Mixing Of Different Gases Research Articles

Polarized-depolarized Rayleigh scattering for simultaneous composition and temperature measurements in non-isothermal gaseous mixtures.

This paper demonstrates the application of polarized-depolarized Rayleigh scattering (PDRS) as a simultaneous mixture fraction and temperature diagnostic for non-reacting gaseous mixtures. Previous implementations of this technique have been beneficial when used for combustion and reacting flow applications. This work sought to extend its applicability to non-isothermal mixing of different gases. The use of PDRS shows promise in a range of applications outside combustion, such as in aerodynamic cooling technologies and turbulent heat transfer studies. The general procedure and requirements for applying this diagnostic are elaborated using a proof-of-concept experiment involving gas jet mixing. A numerical sensitivity analysis is then presented, providing insight into the applicability of this technique using different gas combinations and the likely measurement uncertainty. This work demonstrates that appreciable signal-to-noise ratios can be obtained from this diagnostic in gaseous mixtures, yielding simultaneous temperature and mixture fraction visualization, even for an optically non-optimal selection of mixing species.

Optimization Analysis of Pretreatment Device Structural Parameters for Low-Concentration CBM Utilization

The unstable concentration of the difficulty in utilizing low-concentration CBM causes a large amount of CBM to be discharged into the atmosphere. In order to ensure the safe and stable operation of the CBM utilization device, the gas mixing unit is used to stabilize the concentration of feed gas. Generally, the resistance of the gas mixing unit is not higher than 500 Pa and the uniformity of gas is not less than 90%. In order to solve the problems of heavy resistance and low uniformity of the existing CBM mixing unit, a three-dimensional calculation model is established, and the structural parameters such as the number of spiral blades, blade length, and pitch in the gas mixing unit are adjusted and verified by experiments to achieve optimal performance. The dimensionless mathematical correlation between the resistance loss and the uniformity of gas is refined, and the maximum error between the resistance loss and the simulation results is controlled within 10%; it provides a theoretical basis for the uniformity and low resistance mixing of different gases in the gas industry. When the flow is 7000 Nm3/h, 50000 Nm3/h, and 160000 Nm3/h, respectively, the optimal structural parameters of the mixing zone are as follows: the number of blades is 3, 3, and 2, respectively, the pitch is 1000 mm, 2000 mm, and 2636 mm, respectively, and the length of blades is 500 mm, 1600 mm, and 1845 mm, respectively. The optimal structural parameters of the small pipe area are as follows: the mixing device with a flow of 50000 Nm3/h is not equipped with blades, the number of blades of the other two devices is 4, the pitch is 1400 mm, and the length of blades is 700 mm.

DNS of starting turbulent jets with variable density

We study starting turbulent round jets with variable density using Direct numerical simulations (DNS). A fully developed turbulent air flow at constant Reynolds number Re = 5300 is injected to space, filled with air, carbon dioxide or helium with a small co-flow, with variable density being due to the mixing of different gases. We compare the celerity factor, centreline velocity and dynamics of the vortex dipole in front of the jet between all the considered cases.

Experimental study of the interaction of shock waves with the contact boundary and zone of turbulent mixing of different gases

The interaction of a shock wave with turbulent flow was experimentally investigated. The case where a shock wave formed at one end of the tube, passed through the interface between two quiescent gases with different densities (air–CO2 or air–Ar), was reflected from the end of the tube, and interacted with the zone of turbulent mixing formed at the interface. The Mach number of the shock wave incident on the interface in air was M ≈ 2.37–2.57. The flow field was recorded using the schlieren method and high-speed video recording. It was found that after passing the mixing zone, the shock-wave front was deformed and became unstable.

Experimental Study of Interaction of Shock Waves with the Contact Boundary Zone and Turbulent Mixing of Different Gases

Experimental Study of Interaction of Shock Waves with the Contact Boundary Zone and Turbulent Mixing of Different Gases

Properties of power electronic substrates based on thick printed copper technology

The aim of this work is to develop new metallisation procedures of 96% alumina substrates with copper using thick film technology and firing in a special batch furnace, designed for the process. Standard firing process of copper pastes is done in conveyor furnaces and it has been described in literature. The firing process in batch furnaces is characterised by different problems and it has not yet been published. The developed batch furnace can combine firing in a protective atmosphere e.g. that of high nitrogen purity gas, automated mixing of different gases, and evacuation of the furnace chamber using rotary pump. The work is concentrated on Heraeus pastes that make it possible to reach up to about 300μm film thickness and, if needed, high resolution pattern of lower film thickness on the same substrate, metallised through holes and application of ENIG metallisation. Principles and characteristics of particular firing phases in the batch furnace as well as morphology and film properties of the fired copper films are described in the paper. The whole metallisation process proved to be effective offering high quality substrates for power electronics at reasonable investment and production costs.

Influence of spray characteristics on local light gas mixing in nuclear containment reactor applications

The action of spray on the mixing of different gases is used in numerous industrial applications, such as the chemical industry or the nuclear containment. The present paper concerns the impact of a spray on the break-up of a light gas layer (helium) initially confined in the top of a closed volume. Numerical calculations were performed in order to simulate the evolution of the helium concentration when the spray is activated. The objective of the paper is to show how the boundary conditions used for describing the spray can be important on the local gas mixing. Several sensitivity studies were performed that show the importance of the droplet boundary conditions: droplet size distribution, droplet velocity profiles, number of droplet classes, etc. Influence of these parameters on local gas concentration can be even higher than the one induced by a different turbulence model or some numerical parameters. Influence of the nozzle position inside the vessel is also analyzed. Extrapolation to an industrial application based on nuclear reactor containment is then discussed and recommendations are given for CFD simulations on the impact of spray systems on the gas mixing in nuclear reactors.

Entropy generation and exergy efficiency in adiabatic mixing of nitrogen and oxygen streams of different temperatures and environmental pressures

The paper presents a non-dimensional model of entropy generation and exergy efficiency in the adiabatic mixing of a nitrogen stream and oxygen stream with different temperatures and environmental pressure. The resulting mixture has the same, i.e. environmental, pressure. Non-dimensional variables in the model represent the ratio of thermodynamic stream temperatures u, the ratio between the thermodynamic temperature of one stream and the environmental temperature u1, and the mole fraction y1 of one of the streams. The model comprises irreversibility due to different temperatures of streams because of the mixing of different gases, while exergies of streams also comprise their mole fractions in the ambient air (atmosphere). In this respect, the model takes the standard values of mole fractions of oxygen and nitrogen of yO2 = 0.21 and yN2 = 0.79. The values of stream mole fractions at which maximum values of entropy generation and minimum values of exergy efficiencies occur are given. Calculation results are given in respective diagrams.

CAST3M/ARCTURUS: A coupled heat transfer CFD code for thermal–hydraulic analyzes of gas cooled reactors

The safety of gas cooled reactors (High Temperature Reactors (HTR), Very High Temperature Reactors (VHTR) or Gas Cooled Fast Reactors (GFR)) must be ensured by systems (active or passive) which maintain loads on component (fuel) and structures (vessel, containment) within acceptable limits under accidental conditions. To achieve this objective, thermal–hydraulics computer codes are necessary tools to design, enhance the performance and ensure a high safety level of the different reactors. Some key safety questions are related to the evaluation of decay heat removal and containment pressure and thermal loads. This requires accurate simulations of conduction, convection, thermal radiation transfers and energy storage. Coupling with neutronics is also an important modeling aspect for the determination of representative parameters such as neutronics coefficient (Doppler coefficient, Moderator coeffcient, …), critical position of control rods, reactivity insertion aspects, …. For GFR, the high power density of the core and its necessary reduced dimension cannot rely only on passive systems for decay heat removal. Therefore, forced convection using active safety systems (gas blowers, heat exchangers, …) are highly recommended. Nevertheless, in case of station black-out, the safety demonstration of the concept should be guaranteed by natural circulation heat removal. This could be performed by keeping a relatively high back-up pressure for pure helium convection and also by heavy gas injection. So, it is also necessary to model mixing of different gases, the on-set of natural convection and the pressure and thermal loads onto the proximate or guard containment. In this paper, we report on the developments of the CAST3M/ARCTURUS thermal–hydraulics (Lumped Parameter and CFD) code developed at CEA, including its coupling to the neutronics code CRONOS2 and the system code CATHARE. Elementary validation cases are detailed, as well as application of the code to benchmark problems such as the HTR-10 thermal–hydraulic exercise. Examples of containment thermal–hydraulics calculations for fast reactor design (GFR) are also detailed.

Paradoxes of gas mixing

A unified explanation of the Gibbs and Einstein paradoxes and of a new paradox in the mixing of quantum ideal gases is given. It is shown that all three paradoxes are due to the same physical cause–the corresponding discontinuity in the partial density on going from mixing of different gases to mixing of identical gases.