though the flow velocity is much smaller than the sound speed, the compressibility effect and the flow velocity variation with the position have to be considered. The working conditions of our micro-column are: outlet pressure of 1atm and temperature of 65°C. Under these conditions, the mean free path of Nitrogen, th

Viscous slip coefficients for binary gas mixtures measured from mass flow rates through a single microtube.

International audienceArticles you may be interested in A slip model for rarefied gas flows above a moving surface with mass transfe

Mass flow rate measurement of thermal creep flow from transitional to slip flow regime

Measurements of the thermal creep flow through a single rectangular microchannel connected to two tanks maintained initially at the same pressure, but at different temperatures, are carried out for five noble gas species, over a large range of pressure and for two temperature differences between the tanks. The time-dependent pressure variations in both cold and hot tanks are investigated, and the temperature-driven (thermal creep) mass flow rate between two tanks is calculated from these data for the rarefaction parameter ranging from the transitional to slip flow regime. The measured mass flow rate is compared with the numerical solution of the S-model kinetic equation, and they show good agreement. A novel approximate expression to calculate the temperature-driven mass flow rate in the transitional and slip flow regimes is proposed. This expression provides results in good agreement with the measured values of the mass flow rate. In the slip flow regime, the thermal slip coefficient is calculated by employing the previously reported methodology, and the influence of the nature of the gas on this coefficient is investigated. The measured values of the thermal slip coefficient agree well with the values available in the literature, indicating that this coefficient is independent of the shape of a channel

Continuum and kinetic simulations of Heat Transfer trough Rarefied Gas in Annular and Planar Geometries in the Slip Regime

International audienceSteady-state heat transfer through a rarefied gas confined between parallel plates or coaxial cylinders, whose surfaces are maintained at different temperatures is investigated using the non-linear Shakhov (S) model kinetic equation and DSMC technique in the slip regime. The profiles of heat flux and temperature are reported for different values of gas rarefaction parameter δ, ratios of hotter to cooler surface temperatures T , and inner to outer radii ratio R. The results of S-model kinetic equation and DSMC technique are compared to the numerical and analytical solutions of the Fourier equation subjected to the Lin & Willis temperature-jump boundary condition. The analytical expressions are derived for temperature and heat flux for both geometries with hotter and colder surfaces having different values of the thermal accommodation coefficient. The results of the comparison between the kinetic and continuum approaches showed that the Lin & Willis temperature-jump model accurately predicts heat flux and temperature profiles for small temperature ratio T = 1.1 and large radius ratios R ≥ 0.5, however, for large temperature ratio, a pronounced disagreement is observed

SYNTHESIS, CHARACTERIZATION AND BIOLOGICAL ACTIVITY OF COPPER(II), NICKEL(II), COBALT(III) AND IRON(III) COORDINATION COMPOUNDS WITH 2-HYDROXY-3-METHOXYBENZALDEHYDE N(4)-ALLYL-S-METHYLISOTHIOSEMICARBAZONE

The paper presents the synthesis of the 2-hydroxy-3-methoxybenzaldehyde N(4)-allyl-S-methylisothiosemicarba­zone (HL) and seven coordination compounds of copper, nickel, cobalt and iron with this ligand. The new obtained compounds were studied using IR, 1H and 13C NMR spectroscopy, elemental analysis, molar electric conductibility and magnetic susceptibility. The in vitro antiproliferative activity of the HL and synthesized coordination compounds was screened on HeLa cancer cells and normal MDCK cells. The isothiosemicarbazone HL shows better anticancer activity towards HeLa cancer cells than doxorubicin that is used in medical practice and it also practically does not affect the growth and proliferation of normal cells. Moreover, it manifests high antioxidant activity towards ABTS•+ radical cation that exceeds the activity of trolox.</p

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

SYNTHESIS AND BIOLOGICAL ACTIVITY OF COPPER(II), NICKEL(II) AND COBALT(III) COORDINATION COMPOUNDS WITH 2-BENZOYLPYRIDINE N(4)-ALLYL-SMETHYLISOTHIOSEMICARBAZONE

State University of Moldova State University of Medicine and Pharmacy “Nicolae Testemitanu”Lucrarea conţine descrierea sintezei N(4)-alil-S-metilizotiosemicarbazonei 2-benzoilpiridinei (HL) şi a cinci compuşi coordinativi ai cuprului(II), nichelului(II) şi cobaltului(III) cu acest ligand. Compuşii noi obţinuţi au fost studiaţi cu ajutorul spectroscopiei IR şi RMN (1H şi 13C), analizei elementale, conductivitaţii molare şi susceptibilităţii magnetice. Pentru compuşii sintetizaţi a fost determinată in vitro activitatea antibacteriană şi antifungică faţă de spectrul larg de tulpini standard de Staphylococcus aureus (ATCC 25923), Escherihia coli (ATCC 25922), Klebsiella pneumonae şi Candida albicans. Activitatea antiproliferativă in vitro a ligandului şi complecşilor a fost testată pe celule leucemiei mieloide umane HL-60 şi HeLaThis work was fulfilled with the financial support of the Institutional Project 15.817.02.24

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

Comparative study of the Boltzmann and McCormack equations for Couette and Fourier flows of binary gaseous mixtures

We evaluate the accuracy of the McCormack model by comparing its solutions for Couette and Fourier flows of binary gaseous mixtures with results from the linearized Boltzmann equation. Numerical simulations of Ne-Ar and He-Xe gas mixtures are carried out from slip to near free-molecular flow regimes for different values of the molar concentration. Our numerical results show that while there are only small differences in the shear stress in Couette flow and the heat flux in Fourier flow, calculated from the two kinetic equations, differences in other macroscopic quantities can be very large, especially in free-molecular flow regime. Moreover, the difference between results from the two models increases with the molecular mass ratio and the molar concentration of the heavier species. Finally, the applicability of the McCormack model, which was derived for linearized flows only, is investigated by comparing its solutions with those from the Boltzmann equation for Fourier flow with large wall-temperature ratios