Mixture Velocity Research Articles

Cellular instabilities of n-butane/air flat flames probing by PLIF-OH and PLIF-CH2O laser diagnosis

The structure and instability characteristics of non-adiabatic fuel-rich n-butane/air cellular flames on McKenna burner were experimentally investigated at atmospheric pressure. Planar Laser Induced Fluorescence (PLIF-OH and PLIF-CH2O) flame diagnosis technology was utilized to probe the flame structure under varied equivalence ratio and inflow mixture velocity respectively. Results show that, the equivalence ratio plays an important role in forming cellular flames. The flat, wrinkled and cellular flames appear in turn when increasing equivalence ratio and inflow velocity. Differed to the separated cells of cellular flames appeared in direct Digital camera images and PLIF-OH images, the PLIF-CH2O images clearly display that all cellular flames are connected. In the PLIF-OH images of cellular flames, the OH radical fluorescence signal intensity is higher in the convex region toward unburned mixture than in the concave region, but in PLIF-CH2O images, the fluorescence signal intensity is nearly unchanged in both convex and concave regions. Quantitative stand-off distance and amplitude data probed by PLIF-OH and PLIF-CH2O diagnosis together reveal that the onset of non-adiabatic n-butane/air cellular flames on flat flame burner is dominantly governed by diffusive-thermal mechanism.

Physico-chemical properties of binary systems involving modifier (methanol or propionic acid) and an acidic extractant di (2-ethylhexyl) phosphoric acid (DEHPA): volumetric, acoustic and viscometric routes

In solvent extraction, a suitable modifier, basically polar liquid is used with extractant like DEHPA, TBP, TOPO and MIBK to enhance the efficiency in extraction processes. This paper is related to the study of physico-chemical properties of polar – polar binary mixtures at 303.15K and 0.1 MPa. Molar volume, free volume, isentropic compressibility, intermolecular free length, specific acoustic impedance, relaxation time, Rao’s constant, Wada’s constant, absorption coefficient have been calculated from the experimentally measured data of density, ultrasonic velocity and viscosity of pure components and binary mixtures of methanol/ propionic acid + DEHPA. In addition, excess molar volume, excess Gibb’s energy of activation of viscous flow, deviations in viscosity, isentropic compressibility, free volume, intermolecular free length and acoustic impedance were also computed from the experimental data. The observed variations of excess/deviation functions with the composition of DEHPA have been discussed in terms of molecular interaction between unlike molecules in two binary mixtures due to chemical, physical and structural effects. It is found that the molecular interaction of methanol with extractant DEHPA is better than that of propionic acid and so methanol may be used as a suitable modifier with DEHPA in the solvent extraction process.

Particle velocity measurement of binary mixtures in the riser of a circulating fluidized bed by the combined use of electrostatic sensing and high-speed imaging

The flow dynamics of binary particle mixtures in the fluidized bed needs to be monitored in order to optimize the related industrial processes. In this paper, electrostatic sensing and high-speed imaging are applied to measure the velocities of polyethylene and sand particles in the binary particle mixtures in fluidization. Experimental studies were conducted on a lab-scale cold circulating fluidized bed. Correlation function between electrostatic signals from upstream and downstream electrodes placed along the riser shows two peaks that represent transit times for the two types of particles. To verify the above results, high-speed imaging was adopted to capture the flow images of particle mixtures. Particle Image Velocimetry and Particle Tracking Velocimetry algorithms were utilized to process the resulted images in order to measure the velocities of polyethylene and sand particles. The reasons for two-peak correlation functions are illustrated based on the frequency spectrums of the mono-solid-phase electrostatic signals and the velocity difference between polyethylene and sand particles. Finally, comparisons on the velocities obtained from electrostatic sensing and high-speed imaging demonstrate the electrostatic sensor can roughly estimate the particle velocity of binary particle mixtures in the near wall region of the circulating fluidized bed.

Investigation of the impact of the reactants temperature and equivalence ratio on the outlet mixture temperature, velocity and mole fraction for the combustion of the carbon monoxide and nitrous

In the present study, a numerical code is used for three-dimensional simulation of non-premixed form of the combustion of nitrous-carbon monoxide mixture. This code includes standard K-ε as turbulent model and Probability Density Function (PDF) as thermo-chemistry approach. Ten species i.e. nitrous, carbon monoxide, carbon dioxide, nitrogen, nitrogen monoxide, atomic oxygen, oxygen, ozone, cyanate and atomic carbon are assumed contributing in this reaction. For the validation of model, experimental measurement of previous studies are applied. The influence of equivalence ratio and inlet gases temperature, on outlet mixture velocity, temperature and outlet species mole fraction are obtained in the form of charts for wide ranges, which was not clearly obtained in previous works. These charts are useful for designer of these systems. Results indicate, when Ø ≥ 0.15 N2O is decomposed completely and the maximum mole fractions for O2(approximately 0.27), N2 (approximately 0.77) and O3 (depending on the temperature) are obtained. Furthermore, it was found the mole fraction of the outlet carbon dioxide and dimensionless temperature of the outlet mixture are maximum at equivalence ratio equal to unity and if the temperature of the inlet gases is kept constant and the equivalence ratio reduces, the outlet carbon monoxide mole fraction decreases.

An Insight on Thermophysical Properties of Binary Mixtures of Hydrocarbons with Spectroscopic Evidence; Essential Components of Transformer Oils

The aim of the present investigation is to analyze the effect of carbon chain length in benzene + (hexane/heptane) binary mixtures at different temperatures through density (ρ), ultrasonic velocity (U), viscosity (η) and dielectric (ε) measurements. Derived properties such as molar volume (V), isentropic compressibility (βs), acoustic impedance (Z) and intermolecular free length (Lf) have been calculated for T = 298.15, 308.15 and 318.15K. The excess values of the above mentioned properties of the binary mixtures of benzene + (hexane/heptane) are determined at different temperatures and have been fitted to Redlich – Kister polynomial equation. The dielectric permittivity results demonstrate that deviations from pure components are mostly negative in both the mixtures except for few cases in benzene rich region. Excess Gibb’s free energy of activation of viscous flow (GE) has been calculated using the viscosity measurements at different temperatures. Mixing rules have been adopted to calculate the ultrasonic velocities of the binary mixtures of benzene + (hexane/heptane) at the above said temperatures. FT-IR and NMR analysis have been done to check the accuracy of the results.

Experimental study using advanced diagnostics to investigate slug aeration and bubble behavior in high liquid viscosity horizontal slug flow

Accurate prediction of slug liquid holdup is critical for accurate calculation of pressure gradient and average liquid holdup in pipes. However, most of the existing slug liquid holdup models are only accurate for a specific range of operating conditions, pipe dimensions, and fluid properties. The majority of these models are empirical, lacking the physical basis of slug aeration mechanisms. In this study, bubble entrainment mechanisms, bubble trajectories, and bubble loss from the slug body were identified. The experimental results from the high-speed camera (HSC) and particle image velocimetry (PIV) enabled detailed investigation of bubble entrainment mechanisms at slug front, bubble deformation and trajectories in slug body. These experimental observations were further analyzed and related to operating conditions and fluid properties. A horizontal 50.8-mm (2-in.) inner diameter (ID) pipe, and high viscosity liquid/air-fluid system (μL ≈ 0.51, 0.68 and 0.96 Pa s) were utilized. Experimental results revealed that the rate of gas entrainment at slug front, the bubble deformation in the slug body, and the number of fragmented bubbles in the slug unit all increase as mixture velocity and liquid viscosity increase, and as surface tension decreases. The proposed slug aeration mechanisms, and bubble behavior and characteristics in the slug body can form the basis for further mechanistic modeling of slug liquid holdup and other parameters required for proper slug flow modeling.

Two-phase flow simulations at [formula omitted] inclination in an eccentric annulus

Co-current two-phase simulations of gas-liquid flow with mixture velocities from 1.2 to 4.2 m/s were run in a partially eccentric annulus and compared with entirely eccentric and concentric experimental data collected at the Institute for Energy Technology in Norway. The gas-phase was sulphur hexafluoride (SF6) for all cases, while the liquid-phase was Exxsol D60 for the horizontal cases and a mixture of Exxsol D60 and Marcol 82 for the inclined case. The outer diameter of the annulus was 0.1 m for all cases, while the inner diameter was 0.05 m in the horizontal configuration and 0.04 m for the inclined configuration. The purpose of this paper is to explore the effect of the holdup fraction, mixture velocity, and interior pipe’s position on the pressure gradient and flow regime, in effect a study of the pressure gradient and holdup fraction transients. The comparisons between simulations and experiments indicate that moving the pipe from an entirely eccentric to the partially eccentric configuration has a drastic impact on the pressure gradient. In all 4 cases where the inner pipe was changed from a completely eccentric geometry in the experiments to a less eccentric configuration in the simulations, we notice an increase of 48–303% of the mean pressure gradient. Comparatively, the 4 cases where the pipe was moved from a concentric experimental configuration to a more eccentric configuration in the simulations result in less drastic pressure gradient changes. Two cases were within 22% of the experimental results for mean, maximum, and minimum pressure gradient, while the last two cases exceeded the minimum and mean pressure gradients by 25–250%, respectively. The flow regime is rarely significantly affected by a change in eccentricity; 2 out of the 8 horizontal cases indicate either a transition from wavy flow to slug flow or significantly larger waves. The most prominent and frequent discrepancies identified were altered slug and wave frequencies. The last case, a 4o inclined, partially eccentric simulation was compared to an entirely eccentric experiment and results in a 0.2 Hz increase in wave frequency, up from the experimental 0.56 Hz and a 49% increase in the mean pressure gradient.

INCREASING OF REABILITY OF WORK OF BOILERS BY EQUAL DISTRIBUTION OF THE HEAT LOAD OVER THE HEIGHT OF FIREBOX

Detection of one of the methods for reducing the emergency screens of boiler units pipes is in the process of being discovered. Specially used in the even distribution of heat load in the active combustion zone, replacing the burners with 1-2 tier arrangement by 2-4 tier, reducing the single power of the finger. Investigation of the supported solution, with the posture of the boiler. The mathematical calculation model and graphical division of the boiler furnace into combustion zones are presented. The results of the research showed that a large number of burners and a decrease in the unit power of the population, which reaches a greater uniform thermal voltage, are detected by the height of the shielded pipe, reducing peak maximum consumption from 100% to 86.5% (590 kW / m2 to 510 kW / m2) As the number of burners increases, the thermal load in the lower part of the combustion zone increases, which results in more intense boiling, as a consequence of the increase in the velocity of the vapor-liquid mixture in the screen tubes and, accordingly, the cooling of the evaporator tubes in the regions of the highest heat load. The temperature of the screen metal in the zones of maximum heat load of the pipes is reduced by 20-30 0C, which, with a long service life, leads to a decrease in temperature aging, and consequently an extension of the inter-repair life of the boiler. The disadvantage of this method is the complication and complication of the manufacture of screen pipes, increase the hydraulic resistance of the lifting pipes by increasing the number of bends of pipes, complicates the system of supply of fuel and air. The results of the calculations are presented in graphical form, as the dependence of the specific heat load, the temperature of the outer wall of the pipe, the allowable thermal stress, the height of the pipe at one-, two- and four-tier arrangement of burners in the zone of active combustion.

Electron swarm coefficients and critical field strength of the gaseous ternary mixtures CF3I-SF6-N2 and CF3I-SF6-CO2

The electron drift velocity, longitudinal diffusion and effective ionization coefficients in the gaseous ternary mixtures CF3I-SF6-N2 and CF3I-SF6-CO2 have been measured using a pulsed Townsend apparatus over the density-normalized electric field intensity, E/N, from 230 to 470 Td and 230 to 430 Td, respectively (1 Td = 10−17 V cm2). Several ternary gas mixture compositions containing 10% to 50% CF3I or SF6 and either N2 or CO2 have been studied. Also, we have measured the critical field strength, E/Ncrit, for all of these gaseous mixtures, finding out that the 40% CF3I–40% SF6–20% N2 and 40% CF3I–40% SF6–20% CO2 have an E/Ncrit value smaller by only 4.0% and 1.0%, respectively than that of pure SF6 (360 Td). Provided that both CF3I, CO2 and N2 are environmentally friendly, its addition to SF6 may be highly advantageous over other binary SF6 mixtures with gases having relatively high warming potentials, since these mixtures have only 40% SF6 and behave, from the swarm physics point of view as good candidates to ameliorate impact of SF6 when released into the atmosphere. An interesting synergetic effect has been found for the CF3I-SF6 mixture when N2 added and has been interpreted in terms of the efficient low-energy electron scattering of N2 at low collision energies up to 2 eV.

Characterization of a kHz atmospheric pressure plasma jet: comparison of discharge propagation parameters in experiments and simulations without target

This paper quantitatively characterizes a kHz atmospheric pressure He plasma jet without target powered by a pulse of positive applied voltage. It focuses on a quantitative comparison between experimental measurements and numerical results of a two-dimensional fluid model using the same configuration, for different values of magnitude and width of pulsed applied voltage. Excellent agreement is obtained between experiments and simulations on the gas mixture distribution, the length and velocity of discharge propagation and the electric field in the discharge front. For the first time in the same jet, the experimentally measured increase of the electric field in the plume is confirmed by the simulations. The electron density and temperature, measured behind the high field front, are found to agree qualitatively. Moreover, the comparison with simulations shows that discharge propagation stops when the potential in the discharge head is lower than a critical value. Hence, pulse width and magnitude allow to control propagation length. For long pulses ( ns), the potential in the discharge front reaches this critical value during the pulse. For shorter pulses, propagation is determined by the pulse shape, as the critical value is reached around 90–130 ns after the fall of the pulse. The results suggest that the magnitude of this critical value is defined by the gas mixture at the position of the front.

Frictional Factor Correlation for Laminar High-Viscosity Oil/Gas Flow in Horizontal Pipes

Summary Pressure drop prediction of high-viscosity oil/gas flow is an important issue in several industries, and it has a great interest for many researchers. This paper presents a simplified correlation for two-phase high-viscosity oil/gas flow friction factor in horizontal pipes. The developed friction factor is a sole function of Reynolds number on the basis of the mixture velocity and liquid properties. The recently developed friction factor correlation for laminar and turbulent gas/liquid flow is not suitable for the high-viscosity liquid/gas flow for which Reynolds number is less than 2,000. The validation of the proposed correlation against experimental data and the newly developed correlation showed accurate results for the two-phase friction factor for the cases matching gas/heavy oil flow with liquid holdup greater than 0.5 and mixture Reynolds number on the basis of liquid properties less than 2,000. The proposed correlation accuracy is better than the generalized correlation developed for all viscosities and Reynolds numbers and liquid holdup greater than 0.5. The less the Reynolds number, the more accurate the results.

Swirled Jet Flame Simulation and Flow Visualization Inside Rotary Kiln—CFD with PDF Approach

CFD (computational fluid dynamics) simulation using a commercial package (Fluent-ANSYS) on industrial rotary kilns using annulus-type burners and methane gas was carried out to examine the characteristics of the flame length and flow visualization. New influencing design and operating parameters—primary air swirl number, primary air inlet annulus diameter, and secondary air temperature—were investigated and discussed. The influence of these parameters on axial temperature distribution, axial mean mixture fractions, velocity vectors, mixture fractions, and temperature contours were investigated. The current numerical findings were compared with existing experimental results to validate the simulation approach. The results showed that the primary air swirl number had a remarkable influence on the flame length at a lower primary air inlet annulus diameter ratio of 2.3. Moreover, the flame length increased by 20% and 6% with increasing the swirl number from zero to one for primary air inlet annulus diameter ratios of 2.3 and 5, respectively, and it also increased by 19% with increasing primary air inlet annulus diameter ratio from 2.3 to 5.

AN ENERGY DISSIPATIVE SPATIAL DISCRETIZATION FOR THE REGULARIZED COMPRESSIBLE NAVIER-STOKES-CAHN-HILLIARD SYSTEM OF EQUATIONS

We consider the regularized 3D Navier-Stokes-Cahn-Hilliard equations describing isothermal flows of viscous compressible two-component fluids with interphase effects. We construct for them a new energy dissipative finite-difference discretization in space, i.e., with the non-increasing total energy in time. This property is preserved in the absence of a regularization. In addition, the discretization is well-balanced for equilibrium flows and the potential body force. The sought total density, mixture velocity and concentration of one of the components are defined at nodes of one and the same grid. The results of computer simulation of several 2D test problems are presented. They demonstrate advantages of the constructed discretization including the absence of the so-called parasitic currents.

Towards the development of a high power density, high efficiency, micro power generator

An innovative method to use combustion-based source for portable power generation for Microelectromechanical systems with significant improvement in power density and conversion efficiency has been reported in this study. A triple microcombustor configuration with backward facing steps and associated provision for efficient heat recirculation is proposed for flame stabilization. The presence of three parallel combustion zones increases the combustion intensity compared to a single combustor configuration and enhances the overall thermal performance. A novel technique to extract maximum heat from the hot combustion products for thermoelectric power generation is implemented. The thermoelectric modules are mounted to facilitate direct contact of the module surface with the hot combustion products. A significant improvement in heat transfer rate from the hot combustion gases to the thermoelectric modules (~16 times) is achieved. An electric power output of 4.9 W with overall conversion efficieny of 5.09% at a mixture velocity of 10 m/s and a mixture equivalence ratio of 0.9 is achieved. This signifies an improvement of ~10–20% in overall conversion efficiency as compared to previously reported systems.

Ultrasonic Velocities of Binary Mixtures of Homologous Series of Ethylene Glycol and Glycerol at Different Temperatures: A Comparative Study

Abstract The densities and ultrasonic velocities of binary mixtures of ethylene glycol and glycerol are measured at different temperatures and at frequency of 2 MHz over entire range of mole fraction. Various theoretical models such as Nomoto, Impedance, Junjie, Van Dael and Vangeel have been used to compute theoretical ultrasonic velocities. The average percentage error has been calculated and chi-square test for goodness of fit has also been to check the validity of theoretical models. The deviation from experimental results is interpreted in terms of molecular interactions among the components of the binary mixtures.

Определение жёлто-зелёной флуоресценции в зерне кукурузы

Проведены экспериментальные исследования, выполнены расчёты по определению динамики роста горючих отложений в воздуховодах вентиляционных систем в зависимости от температуры среды, диаметра воздуховода и скорости потока пылевоздушной смеси в нём. На основе этих исследований разработаны зависимости, которые могут быть использованы при установлении кратности чистки воздуховодов. Abstract. Conducted full-scale experimental studies, the calculations to identify the dynamics of combustible deposits in the ducts of ventilation systems depending on the temperature, the diameter of the duct and the flow velocity of dust-air mixture therein. Based on these studies, dependencies have been developed that can be used to determine the multiplicity of air duct cleaning.

Simulation of combustion and combustion of fl ow products in K-2 thermal spraying torch for thermal spraying of protective coatings

The finite volume method to solve of the Reynolds-averaged Navier—Stokes equations in the SST model together with the equation for the total energy with the viscosity terms is used to analyze of combustion and combustion products flow in kerosene-oxygen torch used for protective coatings high-velocity spraying (HVOF technology). The distributions of the flame temperature and the flow velocity of the gas mixture are calculated. The most heat-stressed section of the device is found. Two calculation methods are compared. These are the modeling of chemical reaction in combustion chamber and the flow of mixture of oxidation reaction products of fixed (frozen) composition determined by thermodynamic calculation of isobaric combustion chamber. The thermodynamic calculation is carried out by means of specially created computer code. It is based on the thermodynamic potential minimization. Comparative analysis is carried out for lean, enriched, and stoichiometric mixture of fuel and oxidizer. Methodically important conclusion is made on the possibility of replacing of complex calculation with chemical reaction by simpler calculation with predetermined thermodynamically equilibrium gases composition. The error is about 3 %.

Пожаро- и взрывоопасность систем вентиляции, аспирации и местных отсосов на предприятиях по хранению и переработке зерна. Исследование процессов образования и роста горючих отложений в системах местных отсосов

Проведены экспериментальные исследования, выполнены расчёты по определению динамики роста горючих отложений в воздуховодах вентиляционных систем в зависимости от температуры среды, диаметра воздуховода и скорости потока пылевоздушной смеси в нём. На основе этих исследований разработаны зависимости, которые могут быть использованы при установлении кратности чистки воздуховодов. Abstract. Conducted full-scale experimental studies, the calculations to identify the dynamics of combustible deposits in the ducts of ventilation systems depending on the temperature, the diameter of the duct and the flow velocity of dust-air mixture therein. Based on these studies, dependencies have been developed that can be used to determine the multiplicity of air duct cleaning.

OXIDATIVE DEHYDROGENATION OF METHYLCYCLOHEXANE OVER MODIFIED ZEOLITES

In the temperature range 280-390°C, at different ratios of methylcyclohexane:oxygen:nitrogen, space velocity of the gas mixture 1000-3000 h-1 and at atmospheric pressure it has been investigated the catalytic properties of synthetic and natural zeolites modified with various cations of transition and non-transition elements in the vapor-phase reaction of oxidative dehydrogenation of methylcyclohexane to methylcyclohexadiene-1,3. It has been found that the natural clinoptilolite with a combination of cations Co2+; Cr3+ in amounts of 0,5; and 0,25% wt., respectively, is an active catalyst for the oxidative dehydrogenation of methylcyclohexane to metylcyclohexadiene-1,3.

Laminar Burning Velocity of the Dimethyl Carbonate-Air Mixture Formed by the Li-Ion Electrolyte Solvent

Laminar Burning Velocity of the Dimethyl Carbonate-Air Mixture Formed by the Li-Ion Electrolyte Solvent