Counter-flow Injection Research Articles

Thermodynamic analysis of counter flow injection

Present computational investigation is carried out to reveal the effect of jet and freestream parameters on flow field alteration and associated properties. Further, thermodynamic analysis is also performed to account the irreversibilities in lower and higher enthalpy flows and various opposing conditions with real gas effects. In this regard, a computationally efficient non-equilibrium real gas solver is developed which accounts five species and eleven chemical elementary reactions. After validation of this solver, simulations are performed for various parameters of jet and freestream to examine the real gas effect on flow field and different thermodynamic parameters such as entropy generation rate, exergy destruction etc. The computed result reveals that freestream parameters have minor effect on drag coefficient and flow field but there is monotonic variation in entropy generation rate and exergy destruction for constant momentum ratio of the jet. For given momentum ratio, jet parameters give small reduction in entropy generation rate and exergy destruction while minor alterations in flow field and drag coefficient are observed. Linear reduction in drag coefficient and sharp rise in entropy generation rate and exergy destruction is obtained with momentum ratio of the jet. These proposed thermodynamic parameters and drag coefficient portrayed opposite variation with given freestream or jet parameter for constant jet momentum ratio. Jet momentum ratio is noted to be the major governing parameter for the extent of jet penetration in the freestream flow which restructures the shock wave and recirculation zone resulting in significant drag reduction and flow field alterations for hypersonic reacting flows as well. Larger shock stand-off distance for higher jet momentum ratio gives lesser drag but results in higher entropy generation rate and exergy destruction which makes the process much more irreversible.

Analysis of counter flow injection technique at elevated enthalpy hypersonic reacting flows

Large wave drag and high surface heating are common problems encountered at hypersonic speeds and these should be properly dealt for the effective and safe flights. Many studies have been carried out to mitigate these problems by employing various active and passive techniques but most of these computational or experimental studies account lower stagnation enthalpy flows or perfect gas assumption. Hence the current study examines the effect of higher freestream stagnation enthalpy on flow field alteration for counter - jet drag reduction technique for a hemispherical object. Results also includes the real gas effects on flow field, wave drag and wall heat flux. Further the effect of various flow parameters is observed on surface pressure distribution, surface heat flux and drag force for the hypersonic flow over the hemisphere, using the in house developed perfect gas and non - equilibrium N - S flow solvers. Results reveal that the perfect gas assumption overestimates surface properties and wave drag value. Drag coefficient reduces with freestream total enthalpy (Ho) in the presence of real gas effects. Around 30% drag reduction is observed at Ho=1 MJ/kg for Mach number 5 as compared to no - jet case and this reduction increases at higher freestream total enthalpy for same injection pressure ratio. Higher pressure ratio of the jet results in lower surface pressure and Stanton number on the object which gives lower wave drag.

Drag and Heat Flux Reduction using Counterflow Jet and Spike - Analysis of their Equivalence for a Blunt Cone Geometry at Mach 8

This study aims to explore equivalence between active and passive flow control techniques in reducing the wave drag and surface heat flux over a blunt cone model kept in Mach 8 stream. Computational investigations were carried out by using finite volume-based compressible flow solver. Throughout the study, the solution of governing equations is sought by assuming two dimensional-axisymmetric nature of the flowfield. Both counter flow-stagnation point injection and forward facing-physical spike are considered to mitigate the excess drag and heat flux experienced by a blunt body representing the nose cone section of a hypersonic vehicle. Eventually, based on identified drag reductions, the present study proposes equivalence cases between these two methods. It is shown that a pointed spike of L/D=1 provides almost the same drag reduction as the counterflow injection jet with a pressure ratio of 8.25. Similarly, other equivalence cases are identified and the physics behind them is explored. The identified equivalence is expected to help the designers in effectively replacing one technique with another according to the requirement. Equivalence matrix is presented for different spike cases in terms of injection ratios of counterflow injection.

Numerical analysis of ammonia homogenization for selective catalytic reduction application

Selective catalytic reduction based on urea water solution as ammonia precursor is a promising method for the NOx abatement form exhaust gasses of mobile diesel engine units. It consists of injecting the urea-water solution in the hot flue gas stream and reaction of its products with the NOx over the catalyst surface. During this process flue gas enthalpy is used for the urea-water droplet heating and for the evaporation of water content. After water evaporates, thermolysis of urea occurs, during which ammonia, a known NOx reductant, and isocyanic acid are generated. The uniformity of the ammonia before the catalyst as well as ammonia slip to the environment are important counteracting design requirements, optimization of which is crucial for development of efficient deNOx systems.The aim of this paper is to show capabilities of the developed mathematical framework implemented in the commercial CFD code AVL FIRE®, to simulate physical processes of all relevant phenomena occurring during the SCR process including chemical reactions taking part in the catalyst. First, mathematical models for description of SCR process are presented and afterwards, models are used on the 3D geometry of a real SCR reactor in order to predict ammonia generation, NOx reduction and resulting ammonia slip. Influence of the injection direction and droplet sizes was also investigated on the same geometry. The performed study indicates importance of droplet sizes on the SCR process and shows that counterflow injection is beneficial, especially in terms of minimizing harmful ammonia slip to environment.

Preparation of Silicon Nanopowder by Recycling Silicon Wafer Waste in Radio-Frequency Thermal Plasma Process

Silicon nanopowders were prepared from silicon waste by using radio-frequency thermal plasma. Silicon waste, generated from the manufacturing process of silicon wafers, was pulverized to form micrometer-sized silicon starting powder. In order to obtain as much silicon nanopowder as possible from thermal plasma processing, the enhancement of vaporization and the quenching rate of the silicon starting powder were considered as major factors. A counter-flow injection apparatus (CFIA) was introduced for improved vaporization and homogeneous nanoparticles. It was designed to inject argon as a quenching gas in the direction opposite the thermal plasma flame flow. The controlled location of the CFIA injection nozzle and the flow rate of the quenching gas affect the residence time of the injected staring powder by recirculating flow and the vapor density by gas mixing. The variation of the flow pattern inside the reactor and the characteristics of the products were investigated to determine the optimal processing environment to prepare uniform and small silicon nanopowder particles. The environment was defined by two parameters: the flow rate of the counter quenching gas and the distance between the torch and CFIA nozzles. The flow rate of the quenching gas was controlled from 30 to 70 L/min. The distance between the torch and CFIA nozzles was adjusted from 150 to 350 mm. When the quenching gas flow rate of 70 L/min and the distance of 350 mm were applied, the uniform and smallest silicon nanopowders were obtained.

A fully automated effervescence assisted dispersive liquid–liquid microextraction based on a stepwise injection system. Determination of antipyrine in saliva samples

A first attempt to automate the effervescence assisted dispersive liquid–liquid microextraction (EA-DLLME) has been reported. The method is based on the aspiration of a sample and all required aqueous reagents into the stepwise injection analysis (SWIA) manifold, followed by simultaneous counterflow injection of the extraction solvent (dichloromethane), the mixture of the effervescence agent (0.5 mol L−1 Na2CO3) and the proton donor solution (1 mol L−1 CH3COOH). Formation of carbon dioxide microbubbles generated in situ leads to the dispersion of the extraction solvent in the whole aqueous sample and extraction of the analyte into organic phase. Unlike the conventional DLLME, in the case of EA-DLLME, the addition of dispersive solvent, as well as, time consuming centrifugation step for disruption of the cloudy state is avoided. The phase separation was achieved by gentle bubbling of nitrogen stream (2 mL min−1 during 2 min).The performance of the suggested approach is demonstrated by determination of antipyrine in saliva samples. The procedure is based on the derivatization of antipyrine by nitrite-ion followed by EA-DLLME of 4-nitrosoantipyrine and subsequent UV–Vis detection using SWIA manifold. The absorbance of the yellow-colored extract at the wavelength of 345 nm obeys Beer's law in the range of 1.5–100 µmol L−1 of antipyrine in saliva. The LOD, calculated from a blank test based on 3σ, was 0.5 µmol L−1.

Numerical Simulation of Interaction of Sonic Jet with High Speed Flow over a Blunt Body using Solution Mapped Higher Order Accurate AUSM+-UP Based Flow Solver

The development of a numerical procedure based on AUSM+-UP scheme using higher order accurate reconstruction method is presented. A code based on this is used for the simulation of film cooling for reentry module. Here the convective fluxes are evaluated using AUSM+-UP scheme. Least square based derivative evaluation is used to compute diffusive fluxes. The numerical code has been successfully validated using standard experimental data for counter flow injection. Analysis has been carried out for a simple axisymmetric reentry module with and without film cooling, for a free stream Mach number of 8.0. The predicted adiabatic wall temperatures were compared for both the cases. Film cooling is found to be effective for this configuration and injected coolant remains confined to the boundary layer formed by the free stream from nose tip to the aft end of the module. Numerical simulation of film cooling provides vital information required for design of effective cooling system such as number of counter flow injectors, their dimensions and locations, injection pressure and temperature, mass flow rate required etc.

Gas-Phase Synthesis of Silicon Nanoparticles and Mixing with Graphite Powders by Using Counter-Flow Injection

Mixing between nano-sized silicon particles and micro-sized graphite powders was performed for anode materials of lithium ion batteries, in which the silicon nanoparticles were synthesized by silane pyrolysis under optimized conditions and were subsequently coated onto the surface of graphite powders at mixing chamber by counter-flow injection. The counter-flow injection was employed as a dry particle mixing process in order to generate uniform silicon-coated graphite powders. Furthermore, this method also made it possible to combine particle synthesis and mixing into one single operation. Energy dispersive X-ray spectroscopy (EDS) was utilized to examine the degree of mixing through surface chemical composition analysis of the mixture. Experimental results indicate that the jet Reynolds number can be considered as the key parameter to determine the homogeneity of the mixture and its critical value may be in the range of 120 to 180 for good mixing performance, being in reasonable agreement with previous studies.

Control of particle size and phase formation of TiO2 nanoparticles synthesized in RF induction plasma

TiO2 nanoparticles have been synthesized in this work via Ar/O2 RF thermal plasma oxidation of atomized liquid precursors containing titanium tetrabutoxide and diethanolamine. Quench gases (Ar or He), either injected from the shoulder of the reactor (transverse injection) or injected counter to the plasma plume from the bottom of the reactor (counter-flow injection), are used to affect the quench rate and therefore the particle size and phase constituent of the resultant powders. The experimental results show that counter-flow injection is more effective in reducing the particle size, while He is more effective than Ar. As a result, well-dispersed TiO2 nanopowders with controllable phase structure (up to ∼90% of anatase) and average particle size (down to 20 nm) are obtained. The experimental results are well supported by numerical analysis on the effects of the quench gas on flow pattern and temperature field of the thermal plasma as well as trajectory and temperature history of the particles.

A Novel Method for Producing Spatially Uniform Aerosols in a Low Pressure Environment

Aerosols flowing in a tube under vacuum conditions, e.g., in semiconductor processing equipment, are often found to have a nonuniform profile due to low Reynolds number flow (Bae et al. 1998). A novel method to produce spatially uniform aerosols in a flow tube at low pressure has been developed. The method employs a counter-flow injection configuration. Two identical critical orifices of 200 w m in diameter are installed opposite each other in an aerosol mixing chamber. The opposing aerosol jets from the two orifices result in turbulent and uniform mixing of the two aerosol streams. Aerosols 0.3 w m or less in diameter, at a pressure as low as 1 Torr, are shown to be distributed uniformly over a cross section of a tube with an inner diameter of 3.48 cm. This method has been further improved to provide spatially uniform aerosols at lower pressures by using a pressure reducer downstream of the aerosol mixing chamber. The arrangement provides spatially uniform aerosols at a pressure as low as 0.2 Torr.

96/00432 Characteristics of multi-phase flow with particle evaporation in a combustor with counter-flow injection

A new approach using differential geometric theory to nonlinear control design for dual-excited synchronous generators is presented in this paper. As an example, a novel rotor angle and voltage stabilizing nonlinear optimal excitation control law of dual-excited synchronous generators is obtained, which is based on coordinate transformers and state feedback linearization combined with dynamic system. The computer simulation results on a single-machine infinite-bus power system show that dual-excited synchronous generator with proposed controller can improve dynamic stability and transient stability of power system to a great extent and has better dynamic characteristics than conventional synchronous generator.

Characteristics of multi-phase flow with particle evaporation in a combustor with counter-flow injection

Seed particles are added to a high temperature reacting flow to achieve the desired electric conductivity for magnetohydrodynamic (MHD) power generation. The evaporation rate of the see particles and the uniformity of the seed vapor distribution in the reacting flow are major factors affecting the performance of the MHD system. An integral reacting flow (IRF) computer code was used to calculate the multi-phase flow characteristics in an MHD combustor and predict the optimum operating conditions of the combustor. The IRF code is a general hydrodynamics computer code for multi-phase, two dimensional, steady state, turbulent, and reacting flows, based on mass, momentum, and energy conservation laws. A unique integral reaction submodel in the IRF code enhances numerical convergence while preserving the major physical effects of the complex combustion processes. The combustor is a rectangular channel in which a mixture of fuel gas and seed particles enters from one end and exits at the other, while the oxidizer is injected from the sides. The major findings of a parametric study included: (1) the seed particle evaporation rate varies for different oxidizer injection angles; (2) the optimal evaporation rate was found at an injection angle around 130°; (3) the seed particle size had a major effect on particle dispersion and vapor mixing; (4) seed particles with a diameter of 34 μm or larger were only partially vaporized in the combustor, and the seed vapor distribution at the combustor exit was highly non-uniform; and (5) significant particle deposition was found on the side walls upstream of the oxidizer injection slots. Theoretical predictions were in general agreement with experimental trends.

Integral Combustion Simulation of a Turbulent Reacting Flow in a Channel with Cross-Stream Injection

A new integral one-step reaction submodel has been developed for an Argonne combustion computer code to simulate reacting flows of an advanced combustor for magnetohydrody-narmic power generation. The integral combustion code makes numerical calculations of a reacting flow more efficient and mart stable while still preserving the major physical effects of the complex combustion processes. Results of the simulation indicate that (1) fluid mixing is mainly responsible for combustion performance and (2) counterflow injection with an injection angle in the range of 120° to 140° yields the best mixing and combustion performance.

Plasma Synthesis of Fine Ceramic Powders by a Novel Counter-Flow Liquid Injection Method.

ABSTRACTCeramic powders of carbides, oxides, solid solutions of oxides, magnetic and non-magnetic spinels, superconductors and composites have been successfully synthesized in a thermal plasma jet reactor using a novel counter-flow liquid injection plasma synthesis (CF LIPS) method developed to overcome the problems associated with solid injection and to realize the benefits of gas phase reactions and counter-flow injection. Standard material characterization techniques have been used for powder analysis.

Counter-Flow Liquid Injection Plasma Synthesis (CF LIPS) of Spinel Fine Powders

Fine powders of aluminate, ferrite, and chromite spinels were successfully produced by a novel Counter-Flow Liquid Injection Plasma Synthesis (CF LIPS) method using a DC plasma jet. CF LIPS has been demonstrated to be an excellent method to produce fine ceramic powders with a narrow particle size distribution. The spinels produced by this techniques, both magnetic and non-magnetic, have a very similar particle size distribution. The powders produced were spherical, non-agglomerating and dispersable with average sizes of 1 µm.

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Measurements of the nearly isotropic turbulence behind a uniform jet grid

Wind-tunnel turbulence behind a parallel-rod grid with jets evenly distributed along each rod is nearly isotropic. Homogeneity improvement over prior related experiments was attained by the use of controllable nozzles. Compared with the ‘passive’ case, the downwind-jet ‘active’ grid has a smaller static pressure drop across it and gives a smaller turbulence level at a prescribed distance from it, while the upwind-jet grid gives a larger static pressure drop and larger turbulence level. ‘Counterflow injection’ generates larger turbulence energy and larger scales, both events being evidently associated with instability of the jet system. This behaviour is much like that commonly observed behind passive grids of higher solidities.If the turbulent kinetic energy is approximated as an inverse power law in distance, the (positive) exponent decreases with increasing (downwind or upwind) jet strength, corresponding to slower absolute decay rates. No peculiar decay behaviour occurs when the jet grid is ‘self-propelled’ (zero net average force), or when the static pressure drop across it is zero.The injection does not change the general behaviour of the energy spectra, although the absolute spectra change inasmuch as the turbulence kinetic energy changes.