Numerical modelling of flow pattern for high swirling flows

Directory of Open Access Journals (Sweden)

Parra Teresa

2015-01-01

Full Text Available This work focuses on the interaction of two coaxial swirling jets. High swirl burners are suitable for lean flames and produce low emissions. Computational Fluid Dynamics has been used to study the isothermal behaviour of two confined jets whose setup and operating conditions are those of the benchmark of Roback and Johnson. Numerical model is a Total Variation Diminishing and PISO is used to pressure velocity coupling. Transient analysis let identify the non-axisymmetric region of reverse flow. The center of instantaneous azimuthal velocities is not located in the axis of the chamber. The temporal sampling evidences this center spins around the axis of the device forming the precessing vortex core (PVC whose Strouhal numbers are more than two for Swirl numbers of one. Influence of swirl number evidences strong swirl numbers are precursor of large vortex breakdown. Influence of conical diffusers evidence the reduction of secondary flows associated to boundary layer separation.

NOx emissions from high swirl turbulent spray flames with highly oxygenated fuels

KAUST Repository

Bohon, Myles

2013-01-01

Combustion of fuels with fuel bound oxygen is of interest from both a practical and a fundamental viewpoint. While a great deal of work has been done studying the effect of oxygenated additives in diesel and gasoline engines, much less has been done examining combustion characteristics of fuels with extremely high mass fractions of fuel bound oxygen. This work presents an initial investigation into the very low NOx emissions resulting from the combustion of a model, high oxygen mass fraction fuel. Glycerol was chosen as a model fuel with a fuel bound oxygen mass fraction of 52%, and was compared with emissions measured from diesel combustion at similar conditions in a high swirl turbulent spray flame. This work has shown that high fuel bound oxygen mass fractions allow for combustion at low global equivalence ratios with comparable exhaust gas temperatures due to the significantly lower concentrations of diluting nitrogen. Despite similar exhaust gas temperatures, NOx emissions from glycerol combustion were up to an order of magnitude lower than those measured using diesel fuel. This is shown to be a result not of specific burner geometry, but rather is influenced by the presence of higher oxygen and lower nitrogen concentrations at the flame front inhibiting NOx production. © 2012 The Combustion Institute.

Numerical simulation of the effect of upstream swirling flow on swirl meter performance

Science.gov (United States)

Chen, Desheng; Cui, Baoling; Zhu, Zuchao

2018-04-01

Flow measurement is important in the fluid process and transmission system. For the need of accuracy measurement of fluid, stable flow is acquired. However, the elbows and devices as valves and rotary machines may produce swirling flow in the natural gas pipeline networks system and many other industry fields. In order to reveal the influence of upstream swirling flow on internal flow fields and the metrological characteristics, numerical simulations are carried out on the swirl meter. Using RNG k-ɛ turbulent model and SIMPLE algorithm, the flow field is numerically simulated under swirling flows generated from co-swirl and counter-swirl flow. Simulation results show fluctuation is enhanced or weakened depending on the rotating direction of swirling flow. A counter- swirl flow increases the entropy production rate at the inlet and outlet of the swirler, the junction region between throat and divergent section, and then the pressure loss is increased. The vortex precession dominates the static pressure distributions on the solid walls and in the channel, especially at the end region of the throat.

Aperiodic pressure pulsation under non optimal hydraulic turbine regimes at low swirl number

Science.gov (United States)

Skripkin, S. G.; Tsoy, M. A.; Kuibin, P. A.; Shtork, S. I.

2017-09-01

Off-design operating conditions of hydraulic turbines is hindered by pressure fluctuations in the draft tube of the turbine. A precessing helical vortex rope develops, which imperils the mechanical structure and limits the operation flexibility of hydropower station. Understanding of the underlying instabilities of precessing vortex rope at low swirl number is incomplete. In this paper flow regimes with different residual swirl is analysed, particular attention is paid to the regime with a small swirl parameter. Study defines upper and low boundaries of regime where aperiodic pressure surge is observed. Flow field at the runner exit is investigated by Laser Doppler Velocimetry and high-speed visualizations, which are complemented draft tube wall pressure measurements.

The influence of fuel-air swirl intensity on flame structures of syngas swirl-stabilized diffusion flame

Science.gov (United States)

Shao, Weiwei; Xiong, Yan; Mu, Kejin; Zhang, Zhedian; Wang, Yue; Xiao, Yunhan

2010-06-01

Flame structures of a syngas swirl-stabilized diffusion flame in a model combustor were measured using the OH-PLIF method under different fuel and air swirl intensity. The flame operated under atmospheric pressure with air and a typical low heating-value syngas with a composition of 28.5% CO, 22.5% H2 and 49% N2 at a thermal power of 34 kW. Results indicate that increasing the air swirl intensity with the same fuel, swirl intensity flame structures showed little difference except a small reduction of flame length; but also, with the same air swirl intensity, fuel swirl intensity showed great influence on flame shape, length and reaction zone distribution. Therefore, compared with air swirl intensity, fuel swirl intensity appeared a key effect on the flame structure for the model combustor. Instantaneous OH-PLIF images showed that three distinct typical structures with an obvious difference of reaction zone distribution were found at low swirl intensity, while a much compacter flame structure with a single, stable and uniform reaction zone distribution was found at large fuel-air swirl intensity. It means that larger swirl intensity leads to efficient, stable combustion of the syngas diffusion flame.

Ammonia-methane combustion in tangential swirl burners for gas turbine power generation

OpenAIRE

Valera Medina, Agustin; Marsh, Richard; Runyon, Jon; Pugh, Daniel; Beasley, Paul; Hughes, Timothy Richard; Bowen, Philip John

2017-01-01

Ammonia has been proposed as a potential energy storage medium in the transition towards a low-carbon economy. This paper details experimental results and numerical calculations obtained to progress towards optimisation of fuel injection and fluidic stabilisation in swirl burners with ammonia as the primary fuel. A generic tangential swirl burner has been employed to determine flame stability and emissions produced at different equivalence ratios using ammonia–methane blends. Experiments were...

Case study for co and counter swirling domestic burners

Directory of Open Access Journals (Sweden)

Ashraf Kotb

2018-03-01

Full Text Available In this case study, the influence of equivalence ratio for co and counter-swirl domestic burners compared with non-swirl design on the thermal efficiency as well as CO emissions has been studied using liquefied petroleum gas (LPG. Also, the flame stability, and pot height, which is defined as the burner-to-pot distance (H, of the co and counter domestic burners were compared. The analysis of the results showed that, for both swirl burners co and counter one the thermal efficiency under all operation conditions tested is higher than the non-swirled burner (base burner. For example, the thermal efficiency increased by 8.8%, and 5.8% than base burner for co and counter swirl, respectively at Reynolds number equal 2000 and equivalence ratio 1. The co and counter swirl burners show lower CO emission than the base burner. The co swirl burner has wider operation range than counter swirl. With the increase of pot height, the thermal efficiency of all burners decreases because the flame and combustion gases are cooled due to mixing with ambient air. As a result, the heat transfer is decreased due to atmospheric loss, which decrease the thermal efficiency.

Emissions Control in Swirl-Stabilized Combustors

National Research Council Canada - National Science Library

Hanson, Ronald K

2006-01-01

...) fabricate a swirl-stabilized gas and liquid fuel burner with optical access to enable diagnostic development that mimics the atmospheric pressure performance of the University of Cincinnati facility, and 4...

A comparison of the thermal, emission and heat transfer characteristics of swirl-stabilized premixed and inverse diffusion flames

Energy Technology Data Exchange (ETDEWEB)

Zhen, H.S.; Leung, C.W.; Cheung, C.S. [Department of Mechanical Engineering, The Hong Kong Polytechnic University, Hung Hom, Hong Kong (China)

2011-02-15

Two swirl-stabilized flames, a premixed flame (PMF-s) and an inverse diffusion flame (IDF-s), were investigated experimentally in order to obtain information on their thermal, emission and heat transfer characteristics. The two flames, having different global air/fuel mixing mechanisms, were compared under identical air and fuel flow rates. Results showed that the two flames have similar visual features such as flame shape, size and structure because the Reynolds number and the swirl number which are important parameters representative of the aerodynamic characteristics of a swirling jet flow, are almost the same for the two flames. The minor dissimilarity in flame color and flame length indicates that the IDF-s is more diffusional. Both the PMF-s and IDF-s are stabilized by the internal recirculation zone (IRZ) and the IDF-s is more stable. Flame temperature is uniformly distributed in the IRZ due to the strong mixing caused by flow recirculation. The highest flame temperature is achieved at the main reaction zone and it is higher for the PMF-s due to more rapid and localized heat release. For the IDF-s, the thermal NO mechanism dominates the NO{sub x} formation. For the PMF-s, both the thermal and prompt mechanisms tend to play important roles in the global NO{sub x} emission under rich conditions. The comparison of EINO{sub x} and EICO shows that the PMF-s has lower level of NO{sub x} emission under lean combustion and lower level of CO emission under all conditions. The reason is that the air/fuel premixing in the PMF-s significantly enhances the mixedness of the supplied air/fuel mixture. The analysis of the behaviors of the impinging PMF-s and IDF-s heat transfer reveals that because the PMF-s has more rapid and localized heat release at the main reaction zone, the peak heat flux is higher than that of the IDF-s and the IDF-s has more uniform heating effect. A comparison of the overall heat transfer rates shows that, due to more complete combustion, the PMF

A comparison of the thermal, emission and heat transfer characteristics of swirl-stabilized premixed and inverse diffusion flames

International Nuclear Information System (INIS)

Zhen, H.S.; Leung, C.W.; Cheung, C.S.

2011-01-01

Two swirl-stabilized flames, a premixed flame (PMF-s) and an inverse diffusion flame (IDF-s), were investigated experimentally in order to obtain information on their thermal, emission and heat transfer characteristics. The two flames, having different global air/fuel mixing mechanisms, were compared under identical air and fuel flow rates. Results showed that the two flames have similar visual features such as flame shape, size and structure because the Reynolds number and the swirl number which are important parameters representative of the aerodynamic characteristics of a swirling jet flow, are almost the same for the two flames. The minor dissimilarity in flame color and flame length indicates that the IDF-s is more diffusional. Both the PMF-s and IDF-s are stabilized by the internal recirculation zone (IRZ) and the IDF-s is more stable. Flame temperature is uniformly distributed in the IRZ due to the strong mixing caused by flow recirculation. The highest flame temperature is achieved at the main reaction zone and it is higher for the PMF-s due to more rapid and localized heat release. For the IDF-s, the thermal NO mechanism dominates the NO x formation. For the PMF-s, both the thermal and prompt mechanisms tend to play important roles in the global NO x emission under rich conditions. The comparison of EINO x and EICO shows that the PMF-s has lower level of NO x emission under lean combustion and lower level of CO emission under all conditions. The reason is that the air/fuel premixing in the PMF-s significantly enhances the mixedness of the supplied air/fuel mixture. The analysis of the behaviors of the impinging PMF-s and IDF-s heat transfer reveals that because the PMF-s has more rapid and localized heat release at the main reaction zone, the peak heat flux is higher than that of the IDF-s and the IDF-s has more uniform heating effect. A comparison of the overall heat transfer rates shows that, due to more complete combustion, the PMF-s has higher overall

Microjet Injection Strategies for Mitigating Dynamics in a Lean Premixed Swirl-Stabilized Combustor

KAUST Repository

LaBry, Zachary; Shanbhogue, Santosh; Ghoniem, Ahmed

2011-01-01

Combustion dynamics remain a challenge in the development of low-emission, air-breathing combustors for power generation and aircraft propulsion. In this paper, we presenta parametric study on the use of microjet injectors for suppressing or mitigating the combustion dynamics that energize the thermoacoustic instability in a swirl-stabilized, premixed combustor. Microjet injectors consist of small inlet ports intended to inject flow with high momentum at relatively low mass flow rates into the flame-anchoring region. The microjets were configured to inject flow either axially, into the outer recirculation zone, or radially into the inner recirculation zone. Additionally, different injectors were tested with different relative senses of swirl (signs of angular momentum)with respect to the main flow: co-swirling, not swirling, or counter-swirling. We observed that injecting air or premixed fuel/air into the inner recirculation zone via counter-swirling radial microjets, we were able to reduce the overall sound pressure level in the combustor by over 20 dB in the lean end of the operating range. Other injector configurations were not observed to positively influence the combust or stability. Detailed PIV measurements are used to examine possible mechanisms of how the microjets impact the combustion dynamics, and the technology implications of our experiments are discussed.

Microjet Injection Strategies for Mitigating Dynamics in a Lean Premixed Swirl-Stabilized Combustor

KAUST Repository

LaBry, Zachary

2011-01-04

Combustion dynamics remain a challenge in the development of low-emission, air-breathing combustors for power generation and aircraft propulsion. In this paper, we presenta parametric study on the use of microjet injectors for suppressing or mitigating the combustion dynamics that energize the thermoacoustic instability in a swirl-stabilized, premixed combustor. Microjet injectors consist of small inlet ports intended to inject flow with high momentum at relatively low mass flow rates into the flame-anchoring region. The microjets were configured to inject flow either axially, into the outer recirculation zone, or radially into the inner recirculation zone. Additionally, different injectors were tested with different relative senses of swirl (signs of angular momentum)with respect to the main flow: co-swirling, not swirling, or counter-swirling. We observed that injecting air or premixed fuel/air into the inner recirculation zone via counter-swirling radial microjets, we were able to reduce the overall sound pressure level in the combustor by over 20 dB in the lean end of the operating range. Other injector configurations were not observed to positively influence the combust or stability. Detailed PIV measurements are used to examine possible mechanisms of how the microjets impact the combustion dynamics, and the technology implications of our experiments are discussed.

Powerful Swirl Generation of Flow-driven Rotating Mixing Vane for Enhancing CHF

International Nuclear Information System (INIS)

Seo, Han; Seo, Seok Bin; Heo, Hyo; Bang, In Cheol

2014-01-01

Mixing vanes are utilized to improve CHF and heat transfer performance in the rod bundle during normal operation. Experimental measurement of the swirling flow from a split vane pair was conducted using particle image velocimetry (PIV) and boroscope. The lateral velocity fields show that the swirling flow was initially centered in the subchannel and the computational fluid dynamics (CFD) analysis was performed based on the experiment. To visualize flow patterns in the 5Χ5 subchannel using PIV, matching the refraction between the working fluid and the structure was considered and the experiment aimed to develop the experimental data for providing fundamental information of the CFD analysis. The fixed split vane is the main mixing inducer in the fuel assembly. In a heat exchanger research, propeller type swirl generates at several pitch ratios and different blades angles were used to enhance heat transfer rate. Significant improvements of the heat transfer rate using the propellers were confirmed due to creation of tangential flow. In the present study, the mixing effect of rotation vane which has a shape of propeller was studied using PIV. A split vane was considered in the experiment to show the effect of rotation vane. Vertical and horizontal flow analyses were conducted to show the possible use of rotation vane in a subchannel. In the present work, the study of flow visualization using three types of vanes is conducted to show the mixing effect. The vertical flow and the horizontal flow distributions were analyzed in the two experimental facilities. For the vertical flow facility, flow distributions, flow profiles, and the turbulence kinetic energy are analyzed at the centerline of the channel. The results show that the rotation vane has the highest flow and turbulence kinetic intensity at the centerline of the channel. For the horizontal flow facility, the results indicate that lateral flow of the rotation vane is generated and maintained along with the flow

Numerical Research of Nitrogen Oxides Formation for Justification of Modernization of P-49 Nazarovsky State District Power Plant Boiler on the Low-temperature Swirl Technology of Burning

Science.gov (United States)

Trinchenko, A. A.; Paramonov, A. P.; Skouditskiy, V. E.; Anoshin, R. G.

2017-11-01

Compliance with increasingly stringent normative requirements to the level of pollutants emissions when using organic fuel in the energy sector as a main source of heat, demands constant improvement of the boiler and furnace equipment and the power equipment in general. The requirements of the current legislation in the field of environmental protection prescribe compliance with established emission standards for both new construction and the improvement of energy equipment. The paper presents the results of numerical research of low-temperature swirl burning in P-49 Nazarovsky state district power plant boiler. On the basis of modern approaches of the diffusion and kinetic theory of burning and the analysis physical and chemical processes of a fuel chemically connected energy transition in thermal, generation and transformation of gas pollutants, the technological method of nitrogen oxides decomposition on the surface of carbon particles with the formation of environmentally friendly carbonic acid and molecular nitrogen is considered during the work of low-temperature swirl furnace. With the use of the developed model, methodology and computer program, variant calculations of the combustion process were carried out and a quantitative estimate of the emission level of the nitrogen oxides of the boiler being modernized. The simulation results the and the experimental data obtained during the commissioning and balance tests of the P-49 boiler with a new furnace are confirmed that the organization of swirl combustion has allowed to increase the efficiency of work, to reduce slagging, to significantly reduce nitrogen oxide emissions, to improve ignition and burnout of fuel.

Measurements of non-reacting and reacting flow fields of a liquid swirl flame burner

Science.gov (United States)

Chong, Cheng Tung; Hochgreb, Simone

2015-03-01

The understanding of the liquid fuel spray and flow field characteristics inside a combustor is crucial for designing a fuel efficient and low emission device. Characterisation of the flow field of a model gas turbine liquid swirl burner is performed by using a 2-D particle imaging velocimetry(PIV) system. The flow field pattern of an axial flow burner with a fixed swirl intensity is compared under confined and unconfined conditions, i.e., with and without the combustor wall. The effect of temperature on the main swirling air flow is investigated under open and non-reacting conditions. The result shows that axial and radial velocities increase as a result of decreased flow density and increased flow volume. The flow field of the main swirling flow with liquid fuel spray injection is compared to non-spray swirling flow. Introduction of liquid fuel spray changes the swirl air flow field at the burner outlet, where the radial velocity components increase for both open and confined environment. Under reacting condition, the enclosure generates a corner recirculation zone that intensifies the strength of radial velocity. The reverse flow and corner recirculation zone assists in stabilizing the flame by preheating the reactants. The flow field data can be used as validation target for swirl combustion modelling.

Search for Magnetically Broadened Cascade Emission from Blazars with VERITAS

Energy Technology Data Exchange (ETDEWEB)

Archambault, S.; Griffin, S. [Physics Department, McGill University, Montreal, QC H3A 2T8 (Canada); Archer, A.; Bugaev, V. [Department of Physics, Washington University, St. Louis, MO 63130 (United States); Benbow, W.; Cerruti, M. [Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645 (United States); Buchovecky, M. [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States); Connolly, M. P. [School of Physics, National University of Ireland Galway, University Road, Galway (Ireland); Cui, W.; Finley, J. P. [Department of Physics and Astronomy, Purdue University, West Lafayette, IN 47907 (United States); Falcone, A. [Department of Astronomy and Astrophysics, 525 Davey Lab, Pennsylvania State University, University Park, PA 16802 (United States); Alonso, M. Fernández [Instituto de Astronomía y Física del Espacio (IAFE, CONICET-UBA), CC 67—Suc. 28, (C1428ZAA) Ciudad Autónoma de Buenos Aires (Argentina); Fleischhack, H.; Hütten, M. [DESY, Platanenallee 6, D-15738 Zeuthen (Germany); Fortson, L. [School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455 (United States); Furniss, A. [Department of Physics, California State University—East Bay, Hayward, CA 94542 (United States); Hervet, O.; Johnson, C. A. [Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064 (United States); Holder, J. [Department of Physics and Astronomy and the Bartol Research Institute, University of Delaware, Newark, DE 19716 (United States); Humensky, T. B., E-mail: elisa.pueschel@ucd.ie, E-mail: weisgarber@physics.wisc.edu [Physics Department, Columbia University, New York, NY 10027 (United States); and others

2017-02-01

We present a search for magnetically broadened gamma-ray emission around active galactic nuclei (AGNs), using VERITAS observations of seven hard-spectrum blazars. A cascade process occurs when multi-TeV gamma-rays from an AGN interact with extragalactic background light (EBL) photons to produce electron–positron pairs, which then interact with cosmic microwave background photons via inverse-Compton scattering to produce gamma-rays. Due to the deflection of the electron–positron pairs, a non-zero intergalactic magnetic field (IGMF) would potentially produce detectable effects on the angular distribution of the cascade emission. In particular, an angular broadening compared to the unscattered emission could occur. Through non-detection of angularly broadened emission from 1ES 1218+304, the source with the largest predicted cascade fraction, we exclude a range of IGMF strengths around 10{sup −14} G at the 95% confidence level. The extent of the exclusion range varies with the assumptions made about the intrinsic spectrum of 1ES 1218+304 and the EBL model used in the simulation of the cascade process. All of the sources are used to set limits on the flux due to extended emission.

PULSE MODULATION POWER AMPLIFIER WITH ENHANCED CASCADE CONTROL METHOD

DEFF Research Database (Denmark)

1998-01-01

a single local feedback path A (7) with a lowpass characteristic and local forward blocks B¿1? or B (3, 4). The leads to a much improved system with a very low sensitivity to errors in the switching power stage. In the second preferred embodiment of the invention the control structure is extended...... and feedback path A to determine stable self-oscillating conditions. An implemented 250W example MECC digital power amplifier has proven superior performance in terms of audio performance (0.005 % distortion, 115 dB dynamic range) and efficiency (92 %).......A digital switching power amplifier with Multivariable Enhanced Cascade Controlled (MECC) includes a modulator, a switching power stage and a low pass filter. In the first preferred embodiment an enhanced cascade control structure local to the switching power stage is added, characterised by having...

A generalized relationship for swirl decay in laminar pipe flow

Indian Academy of Sciences (India)

Swirling flow is of great importance in heat and mass transfer enhancements and in flow measurements. In this study, laminar swirling flow in a straight pipe was considered. Steady three-dimensional axisymmetric Navier–Stokes equations were solved numerically using a control volume approach. The swirl number ...

Numerical investigation of a perturbed swirling annular two-phase jet

Energy Technology Data Exchange (ETDEWEB)

Siamas, George A. [Mechanical Engineering, School of Engineering and Design, Brunel University, Uxbridge UB8 3PH (United Kingdom)], E-mail: siamas@spidernet.com.cy; Jiang, Xi; Wrobel, Luiz C. [Mechanical Engineering, School of Engineering and Design, Brunel University, Uxbridge UB8 3PH (United Kingdom)

2009-06-15

A swirling annular gas-liquid two-phase jet flow system has been investigated by solving the compressible, time-dependent, non-dimensional Navier-Stokes equations using highly accurate numerical methods. The mathematical formulation for the flow system is based on an Eulerian approach with mixed-fluid treatment while an adjusted volume of fluid method is utilised to account for the gas compressibility. Surface tension effects are captured by a continuum surface force model. Swirling motion is applied at the inlet while a small helical perturbation is also applied to initiate the instability. Three-dimensional spatial direct numerical simulation has been performed with parallelisation of the code based on domain decomposition. The results show that the flow is characterised by a geometrical recirculation zone adjacent to the nozzle exit and by a central recirculation zone further downstream. Swirl enhances the flow instability and vorticity and promotes liquid dispersion in the cross-streamwise directions. A dynamic precessing vortex core is developed demonstrating that the growth of such a vortex in annular configurations can be initiated even at low swirl numbers, in agreement with experimental findings. Analysis of the averaged results revealed the existence of a geometrical recirculation zone and a swirl induced central recirculation zone in the flow field.

A study on the effects of the intake port configurations on the swirl flow generated in a small D.I. diesel engine

Science.gov (United States)

Kim, Yungjin; Han, Yongtaek; Lee, Kihyung

2014-06-01

This paper investigates the effect of intake port configuration on the swirl that is generated within a direct injection (D.I.) diesel engine. The in-cylinder flow characteristics are known to have significant effects on fuel-air mixing, combustion, and emissions. To clarify how to intensify the swirl flow, a swirl control valve (SCV) and a bypass were selected as design parameters for enhancing the swirl flow. The optimal intake port shape was also chosen as a parameter needed to efficiently generate a high swirl ratio. The results revealed that a key factor in generating a high swirl ratio was to control the intake airflow direction passing through the intake valve seat. Further, the swirl intensity was influenced by changing the distance between the helical and tangential ports, and the swirl flow was changed by the presence of a bypass near the intake valve seat. Additionally, the effect of intake port geometry on the in-cylinder flow field was investigated by using a laser sheet visualization method. The experimental results showed a correlation of swirl ratio and mass flow rate. In addition, we found that employing the bypass was an effective method to increase swirl ratio without sacrificing mass flow rate.

Structure of a swirling jet with vortex breakdown and combustion

Science.gov (United States)

Sharaborin, D. K.; Dulin, V. M.; Markovich, D. M.

2018-03-01

An experimental investigation is performed in order to compare the time-averaged spatial structure of low- and high-swirl turbulent premixed lean flames by using the particle image velocimetry and spontaneous Raman scattering techniques. Distributions of the time-average velocity, density and concentration of the main components of the gas mixture are measured for turbulent premixed swirling propane/air flames at atmospheric pressure for the equivalence ratio Φ = 0.7 and Reynolds number Re = 5000 for low- and high-swirl reacting jets. For the low-swirl jet (S = 0.41), the local minimum of the axial mean velocity is observed within the jet center. The positive value of the mean axial velocity indicates the absence of a permanent recirculation zone, and no clear vortex breakdown could be determined from the average velocity field. For the high-swirl jet (S = 1.0), a pronounced vortex breakdown took place with a bubble-type central recirculation zone. In both cases, the flames are stabilized in the inner mixing layer of the jet around the central wake, containing hot combustion products. O2 and CO2 concentrations in the wake of the low-swirl jet are found to be approximately two times smaller and greater than those in the recirculation zone of the high-swirl jet, respectively.

Modeling of Turbulent Swirling Flows

Science.gov (United States)

Shih, Tsan-Hsing; Zhu, Jiang; Liou, William; Chen, Kuo-Huey; Liu, Nan-Suey; Lumley, John L.

1997-01-01

Aircraft engine combustors generally involve turbulent swirling flows in order to enhance fuel-air mixing and flame stabilization. It has long been recognized that eddy viscosity turbulence models are unable to appropriately model swirling flows. Therefore, it has been suggested that, for the modeling of these flows, a second order closure scheme should be considered because of its ability in the modeling of rotational and curvature effects. However, this scheme will require solution of many complicated second moment transport equations (six Reynolds stresses plus other scalar fluxes and variances), which is a difficult task for any CFD implementations. Also, this scheme will require a large amount of computer resources for a general combustor swirling flow. This report is devoted to the development of a cubic Reynolds stress-strain model for turbulent swirling flows, and was inspired by the work of Launder's group at UMIST. Using this type of model, one only needs to solve two turbulence equations, one for the turbulent kinetic energy k and the other for the dissipation rate epsilon. The cubic model developed in this report is based on a general Reynolds stress-strain relationship. Two flows have been chosen for model evaluation. One is a fully developed rotating pipe flow, and the other is a more complex flow with swirl and recirculation.

Effects of operating conditions and fuel properties on emission performance and combustion efficiency of a swirling fluidized-bed combustor fired with a biomass fuel

International Nuclear Information System (INIS)

Kuprianov, Vladimir I.; Kaewklum, Rachadaporn; Chakritthakul, Songpol

2011-01-01

This work reports an experimental study on firing 80 kg/h rice husk in a swirling fluidized-bed combustor (SFBC) using an annular air distributor as the swirl generator. Two NO x emission control techniques were investigated in this work: (1) air staging of the combustion process, and (2) firing rice husk as moisturized fuel. In the first test series for the air-staged combustion, CO, NO and C x H y emissions and combustion efficiency were determined for burning 'as-received' rice husk at fixed excess air of 40%, while secondary-to-primary air ratio (SA/PA) was ranged from 0.26 to 0.75. The effects of SA/PA on CO and NO emissions from the combustor were found to be quite weak, whereas C x H y emissions exhibited an apparent influence of air staging. In the second test series, rice husks with the fuel-moisture content of 8.4% to 35% were fired at excess air varied from 20% to 80%, while the flow rate of secondary air was fixed. Radial and axial temperature and gas concentration (O 2 , CO, NO) profiles in the reactor, as well as CO and NO emissions, are discussed for the selected operating conditions. The temperature and gas concentration profiles for variable fuel quality exhibited significant effects of both fuel-moisture and excess air. As revealed by experimental results, the emission of NO from this SFBC can be substantially reduced through moisturizing rice husk, while CO is effectively mitigated by injection of secondary air into the bed splash zone, resulting in a rather low emission of CO and high (over 99%) combustion efficiency of the combustor for the ranges of operating conditions and fuel properties.

Computational Investigation of Swirling Supersonic Jets Generated Through a Nozzle-Twisted Lance

Science.gov (United States)

Li, Mingming; Li, Qiang; Zou, Zongshu; An, Xizhong

2017-02-01

The dynamic characteristics of supersonic swirling jets generated through a nozzle-twisted lance are numerically studied. The essential features of the swirling jets are identified by defining a deviation angle. The effects of nozzle twist angle (NTA) on swirling flow intensity, coalescence characteristics, and dynamic parameter distributions of the jets are discussed. The rotational flow characteristics are revealed. The results show that the jets from the nozzle-twisted lance are imparted to a circumferential rotating movement around the lance axis, and such swirling flow is enhanced by increasing NTA. The enhanced swirling flow causes weaker coalescence of the jets, faster attenuations of the axial velocity, and higher heat transfer rate between the jets and surroundings. The supersonic core length, however, is found to be less sensitive to the swirling flow intensity. The radial spreading of the jets, changing non-monotonically with NTA, arrives at its maximum at 5 deg of NTA. Furthermore, the swirling flow induces a considerable tangential velocity component, and as a result, a holistic and effective horizontal swirling flow field develops. The y-vorticity distribution range and the corresponding magnitude turn larger with increasing NTA, which promote the vortex motion of the local fluid element and thus intensify the local mixing.

EINOx scaling in a non-premixed turbulent hydrogen jet with swirled coaxial air

Energy Technology Data Exchange (ETDEWEB)

Oh, Jeongseog; Hwang, Jeongjae; Yoon, Youngbin [School of Mechanical and Aerospace Engineering, Seoul National University, Seoul 151-742 (Korea)

2010-08-15

The effect of swirl flow on pollutant emission (nitrous oxide) was studied in a non-premixed turbulent hydrogen jet with coaxial air. A swirl vane was equipped in a coaxial air feeding line and the angle of the swirl vane was varied from 30 to 90 degrees. Under a fixed global equivalence ratio of {phi}{sub G} = 0.5, fuel jet air velocity and coaxial air velocity were varied in an attached flame region as u{sub F} = 85.7-160.2 m/s and u{sub A} = 7.4-14.4 m/s. In the present study, two mixing variables of coaxial air and swirl flow were considered: the flame residence time and global strain rate. The objective of the current study was to analyze the flame length behavior, and the characteristics of nitrous oxide emissions under a swirl flow conditions, and to suggest a new parameter for EINOx (the emission index of nitrous oxide) scaling. From the experimental results, EINOx decreased with the swirl vane angle and increased with the flame length (L). We found the scaling variables for the flame length and EINOx using the effective diameter (d{sub F,eff}) in a far-field concept. Normalized flame length (L divided by d{sub F,eff}) fitted well with the theoretical expectations. EINOx increased in proportion to the flame residence time ({proportional_to}{tau}{sub R}{sup 1/2.8}) and the global strain rate ({proportional_to}S{sub G}{sup 1/2.8}). (author)

An Assessment of Combustion Dynamics in a Low-Nox, Second-Generation Swirl-Venturi Lean Direct Injection Combustion Concept

Science.gov (United States)

Tacina, K. M.; Chang, C. T.; Lee, P.; Mongia, H.; Podboy, D. P.; Dam, B.

2015-01-01

Dynamic pressure measurements were taken during flame-tube emissions testing of three second-generation swirl-venturi lean direct injection (SV-LDI) combustor configurations. These measurements show that combustion dynamics were typically small. However, a small number of points showed high combustion dynamics, with peak-to-peak dynamic pressure fluctuations above 0.5 psi. High combustion dynamics occurred at low inlet temperatures in all three SV-LDI configurations, so combustion dynamics were explored further at low temperature conditions. A point with greater than 1.5 psi peak-to-peak dynamic pressure fluctuations was identified at an inlet temperature of 450!F, a pressure of 100 psia, an air pressure drop of 3%, and an overall equivalence ratio of 0.35. This is an off design condition: the temperature and pressure are typical of 7% power conditions, but the equivalence ratio is high. At this condition, the combustion dynamics depended strongly on the fuel staging. Combustion dynamics could be reduced significantly without changing the overall equivalence ratio by shifting the fuel distribution between stages. Shifting the fuel distribution also decreased NOx emissions.

Central recirculation zone analysis in an unconfined tangential swirl burner with varying degrees of premixing

Energy Technology Data Exchange (ETDEWEB)

Valera-Medina, A. [CIATEQ, Parque Industrial Bernardo Quintana, Turbomachinery Department, Queretaro (Mexico); Syred, N.; Kay, P.; Griffiths, A. [Cardiff University, School of Engineering, Cardiff, Wales (United Kingdom)

2011-06-15

Swirl-stabilised combustion is one of the most widely used techniques for flame stabilisation, uses ranging from gas turbine combustors to pulverised coal-fired power stations. In gas turbines, lean premixed systems are of especial importance, giving the ability to produce low NOx systems coupled with wide stability limits. The common element is the swirl burner, which depends on the generation of an aerodynamically formed central recirculation zone (CRZ) and which serves to recycle heat and active chemical species to the root of the flame as well as providing low-velocity regions where the flame speed can match the local flow velocity. Enhanced mixing in and around the CRZ is another beneficial feature. The structure of the CRZ and hence that of the associated flames, stabilisation and mixing processes have shown to be extremely complex, three-dimensional and time dependent. The characteristics of the CRZ depend very strongly on the level of swirl (swirl number), burner configuration, type of flow expansion, Reynolds number (i.e. flowrate) and equivalence ratio. Although numerical methods have had some success when compared to experimental results, the models still have difficulties at medium to high swirl levels, with complex geometries and varied equivalence ratios. This study thus focuses on experimental results obtained to characterise the CRZ formed under varied combustion conditions with different geometries and some variation of swirl number in a generic swirl burner. CRZ behaviour has similarities to the equivalent isothermal state, but is strongly dependent on equivalence ratio, with interesting effects occurring with a high-velocity fuel injector. Partial premixing and combustion cause more substantive changes to the CRZ than pure diffusive combustion. (orig.)

Numerical simulation of a low-swirl impinging jet with a rotating convergent nozzle

Science.gov (United States)

Borynyak, K.; Hrebtov, M.; Bobrov, M.; Kozyulin, N.

2018-03-01

The paper presents the results of Large Eddy Simulation of a swirling impinging jet with moderate Reynolds number (104), where the swirl is organized via the rotation of a convergent nozzle. The results show that the effect of the swirl in this configuration leads to an increase of axial velocity, compared to the non-swirling case. It is shown that turbulent stress plays an important role in this effect. The vortex structure of the jet consists of multiple pairs of nearly parallel helical vortices with opposite signs of rotation. The interaction of vortices in the near region of the jet leads to radial contraction of the jet’s core which in turn, causes an the increase in the axial velocity.

A generalized relationship for swirl decay in laminar pipe flow

Indian Academy of Sciences (India)

MS received 24 July 2008; revised 28 January 2010; accepted 1 February 2010. Abstract. Swirling flow is of great importance in heat and mass transfer enhance- ments and in flow measurements. In this study, laminar swirling flow in a straight pipe was considered. Steady three-dimensional axisymmetric Navier–Stokes ...

Effect of Chamber Backpressure on Swirl Injector Fluid Mechanics

Science.gov (United States)

Kenny, R. Jeremy; Hulka, James R.; Moser, Marlow D.; Rhys, Noah O.

2008-01-01

A common propellant combination used for high thrust generation is GH2/LOX. Historical GH2/LOX injection elements have been of the shear-coaxial type. Element type has a large heritage of research work to aid in element design. The swirl-coaxial element, despite its many performance benefits, has a relatively small amount of historical, LRE-oriented work to draw from. Design features of interest are grounded in the fluid mechanics of the liquid swirl process itself, are based on data from low-pressure, low mass flow rate experiments. There is a need to investigate how high ambient pressures and mass flow rates influence internal and external swirl features. The objective of this research is to determine influence of varying liquid mass flow rate and ambient chamber pressure on the intact-length fluid mechanics of a liquid swirl element.

Triaxial Swirl Injector Element for Liquid-Fueled Engines

Science.gov (United States)

Muss, Jeff

2010-01-01

A triaxial injector is a single bi-propellant injection element located at the center of the injector body. The injector element consists of three nested, hydraulic swirl injectors. A small portion of the total fuel is injected through the central hydraulic injector, all of the oxidizer is injected through the middle concentric hydraulic swirl injector, and the balance of the fuel is injected through an outer concentric injection system. The configuration has been shown to provide good flame stabilization and the desired fuel-rich wall boundary condition. The injector design is well suited for preburner applications. Preburner injectors operate at extreme oxygen-to-fuel mass ratios, either very rich or very lean. The goal of a preburner is to create a uniform drive gas for the turbomachinery, while carefully controlling the temperature so as not to stress or damage turbine blades. The triaxial injector concept permits the lean propellant to be sandwiched between two layers of the rich propellant, while the hydraulic atomization characteristics of the swirl injectors promote interpropellant mixing and, ultimately, good combustion efficiency. This innovation is suited to a wide range of liquid oxidizer and liquid fuels, including hydrogen, methane, and kerosene. Prototype testing with the triaxial swirl injector demonstrated excellent injector and combustion chamber thermal compatibility and good combustion performance, both at levels far superior to a pintle injector. Initial testing with the prototype injector demonstrated over 96-percent combustion efficiency. The design showed excellent high -frequency combustion stability characteristics with oxygen and kerosene propellants. Unlike the more conventional pintle injector, there is not a large bluff body that must be cooled. The absence of a protruding center body enhances the thermal durability of the triaxial swirl injector. The hydraulic atomization characteristics of the innovation allow the design to be

Swirl effect on flow structure and mixing in a turbulent jet

Science.gov (United States)

Kravtsov, Z. D.; Sharaborin, D. K.; Dulin, V. M.

2018-03-01

The paper reports on experimental study of turbulent transport in the initial region of swirling turbulent jets. The particle image velocimetry and planar laser-induced fluorescence techniques are used to investigate the flow structure and passive scalar concentration, respectively, in free air jet with acetone vapor. Three flow cases are considered, viz., non-swirling jets and swirling jets with and without vortex breakdown and central recirculation zone. Without vortex breakdown, the swirl is shown to promote jet mixing with surrounding air and to decrease the jet core length. The vortex core breakdown further enhances mixing as the jet core disintegrates at the nozzle exit.

Numerical assessment of flow dynamics for various DI diesel engine designs considering swirl number and uniformity index

International Nuclear Information System (INIS)

Jafarmadar, S.; Taghavifar, Hadi; Taghavifar, Hamid; Navid, A.

2016-01-01

Highlights: • Swirl ratio and uniformity index was assessed for six different engine designs. • Lower bowl-depth and higher bowl radius create higher squish and swirl. • The best design for power boost and emission control strategies were identified. • The flow dynamics are considered based on TKE and also the flow field vectors. - Abstract: Geometrical features of combustion chamber are important factors in subsequent engine’s combustion and emissions. Location and configuration of bowl in diesel engine has been the dynamic field of research especially for optimization procedure. This study considers six different engine patterns with outlined parameters. It follows that different designs are characterized with different swirl motions and tumble flows within the combustion chamber. It was determined that maximum and minimum peak swirl number pertains to “Design5” and “Design1” with 1.59 and 1.1 values, respectively. By using “Design5” case instead of “Design1” (baseline case), uniformity index increased by 25.83% whereby peak soot concentration was reduced over 46.7%. The bigger bowl radius (R1) makes higher swirl ratio and this eventually leads to lower soot emission. Lower bowl depth (T), however, gives way to stronger squish pressure and engine-out power.

Investigation of the Swirl Effect on Engine Using Designed Swirl Adapter

Directory of Open Access Journals (Sweden)

Mohiuddin AKM

2011-12-01

Full Text Available Swirl is the rotational flow of charge within the cylinder about its axis. The engine used in this investigation is a basic Double Overhead Camshaft (DOHC which has a capacity of 1597 cc and installed with a total of 16 valves developed by Malaysian car manufacturer PROTON. The swirl adapter is placed inside the intake port of the Engine. The Adapter angle is set to 30o to force the charge to bounce off the wall of the port to create swirl. The objective of this paper is to find the effect of swirl on the engine and to compare it with the normal turbulence mixing process. The swirl effect analysis is done by using the GT-SUITE which has a standard swirl flow embedded in the software. The effect is simulated on the GT-SUITE and it is found that the swirl affects the engine in reducing the fuel consumption and increasing the volumetric efficiency. The experimental result shows that the effect of swirl increases the power as well as torque in the idle and cruising speed conditions in comparison with normal turbulence. But it decreases rapidly in the acceleration speed. This happens due to the inability of the swirl adapter to generate swirl at higher wind flow velocity during the higher throttle opening condition.ABSTRAK: Pusar merupakan aliran putaran cas melingkungi silinder pada paksinya. Enjin yang digunakan untuk penyelidikan ini merupakan Enjin Aci Sesondol Stas Kembar (Double Overhead Camshaft (DOHC asas, yang mempunyai kapasiti 1597 cc. Ia dipasangkan dengan 16 injap yang dibangunkan oleh pembuat kereta Malaysia, PROTON. Penyesuai pusar diletakkan di dalam masukan liang enjin. Sudut penyesuai di tetapkan pada 30o untuk memaksa cas supaya melantun kepada dinding liang agar membentuk pusaran. Tujuan tesis ini ditulis adalah untuk mendapatkan kesan pusar ke atas enjin dan membandingkannya dengan proses percampuran gelora normal. Analisis kesan pusaran dilakukan dengan menggunakan GT-SUITE yang mempunyai aliran pusar yang telah dipiawaikan di

Visualization system of swirl motion

International Nuclear Information System (INIS)

Nakayama, K.; Umeda, K.; Ichikawa, T.; Nagano, T.; Sakata, H.

2004-01-01

The instrumentation of a system composed of an experimental device and numerical analysis is presented to visualize flow and identify swirling motion. Experiment is performed with transparent material and PIV (Particle Image Velocimetry) instrumentation, by which velocity vector field is obtained. This vector field is then analyzed numerically by 'swirling flow analysis', which estimates its velocity gradient tensor and the corresponding eigenvalue (swirling function). Since an instantaneous flow field in steady/unsteady states is captured by PIV, the flow field is analyzed, and existence of vortices or swirling motions and their locations are identified in spite of their size. In addition, intensity of swirling is evaluated. The analysis enables swirling motion to emerge, even though it is hidden in uniform flow and velocity filed does not indicate any swirling. This visualization system can be applied to investigate condition to control flow or design flow. (authors)

Investigation of mass transfer in swirling turbulent flames

International Nuclear Information System (INIS)

Sharaborin, D; Abdurakipov, S; Dulin, V

2016-01-01

The present paper reports on analysis of flow structure and turbulent transport in swirling flames. The particle image velocimetry and spontaneous Raman scattering techniques were used for the measurements of 2D velocity and density distributions. The focus was placed on comparison between low- and high-swirl flows. A pronounced bubble-type vortex breakdown with strong flow precession took place in the latter case. (paper)

Experimental investigation of the cascadability of a cross-gain modulation wavelength converter

DEFF Research Database (Denmark)

Zheng, Xueyan; Liu, Fenghai; Kloch, Allan

2000-01-01

by adding a fiber grating-based optical add-drop multiplexer after the semiconductor optical amplifier (SOA) to enhance the high-frequency response of the wavelength converter. However, the low-frequency degradation of the signal together with amplified spontaneous emission (ASE) noise and jitter......The cascading characteristics of a wavelength converter based on cross-gain modulation (XGM) are studied experimentally using a recirculating loop at 10 Gb/s. The maximum cascaded number of the wavelength converter converting the signal to the same wavelength is improved from five to eight...

Effect of a microwave field on the cascade arc light emission

NARCIS (Netherlands)

Gerasimov, N.T.; Rosado, R.J.; Schram, D.C.

1977-01-01

The effect of a pulsed microwave field on the integral light emission from the argon plasma of a DC atmospheric-pressure cascade arc is investigated experimentally. An intensive light pulse and oscillations of light emission at frequencies of the order of 10 kHz are observed. The shape and amplitude

Response of a swirl-stabilized flame to transverse acoustic excitation

Science.gov (United States)

O'Connor, Jacqueline

This work addresses the issue of transverse combustion instabilities in annular gas turbine combustor geometries. While modern low-emissions combustion strategies have made great strides in reducing the production of toxic emissions in aircraft engines and power generation gas turbines, combustion instability remains one of the foremost technical challenges in the development of next generation combustor technology. To that end, this work investigates the response of a swirling flow and swirl-stabilized flame to a transverse acoustic field is using a variety of high-speed laser techniques, especially high-speed particle image velocimetry (PIV) for detailed velocity measurements of this highly unsteady flow phenomenon. Several important issues are addressed. First, the velocity-coupled pathway by which the unsteady velocity field excites the flame is described in great detail. Here, a transfer function approach has been taken to illustrate the various pathways through which the flame is excited by both acoustic and vortical velocity fluctuations. It has been shown that while the direct excitation of the flame by the transverse acoustic field is a negligible effect in most combustor architectures, the coupling between the transverse acoustic mode in the combustor and the longitudinal mode in the nozzle is an important pathway that can result in significant flame response. In this work, the frequency response of this pathway as well as the resulting flame response is measured using PIV and chemiluminescence measurements, respectively. Next, coupling between the acoustic field and the hydrodynamically unstable swirling flow provides a pathway that can lead to significant flame wrinkling by large coherent structures in the flow. Swirling flows display two types of hydrodynamic instability: an absolutely unstable jet and convectively unstable shear layers. The absolute instability of the jet results in vortex breakdown, a large recirculation zone along the centerline of

Numerical analysis on the combustion and emission characteristics of forced swirl combustion system for DI diesel engines

International Nuclear Information System (INIS)

Su, LiWang; Li, XiangRong; Zhang, Zheng; Liu, FuShui

2014-01-01

Highlights: • A new combustion system named FSCS for DI diesel engines was proposed. • Fuel/air mixture formation was improved for the application of FSCS. • The FSCS showed a good performance on emission characteristics. - Abstract: To optimize the fuel/air mixture formation and improve the environmental effect of direct injection (DI) diesel engines, a new forced swirl combustion system (FSCS) was proposed concerned on unique design of the geometric shape of the combustion chamber. Numerical simulation was conducted to verify the combustion and emission characteristics of the engines with FSCS. The fuel/air diffusion, in-cylinder velocity distribution, turbulent kinetic energy and in-cylinder temperature distribution were analyzed and the results shown that the FSCS can increase the area of fuel/air diffusion and improve the combustion. The diesel engine with FSCS also shown excellent performance on emission. At full load condition, the soot emission was significantly reduced for the improved fuel/air mixture formation. There are slightly difference for the soot and NO emission between the FSCS and the traditional omega combustion system at lower load for the short penetration of the fuel spray

Influence of swirl ratio on fuel distribution and cyclic variation under flash boiling conditions in a spark ignition direct injection gasoline engine

International Nuclear Information System (INIS)

Yang, Jie; Xu, Min; Hung, David L.S.; Wu, Qiang; Dong, Xue

2017-01-01

Highlights: • Influence of swirl on fuel distribution studied using laser induced fluorescence. • Gradient is sufficient for fuel spatial distribution variation analysis. • Close relation between fuel distribution and flame initiation/development. • Quantitative analysis shows high swirl suppresses variation of fuel distribution. • High order modes capable of identifying the distribution fluctuation patterns. - Abstract: One effective way of suppressing the cycle-to-cycle variation in engine is to design a combustion system that is robust to the root causes of engine variation over the entire engine working process. Flash boiling has been demonstrated as an ideal technique to produce stable fuel spray. But the generation of stable intake flow and fuel mixture remains challenging. In this study, to evaluate the capability of enhanced swirl flow to produce repeatable fuel mixture formation, the fuel distribution inside a single cylinder optical engine under two swirl ratios were measured using laser induced fluorescence technique. The swirl ratio was regulated by a swirl control valve installed in one of the intake ports. A 266 nm wavelength laser sheet from a frequency-quadrupled laser was directed into the optical engine through the quartz liner 15 mm below the tip of the spark plug. The fluorescence signal from the polycyclic aromatic hydrocarbon in gasoline was collected by applying a 320–420 nm band pass filter mounted in front of an intensified charge coupled device camera. Test results show that the in-cylinder fuel distribution is strongly influenced by the swirl ratio. Specifically, under high swirl condition, the fuel is mainly concentrated on the left side of the combustion chamber. While under the low swirl flow, fuel is distributed more randomly over the observing plane. This agrees well with the measurements of the stable flame location. Additionally, the cycle-to-cycle variation of the fuel distribution were analyzed. Results show that well

Superradiant cascade emissions in an atomic ensemble via four-wave mixing

Energy Technology Data Exchange (ETDEWEB)

Jen, H.H., E-mail: sappyjen@gmail.com

2015-09-15

We investigate superradiant cascade emissions from an atomic ensemble driven by two-color classical fields. The correlated pair of photons (signal and idler) is generated by adiabatically driving the system with large-detuned light fields via four-wave mixing. The signal photon from the upper transition of the diamond-type atomic levels is followed by the idler one which can be superradiant due to light-induced dipole–dipole interactions. We then calculate the cooperative Lamb shift (CLS) of the idler photon, which is a cumulative effect of interaction energy. We study its dependence on a cylindrical geometry, a conventional setup in cold atom experiments, and estimate the maximum CLS which can be significant and observable. Manipulating the CLS of cascade emissions enables frequency qubits that provide alternative robust elements in quantum network. - Highlights: • Superradiance from a cascade atomic transition. • Correlated photon pair generation via four-wave mixing. • Dynamical light–matter couplings in a phased symmetrical state. • Cooperative Lamb shift in a cylindrical atomic ensemble.

Enhanced two-photon emission from a dressed biexciton

International Nuclear Information System (INIS)

Sánchez Muñoz, Carlos; Laussy, Fabrice P; Tejedor, Carlos; Valle, Elena del

2015-01-01

Radiative two-photon cascades from biexcitons in semiconductor quantum dots under resonant two-photon excitation are promising candidates for the generation of photon pairs. In this work, we propose a scheme to obtain two-photon emission that allows us to operate under very intense driving fields. This approach relies on the Purcell enhancement of two-photon virtual transitions between states of the biexciton dressed by the laser. The richness provided by the biexcitonic level structure allows to reach a variety of regimes, from antibunched and bunched photon pairs with polarization orthogonal to the driving field, to polarization entangled two-photon emission. This provides evidence that the general paradigm of two-photon emission from a ladder of dressed states can find interesting, particular implementations in a variety of systems. (paper)

Improvement of Swirl Chamber Structure of Swirl-Chamber Diesel Engine Based on Flow Field Characteristics

Directory of Open Access Journals (Sweden)

Wenhua Yuan

2014-10-01

Full Text Available In order to improve combustion characteristic of swirl chamber diesel engine, a simulation model about a traditional cylindrical flat-bottom swirl chamber turbulent combustion diesel engine was established within the timeframe of the piston motion from the bottom dead centre (BDC to the top dead centre (TDC with the fluent dynamic mesh technique and flow field vector of gas in swirl chamber and cylinder; the pressure variation and temperature variation were obtained and a new type of swirl chamber structure was proposed. The results reveal that the piston will move from BDC; air in the cylinder is compressed into the swirl chamber by the piston to develop a swirl inside the chamber, with the ongoing of compression; the pressure and temperature are also rising gradually. Under this condition, the demand of diesel oil mixing and combusting will be better satisfied. Moreover, the new structure will no longer forma small fluid retention zone at the lower end outside the chamber and will be more beneficial to the mixing of fuel oil and air, which has presented a new idea and theoretical foundation for the design and optimization of swirl chamber structure and is thus of good significance of guiding in this regard.

Optimization of a premixed low-swirl burner for industrial applications

International Nuclear Information System (INIS)

Fable, S.E.; Cheng, R.K.

2000-01-01

This study was motivated by recent tests results showing that a 5cm i.d. low-swirl burner (LSB) stabilizes ultra-lean premixed turbulent flames up to 600kW. A parametric study has been performed to determine the optimum ultra-lean LSB configuration, i.e. one that will achieve low NOx and flame stability, for thermal input between 15kW to 150kW. Using Laser Doppler Velocimetry (LDV), non-reacting centerline velocity and rms fluctuation profiles were measured, and were found to show self-similar behavior. This self-similarity may explain why the flame remains stationary relative to the burner exit despite a change in bulk flow velocity from 5 to 90m/s. The recess distance of the swirler affects the shape of the mean and rms velocity profiles. Lean blow-off limits were also determined for various recess distances, and an optimum exit length was found that provides stable operation for ultra-lean flames

Far-Ultraviolet Characteristics of Lunar Swirls

Science.gov (United States)

Hendrix, A. R.; Greathouse, T. K.; Retherford, K. D.; Mandt, K. E.; Gladstone, G. R.; Kaufmann, D. E.; Hurley, D. M.; Feldman, P. D.; Pryor, W. R.; Bullock, M. A.; Stern, S. A.

2015-10-01

Lunar swirls are often described as bright sinuous regions of the Moon that appear to be relatively immature -i.e. less space-weathered than surrounding regions. Swirls are mysterious but seem to be linked to the interaction between the solar wind and the lunar magnetic anomalies (e.g., [1]). Commonly-studied swirls include Mare Ingenii (in a mare- highlands boundary region), Reiner Gamma (in a mare region), and Gerasimovich (in a highlands region). Swirls are known to be surface features: they have no expression at radar depths [2], exhibit no topography, and craters on swirls that penetrate the bright surface terrain reveal underlying dark material [3].

A study of swirl flow in draft tubes

Energy Technology Data Exchange (ETDEWEB)

Dahlhaug, Ole Gunnar

1997-12-31

This thesis presents measurements performed inside conical diffuser and bend, draft tubes of model hydro turbines, and draft tube of a prototype hydro turbine. Experimental results for swirling flow in conical diffuser and bend are presented in three different geometries. The axial velocity decreases at the centre of the tube at high swirl numbers because of an axial pressure gradient set up by the downstream frictional damping of the tangential velocities and the pressure increase downstream of the diffuser. Analytical models of the tangential velocity profiles are found and the radial pressure distribution calculated. Good correlation to the measured pressure distribution was achieved. Diffuser efficiency was calculated based on the equations for velocity and pressure profiles, which gave a qualified estimate of the diffuser hydraulic performance. The calculation shows that the bend reduces the efficiency by more than 30%. For a straight tube followed by a diffuser, numerical calculations were done, using K{epsilon}, RNG and RSM turbulence models for all measured swirl numbers. The K{epsilon} model gave best results for the forced vortex profile at low swirl numbers, while the RSM model gave best results at high swirl number. The turbulent kinetic energy at high swirl numbers gave the largest difference between the calculated and the measured values. Measurements on draft tubes in model turbines show the importance of good draft tube design. Prototype measurements on a Francis turbine show how the outlet draft tube flow should be measured for prototype draft tube evaluation. 54 refs., 118 figs., 2 tabs.

A study of swirl flow in draft tubes

Energy Technology Data Exchange (ETDEWEB)

Dahlhaug, Ole Gunnar

1998-12-31

This thesis presents measurements performed inside conical diffuser and bend, draft tubes of model hydro turbines, and draft tube of a prototype hydro turbine. Experimental results for swirling flow in conical diffuser and bend are presented in three different geometries. The axial velocity decreases at the centre of the tube at high swirl numbers because of an axial pressure gradient set up by the downstream frictional damping of the tangential velocities and the pressure increase downstream of the diffuser. Analytical models of the tangential velocity profiles are found and the radial pressure distribution calculated. Good correlation to the measured pressure distribution was achieved. Diffuser efficiency was calculated based on the equations for velocity and pressure profiles, which gave a qualified estimate of the diffuser hydraulic performance. The calculation shows that the bend reduces the efficiency by more than 30%. For a straight tube followed by a diffuser, numerical calculations were done, using K{epsilon}, RNG and RSM turbulence models for all measured swirl numbers. The K{epsilon} model gave best results for the forced vortex profile at low swirl numbers, while the RSM model gave best results at high swirl number. The turbulent kinetic energy at high swirl numbers gave the largest difference between the calculated and the measured values. Measurements on draft tubes in model turbines show the importance of good draft tube design. Prototype measurements on a Francis turbine show how the outlet draft tube flow should be measured for prototype draft tube evaluation. 54 refs., 118 figs., 2 tabs.

Vorticity Dynamics in Single and Multiple Swirling Reacting Jets

Science.gov (United States)

Smith, Travis; Aguilar, Michael; Emerson, Benjamin; Noble, David; Lieuwen, Tim

2015-11-01

This presentation describes an analysis of the unsteady flow structures in two multinozzle swirling jet configurations. This work is motivated by the problem of combustion instabilities in premixed flames, a major concern in the development of modern low NOx combustors. The objective is to compare the unsteady flow structures in these two configurations for two separate geometries and determine how certain parameters, primarily distance between jets, influence the flow dynamics. The analysis aims to differentiate between the flow dynamics of single nozzle and triple nozzle configurations. This study looks at how the vorticity in the shear layers of one reacting swirling jet can affect the dynamics of a nearby similar jet. The distance between the swirling jets is found to have an effect on the flow field in determining where swirling jets merge and on the dynamics upstream of the merging location. Graduate Student, School of Aerospace Engineering, Georgia Institute of Technology, Atlanta, GA.

Experimental study of the effects of swirl and air dilution on biogas non-premixed flame stability

Directory of Open Access Journals (Sweden)

Rowhani Amir

2015-01-01

Full Text Available An experimental investigation of the stability limits of biogas in a swirling non-premixed burner has been carried out. A mixture of 60% methane (CH4 and 40% carbon dioxide (CO2 was used to reach the typical biogas composition. Vane swirlers with 30º, 45º and 60º angles were used to make the swirling air. The biogas stability limits and flame behavior under swirling conditions were tested. Besides, effects of air dilution with nitrogen (N2 and CO2 on biogas stability limits were investigated. The results show that using swirl can enhance the flame stability limits approximately four or five times comparing to non-swirling air stream. Adding N2/CO2 to the air had negative effects on the flame stability but no changes were observed in the flame structure. The maximum air dilution was also obtained when 27% and 15% N2 was added to the swirling air under strong and weak swirl, respectively.

Effect of pulse pressure on borehole stability during shear swirling flow vibration cementing.

Directory of Open Access Journals (Sweden)

Zhihua Cui

Full Text Available The shear swirling flow vibration cementing (SSFVC technique rotates the downhole eccentric cascade by circulating cementing fluid. It makes the casing eccentrically revolve at high speed around the borehole axis. It produces strong agitation action to the annulus fluid, makes it in the state of shear turbulent flow, and results in the formation of pulse pressure which affects the surrounding rock stress. This study was focused on 1 the calculation of the pulse pressure in an annular turbulent flow field based on the finite volume method, and 2 the analysis of the effect of pulse pressure on borehole stability. On the upside, the pulse pressure is conducive to enhancing the liquidity of the annulus fluid, reducing the fluid gel strength, and preventing the formation of fluid from channeling. But greater pulse pressure may cause lost circulation and even formation fracturing. Therefore, in order to ensure smooth cementing during SSFVC, the effect of pulse pressure should be considered when cementing design.

Controlled Growth of Gigantic Swirls in a Laboratory Magnetosphere

Science.gov (United States)

Worstell, M. W.; Mauel, M. E.; Roberts, T. M.

2012-10-01

Space and laboratory plasma confined by a strong magnetic field have remarkable properties. Low frequency mixing of the plasma occurs through the interchange of long plasma-filled tubes aligned with the magnetic field. The plasma dynamics becomes two-dimensional because these tubes can only move radially or circulate around the poles of the magnetic dipole. Studies of turbulent interchange dynamics made using the Collisionless Terella Experiment (CTX) show that turbulence appears as chaotic time-varying modes with broad global mode structures that interact nonlinearly and form an inverse cascade.footnotetextB.A. Grierson, M.W. Worstell, M.E. Mauel, Phys. Plasmas 16 055902 (2009) When we drive vortex mixing through the application of electrostatic bias to multiple probes, we break the rotational symmetry of the plasma and small vortex tubes are seen to drive larger ``gigantic'' swirls. Statistical analysis of the time-evolving spectra and measurement of the bicoherence of the turbulence show an increase of three wave coupling during non-axisymmetric electrostatic drive of the probe array.

Influence of the burner swirl on the azimuthal instabilities in an annular combustor

Science.gov (United States)

Mazur, Marek; Nygård, Håkon; Worth, Nicholas; Dawson, James

2017-11-01

Improving our fundamental understanding of thermoacoustic instabilities will aid the development of new low emission gas turbine combustors. In the present investigation the effects of swirl on the self-excited azimuthal combustion instabilities in a multi-burner annular annular combustor are investigated experimentally. Each of the burners features a bluff body and a swirler to stabilize the flame. The combustor is operated with an ethylene-air premixture at powers up to 100 kW. The swirl number of the burners is varied in these tests. For each case, dynamic pressure measurements at different azimuthal positions, as well as overhead imaging of OH* of the entire combustor are conducted simultaneously and at a high sampling frequency. The measurements are then used to determine the azimuthal acoustic and heat release rate modes in the chamber and to determine whether these modes are standing, spinning or mixed. Furthermore, the phase shift between the heat release rate and pressure and the shape of these two signals are analysed at different azimuthal positions. Based on the Rayleigh criterion, these investigations allow to obtain an insight about the effects of the swirl on the instability margins of the combustor. This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (Grant agreement n° 677931 TAIAC).

A Second Generation Swirl-Venturi Lean Direct Injection Combustion Concept

Science.gov (United States)

Tacina, Kathleen M.; Chang, Clarence T.; He, Zhuohui Joe; Lee, Phil; Dam, Bidhan; Mongia, Hukam

2014-01-01

A low-NO (sub x) aircraft gas turbine engine combustion concept was developed and tested. The concept is a second generation swirl-venturi lean direct injection (SV-LDI) concept. LDI is a lean-burn combustion concept in which the fuel is injected directly into the flame zone. Three second generation SV-LDI configurations were developed. All three were based on the baseline 9-point SV-LDI configuration reported previously. These second generation configurations had better low power operability than the baseline 9-point configuration. Two of these second generation configurations were tested in a NASA Glenn Research Center flametube; these two configurations are called the at dome and 5-recess configurations. Results show that the 5-recess configuration generally had lower NO (sub x) emissions than the flat dome configuration. Correlation equations were developed for the flat dome configuration so that the landing-takeoff NO (sub x) emissions could be estimated. The flat dome landing-takeoff NO (sub x) is estimated to be 87-88 percent below the CAEP/6 standards, exceeding the ERA project goal of 75 percent reduction.

The generation of sound by vorticity waves in swirling duct flows

Science.gov (United States)

Howe, M. S.; Liu, J. T. C.

1977-01-01

Swirling flow in an axisymmetric duct can support vorticity waves propagating parallel to the axis of the duct. When the cross-sectional area of the duct changes a portion of the wave energy is scattered into secondary vorticity and sound waves. Thus the swirling flow in the jet pipe of an aeroengine provides a mechanism whereby disturbances produced by unsteady combustion or turbine blading can be propagated along the pipe and subsequently scattered into aerodynamic sound. In this paper a linearized model of this process is examined for low Mach number swirling flow in a duct of infinite extent. It is shown that the amplitude of the scattered acoustic pressure waves is proportional to the product of the characteristic swirl velocity and the perturbation velocity of the vorticity wave. The sound produced in this way may therefore be of more significance than that generated by vorticity fluctuations in the absence of swirl, for which the acoustic pressure is proportional to the square of the perturbation velocity. The results of the analysis are discussed in relation to the problem of excess jet noise.

A Comparison of Three Second-generation Swirl-Venturi Lean Direct Injection Combustor Concepts

Science.gov (United States)

Tacina, Kathleen M.; Podboy, Derek P.; He, Zhuohui Joe; Lee, Phil; Dam, Bidhan; Mongia, Hukam

2016-01-01

Three variations of a low emissions aircraft gas turbine engine combustion concept were developed and tested. The concept is a second generation swirl-venturi lean direct injection (SV-LDI) concept. LDI is a lean-burn combustion concept in which the fuel is injected directly into the flame zone. All three variations were based on the baseline 9- point SV-LDI configuration reported previously. The three second generation SV-LDI variations are called the 5-recess configuration, the flat dome configuration, and the 9- recess configuration. These three configurations were tested in a NASA Glenn Research Center medium pressure flametube. All three second generation variations had better low power operability than the baseline 9-point configuration. All three configurations had low NO(sub x) emissions, with the 5-recess configuration generally having slightly lower NO(x) than the flat dome or 9-recess configurations. Due to the limitations of the flametube that prevented testing at pressures above 20 atm, correlation equations were developed for the at dome and 9-recess configurations so that the landing-takeoff NO(sub x) emissions could be estimated. The flat dome and 9-recess landing-takeoff NO(x) emissions are estimated to be 81-88% below the CAEP/6 standards, exceeding the project goal of 75% reduction.

Assessing wood use efficiency and greenhouse gas emissions of wood product cascading in the European Union

NARCIS (Netherlands)

Bais-Moleman, A.L.; Sikkema, Richard; Vis, Martijn; Reumerman, Patrick; Theurl, Michaela; Erb, Karl Heinz

2017-01-01

Cascading use of biomass is a recognized strategy contributing to an efficient development of the bioeconomy and for mitigating climate change. This study aims at assessing the potential of cascading use of woody biomass for reducing GHG (greenhouse gas) emissions and increasing the overall wood

Cascade defect production and irradiation enhanced diffusion in Cu3Au

International Nuclear Information System (INIS)

Kirk, M.A.; Funk, L.L.

1986-03-01

By using the ordering alloy Cu 3 Au and measuring resistivity changes during and following fast-neutron irradiations at IPNS, we have studied cascade defect production and irradiation enhanced diffusion between 10 and 460 0 K. Ordering and disordering rates were measured as functions of irradiation temperature, neutron dose, neutron dose rate, time following cessation of flux, and step annealing. Free and clustered vacancy production was observed. The temperature dependence of the production of total migrating vacancy concentrations was determined. Vacancy sink production was linear with neutron dose and is compared with recent transmission electron microscopy experiments on the production of dislocation loops in this alloy. Time dependent and quasi-steady state vacancy concentrations were measured and compared with solutions of reaction rate equations for irradiation enhanced diffusion. The influence of recombination of vacancies with interstitials is observed at low sink concentrations (low neutron doses)

Planar Pressure Field Determination in the Initial Merging Zone of an Annular Swirling Jet Based on Stereo-PIV Measurements

Directory of Open Access Journals (Sweden)

Eric Van den Bulck

2008-11-01

Full Text Available In this paper the static pressure field of an annular swirling jet is measured indirectly using stereo-PIV measurements. The pressure field is obtained from numerically solving the Poisson equation, taken into account the axisymmetry of the flow. At the boundaries no assumptions are made and the exact boundary conditions are applied. Since all source terms can be measured using stereo-PIV and the boundary conditions are exact, no assumptions other than axisymmetry had to be made in the calculation of the pressure field. The advantage of this method of indirect pressure measurement is its high spatial resolution compared to the traditional pitot probes. Moreover this method is non-intrusive while the insertion of a pitot tube disturbs the flow. It is shown that the annular swirling flow can be divided into three regimes: a low, an intermediate and a high swirling regime. The pressure field of the low swirling regime is the superposition of the pressure field of the non-swirling jet and a swirl induced pressure field due to the centrifugal forces of the rotating jet. As the swirl increases, the swirl induced pressure field becomes dominant and for the intermediate and high swirling regimes, the simple radial equilibrium equation holds.

Planar Pressure Field Determination in the Initial Merging Zone of an Annular Swirling Jet Based on Stereo-PIV Measurements.

Science.gov (United States)

Vanierschot, Maarten; Van den Bulck, Eric

2008-11-28

In this paper the static pressure field of an annular swirling jet is measured indirectly using stereo-PIV measurements. The pressure field is obtained from numerically solving the Poisson equation, taken into account the axisymmetry of the flow. At the boundaries no assumptions are made and the exact boundary conditions are applied. Since all source terms can be measured using stereo-PIV and the boundary conditions are exact, no assumptions other than axisymmetry had to be made in the calculation of the pressure field. The advantage of this method of indirect pressure measurement is its high spatial resolution compared to the traditional pitot probes. Moreover this method is non-intrusive while the insertion of a pitot tube disturbs the flow. It is shown that the annular swirling flow can be divided into three regimes: a low, an intermediate and a high swirling regime. The pressure field of the low swirling regime is the superposition of the pressure field of the non-swirling jet and a swirl induced pressure field due to the centrifugal forces of the rotating jet. As the swirl increases, the swirl induced pressure field becomes dominant and for the intermediate and high swirling regimes, the simple radial equilibrium equation holds.

Quantum Cascade Lasers Modulation and Applications

Science.gov (United States)

Luzhansky, Edward

The mid-wave IR (MWIR) spectral band, extending from 3 to 5 microns, is considered to be a low loss atmospheric window. There are several spectral sub-bands with relatively low atmospheric attenuation in this region making it popular for various commercial and military applications. Relatively low thermal and solar background emissions, effective penetration through the natural and anthropogenic obscurants and eye safety add to the long list of advantages of MWIR wavelengths. Quantum Cascade Lasers are compact semiconductor devices capable of operating in MWIR spectrum. They are based on inter-subband transitions in a multiple-quantum-well (QW) hetero-structure, designed by means of band-structure engineering. The inter-subband nature of the optical transition has several key advantages. First, the emission wavelength is primarily a function of the QW thickness. This characteristic allows choosing well-understood and reliable semiconductors for the generation of light in a wavelength range of interest. Second, a cascade process in which tens of photons are generated per injected electron. This cascading process is behind the intrinsic high-power capabilities of QCLs. This dissertation is focused on modulation properties of Quantum Cascade Lasers. Both amplitude and phase/frequency modulations were studied including modulation bandwidth, modulation efficiency and chirp linearity. Research was consisted of the two major parts. In the first part we describe the theory of frequency modulation (FM) response of Distributed Feedback Quantum Cascade Lasers (DFB QCL). It includes cascading effect on the QCL's maximum modulation frequency. The "gain levering" effect for the maximum FM response of the two section QCLs was studied as well. In the second part of research we concentrated on the Pulse Position Amplitude Modulation of a single section QCL. The low complexity, low size, weight and power Mid-Wavelength Infra-Red optical communications transceiver concept is

Heat and mass transfer and hydrodynamics in swirling flows (review)

Science.gov (United States)

Leont'ev, A. I.; Kuzma-Kichta, Yu. A.; Popov, I. A.

2017-02-01

Research results of Russian and foreign scientists of heat and mass transfer in whirling flows, swirling effect, superficial vortex generators, thermodynamics and hydrodynamics at micro- and nanoscales, burning at swirl of the flow, and technologies and apparatuses with the use of whirling currents for industry and power generation were presented and discussed at the "Heat and Mass Transfer in Whirling Currents" 5th International Conference. The choice of rational forms of the equipment flow parts when using whirling and swirling flows to increase efficiency of the heat-power equipment and of flow regimes and burning on the basis of deep study of the flow and heat transfer local parameters was set as the main research prospect. In this regard, there is noticeable progress in research methods of whirling and swirling flows. The number of computational treatments of swirling flows' local parameters has been increased. Development and advancement of the up to date computing models and national productivity software are very important for this process. All experimental works are carried out with up to date research methods of the local thermoshydraulic parameters, which enable one to reveal physical mechanisms of processes: PIV and LIV visualization techniques, high-speed and infrared photography, high speed registration of parameters of high-speed processes, etc. There is a problem of improvement of researchers' professional skills in the field of fluid mechanics to set adequately mathematics and physics problems of aerohydrodynamics for whirling and swirling flows and numerical and pilot investigations. It has been pointed out that issues of improvement of the cooling system and thermal protection effectiveness of heat-power and heat-transfer equipment units are still actual. It can be solved successfully using whirling and swirling flows as simple low power consumption exposing on the flow method and heat transfer augmentation.

Modelling of flow stabilization by the swirl of a peripheral flow as applied to plasma reactors

International Nuclear Information System (INIS)

Volchkov, E.P.; Lebedev, V.P.; Terekhov, V.I.; Shishkin, N.E.

2000-01-01

The gas-swirl stabilization of plasma jets is one of effective methods of its retention in the near-axial area of channels in generators of low-temperature plasma. Except the effect of gas-dynamic compression, the peripheral swirl allows to solve another urgent problem - to protect the reactor walls from the heat influence of the plasma jet. Swirl flows are also used for the flow structure formation and control of the heat and gas-dynamic characteristics of different power devices and apparatuses, using high-temperature working media: in swirl furnaces and burners, in aviation engines, etc. Investigations show that during swirl stabilization the gas-dynamic structure of the flow influences significantly the spatial stability of the plasma column and its characteristics

Numerical simulation of strongly swirling turbulent flows through an abrupt expansion

International Nuclear Information System (INIS)

Paik, Joongcheol; Sotiropoulos, Fotis

2010-01-01

Turbulent swirling flow through an abrupt axisymmetric expansion is investigated numerically using detached-eddy simulation at Reynolds numbers = 3.0 x 10 4 and 1.0 x 10 5 . The effects of swirl intensity on the coherent dynamics of the flow are systematically studied by carrying out numerical simulations over a range of swirl numbers from 0.17 to 1.23. Comparison of the computed solutions with the experimental measurements of shows that the numerical simulations resolve both the axial and swirl mean velocity and turbulence intensity profiles with very good accuracy. Our simulations show that, along with moderate mesh refinement, critical prerequisite for accurate predictions of the flow downstream of the expansion is the specification of inlet conditions at a plane sufficiently far upstream of the expansion in order to avoid the spurious suppression of the low-frequency, large-scale precessing of the vortex core. Coherent structure visualizations with the q-criterion, friction lines and Lagrangian particle tracking are used to elucidate the rich dynamics of the flow as a function of the swirl number with emphasis on the onset of the spiral vortex breakdown, the onset and extent of the on-axis recirculation region and the large-scale instabilities along the shear layers and the pipe wall.

Use Deflected Trailing Edge to Improve the Aerodynamic Performance and Develop Low Solidity LPT Cascade

Science.gov (United States)

Chao, Li; Peigang, Yan; Xiangfeng, Wang; Wanjin, Han; Qingchao, Wang

2017-08-01

This paper investigates the feasibility of improving the aerodynamic performance of low pressure turbine (LPT) blade cascades and developing low solidity LPT blade cascades through deflected trailing edge. A deflected trailing edge improved aerodynamic performance of both LPT blade cascades and low solidity LPT blade cascades. For standard solidity LPT cascades, deflecting the trailing edge can decrease the energy loss coefficient by 20.61 % for a Reynolds number (Re) of 25,000 and freestream turbulence intensities (FSTI) of 1 %. For a low solidity LPT cascade, aerodynamic performance was also improved by deflecting the trailing edge. Solidity of the LPT cascade can be reduced by 12.5 % for blades with a deflected trailing edge without a drop in efficiency. Here, the flow control mechanism surrounding a deflected trailing edge was also revealed.

Precessing vortex core in a swirling wake with heat release

International Nuclear Information System (INIS)

Gorbunova, A.; Klimov, A.; Molevich, N.; Moralev, I.; Porfiriev, D.; Sugak, S.; Zavershinskii, I.

2016-01-01

Highlights: • Precessing vortex core is left-handed co-rotated bending single-vortex structure. • The precession frequency grows with the heat-source power. • Growth of the heat-source power decreases vortex core oscillations. • The left-handed bending mode is the most unstable mode in the low-density wake. - Abstract: Numerical simulation of the non-stationary three-dimensional swirling flow is presented for an open tube with a paraxial heat source. In the considered type of swirling flows, it is shown that a precessing vortex core (PVC) appears. The obtained PVC is a left-handed co-rotated bending single-vortex structure. The influence of the heat release enhancement on parameters of PVC is investigated. Using various turbulence models (the Spalart–Allmaras, k–ω and SST models), it is shown that an increase in the heat-source power leads to an increase in the PVC frequency and to a decrease in the amplitude of PVC oscillations. Moreover, we conduct the linear stability analysis of the simplified flow model with paraxial heating (the Rankine vortex with the piecewise axial flow and density) and demonstrate that its results correspond to the results of numerical simulations rather well. In particular, we prove that the left-handed bending mode (m = +1) is the most unstable one in the low-density wake and its frequency increases with a decrease of density ratio that is similar to the behavior of precession frequency with an increase of heat-source power.

Enhancement of optical Kerr effect in quantum-cascade lasers with multiple resonance levels.

Science.gov (United States)

Bai, Jing; Citrin, D S

2008-08-18

In this paper, we investigated the optical Kerr lensing effect in quantum-cascade lasers with multiple resonance levels. The Kerr refractive index n2 is obtained through the third-order susceptibility at the fundamental frequency chi(3)( omega; omega, omega,-omega). Resonant two-photon processes are found to have almost equal contributions to chi(3)( omega; omega, omega,-omega) as the single-photon processes, which result in the predicted enhancement of the positive nonlinear (Kerr) refractive index, and thus may enhance mode-locking of quantum-cascade lasers. Moreover, we also demonstrate an isospectral optimization strategy for further improving n2 through the band-structure design, in order to boost the multimode performance of quantum-cascade lasers. Simulation results show that the optimized stepwise multiple-quantum-well structure has n2 approximately 10-8 cm2/W, a twofold enhancement over the original flat quantum-well structure. This leads to a refractive-index change (delta)n of about 0.01, which is at the upper bound of those reported for typical Kerr medium. This stronger Kerr refractive index may be important for quantum-cascade lasers ultimately to demonstrate self-mode-locking.

Swirling flow in bileaflet mechanical heart valve

Science.gov (United States)

Gataulin, Yakov A.; Khorobrov, Svyatoslav V.; Yukhnev, Andrey D.

2018-05-01

Bileaflet mechanical valves are most commonly used for heart valve replacement. Nowadays swirling blood flow is registered in different parts of the cardiovascular system: left ventricle, aorta, arteries and veins. In present contribution for the first time the physiological swirling flow inlet conditions are used for numerical simulation of aortic bileaflet mechanical heart valve hemodynamics. Steady 3-dimensional continuity and RANS equations are employed to describe blood motion. The Menter SST model is used to simulate turbulence effects. Boundary conditions are corresponded to systolic peak flow. The domain was discretized into hybrid tetrahedral and hexahedral mesh with an emphasis on wall boundary layer. A system of equations was solved in Ansys Fluent finite-volume package. Noticeable changes in the flow structure caused by inlet swirl are shown. The swirling flow interaction with the valve leaflets is analyzed. A central orifice jet changes its cross-section shape, which leads to redistribution of wall shear stress on the leaflets. Transvalvular pressure gradient and area-averaged leaflet wall shear stress increase. Physiological swirl intensity noticeably reduces downstream of the valve.

Flow structures in a lean-premixed swirl-stabilized combustor with microjet air injection

KAUST Repository

LaBry, Zachary A.

2011-01-01

The major challenge facing the development of low-emission combustors is combustion instability. By lowering flame temperatures, lean-premixed combustion has the potential to nearly eliminate emissions of thermally generated nitric oxides, but the chamber acoustics and heat release rate are highly susceptible to coupling in ways that lead to sustained, high-amplitude pressure oscillations, known as combustion instability. At different operating conditions, different modes of instability are observed, corresponding to particular flame shapes and resonant acoustic modes. Here we show that in a swirl-stabilized combustor, these instability modes also correspond to particular interactions between the flame and the inner recirculation zone. Two stable and two unstable modes are examined. At lean equivalence ratios, a stable conical flame anchors on the upstream edge of the inner recirculation zone and extends several diameters downstream along the wall. At higher equivalence ratios, with the injection of counter-swirling microjet air flow, another stable flame is observed. This flame is anchored along the upstream edge of a stronger recirculation zone, extending less than one diameter downstream along the wall. Without the microjets, a stationary instability coupled to the 1/4 wave mode of the combustor shows weak velocity oscillations and a stable configuration of the inner and outer recirculation zones. Another instability, coupled to the 3/4 wave mode of the combustor, exhibits periodic vortex breakdown in which the core flow alternates between a columnar mode and a vortex breakdown mode. © 2010 Published by Elsevier Inc. on behalf of The Combustion Institute. All rights reserved.

All passive architecture for high efficiency cascaded Raman conversion

Science.gov (United States)

Balaswamy, V.; Arun, S.; Chayran, G.; Supradeepa, V. R.

2018-02-01

Cascaded Raman fiber lasers have offered a convenient method to obtain scalable, high-power sources at various wavelength regions inaccessible with rare-earth doped fiber lasers. A limitation previously was the reduced efficiency of these lasers. Recently, new architectures have been proposed to enhance efficiency, but this came at the cost of enhanced complexity, requiring an additional low-power, cascaded Raman laser. In this work, we overcome this with a new, all-passive architecture for high-efficiency cascaded Raman conversion. We demonstrate our architecture with a fifth-order cascaded Raman converter from 1117nm to 1480nm with output power of ~64W and efficiency of 60%.

The spray characteristic of gas-liquid coaxial swirl injector by experiment

Directory of Open Access Journals (Sweden)

Chen Chen

2017-01-01

Full Text Available Using the laser phase Doppler particle analyzer (PDPA, the spray characteristics of gas-liquid coaxial swirl injector were studied. The Sauter mean diameter (SMD, axial velocity and size data rate were measured under different gas injecting pressure drop and liquid injecting pressure drop. Comparing to a single liquid injection, SMD with gas presence is obviously improved. So the gas presence has a significant effect on the atomization of the swirl injector. What’s more, the atomization effect of gas-liquid is enhanced with the increasing of the gas pressure drop. Under the constant gas pressure drop, the injector has an optimal liquid pressure drop under which the atomization performance is best.

Heat transfer characteristics in a sudden expansion pipe equipped with swirl generators

International Nuclear Information System (INIS)

Zohir, A.E.; Abdel Aziz, A.A.; Habib, M.A.

2011-01-01

This investigation is aimed at studying the heat transfer characteristics and pressure drop for turbulent airflow in a sudden expansion pipe equipped with propeller type swirl generator or spiral spring with several pitch ratios. The investigation is performed for the Reynolds number ranging from 7500 to 18,500 under a uniform heat flux condition. The experiments are also undertaken for three locations for the propeller fan (N = 15 blades and blade angle of 65 o ) and three pitch ratios for the spiral spring (P/D = 10, 15 and 20). The influences of using the propeller rotating freely and inserted spiral spring on heat transfer enhancement and pressure drop are reported. In the experiments, the swirl generator and spiral spring are used to create a swirl in the tube flow. Mean and relative mean Nusselt numbers are determined and compared with those obtained from other similar cases. The experimental results indicate that the tube with the propeller inserts provides considerable improvement of the heat transfer rate over the plain tube around 1.69 times for X/H = 5. While for the tube with the spiral spring inserts, an improvement of the heat transfer rate over the plain tube around 1.37 times for P/d = 20. Thus, because of strong swirl or rotating flow, the propeller location and the spiral spring pitch become influential on the heat transfer enhancement. The increase in pressure drop using the propeller is found to be three times and for spiral spring 1.5 times over the plain tube. Correlations for mean Nusselt number, fan location and spiral spring pitch are provided.

A multi-objective CFD optimization of liquid fuel spray injection in dry-low-emission gas-turbine combustors

International Nuclear Information System (INIS)

Asgari, Behrad; Amani, Ehsan

2017-01-01

Highlights: •An Eulerian-Lagrangian model for the fuel spray injection is evaluated. •The drop breakup, spray-vortex interaction, and wall-wetting play the key roles. •The injection location and direction are the most important parameters. •The best design candidates are proposed using multi-objective optimizations. •A large central perpendicular injection with high co-rotating swirls is optimal. -- Abstract: The main goal of this research is to investigate the effects of fuel injection strategy on the performance of the premixing chamber of modern Dry-Low-Emission (DLE) Gas-Turbine (GT) combustors. Here, an Eulerian-Lagrangian model for multi-phase multi-component flows is evaluated and used to investigate the effects of different fuel spray design parameters, including the injection location, direction, mass-flow-rate partitioning, and flow Swirl number, on the performance of the premixing chamber. The analysis is enriched by multi-objective optimizations accounting for several goals, including the evaporation efficiency, mixture stratification, entropy generation, and flow recirculation. It is observed that the droplet breakup, spray-vortex interactions, and wall-wetting have significant influences on the performance objectives while the droplet residence time effect is minor. Among the design parameters, the injection location and direction have a profound impact on the droplet breakup which predominately controls the evaporation efficiency. In addition, the interactions between the spray and the two swirling vertices inside the chamber strongly affect the mixture stratification (uniformity), e.g. the location and direction of the injection should not be chosen such that a large proportion of fuel droplets are trapped in the shear layer between the two vortices (otherwise the evaporation efficiency drops significantly) or trapped in the strong outer swirling vortex (if large mixture non-uniformity should be avoided). Finally, the best designs meeting

Research on variable swirl intake port for high-speed multivalve DI diesel engine. Effects of port configuration on flow characteristics and swirl generation capacity; 4 ben kogata kosoku DI diesel engine no kahen swirl kyuki port ni kansuru kenkyu. Kyuki port haichi ga ryudo tokusei to swirl seino ni oyobosu eikyo

Energy Technology Data Exchange (ETDEWEB)

Kawashima, J; Ogawa, H; Tsuru, Y [Nissan Motor Co. Ltd., Tokyo (Japan)

1997-10-01

In our previous papers, the variable swirl intake port system which can control a wide swirl ratio range (from 4 to 10) was described. This system consisted of two separate intake ports, one of them has a flow control valve for changing the swirl ratio. In this type of variable swirl system, some variations of port combination, port shape, and position can be designed. In this paper, the intake flow characteristics of various port combinations were analyzed on the basis of a steady-state air flow test and 3-dimensional computations. The results indicate that the total performance of the twin ports can be estimated from that of a single port in any kind of port combination. Some difference in flow patterns were found in a variety of port combinations even if each swirl ratio is similar. The selected port combinations in our previous study are good for a wide swirl control range. 11 refs., 9 figs., 1 tab.

Spray structure of a pressure-swirl atomizer for combustion applications

Directory of Open Access Journals (Sweden)

Jicha Miroslav

2012-04-01

Full Text Available In the present work, global as well as spatially resolved parameters of a spray produced by a pressure-swirl atomizer are obtained. Small pressure-swirl atomizer for aircraft combustion chambers was run on a newly designed test bench with Jet A-1 kerosene type aviation fuel. The atomizer was tested in four regimes based on typical operation conditions of the engine. Spray characteristics were studied using two optical measurement systems, Particle Image velocimetry (PIV and Phase-Doppler Particle Analyzer (P/DPA. The results obtained with P/DPA include information about Sauter Mean Diameter of droplets and spray velocity profiles in one plane perpendicular to the spray axis. Velocity magnitudes of droplets in an axial section of the spray were obtained using PIV. The experimental outputs also show a good confirmation of velocity profiles obtained with both instruments in the test plane. These data together will elucidate impact of the spray quality on the whole combustion process, its efficiency and exhaust gas emissions.

Spray structure of a pressure-swirl atomizer for combustion applications

Science.gov (United States)

Durdina, Lukas; Jedelsky, Jan; Jicha, Miroslav

2012-04-01

In the present work, global as well as spatially resolved parameters of a spray produced by a pressure-swirl atomizer are obtained. Small pressure-swirl atomizer for aircraft combustion chambers was run on a newly designed test bench with Jet A-1 kerosene type aviation fuel. The atomizer was tested in four regimes based on typical operation conditions of the engine. Spray characteristics were studied using two optical measurement systems, Particle Image velocimetry (PIV) and Phase-Doppler Particle Analyzer (P/DPA). The results obtained with P/DPA include information about Sauter Mean Diameter of droplets and spray velocity profiles in one plane perpendicular to the spray axis. Velocity magnitudes of droplets in an axial section of the spray were obtained using PIV. The experimental outputs also show a good confirmation of velocity profiles obtained with both instruments in the test plane. These data together will elucidate impact of the spray quality on the whole combustion process, its efficiency and exhaust gas emissions.

Characterization of Swirl-Venturi Lean Direct Injection Designs for Aviation Gas-Turbine Combustion

Science.gov (United States)

Heath, Christopher M.

2013-01-01

Injector geometry, physical mixing, chemical processes, and engine cycle conditions together govern performance, operability and emission characteristics of aviation gas-turbine combustion systems. The present investigation explores swirl-venturi lean direct injection combustor fundamentals, characterizing the influence of key geometric injector parameters on reacting flow physics and emission production trends. In this computational study, a design space exploration was performed using a parameterized swirl-venturi lean direct injector model. From the parametric geometry, 20 three-element lean direct injection combustor sectors were produced and simulated using steady-state, Reynolds-averaged Navier-Stokes reacting computations. Species concentrations were solved directly using a reduced 18-step reaction mechanism for Jet-A. Turbulence closure was obtained using a nonlinear ?-e model. Results demonstrate sensitivities of the geometric perturbations on axially averaged flow field responses. Output variables include axial velocity, turbulent kinetic energy, static temperature, fuel patternation and minor species mass fractions. Significant trends have been reduced to surrogate model approximations, intended to guide future injector design trade studies and advance aviation gas-turbine combustion research.

On the evolution of vortex rings with swirl

International Nuclear Information System (INIS)

Naitoh, Takashi; Okura, Nobuyuki; Gotoh, Toshiyuki; Kato, Yusuke

2014-01-01

A laminar vortex ring with swirl, which has the meridional velocity component inside the vortex core, was experimentally generated by the brief fluid ejection from a rotating outlet. The evolution of the vortex ring was investigated with flow visualizations and particle image velocimetry measurements in order to find the influence of swirling flow in particular upon the transition to turbulence. Immediately after the formation of a vortex ring with swirl, a columnar strong vortex along the symmetric axis is observed in all cases of the present experiment. Then the characteristic fluid discharging from a vortex ring with swirl referred to as “peeling off” appears. The amount of discharging fluid due to the “peeling off” increases with the angular velocity of the rotating outlet. We conjectured that the mechanism generating the “peeling off” is related to the columnar strong vortex by close observations of the spatio-temporal development of the vorticity distribution and the cutting 3D images constructed from the successive cross sections of a vortex ring. While a laminar vortex ring without swirl may develop azimuthal waves around its circumference at some later time and the ring structure subsequently breaks, the swirling flow in a vortex ring core reduces the amplification rate of the azimuthal wavy deformation and preserved its ring structure. Then the traveling distance of a vortex ring can be extended using the swirl flow under certain conditions

On the evolution of vortex rings with swirl

Energy Technology Data Exchange (ETDEWEB)

Naitoh, Takashi, E-mail: naitoh.takashi@nitech.ac.jp [Department of Engineering Physics, Electronics and Mechanics, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan); Okura, Nobuyuki, E-mail: ohkura@meijo-u.ac.jp [Department of Vehicle and Mechanical Engineering, Meijo University, 1-501 Shiogamaguchi Tempaku-ku, Nagoya 468-8502 (Japan); Gotoh, Toshiyuki, E-mail: gotoh.toshiyuki@nitech.ac.jp [Department of Scientific and Engineering Simulation, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan); Kato, Yusuke [Controller Business Unit Engineering Division 1, Engineering Department 3, Denso Wave Incorporated, 1 Yoshiike Kusagi Agui-cho, Chita-gun Aichi 470-2297 (Japan)

2014-06-15

A laminar vortex ring with swirl, which has the meridional velocity component inside the vortex core, was experimentally generated by the brief fluid ejection from a rotating outlet. The evolution of the vortex ring was investigated with flow visualizations and particle image velocimetry measurements in order to find the influence of swirling flow in particular upon the transition to turbulence. Immediately after the formation of a vortex ring with swirl, a columnar strong vortex along the symmetric axis is observed in all cases of the present experiment. Then the characteristic fluid discharging from a vortex ring with swirl referred to as “peeling off” appears. The amount of discharging fluid due to the “peeling off” increases with the angular velocity of the rotating outlet. We conjectured that the mechanism generating the “peeling off” is related to the columnar strong vortex by close observations of the spatio-temporal development of the vorticity distribution and the cutting 3D images constructed from the successive cross sections of a vortex ring. While a laminar vortex ring without swirl may develop azimuthal waves around its circumference at some later time and the ring structure subsequently breaks, the swirling flow in a vortex ring core reduces the amplification rate of the azimuthal wavy deformation and preserved its ring structure. Then the traveling distance of a vortex ring can be extended using the swirl flow under certain conditions.

U.S. Government Supports Low Emission Economic Growth

Energy Technology Data Exchange (ETDEWEB)

2015-11-01

Countries around the world face the challenge of maintaining long-term sustainable economic growth and development under the threat of climate change. By identifying and pursuing a sustainable development pathway now, they are better positioned to reach their economic growth goals while addressing climate change impacts and lowering greenhouse gas (GHG) emissions. Low emission development strategies - development plans that promote sustainable social and economic development while reducing long-term GHG emissions - provide a pathway to preparing for a global low emission future. Partner country governments are working with the U.S. government through the Enhancing Capacity for Low Emission Development Strategies (EC-LEDS) program to further their national development objectives.

Search for Astrophysical Sources of Neutrinos Using Cascade Events in IceCube

Energy Technology Data Exchange (ETDEWEB)

Aartsen, M. G. [Department of Physics, University of Adelaide, Adelaide, 5005 (Australia); Ackermann, M. [DESY, D-15735 Zeuthen (Germany); Adams, J.; Bagherpour, H. [Dept. of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch (New Zealand); Aguilar, J. A.; Ansseau, I. [Université Libre de Bruxelles, Science Faculty CP230, B-1050 Brussels (Belgium); Ahlers, M. [Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen (Denmark); Ahrens, M. [Oskar Klein Centre and Dept. of Physics, Stockholm University, SE-10691 Stockholm (Sweden); Al Samarai, I. [Département de physique nucléaire et corpusculaire, Université de Genève, CH-1211 Genève (Switzerland); Altmann, D.; Anton, G. [Erlangen Centre for Astroparticle Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg, D-91058 Erlangen (Germany); Andeen, K. [Department of Physics, Marquette University, Milwaukee, WI, 53201 (United States); Anderson, T. [Dept. of Physics, Pennsylvania State University, University Park, PA 16802 (United States); Argüelles, C.; Axani, S. [Dept. of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Auffenberg, J. [III. Physikalisches Institut, RWTH Aachen University, D-52056 Aachen (Germany); Bai, X. [Physics Department, South Dakota School of Mines and Technology, Rapid City, SD 57701 (United States); Barwick, S. W. [Dept. of Physics and Astronomy, University of California, Irvine, CA 92697 (United States); Baum, V. [Institute of Physics, University of Mainz, Staudinger Weg 7, D-55099 Mainz (Germany); Collaboration: IceCube Collaboration; and others

2017-09-10

The IceCube neutrino observatory has established the existence of a flux of high-energy astrophysical neutrinos, which is inconsistent with the expectation from atmospheric backgrounds at a significance greater than 5 σ . This flux has been observed in analyses of both track events from muon neutrino interactions and cascade events from interactions of all neutrino flavors. Searches for astrophysical neutrino sources have focused on track events due to the significantly better angular resolution of track reconstructions. To date, no such sources have been confirmed. Here we present the first search for astrophysical neutrino sources using cascades interacting in IceCube with deposited energies as small as 1 TeV. No significant clustering was observed in a selection of 263 cascades collected from 2010 May to 2012 May. We show that compared to the classic approach using tracks, this statistically independent search offers improved sensitivity to sources in the southern sky, especially if the emission is spatially extended or follows a soft energy spectrum. This enhancement is due to the low background from atmospheric neutrinos forming cascade events and the additional veto of atmospheric neutrinos at declinations ≲−30°.

Lean premixed reacting flows with swirl and wall-separation zones in a contracting chamber

Science.gov (United States)

Zhang, Yuxin; Rusak, Zvi; Wang, Shixiao

2017-11-01

Low Mach number lean premixed reacting swirling flows with wall-separation zones in a contracting circular finite-length open chamber are studied. Assuming a complete reaction with high activation energy and chemical equilibrium behind the reaction zone, a nonlinear partial differential equation is derived for the solution of the flow stream function behind the reaction zone in terms of the inlet total enthalpy for a reacting flow, specific entropy and the circulation functions. Bifurcation diagrams of steady flows are described as the inlet swirl level is increased at fixed chamber contraction and reaction heat release. The approach is applied to an inlet solid-body rotation flow with constant profiles of the axial velocity, temperature and mixture reactant mass fraction. The computed results provide predictions of the critical inlet swirl levels for the first appearance of wall-separation states and for the size of the separation zone as a function of the inlet swirl ratio, Mach number, chamber contraction and heat release of the reaction. The methodology developed in this paper provides a theoretical feasibility for the development of the technology of swirl-assisted combustion where the reaction zone is supported and stabilized by a wall-separation zone.

Swirling flow in a two-stroke marine diesel engine

DEFF Research Database (Denmark)

Hemmingsen, Casper Schytte; Ingvorsen, Kristian Mark; Walther, Jens Honore

2013-01-01

Computational fluid dynamic simulations are performed for the turbulent swirling flow in a scale model of a low-speed two-stroke diesel engine with a moving piston. The purpose of the work is to investigate the accuracy of different turbulence models including two-equation Reynolds- Averaged Navier...

Cascading metallic gratings for broadband absorption enhancement in ultrathin plasmonic solar cells

International Nuclear Information System (INIS)

Wen, Long; Sun, Fuhe; Chen, Qin

2014-01-01

The incorporation of plasmonic nanostructures in the thin-film solar cells (TFSCs) is a promising route to harvest light into the nanoscale active layer. However, the light trapping scheme based on the plasmonic effects intrinsically presents narrow-band resonant enhancement of light absorption. Here we demonstrate that by cascading metal nanogratings with different sizes atop the TFSCs, broadband absorption enhancement can be realized by simultaneously exciting multiple localized surface plasmon resonances and inducing strong coupling between the plasmonic modes and photonic modes. As a proof of concept, we demonstrate of 66.5% in the photocurrent in an ultrathin amorphous silicon TFSC with two-dimensional cascaded gratings over the reference cell without gratings

An experimental and numerical investigation of the combustion characteristics of a dual fuel engine with a swirl chamber

Energy Technology Data Exchange (ETDEWEB)

Liu, C.; Karim, G.A.; Xiao, F.; Sohrabi, A. [Calgary Univ., AB (Canada). Schulich School of Engineering, Mechanical and Manufacturing Dept.

2007-07-01

The results of an experimental investigation of the performance of a small bore engine with a swirl chamber when operating as a dual fuel engine with commercial methane as the gaseous fuel were presented in this paper. The experiment involved using a 3-dimensional computational fluid dynamics model to predict the performance of the engine. A detailed chemical kinetics for the gaseous fuel component, consisting primarily of methane and a reduced detailed chemical kinetics for the diesel fuel while considering the turbulent combustion processes an associated performance of a dual fuel engine with a swirl chamber were incorporated in the simulation. The study experimentally and numerically investigated the effects of changes in the quantities of the liquid fuel pilot and gaseous fuels on the combustion processes, engine performance, cyclic variations, and emissions. The paper discussed the experimental approach and results. It also discussed the simulation of the dual fuel engine combustion process. It was concluded that dual fuel combustion was an effective method to burn a gaseous fuel-air mixture with a low energy density. 9 refs., 6 figs.

Simulation of blood flow in a small-diameter vascular graft model with a swirl (spiral) flow guider.

Science.gov (United States)

Zhang, ZhiGuo; Fan, YuBo; Deng, XiaoYan; Wang, GuiXue; Zhang, He; Guidoin, Robert

2008-10-01

Small-diameter vascular grafts are in large demand for coronary and peripheral bypass procedures, but present products still fail in long-term clinical application. In the present communication, a new type of small-diameter graft with a swirl flow guider was proposed to improve graft patency rate. Flow pattern in the graft was simulated numerically and compared with that in a conventional graft. The numerical results revealed that the swirl flow guider could indeed make the blood flow rotate in the new graft. The swirling flow distal to the flow guider significantly altered the flow pattern in the new graft and the velocity profiles were re-distributed. Due to the swirling flow, the blood velocity near the vessel wall and wall shear rate were greatly enhanced. We believe that the increased blood velocity near the wall and the wall shear rate can impede the occurrence of acute thrombus formation and intimal hyperplasia, hence can improve the graft patency rate for long-term clinical use.

Enhancement of the efficiency of the Open Cycle Phillips Optimized Cascade LNG process

International Nuclear Information System (INIS)

Fahmy, M.F.M.; Nabih, H.I.; El-Nigeily, M.

2016-01-01

Highlights: • Expanders replaced JT valves in the Phillips Optimized Cascade liquefaction process. • Improvement in plant liquefaction efficiency was evaluated in presence of expanders. • Comparison of the different optimum cases for the liquefaction process was presented. - Abstract: This study aims to improve the performance of the Open Cycle Phillips Optimized Cascade Process for the production of liquefied natural gas (LNG) through the replacement of Joule–Thomson (JT) valves by expanders. The expander has a higher thermodynamic efficiency than the JT valve. Moreover, the produced shaft power from the expander is integrated into the process. The study is conducted using the Aspen HYSYS-V7 simulation software for simulation of the Open Cycle Phillips Optimized Cascade Process having the JT valves. Simulation of several proposed cases in which expanders are used instead of JT valves at different locations in the process as at the propane cycle, ethylene cycle, methane cycle and the upstream of the heavies removal column is conducted. The optimum cases clearly indicate that expanders not only produce power, but also offer significant improvements in the process performance as shown by the total plant power consumption, LNG production, thermal efficiency, plant specific power and CO_2 emissions reduction. Results also reveal that replacing JT valves by expanders in the methane cycle has a dominating influence on all performance criteria and hence, can be considered as the main key contributor affecting the Phillips Optimized Cascade Process leading to a notable enhancement in its efficiency. This replacement of JT valves by liquid expanders at different locations of the methane cycle encounters power savings in the range of 4.92–5.72%, plant thermal efficiency of 92.64–92.97% and an increase in LNG production of 5.77–7.04%. Moreover, applying liquid expanders at the determined optimum cases for the different cycles, improves process performance and

Hot Wire Measurements in a Axisymmetric Shear Layer with Swirl

Science.gov (United States)

Ewing, D.; Pollard, A.

1996-11-01

It is well known that the introduction of swirl in an axisymmetric jet can influence the development of and mixing in the near field of the jet. Recent efforts to compute this flow have demonstrated that the development of the near field is dependent on parameters at the jet outlet other than distribution of the swirl component, such as the distribution the mean radial velocity (Xai, J.L., Smith, B.L., Benim, A. C., Schmidli, J., and Yadigaroglu, G. (1996) Influence of Boundary Conditions on Swirling Flow in Combustors, Proc. ASME Fluid. Eng. Div. Summer Meeting), San Diego, Ca., July 7-11.. An experimental rig has been designed to produce co-axial round and annular swirling jets with uniform outlet conditions in each flow. The flow rate and swirl component from each of these jets can be controlled independently and the rig can be configured to produce both co- and counter-swirling flows. Thus, the rig can be used to carry out an extensive investigation of the effect of swirl on the development of axisymmetric flows. The key design features of the rig and the first sets of hot-wire measurements in the shear layer will be reported here.

Influence of Reduced Mass Flow Rate and Chamber Backpressure on Swirl Injector Fluid Mechanics

Science.gov (United States)

Kenny, R Jeremy; Hulka, James R.

2008-01-01

Industry interest in variable-thrust liquid rocket engines places a demand on engine injector technology to operate over a wide range of liquid mass flow rates and chamber backpressures. One injection technology of current interest for variable thrust applications is an injector design with swirled fluids. Current swirl injector design methodologies do not take into account how swirl injector design parameters respond to elevated chamber backpressures at less than design mass flow rates. The current work was created to improve state-of-the-art swirl injector design methods in this area. The specific objective was to study the effects of elevated chamber backpressure and off-design mass flow rates on swirl injector fluid mechanics. Using a backpressure chamber with optical access, water was flowed through a swirl injector at various combinations of chamber backpressure and mass flow rates. The film thickness profile down the swirl injector nozzle section was measured through a transparent nozzle section of the injector. High speed video showed measurable increases in the film thickness profile with application of chamber backpressure and mass flow rates less than design. At prescribed combinations of chamber backpressure and injected mass flow rate, a discrete change in the film thickness profile was observed. Measured injector discharge coefficient values showed different trends with increasing chamber backpressure at low mass flow rates as opposed to near-design mass flow rates. Downstream spray angles showed classic changes in morphology as the mass flow rate was decreased below the design value. Increasing chamber backpressure decreased the spray angle at any injection mass flow rate. Experimental measurements and discussion of these results are reported in this paper.

Mathematical modeling of swirled flows in industrial applications

Science.gov (United States)

Dekterev, A. A.; Gavrilov, A. A.; Sentyabov, A. V.

2018-03-01

Swirled flows are widely used in technological devices. Swirling flows are characterized by a wide range of flow regimes. 3D mathematical modeling of flows is widely used in research and design. For correct mathematical modeling of such a flow, it is necessary to use turbulence models, which take into account important features of the flow. Based on the experience of computational modeling of a wide class of problems with swirling flows, recommendations on the use of turbulence models for calculating the applied problems are proposed.

Image processing analysis of combustion for D. I. diesel engine with high pressure fuel injection. ; Effects of air swirl and injection pressure. Nensho shashin no gazo shori ni yoru koatsu funsha diesel kikan no nensho kaiseki. ; Swirl oyobi funsha atsuryoku no eikyo

Energy Technology Data Exchange (ETDEWEB)

Yamaguchi, I. (Japan Automobile Research Institute, Inc., Tsukuba (Japan)); Tsujimura, K.

1994-02-25

This paper reports an image processing analysis of combustion for a high-pressure direct injection diesel engine on the effects of air swirl and injection pressure upon combustion in the diesel engine. The paper summarizes a method to derive gas flow and turbulence strengths, and turbulent flow mixing velocity. The method derives these parameters by detecting movement of brightness unevenness on two flame photographs through utilizing the mutual correlative coefficients of image concentrations. Five types of combustion systems having different injection pressures, injection devices, and swirl ratios were used for the experiment. The result may be summarized as follows: variation in the average value of the turbulent flow mixing velocities due to difference in the swirl ratio is small in the initial phase of diffusion combustion; the difference is smaller in the case of high swirl ratio than in the case of low swirl ratio after the latter stage of the injection; the average value is larger with the higher the injection pressure during the initial stage of the combustion; after termination of the injection, the value is larger in the low pressure injection; and these trends agree with the trend in the time-based change in heat generation rates measured simultaneously. 6 refs., 14 figs., 2 tabs.

Discussion on boundary conditions for simplified numerical simulation of swirl velocity in a cylinder of engine; Engine nai swirl no kan`i suchi simulation ni okeru kyokai joken no kento

Energy Technology Data Exchange (ETDEWEB)

Matsumoto, K; Tasaka, H; Tan, H [Miyazaki University, Miyazaki (Japan)

1997-10-01

A simplified and quantitative simulation to calculate a swirl velocity in a cylinder with short time and low cost was offered by one of the authors. But the discussion on boundary conditions for the simulation was not enough. In this paper, measurements of diminution of the swirl velocity in a vessel packed with a fluid and simulations corresponding to the measurements were carried out varying aspect ratio of the vessel. From the measurement and calculating results, boundary conditions were obtained. The validity of the obtained boundary conditions was discussed and the adequate boundary conditions were determined. 4 refs., 6 figs., 2 tabs.

Electrochemical immunoassay for thyroxine detection using cascade catalysis as signal amplified enhancer and multi-functionalized magnetic graphene sphere as signal tag

Energy Technology Data Exchange (ETDEWEB)

Han, Jing; Zhuo, Ying, E-mail: yingzhuo@swu.edu.cn; Chai, Yaqin; Yu, Yanqing; Liao, Ni; Yuan, Ruo, E-mail: yuanruo@swu.edu.cn

2013-08-06

Graphical abstract: -- Highlights: •A reusable electrochemical immunosensor is developed for thyroxine detection. •Cascade catalysis as signal amplified enhancer. •Multi-functionalized magnetic graphene sphere as signal tag. •The novel strategy has the advantages of high sensitivity, good selectivity and reproducibility. -- Abstract: This paper constructed a reusable electrochemical immunosensor for the detection of thyroxine at an ultralow concentration using cascade catalysis of cytochrome c (Cyt c) and glucose oxidase (GOx) as signal amplified enhancer. It is worth pointing out that numerous Cyt c and GOx were firstly carried onto the double-stranded DNA polymers based on hybridization chain reaction (HCR), and then the amplified responses could be achieved by cascade catalysis of Cyt c and GOx recycling with the help of glucose. Moreover, multi-functionalized magnetic graphene sphere was synthesized and used as signal tag, which not only exhibited good mechanical properties, large surface area and an excellent electron transfer rate of graphene, but also possessed excellent redox activity and desirable magnetic property. With a sandwich-type immunoreaction, the proposed cascade catalysis amplification strategy could greatly enhance the sensitivity for the detection of thyroxine. Under the optimal conditions, the immunosensor showed a wide linear ranged from 0.05 pg mL{sup −1} to 5 ng mL{sup −1} and a low detection limit down to 15 fg mL{sup −1}. Importantly, the proposed method offers promise for reproducible and cost-effective analysis of biological samples.

Performance study on a low-temperature absorption–compression cascade refrigeration system driven by low-grade heat

International Nuclear Information System (INIS)

Xu, Yingjie; Chen, Guangming; Wang, Qin; Han, Xiaohong; Jiang, Ning; Deng, Shiming

2016-01-01

Highlights: • An absorption–compression system for low-temperature is developed and analyzed. • Cooling capacity, compression power, and discharge temperature are all improved. • At −170 °C, giving 200 W low-grade cooling capacity, COP increases by 28.6%. • Simulation results are verified experimentally, showing good agreement. - Abstract: This paper presents a performance study on a low-temperature absorption–compression cascade refrigeration system (LACRS), which consists of an absorption subsystem (AS) and a vapor compression auto-cascade subsystem (CS). In the system, low-grade heat of AS is used to subcool the CS, which can obtain cold energy at −170 °C. A simulation study is carried out to investigate the effects of evaporating temperature and low-grade cooling capacity on system performance. The study results show that as low-grade cooling capacity from the AS is provided to the CS, high-grade cooling capacity increases, compressor power consumption decreases, and the COP of the CS therefore increases. Comparing with compression auto-cascade cycle, the largest COP improvement of LACRS is about 38%. The model is verified by experimental data. An additional high-grade cooling capacity is obtained experimentally at −170 °C. The study results presented in this paper not only demonstrate the excellent performance of the LACRS, but also provide important guidance to further system design, and practical application.

Swirl Coaxial Injector Testing with LOX/RP-J

Science.gov (United States)

Greene, Sandra Elam; Casiano, Matt

2013-01-01

Testing was conducted at NASA fs Marshall Space Flight Center (MSFC) in the fall of 2012 to evaluate the operation and performance of liquid oxygen (LOX) and kerosene (RP ]1) in an existing swirl coaxial injector. While selected Russian engines use variations of swirl coaxial injectors, component level performance data has not been readily available, and all previously documented component testing at MSFC with LOX/RP ]1 had been performed using a variety of impinging injector designs. Impinging injectors have been adequate for specific LOX/RP ]1 engine applications, yet swirl coaxial injectors offer easier fabrication efforts, providing cost and schedule savings for hardware development. Swirl coaxial elements also offer more flexibility for design changes. Furthermore, testing with LOX and liquid methane propellants at MSFC showed that a swirl coaxial injector offered improved performance compared to an impinging injector. So, technical interest was generated to see if similar performance gains could be achieved with LOX/RP ]1 using a swirl coaxial injector. Results would allow such injectors to be considered for future engine concepts that require LOX/RP ]1 propellants. Existing injector and chamber hardware was used in the test assemblies. The injector had been tested in previous programs at MSFC using LOX/methane and LOX/hydrogen propellants. Minor modifications were made to the injector to accommodate the required LOX/RP ]1 flows. Mainstage tests were performed over a range of chamber pressures and mixture ratios. Additional testing included detonated gbombs h for stability data. Test results suggested characteristic velocity, C*, efficiencies for the injector were 95 ]97%. The injector also appeared dynamically stable with quick recovery from the pressure perturbations generated in the bomb tests.

An experimental study of interacting swirl flows in a model gas turbine combustor

Science.gov (United States)

Vishwanath, Rahul B.; Tilak, Paidipati Mallikarjuna; Chaudhuri, Swetaprovo

2018-03-01

In this experimental work, we analyze the flow structures emerging from the mutual interaction between adjacent swirling flows at variable degrees of swirl, issued into a semi-confined chamber, as it could happen in a three cup sector of an annular premixed combustor of a modern gas turbine engine. Stereoscopic particle image velocimetry ( sPIV) is used to characterize both the non-reacting and reacting flow fields in the central diametrical (vertical) plane of the swirlers and the corresponding transverse (horizontal) planes at different heights above the swirlers. A central swirling flow with a fixed swirl vane angle is allowed to interact with its neighboring flows of varied swirl levels, with constant inlet bulk flow velocity through the central port. It is found that the presence of straight jets with zero swirl or co-rotating swirling jets with increasing swirl on both sides of the central swirling jet, significantly alters its structures. As such, an increase in the amount of swirl in the neighboring flows increases the recirculation levels in central swirling flow leading to a bubble-type vortex breakdown, not formed otherwise. It is shown with the aid of Helmholtz decomposition that the transition from conical to bubble-type breakdown is captured well by the radial momentum induced by the azimuthal vorticity. Simultaneous sPIV and OH-planar laser-induced fluorescence (PLIF) are employed to identify the influence of the neighboring jets on the reacting vortex breakdown states. Significant changes in the vortex breakdown size and structure are observed due to variation in swirl levels of the neighboring jets alongside reaction and concomitant flow dilatation.

Proximity does not contribute to activity enhancement in the glucose oxidase-horseradish peroxidase cascade

Science.gov (United States)

Zhang, Yifei; Tsitkov, Stanislav; Hess, Henry

2016-12-01

A proximity effect has been invoked to explain the enhanced activity of enzyme cascades on DNA scaffolds. Using the cascade reaction carried out by glucose oxidase and horseradish peroxidase as a model system, here we study the kinetics of the cascade reaction when the enzymes are free in solution, when they are conjugated to each other and when a competing enzyme is present. No proximity effect is found, which is in agreement with models predicting that the rapidly diffusing hydrogen peroxide intermediate is well mixed. We suggest that the reason for the activity enhancement of enzymes localized by DNA scaffolds is that the pH near the surface of the negatively charged DNA nanostructures is lower than that in the bulk solution, creating a more optimal pH environment for the anchored enzymes. Our findings challenge the notion of a proximity effect and provide new insights into the role of DNA scaffolds.

U.S. Government Supports Low Emission Economic Growth (Fact Sheet)

Energy Technology Data Exchange (ETDEWEB)

Watson, A.; Sandor, D.; Butheau, M.

2013-11-01

Countries around the world face the challenge of maintaining long-term sustainable economic growth and development under the threat of climate change. By identifying and pursuing a sustainable development pathway now, they are better positioned to reach their economic growth goals while addressing climate change impacts and lowering greenhouse gas (GHG) emissions. Low emission development strategies - development plans that promote sustainable social and economic development while reducing long-term GHG emissions - provide a pathway to preparing for a global low emission future. Partner country governments are working with the U.S. government through the Enhancing Capacity for Low Emission Development Strategies (EC-LEDS) program to further their national development objectives.

Effects of swirl in turbulent pipe flows : computational studies

Energy Technology Data Exchange (ETDEWEB)

Nygaard, Frode

2011-07-01

The primary objective of this doctoral thesis was to investigate the effect of swirl in steady turbulent pipe flows. The work has been carried out by a numerical approach, with direct numerical simulations as the method of choice. A key target to pursue was the effects of the swirl on the wall friction in turbulent pipe flows. The motivation came from studies of rotating pipe flows in which drag reduction was achieved. Drag reduction was reported to be due to the swirl favourably influencing the coherent turbulent structures in the near-wall region. Based on this, it was decided to investigate if similar behaviour could be obtained by inducing a swirl in a pipe with a stationary wall. To do a thorough investigation of the general three-dimensional swirl flow and particularly of the swirl effects; chosen variations of mean and turbulent flow parameters were explored together with complementary flow visualizations. Two different approaches in order to induce the swirl in the turbulent pipe flow, have been carried out. However, the present thesis might be regarded to be comprised of three parts. The first part consists of the first approach to induce the swirl. Here a prescribed circumferential force was implemented in a serial open source Navier-Stokes solver. In the second approach, the swirl was intended induced by implementing structures at the wall. Simulations of flows through a pipe with one or more helical fin(s) at the pipe wall was decided to be performed. In order to pursue this approach, it was found necessary to do a parallelization of the existing serial numerical code. The key element of this parallelization has been included as a part of the present work. Additionally, the helical fin(s) were implemented into the code by use of an immersed boundary method. A validation of this work is also documented in the thesis. The work done by parallelizing the code and implementing an immersed boundary method constitutes the second part of the present thesis. The

An Experimental Study of Swirling Flows as Applied to Annular Combustors

Science.gov (United States)

Seal, Michael Damian, II

1997-01-01

This thesis presents an experimental study of swirling flows with direct applications to gas turbine combustors. Two separate flowfields were investigated: a round, swirling jet and a non-combusting annular combustor model. These studies were intended to allow both a further understanding of the behavior of general swirling flow characteristics, such as the recirculation zone, as well as to provide a base for the development of computational models. In order to determine the characteristics of swirling flows the concentration fields of a round, swirling jet were analyzed for varying amount of swirl. The experimental method used was a light scattering concentration measurement technique known as marker nephelometry. Results indicated the formation of a zone of recirculating fluid for swirl ratios (rotational speed x jet radius over mass average axial velocity) above a certain critical value. The size of this recirculation zone, as well as the spread angle of the jet, was found to increase with increase in the amount of applied swirl. The annular combustor model flowfield simulated the cold-flow characteristics of typical current annular combustors: swirl, recirculation, primary air cross jets and high levels of turbulence. The measurements in the combustor model made by the Laser Doppler Velocimetry technique, allowed the evaluation of the mean and rms velocities in the three coordinate directions, one Reynold's shear stress component and the turbulence kinetic energy: The primary cross jets were found to have a very strong effect on both the mean and turbulence flowfields. These cross jets, along with a large step change in area and wall jet inlet flow pattern, reduced the overall swirl in the test section to negligible levels. The formation of the strong recirculation zone is due mainly to the cross jets and the large step change in area. The cross jets were also found to drive a four-celled vortex-type motion (parallel to the combustor longitudinal axis) near the

Review on pressure swirl injector in liquid rocket engine

Science.gov (United States)

Kang, Zhongtao; Wang, Zhen-guo; Li, Qinglian; Cheng, Peng

2018-04-01

The pressure swirl injector with tangential inlet ports is widely used in liquid rocket engine. Commonly, this type of pressure swirl injector consists of tangential inlet ports, a swirl chamber, a converging spin chamber, and a discharge orifice. The atomization of the liquid propellants includes the formation of liquid film, primary breakup and secondary atomization. And the back pressure and temperature in the combustion chamber could have great influence on the atomization of the injector. What's more, when the combustion instability occurs, the pressure oscillation could further affects the atomization process. This paper reviewed the primary atomization and the performance of the pressure swirl injector, which include the formation of the conical liquid film, the breakup and atomization characteristics of the conical liquid film, the effects of the rocket engine environment, and the response of the injector and atomization on the pressure oscillation.

Enhanced Performance of Bipolar Cascade Light Emitting Diodes by Doping the Aluminum Oxide Apertures

National Research Council Canada - National Science Library

Siskaninetz, William

2004-01-01

Performance improvements in multiple-stage, single-cavity bipolar cascade light emitting diodes including reduced operating voltages, enhanced light generation, and reduced device heating are obtained...

An Experimental Investigation on the NO and CO Emission Characteristics of a Swirl Convergent-Divergent Nozzle at Elevated Pressure

Directory of Open Access Journals (Sweden)

Zhongya Xi

2018-05-01

Full Text Available The behavior of the pollutants NO and CO at elevated combustor pressure are of special importance due to the continuing trend toward developing engines operating at higher pressure ratios to yield higher thermal efficiency. An experiment was performed to examine the NO and CO emissions for a swirl convergent-divergent nozzle at elevated pressure. The NO and CO correlations were obtained. Meanwhile, the flame length, exhaust gas oxygen concentration, exit temperature and global flame residence time were also determined to analyze the NO and CO emission characteristics. The results showed that, with the increase in combustor pressure P, flame length decreased proportionally to P−0.49; exit O2 volume fraction increased and exit temperature was reduced. The global flame residence time decreased proportionally to P−0.43. As pressure increased, The NO and Emission Index of NO (EINO levels decreased proportionally to P−0.53 and P−0.6 respectively, which is mainly attributed to the influence of global flame residence time; the NO and EINO increased almost proportionally with the increase in global flame residence time. The EINO scaling EINO (ρue/d was proportional to Fr0.42, which indicated that compared with pure fuel, the fuel diluted with primary air can cause a decrease in the exponent of the Fr power function. At higher pressure, the CO and Emission Index of CO (EICO decreased proportionally to P−0.35 and P−0.4, respectively, due to the increased unburned methane and high pressure which accelerated chemical reaction kinetics to promote the conversion of CO to CO2.

New technologies for low emissions

Energy Technology Data Exchange (ETDEWEB)

Burnett, G. [Kansas City Power & Light (USA)

2001-05-01

This paper examines new technology for coal-fired power stations, designed to achieve very low emissions with focus on the post-combustion emissions control systems installed at Howthorn. The first post-combustion system through which the flue gas passes is a selective catalytic reduction (SCR) system, consisting of two catalyst-equipped casing and various support equipment designed to provide continuous control of NOx emissions. The second system is a dry flue gas desulphurisation (dry FGD) system consisting of two spray dry absorber (SDA) vessels and supporting equipment to provide control of SO{sub 2} emissions. The third system consists of a pulse-jet bag house (PJBH) and supporting equipment to control particulate emissions. Finally, the fourth system is a material handling system (ash handling system), consisting of equipment provided to remove, recycle, and dispose of solid wastes associated with the combustion process and the three other pollution control systems. These systems bring the operation of Hawthorn 5 into compliance with federal, state, and local emission standards and enhance the positive relationship KCP & L has with its neighbours. 6 figs., 1 tab.

Turbulent swirling flow in a dynamic model of a uniflow-scavenged two-stroke engine

Science.gov (United States)

Ingvorsen, K. M.; Meyer, K. E.; Walther, J. H.; Mayer, S.

2014-06-01

It is desirable to use computational fluid dynamics for optimization of the in-cylinder processes in low-speed two-stroke uniflow-scavenged marine diesel engines. However, the complex nature of the turbulent swirling in-cylinder flow necessitates experimental data for validation of the used turbulence models. In the present work, the flow in a dynamic scale model of a uniflow-scavenged cylinder is investigated experimentally. The model has a transparent cylinder and a moving piston driven by a linear motor. The flow is investigated using phase-locked stereoscopic particle image velocimetry (PIV) and time-resolved laser Doppler anemometry (LDA). Radial profiles of the phase-locked mean and rms velocities are computed from the velocity fields recorded with PIV, and the accuracy of the obtained profiles is demonstrated by comparison with reference LDA measurements. Measurements are carried out at five axial positions for 15 different times during the engine cycle and show the temporal and spatial development of the swirling in-cylinder flow. The tangential velocity profiles in the bottom of the cylinder near the end of the scavenge process are characterized by a concentrated swirl resulting in wake-like axial velocity profiles and the occurrence of a vortex breakdown. After scavenge port closing, the axial velocity profiles indicate that large transient swirl-induced structures exist in the cylinder. Comparison with profiles obtained under steady-flow conditions shows that the scavenge flow cannot be assumed to be quasi-steady. The temporal development of the swirl strength is investigated by computing the angular momentum. The swirl strength shows an exponential decay from scavenge port closing to scavenge port opening corresponding to a reduction of 34 %, which is in good agreement with theoretical predictions.

Nitrous oxide emissions at low temperatures

International Nuclear Information System (INIS)

Martikainen, P.J.

2002-01-01

Microbial processes in soil are generally stimulated by temperature, but at low temperatures there are anomalies in the response of microbial activities. Soil physical-chemical characteristics allow existence of unfrozen water in soil also at temperatures below zero. Therefore, some microbial activities, including those responsible for nitrous oxide (N 2 0) production, can take place even in 'frozen' soil. Nitrous oxide emissions during winter are important even in boreal regions where they can account for more than 50% of the annual emissions. Snow pack therefore has great importance for N 2 0 emissions, as it insulates soil from the air allowing higher temperatures in soil than in air, and possible changes in snoav cover as a result of global warming would thus affect the N 2 0 emission from northern soils. Freezing-thawing cycles highly enhance N 2 0 emissions from soil, probably because microbial nutrients, released from disturbed soil aggregates and lysed microbial cells, support microbial N 2 0 production. However, the overall interactions between soil physics, chemistry, microbiology and N 2 0 production at low temperatures, including effects of freezing-thawing cycles, are still poorly known. (au)

Emission characteristics and axial flame temperature distribution of producer gas fired premixed burner

Energy Technology Data Exchange (ETDEWEB)

Bhoi, P.R. [Department of Mechanical Engineering, L and T-Sargent and Lundy Limited, L and T Energy Centre, Near Chhani Jakat Naka, Baroda 390 002 (India); Channiwala, S.A. [Department of Mechanical Engineering, Sardar Vallabhbhai National Institute of Technology, Deemed University, Ichchhanath, Surat 395 007, Gujarat (India)

2009-03-15

This paper presents the emission characteristics and axial flame temperature distribution of producer gas fired premixed burner. The producer gas fired premixed burner of 150 kW capacity was tested on open core throat less down draft gasifier system in the present study. A stable and uniform flame was observed with this burner. An instrumented test set up was developed to evaluate the performance of the burner. The conventional bluff body having blockage ratio of 0.65 was used for flame stabilization. With respect to maximum flame temperature, minimum pressure drop and minimum emissions, a swirl angle of 60 seems to be optimal. The experimental results also showed that the NO{sub x} emissions are inversely proportional to swirl angle and CO emissions are independent of swirl angle. The minimum emission levels of CO and NO{sub x} are observed to be 0.167% and 384 ppm respectively at the swirl angle of 45-60 . The experimental results showed that the maximum axial flame temperature distribution was achieved at A/F ratio of 1.0. The adiabatic flame temperature of 1653 C was calculated theoretically at A/F ratio of 1.0. Experimental results are in tune with theoretical results. It was also concluded that the CO and UHC emissions decreases with increasing A/F ratio while NO{sub x} emissions decreases on either side of A/F ratio of 1.0. (author)

Effect of aviation fuel type and fuel injection conditions on the spray characteristics of pressure swirl and hybrid air blast fuel injectors

Science.gov (United States)

Feddema, Rick

Feddema, Rick T. M.S.M.E., Purdue University, December 2013. Effect of Aviation Fuel Type and Fuel Injection Conditions on the Spray Characteristics of Pressure Swirl and Hybrid Air Blast Fuel Injectors. Major Professor: Dr. Paul E. Sojka, School of Mechanical Engineering Spray performance of pressure swirl and hybrid air blast fuel injectors are central to combustion stability, combustor heat management, and pollutant formation in aviation gas turbine engines. Next generation aviation gas turbine engines will optimize spray atomization characteristics of the fuel injector in order to achieve engine efficiency and emissions requirements. Fuel injector spray atomization performance is affected by the type of fuel injector, fuel liquid properties, fuel injection pressure, fuel injection temperature, and ambient pressure. Performance of pressure swirl atomizer and hybrid air blast nozzle type fuel injectors are compared in this study. Aviation jet fuels, JP-8, Jet A, JP-5, and JP-10 and their effect on fuel injector performance is investigated. Fuel injector set conditions involving fuel injector pressure, fuel temperature and ambient pressure are varied in order to compare each fuel type. One objective of this thesis is to contribute spray patternation measurements to the body of existing drop size data in the literature. Fuel droplet size tends to increase with decreasing fuel injection pressure, decreasing fuel injection temperature and increasing ambient injection pressure. The differences between fuel types at particular set conditions occur due to differences in liquid properties between fuels. Liquid viscosity and surface tension are identified to be fuel-specific properties that affect the drop size of the fuel. An open aspect of current research that this paper addresses is how much the type of aviation jet fuel affects spray atomization characteristics. Conventional aviation fuel specifications are becoming more important with new interest in alternative

Residence Time Distributions in a Cold, Confined Swirl Flow

DEFF Research Database (Denmark)

Lans, Robert Pieter Van Der; Glarborg, Peter; Dam-Johansen, Kim

1997-01-01

Residence time distributions (RTD) in a confined, cold swirling flow have been measured with a fast-response probe and helium as a tracer. The test-rig represented a scaled down version of a burner. The effect of variation of flow velocities and swirl angle on the flow pattern in the near...

Turbulent structure and dynamics of swirled, strongly pulsed jet diffusion flames

KAUST Repository

Liao, Ying-Hao

2013-11-02

The structure and dynamics of swirled, strongly pulsed, turbulent jet diffusion flames were examined experimentally in a co-flow swirl combustor. The dynamics of the large-scale flame structures, including variations in flame dimensions, the degree of turbulent flame puff interaction, and the turbulent flame puff celerity were determined from high-speed imaging of the luminous flame. All of the tests presented here were conducted with a fixed fuel injection velocity at a Reynolds number of 5000. The flame dimensions were generally found to be more impacted by swirl for the cases of longer injection time and faster co-flow flow rate. Flames with swirl exhibited a flame length up to 34% shorter compared to nonswirled flames. Both the turbulent flame puff separation and the flame puff celerity generally decreased when swirl was imposed. The decreased flame length, flame puff separation, and flame puff celerity are consistent with a greater momentum exchange between the flame and the surrounding co-flow, resulting from an increased rate of air entrainment due to swirl. Three scaling relations were developed to account for the impact of the injection time, the volumetric fuel-to-air flow rate ratio, and the jet-on fraction on the visible flame length. © 2013 Copyright Taylor and Francis Group, LLC.

Application of a controlled swirl in the XT-ADS spallation target

International Nuclear Information System (INIS)

Roelofs, F.; Siccama, N. B.; Jeanmart, H.; Tichelen, K. V.; Dierckx, M.; Schuurmans, P.

2008-01-01

Within the EUROTRANS project, a windowless spallation target is designed and assessed in which there is direct contact between the proton beamline vacuum from the accelerator and a lead-bismuth free surface flow. Windowless spallation targets, which are designed by SCK.CEN, based on their experience for the MYRRHA concept, are experimentally examined in a well instrumented water-loop at UCL. The design work and the experimental campaign are supported by numerical simulations which are performed at NRG. In the current paper, the application of a mild swirl in the windowless spallation target is assessed. For this purpose, SCK.CEN has designed and fabricate, a spallation target in which a controlled swirl is introduced in the annular feeder of the target nozzle. An experimental programme is performed at UCL in their water-loop to evaluate various swirl strengths in one specific target nozzle design. Prior to the experimental programme, numerical simulations were performed at NRG assessing the influence of various swirl strengths on the free surface behaviour. Experimental and numerical results show that a mild swirl stabilizes the free surface and also indicate that applying a stronger swirl leads to undesired free surface behaviour, ultimately leading to a strong vortex in the central downcomer. (authors)

Hydrodynamics of multi-sized particles in stable regime of a swirling bed

Energy Technology Data Exchange (ETDEWEB)

Miin, Chin Swee; Sulaiman, Shaharin Anwar; Raghavan, Vijay Raj; Heikal, Morgan Raymond; Naz, Muhammad Yasin [Universiti Teknologi PETRONAS, Perak (Malaysia)

2015-11-15

Using particle imaging velocimetry (PIV), we observed particle motion within the stable operating regime of a swirling fluidized bed with an annular blade distributor. This paper presents velocity profiles of particle flow in an effort to determine effects from blade angle, particle size and shape and bed weight on characteristics of a swirling fluidized bed. Generally, particle velocity increased with airflow rate and shallow bed height, but decreased with bed weight. A 3 .deg. increase in blade angle reduced particle velocity by approximately 18%. In addition, particle shape, size and bed weight affected various characteristics of the swirling regime. Swirling began soon after incipience in the form of a supra-linear curve, which is the characteristic of a swirling regime. The relationship between particle and gas velocities enabled us to predict heat and mass transfer rates between gas and particles.

Films with discrete nano-DLC-particles as the field emission cascade

International Nuclear Information System (INIS)

Song Fengqi; Bu Haijun; Wan Jianguo; Wang Guanghou; Zhou Feng; He Longbing; Han Min; Zhou Jianfeng; Wang Xiaoshu

2008-01-01

Films with discrete diamond-like-carbon (DLC) nanoparticles were prepared by the deposition of the carbon nanoparticle beam. Their morphologies were imaged by scanning electron microscopy and atomic force microscopy (AFM). The nanoparticles were found to be distributed on the silicon (1 0 0) substrate discretely. Hemispherical shapes of the nanoparticles were demonstrated by the AFM line profile. Electron energy loss spectra were measured and an sp 3 ratio as high as 86% was found. Field-induced electron emission of the as-prepared cascade (nanoDLC/ Si) was tested and a current density of 1 mA cm -2 was achieved at 10.2 V μm -1 . (fast track communication)

Unidirectional cross polarization rotator with enhanced broadband transparency by cascading twisted nanobars

International Nuclear Information System (INIS)

Wang, Ying-Hua; Shao, Jian; Li, Jie; Zhu, Ming-Jie; Li, Jiaqi; Dong, Zheng-Gao

2016-01-01

We demonstrate the optical activity for linear polarization by twisting cascading multilayer nanobars, for which the x- (y-)polarized light is significantly transformed to a y- (x-)polarized one with enhanced transmittance in a unidirectional manner, and the bandwidth can be broadened by increasing the cascading number of layers. The polarization conversion rate reaches nearly 100% with a maximum cross-polarization transmission coefficient larger than 0.95. This phenomenon is attributed to the chiral structural arrangement and anisotropic resonance of nanobars, which consequently leads to different cross-polarization conversions between forward and backward incident lights, and thus the unidirectional transmission with an extinction ratio up to 10 3 . These characteristics show application potential in optical nano-devices. (paper)

Phase-locked stereoscopic PIV measurements of the turbulent swirling flow in a dynamic model of a uniflow-scavenged two-stroke engine cylinder

DEFF Research Database (Denmark)

Ingvorsen, Kristian Mark; Meyer, Knud Erik; Walther, Jens Honore

2013-01-01

It is desirable to use computational fluid dynamics for the optimization of in-cylinder processes in large two-stroke low-speed uniflowscavenged marine diesel engines. However, the complex nature of the turbulent swirling in-cylinder flow necessitates experimental data for validation of the used...... profiles in general will not be representative for the dynamic conditions. The temporal development of the swirl strength is investigated by computing the angular momentum. The swirl strength shows an exponential decay from scavenge port closing to scavenge port opening corresponding to a reduction of 34%....

An experimental investigation of pneumatic swirl flow induced by a three lobed helical pipe

International Nuclear Information System (INIS)

Fokeer, S.; Lowndes, I.; Kingman, S.

2009-01-01

This paper presents a discussion of the results and conclusions drawn from a series of experiments conducted to investigate the swirl flow that are generated by a three lobed helical pipe mounted within a laboratory scale pneumatic conveying rig. The experiments employed Laser Doppler Anemometry (LDA) to quantify the strength of the induced vortex formations and the decay rates of the observed downstream swirl flows over a range of Reynolds number in the turbulent regime. Instantaneous point velocity measurements were resolved in three directions across regular measurement grids transcribed across parallel planes located at four distances downstream of the swirl inducing pipe section. The equivalent axial, radial and tangential velocities were subsequently computed at these grids points. The degree of swirl measured across each measurement plane was expressed in terms of a defined swirl number. It was concluded that the three lobed helical pipe gave rise to a wall jet type of swirl whose rate of observed downstream decay is related to the Reynolds number of the upstream flow and the distance downstream of the swirl pipe. The decay rates for the swirl flows were found to be inversely proportional to the Reynolds number of the upstream flow. The swirl pipe was observed to create a redistribution of the downstream velocity field from axial to tangential, accompanied by a transfer of axial to angular momentum. The findings of this paper are believed to improve understanding to assist the selective use of swirl flow within lean phase particles pneumatic transport systems.

An experimental investigation of pneumatic swirl flow induced by a three lobed helical pipe

Energy Technology Data Exchange (ETDEWEB)

Fokeer, S. [Department of Aeronautical and Automotive Engineering, University of Loughborough LE11 3TU (United Kingdom)], E-mail: S.Fokeer@lboro.ac.uk; Lowndes, I.; Kingman, S. [Division of Process and Environmental Engineering, University of Nottingham, Nottingham NG7 2RD (United Kingdom)

2009-04-15

This paper presents a discussion of the results and conclusions drawn from a series of experiments conducted to investigate the swirl flow that are generated by a three lobed helical pipe mounted within a laboratory scale pneumatic conveying rig. The experiments employed Laser Doppler Anemometry (LDA) to quantify the strength of the induced vortex formations and the decay rates of the observed downstream swirl flows over a range of Reynolds number in the turbulent regime. Instantaneous point velocity measurements were resolved in three directions across regular measurement grids transcribed across parallel planes located at four distances downstream of the swirl inducing pipe section. The equivalent axial, radial and tangential velocities were subsequently computed at these grids points. The degree of swirl measured across each measurement plane was expressed in terms of a defined swirl number. It was concluded that the three lobed helical pipe gave rise to a wall jet type of swirl whose rate of observed downstream decay is related to the Reynolds number of the upstream flow and the distance downstream of the swirl pipe. The decay rates for the swirl flows were found to be inversely proportional to the Reynolds number of the upstream flow. The swirl pipe was observed to create a redistribution of the downstream velocity field from axial to tangential, accompanied by a transfer of axial to angular momentum. The findings of this paper are believed to improve understanding to assist the selective use of swirl flow within lean phase particles pneumatic transport systems.

Numerical study of effect of compressor swirling flow on combustor design in a MTE

Science.gov (United States)

Mu, Yong; Wang, Chengdong; Liu, Cunxi; Liu, Fuqiang; Hu, Chunyan; Xu, Gang; Zhu, Junqiang

2017-08-01

An effect of the swirling flow on the combustion performance is studied by the computational fluid dynamics (CFD) in a micro-gas turbine with a centrifugal compressor, dump diffuser and forward-flow combustor. The distributions of air mass and the Temperature Pattern Factor (as: Overall Temperature Distribution Factor -OTDF) in outlet are investigated with two different swirling angles of compressed air as 0° and 15° in three combustors. The results show that the influences of swirling flow on the air distribution and OTDF cannot be neglected. Compared with no-swirling flow, the air through outer liner is more, and the air through the inner liner is less, and the pressure loss is bigger under the swirling condition in the same combustor. The Temperature Pattern Factor changes under the different swirling conditions.

Large eddy simulation of the flow through a swirl generator

Energy Technology Data Exchange (ETDEWEB)

Conway, Stephen

1998-12-01

The advances made in computer technology over recent years have led to a great increase in the engineering problems that can be studied using CFD. The computation of flows over and through complex geometries at relatively high Reynolds numbers is becoming more common using the Large Eddy Simulation (LES) technique. Direct numerical simulations of such flows is still beyond the capacity of todays fastest supercomputers, requiring excessive computational times and memory. In addition, traditional Reynolds Averaged Navier Stokes (RANS) methods are known to have limited applicability in a wide range of engineering flow situations. In this thesis LES has been used to simulate the flow through a cascade of guidance vanes, more commonly known as a swirl generator, positioned at the inlet to a gas turbine combustion chamber. This flow case is of interest because of the complex flow phenomena which occur within the swirl generator, which include compressibility effects, different types of flow instabilities, transition, laminar and turbulent separation and near wall turbulence. It is also of interest because it fits very well into the range of engineering applications that can be studied using LES. Two computational grids with different resolutions and two subgrid scale stress models were used in the study. The effects of separation and transition are investigated. A vortex shedding frequency from the guidance vanes is determined which is seen to be dependent on the angle of incident air flow. Interaction between the movement of the separation region and the shedding frequency is also noted. Such vortex shedding phenomena can directly affect the quality of fuel and air mixing within the combustion chamber and can in some cases induce vibrations in the gas turbine structure. Comparisons between the results obtained using different grid resolutions with an implicit and a dynamic divergence (DDM) subgrid scale stress models are also made 32 refs, 35 figs, 2 tabs

Metal-enhanced fluorescence exciplex emission.

Science.gov (United States)

Zhang, Yongxia; Mali, Buddha L; Geddes, Chris D

2012-01-01

In this letter, we report the first observation of metal-enhanced exciplex fluorescence, observed from anthracene in the presence of diethylaniline. Anthracene in the presence of diethylaniline in close proximity to Silver Island Films (SIFs) shows enhanced monomer and exciplex emission as compared to a non-silvered control sample containing no silver nanoparticles. Our findings suggest two complementary methods for the enhancement: (i) surface plasmons can radiate coupled monomer and exciplex fluorescence efficiently, and (ii) enhanced absorption (enhanced electric near-field) further facilitates enhanced emission. Our exciplex studies help us to further understand the complex photophysics of the metal-enhanced fluorescence technology. Copyright © 2011 Elsevier B.V. All rights reserved.

Acoustic Purcell Effect for Enhanced Emission

KAUST Repository

Landi, Maryam

2018-03-13

We observe that our experimentally measured emission power enhancement of a speaker inside a previously proposed metacavity agrees with our numerically calculated enhancement of the density of states (DOS) of the source-cavity system. We interpret the agreement by formulating a relation between the emitted sound power and the acoustic DOS. The formulation is an analog to Fermi’s golden rule in quantum emission. The formulation complements the radiation impedance theory in traditional acoustics for describing sound emission. Our study bridges the gap between acoustic DOS and the acoustic Purcell effect for sound emission enhancement.

Acoustic Purcell Effect for Enhanced Emission

KAUST Repository

Landi, Maryam; Zhao, Jiajun; Prather, Wayne E.; Wu, Ying; Zhang, Likun

2018-01-01

We observe that our experimentally measured emission power enhancement of a speaker inside a previously proposed metacavity agrees with our numerically calculated enhancement of the density of states (DOS) of the source-cavity system. We interpret the agreement by formulating a relation between the emitted sound power and the acoustic DOS. The formulation is an analog to Fermi’s golden rule in quantum emission. The formulation complements the radiation impedance theory in traditional acoustics for describing sound emission. Our study bridges the gap between acoustic DOS and the acoustic Purcell effect for sound emission enhancement.

Flow aerodynamics modeling of an MHD swirl combustor - calculations and experimental verification

International Nuclear Information System (INIS)

Gupta, A.K.; Beer, J.M.; Louis, J.F.; Busnaina, A.A.; Lilley, D.G.

1981-01-01

This paper describes a computer code for calculating the flow dynamics of constant density flow in the second stage trumpet shaped nozzle section of a two stage MHD swirl combustor for application to a disk generator. The primitive pressure-velocity variable, finite difference computer code has been developed to allow the computation of inert nonreacting turbulent swirling flows in an axisymmetric MHD model swirl combustor. The method and program involve a staggered grid system for axial and radial velocities, and a line relaxation technique for efficient solution of the equations. Tue produces as output the flow field map of the non-dimensional stream function, axial and swirl velocity. 19 refs

Modeling and Simulation of Swirl Stabilized Turbulent Non-Premixed Flames

Science.gov (United States)

Badillo-Rios, Salvador; Karagozian, Ann

2017-11-01

Flame stabilization is an important design criterion for many combustion chambers, especially at lean conditions and/or high power output, where insufficient stabilization can result in dangerous oscillations and noisy or damaged combustors. At high flow rates, swirling flow can offer a suitable stabilization mechanism, although understanding the dynamics of swirl-stabilized turbulent flames remains a significant challenge. Utilizing the General Equation and Mesh Solver (GEMS) code, which solves the Navier-Stokes equations along with the energy equation and five species equations, 2D axisymmetric and full 3D parametric studies and simulations are performed to guide the design and development of an experimental swirl combustor configuration and to study the effects of swirl on statistically stationary combustion. Results show that as the momentum of air is directed into the inner air inlet rather than the outer inlet of the swirl combustor, the central recirculating region becomes stronger and more unsteady, improving mixing and burning efficiency in that region. A high temperature region is found to occur as a result of burning of the trapped fuel from the central toroidal vortex. The effects of other parameters on flowfield and flame-stabilization dynamics are explored. Supported by ERC, Inc. (PS150006) and AFOSR (Dr. Chiping Li).

Control of Vortex Breakdown in Critical Swirl Regime Using Azimuthal Forcing

Science.gov (United States)

Oberleithner, Kilian; Lueck, Martin; Paschereit, Christian Oliver; Wygnanski, Israel

2010-01-01

We finally go back to the four swirl cases and see how the flow responds to either forcing m = -1 or m = -2. On the left we see the flow forced at m = -1 We see that the PVC locks onto the applied forcing also for lower swirl number causing this high TKE at the jet center. The amplification of this instability causes VB to occur at a lower swirl number. The opposite can be seen when forcing the flow at m=-2 which is basically growing in the outer shear layer causing VB to move downstream . There is no energy at the center of the vortex showing that the precessing has been damped. The mean flow is most altered at the swirl numbers were VB is unstable.

Enhancement of existing geothermal resource utilization by cascading to intensive aquaculture

Energy Technology Data Exchange (ETDEWEB)

Zachritz, W.H. II; Polka, R.; Schoenmackers, R.

1995-12-04

Aquaculture, the farming and husbandry of freshwater and marine organisms, is the newest and fastest growing US agricultural sector. In New Mexico, low winter temperatures and limited freshwater sources narrow culture production possibilities; however, it has long been recognized that the state has abundant supplies of both saline and geothermal ground waters. The purpose of this project was to demonstrate the achievable energy savings and value enhancement of the byproduct geothermal energy by cascading fluids for the production of commercial aquaculture species. Specifically the project involved evaluating the heating systems performance in terms of heating budget for the geothermal assist, determine the total quantity of water used for culture and heating, amount of geothermal byproduct heat extracted, and ability of the system to maintain culture water temperatures during critical heating periods of the year. In addition, an analysis was conducted to determine the compatibility of this new system with existing greenhouse heating requirements.

Turbulent structure and dynamics of swirled, strongly pulsed jet diffusion flames

KAUST Repository

Liao, Ying-Hao; Hermanson, James C.

2013-01-01

The structure and dynamics of swirled, strongly pulsed, turbulent jet diffusion flames were examined experimentally in a co-flow swirl combustor. The dynamics of the large-scale flame structures, including variations in flame dimensions, the degree

Low crosstalk Arrayed Waveguide Grating with Cascaded Waveguide Grating Filter

International Nuclear Information System (INIS)

Deng Yang; Liu Yuan; Gao Dingshan

2011-01-01

We propose a highly compact and low crosstalk arrayed waveguide grating (AWG) with cascaded waveguide grating (CWGF). The side lobes of the silicon nanowire AWG, which are normally introduced by fabrication errors, can be effectively suppressed by the CWGF. And the crosstalk can be improved about 15dB.

A hybrid plasmonic waveguide terahertz quantum cascade laser

Energy Technology Data Exchange (ETDEWEB)

Degl' Innocenti, Riccardo, E-mail: rd448@cam.ac.uk; Shah, Yash D.; Wallis, Robert; Klimont, Adam; Ren, Yuan; Jessop, David S.; Beere, Harvey E.; Ritchie, David A. [Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE (United Kingdom)

2015-02-23

We present the realization of a quantum cascade laser emitting at around 2.85 THz, based on a hybrid plasmonic waveguide with a low refractive index dielectric cladding. This hybrid waveguide design allows the performance of a double-metal waveguide to be retained, while improving the emission far-field. A set of lasers based on the same active region material were fabricated with different metal layer thicknesses. A detailed characterization of the performance of these lasers revealed that there is an optimal trade-off that yields the best far-field emission and the maximum temperature of operation. By exploiting the pure plasmonic mode of these waveguides, the standard operation conditions of a double-metal quantum cascade laser were retrieved, such that the maximum operating temperature of these devices is not affected by the process. These results pave the way to realizing a class of integrated devices working in the terahertz range which could be further exploited to fabricate terahertz on-chip circuitry.

Vortex breakdown of compressible swirling flows in a pipe

Science.gov (United States)

Lee, Harry; Rusak, Zvi; Wang, Shixiao

2017-11-01

The manifold of branches of steady and axisymmetric states of compressible subsonic swirling flows in a finite-length straight circular pipe are developed. The analysis is based on Rusak et al. (2015) nonlinear partial differential equation for the solution of the flow stream function in terms of the inlet flow total enthalpy, entropy and circulation functions. This equation reflects the complicated thermo-physical interactions in the flows. The flow problem is solved numerically using a finite difference approach with a penalty procedure for identifying vortex breakdown and wall-separation states. Several types of solutions are found and used to form the bifurcation diagram of steady compressible flows with swirl as the inlet swirl level is increased at a fixed inlet Mach number. Results are compared with predictions from the global analysis approach of Rusak et al. (2015). The computed results provide theoretical predictions of the critical swirl levels for the first appearance of vortex breakdown states as a function of the inlet Mach number. The shows the delay in the appearance of breakdown with increase of the inlet axial flow Mach number in the subsonic range of operation.

The turbulence structure in an unconfined swirling diffusion flame

International Nuclear Information System (INIS)

Finzenhagen, F.; Doherty, T.O.; Bates, C.; Wirtz, S.; Kremer, H.

1999-01-01

Turbulent swirling flows are used in many practical combustion systems. The swirl improves the flame stability as a result of the formation of a central recirculation zone combined with fast mixing at the boundaries of this zone. Knowledge about swirl flames has increased over the last few decades as a result of practical experience and fundamental research. Some important questions concerning the influence of the turbulence structure on the flame stability and chemical kinetics of the combustion process remain unresolved. The structure of turbulence, especially turbulent scales and time dependent effects, at the outlet zone controls the mixing process and therefore the flame properties. Understanding of these complex phenomena is far from complete. The present work describes the results of an experimental study of the turbulence structure of a swirled diffusion flame using laser-optical measurement techniques, e.g. Laser Doppler Anemometry (LDA) and Particle Image Velocimetry (PW). All the processed information available from the burst-mode Laser Doppler Anemometry (LDA) measurements has been combined and compared with high spatial resolution PIV measurements of the flow. The extensive statistical post processing of the data has enabled the turbulent microstructure to be characterised. (author)

Experimental evidence of enhancement in the anticipation time by cascading

International Nuclear Information System (INIS)

Baraik, Abhijit; Singh, Harpartap; Parmananda, P.

2014-01-01

We have studied and verified experimentally the enhancement in the anticipation time by cascading Chua's circuits. The experiments have been carried out in a one dimensional array of Chua's circuits (2 to 8) coupled unidirectionally, such that each one acts as a master for the next one. By doing so, it has been observed that the anticipation time increases with an increase in the array size. Moreover, the numerical simulations of an array of eighty Chua's circuits verify the experimental observations.

Pre-swirl mechanism in front of a centrifugal compressor: effects on surge line and on unsteady phenomena in surge area

Directory of Open Access Journals (Sweden)

Danlos Amélie

2017-01-01

Full Text Available Using a pre-swirl mechanism upstream an impeller of a compressor allows to modify its characteristics curve, while weakly damaging its efficiency. Another consequence of the pre-swirl is to push back the surge line limit and to increase the operation zone towards the low flow rate limits. A centrifugal compressor has been modified in order to add a swirl generator device upstream the impeller. The incidence values of blades can vary from 0° (no pre-swirl to ±90°. The variation of the stator blades incidence has several main consequences: to allow a flow rate adjustment with a good efficiency conservation, to increase the angular velocity with a constant shaft power, to produce a displacement of the surge line limit. In this paper, the results of experimental studies are presented to analyze the surge line and the intensity of unsteady phenomena when the compressor works in its surge area.

Investigation of the effects of quarl and initial conditions on swirling non-premixed methane flames: Flow field, temperature, and species distributions

KAUST Repository

Elbaz, Ayman M.

2015-12-19

Detailed measurements are presented of the turbulent flow field, gas species concentrations and temperature field in a non-premixed methane swirl flame. Attention is given to the effect of the quarl geometry on the flame structure and emission characteristics due to its importance in gas turbine and industrial burner applications. Two different quarls were fitted to the burner exit, one a straight quarl and the other a diverging quarl of 15° half cone angle. Stereoscopic Particle Image Velocimetry (SPIV) was applied to obtain the three components of the instantaneous velocity on a vertical plane immediately downstream of the quarl exit. Temperature and gaseous species measurements were made both inside and downstream of the quarls, using a fine wire thermocouple and sampling probe, respectively. This work provides experimental verification by complementary techniques. The results showed that although the main flame structures were governed by the swirl motion imparted to the air stream, the quarl geometry, fuel loading and air loading also had a significant effect on the flow pattern, turbulence intensity, mixture formation, temperature distribution, emissions and flame stabilization. Particularly, in the case of the straight quarl flame, the flow pattern leads to strong, rapid mixing and reduces the residence time for NO formation within the internal recirculation zone (IRZ). However, for the diverging quarl flames, the recirculation zone is shifted radially outward, and the turbulent interaction between the central fuel jet and the internal recirculation zone IRZ induces another small vortex between these two flow features. Less mixing near the diverging quarl exit is observed, with a higher concentration of NO and CO in the post-combustion zone. The instantaneous flow field for both flames showed the existence of small scale vortical structure near the shear layers which were not apparent in the time averaged flow field. These structures, along with high levels

Swirling flow and its influence on dc arcs in a duo-flow hybrid circuit breaker

International Nuclear Information System (INIS)

Kweon, K Y; Lee, H S; Yan, J D; Fang, M T C; Park, K Y

2009-01-01

The effects of swirling flow on the behaviour of dc SF 6 arcs in a duo-flow nozzle are computationally investigated in the electric current range 3-7 kA. A swirling flow is produced by the interaction of the magnetic field of a current-carrying coil and the plasma. Results show that a strong swirling flow is generated in regions where a large radial current density exists as a result of the conducting arc column rapidly changing its radial dimension. The presence of the swirling flow reduces the axis pressure, modifies the arc shape and slightly lowers the arc voltage (2-5%) in comparison with the case without considering the swirling flow. The different natures of swirling flows in a plasma jet/arc heater and in a hybrid circuit breaker are also discussed.

Experimental evidence of enhancement in the anticipation time by cascading

Energy Technology Data Exchange (ETDEWEB)

Baraik, Abhijit; Singh, Harpartap; Parmananda, P.

2014-04-01

We have studied and verified experimentally the enhancement in the anticipation time by cascading Chua's circuits. The experiments have been carried out in a one dimensional array of Chua's circuits (2 to 8) coupled unidirectionally, such that each one acts as a master for the next one. By doing so, it has been observed that the anticipation time increases with an increase in the array size. Moreover, the numerical simulations of an array of eighty Chua's circuits verify the experimental observations.

Demonstration of Li-based alloy coatings as low-voltage stable electron-emission surfaces for field-emission devices

International Nuclear Information System (INIS)

Auciello, O.; Krauss, A.R.; Gruen, D.M.; Shah, P.; Corrigan, T.; Kordesch, M.E.; Chang, R.P.; Barr, T.L.

1999-01-01

Alkali metals have extremely low work functions and are, therefore, expected to result in significant enhancement of the electron emission if they are used as coatings on Mo or Si microtip field-emission arrays (FEAs). However, the alkali metals are physically and chemically unstable in layers exceeding a few Angstrom in thickness. Maximum enhancement of electron emission occurs for alkali - metal layers 0.5 - 1 ML thick, but it is extremely difficult to fabricate and maintain such a thin alkali - metal coating. We present here an alternative means of producing chemically and thermally stable, self-replenishing lithium coatings approximately 1 ML thick, which results in a 13-fold reduction in the threshold voltage for electron emission compared with uncoated Si FEAs. copyright 1999 American Institute of Physics

Introduction on KPS's maintenance experience of the swirl vane assemblies of primary separators for SG model F in Korea

International Nuclear Information System (INIS)

Kim, Yong tae

2003-01-01

Recently, we had experienced to replace the Swirl Vane Assemblies of primary moisture separator for SG model F in Korea because of serious degradation (Thinning) in carbon steel swirl vane blades and carbon steel separator barrel wall adjacent to swirl vane blades. When the symptom was observed by us at the first time on the swirl vane assemblies, there were small or a bit clear erosion / or corrosion marks on the edge regions of the blades but within 3 cycles of operation, we found that those marks became holes which penetrated the most of swirl vane assemblies and even more seriously, some parts of the assemblies were worn-out. Therefore, we concluded that the speed of degradation would be very rapid and serious from the beginning stage. It had been assumed that these kinds of thinning problems would be due to FAC(Flow Accelerated Corrosion) because the plants having these problems are using a highly concentrated hydrazine for the water treatment of secondary side which lead to reduce the oxygen and pH in the water. What are more serious reasons will be that the swirl vane assemblies are very weak to FAC because they were made by a low concentrated chromium carbon steel and the assemblies would have to be under the operation conditions of the highly turbulent steam-water mixed fluid with the operating temperature of higher than 280 .deg. C. Potentially, the damaged swirl vane assemblies of the primary moisture separator may create bad influences for the plant operation because it may cause the rupture of SG Tubes and over-exceed fluid influx onto the turbine and etc. KPS had successfully performed the replacement of the degraded swirl vane assemblies through our own planning and preparation. This was the unique case in all over the world and I would like to introduce you about our unique repair experience to prepare an expected future situation as we see the similar problems in other model F SGs operating in Korea

Enhanced Light Narrow Transmission through Cascaded Metallic Structure with Periodic Aperture Arrays

International Nuclear Information System (INIS)

Yang Hong-Yan; Zhong Yan-Ru; Xiao Gong-Li; Zhang Zhen-Rong

2012-01-01

We present experimental and numerical studies on the enhanced light narrow transmission through cascaded Au/SiO x N y /Au aperture arrays by varying the refractive index and thickness of SiO x N y . It is found that the enhancement as well as narrowing of the optical transmission originates from the coupling role of surface plasmon polaritons. The results indicate that the transmission enhancement is highly dependent on the refractive index and thickness of SiO x N y . A higher transmission efficiency and narrower peak are obtained in Au/SiO 2.1 N 0.3 /Au structure with a small refractive index (1.6) and thin thickness (0.2 μm)

Magnetic Sorting of the Regolith on the Moon: Lunar Swirls

Science.gov (United States)

Pieters, C. M.; Garrick-Bethell, I.; Hemingway, D.

2014-12-01

All of the mysterious albedo features on the Moon called "lunar swirls" are associated with magnetic anomalies, but not all magnetic anomalies are associated with lunar swirls [1]. It is often hypothesized that the albedo markings are tied to immature regolith on the surface, perhaps due to magnetic shielding of the solar wind and prevention of normal space weathering of the soil. Although interaction of the solar wind with the surface at swirls is indeed affected by the local magnetic field [2], this does not appear to result in immature soils on the surface. Calibrated spectra from the Moon Mineralogy Mapper [M3] (in image format) demonstrate that the high albedo markings for swirls are simply not consistent with immature regolith as is now understood from detailed analyses of lunar samples [eg 3]. However, M3 data show that the high albedo features of swirls are distinct and quite different from normal soils (in both the highlands and the mare). They allexhibit a flatter continuum across the near-infrared, but the actual band strength of ferrous minerals shows little (if any) deviation [4]. Recent analyses of magnetic field direction at swirls [5] mimic the observed albedo patterns (horizontal surface fields in bright areas, vertical surface fields in dark lanes). When coupled with the optical properties of magnetic separates of lunar soils [6] and our knowledge that the magnetic component of the soil results from space weathering [3,6], we propose a new and very simple explanation for these enigmatic albedo markings: the lunar swirls result from magnetic sorting of a well developed regolith. With time, normal gardening of the soil over a magnetic anomaly causes some of the dark magnetic component of the soil to be gradually removed from regions (high albedo areas) and accumulated in others (dark lanes). We are modeling predicted sorting rates using realistic rates of dust production. If this mechanism is tenable, only the origin of these magnetic anomalies

Effect of intake swirl on the performance of single cylinder direct injection diesel engine

Science.gov (United States)

Sharma, Vinod Kumar; Mohan, Man; Mouli, Chandra

2017-11-01

In the present work, the effect of inlet manifold geometry and swirl intensity on the direct injection (DI) diesel engine performance was investigated experimentally. Modifications in inlet manifold geometry have been suggested to achieve optimized swirl for the better mixing of fuel with air. The intake swirl intensities of modified cylinder head were measured in swirl test rig at different valve lifts. Later, the overall performance of 435 CC DI diesel engine was measured using modified cylinder head. In addition, the performance of engine was compared for both modified and old cylinder head. For same operating conditions, the brake power and brake specific fuel consumption was improved by 6% and 7% respectively with modified cylinder head compared to old cylinder head. The maximum brake power of 9 HP was achieved for modified cylinder head. The results revealed that the intake swirl has great influence on engine performance.

Combustion characteristics and turbulence modeling of swirling reacting flow in solid fuel ramjet

Science.gov (United States)

Musa, Omer; Xiong, Chen; Changsheng, Zhou

2017-10-01

This paper reviews the historical studies have been done on the solid-fuel ramjet engine and difficulties associated with numerical modeling of swirling flow with combustible gases. A literature survey about works related to numerical and experimental investigations on solid-fuel ramjet as well as using swirling flow and different numerical approaches has been provided. An overview of turbulence modeling of swirling flow and the behavior of turbulence at streamline curvature and system rotation are presented. A new and simple curvature/correction factor is proposed in order to reduce the programming complexity of SST-CC turbulence model. Finally, numerical and experimental investigations on the impact of swirling flow on SFRJ have been carried out. For that regard, a multi-physics coupling code is developed to solve the problems of multi-physics coupling of fluid mechanics, solid pyrolysis, heat transfer, thermodynamics, and chemical kinetics. The connected-pipe test facility is used to carry out the experiments. The results showed a positive impact of swirling flow on SFRJ along with, three correlations are proposed.

Large-eddy simulation of swirling pulverized-coal combustion

Energy Technology Data Exchange (ETDEWEB)

Hu, L.Y.; Luo, Y.H. [Shanghai Jiaotong Univ. (China). School of Mechanical Engineering; Zhou, L.X.; Xu, C.S. [Tsinghua Univ., Beijing (China). Dept. of Engineering Mechanics

2013-07-01

A Eulerian-Lagrangian large-eddy simulation (LES) with a Smagorinsky-Lilly sub-grid scale stress model, presumed-PDF fast chemistry and EBU gas combustion models, particle devolatilization and particle combustion models are used to study the turbulence and flame structures of swirling pulverized-coal combustion. The LES statistical results are validated by the measurement results. The instantaneous LES results show that the coherent structures for pulverized coal combustion is stronger than that for swirling gas combustion. The particles are concentrated in the periphery of the coherent structures. The flame is located at the high vorticity and high particle concentration zone.

The generation of intense heat fluxes by electron bombardment to evaluate the use of swirl flow in the cooling of accelerator targets

International Nuclear Information System (INIS)

Genis, G.J.

1985-11-01

The thermal performance of isotope production targets for accelerators has been shown to be the limiting factor with regard to the cost of isotopes and the specific activity achievable. To allow the investigation of basic aspects of target cooling and the evaluation of certain target concepts off-line from accelerators, an electron bombardment system, including a radial electron accelerator (REA) in a diode configuration, was developed as heat source. Methods were developed to characterise the performance of the REA to supply a homogeneous heat flux to an axial target by which a technique for the construction of thermocouple placement holes in the body of the target can be evaluated from the measured temperatures. Having identified high velocity swirl flow as the most suitable technique to enhance the convective heat transfer in targets, experiments were conducted to determine the heat-transfer coefficient at high heat fluxes to high velocity swirl flow. The heat-transfer results substantiate the advantages of swirl flow for target cooling. Different correlations obtained indicate the importance of using the film properties instead of the bulk coolant properties in correlations and identify centrifugal convection as one of the most important heat transfer mechanisms in swirl flow

Shear layer flame stabilization sensitivities in a swirling flow

Directory of Open Access Journals (Sweden)

Christopher Foley

2017-03-01

Full Text Available A variety of different flame configurations and heat release distributions exist in high swirl, annular flows, due to the existence of inner and outer shear layers as well a vortex breakdown bubble. Each of these different configurations, in turn, has different thermoacoustic sensitivities and influences on combustor emissions, nozzle durability, and liner heating. This paper presents findings on the sensitivities of the outer shear layer- stabilized flames to a range of parameters, including equivalence ratio, bulkhead temperature, flow velocity, and preheat temperature. There is significant hysteresis for flame attachment/detachment from the outer shear layer and this hysteresis is also described. Results are also correlated with extinction stretch rate calculations based on detailed kinetic simulations. In addition, we show that the bulkhead temperature near the flame attachment point has significant impact on outer shear layer detachment. This indicates that understanding the heat transfer between the edge flame stabilized in the shear layer and the nozzle hardware is needed in order to predict shear layer flame stabilization limits. Moreover, it shows that simulations cannot simply assume adiabatic boundary conditions if they are to capture these transitions. We also show that the reference temperature for correlating these transitions is quite different for attachment and local blow off. Finally, these results highlight the deficiencies in current understanding of the influence of fluid mechanic parameters (e.g. velocity, swirl number on shear layer flame attachment. For example, they show that the seemingly simple matter of scaling flame transition points with changes in flow velocities is not understood.

Effect of swirling device on flow behavior in a supersonic separator for natural gas dehydration

DEFF Research Database (Denmark)

Wen, Chuang; Li, Anqi; Walther, Jens Honore

2016-01-01

is designed for an annular supersonic separator. The supersonic swirling separation flow of natural gas is calculated using the Reynolds Stress model. The results show that the viscous heating and strong swirling flow cause the adverse pressure in the annular channel, which may negatively affect......The supersonic separator is a revolutionary device to remove the condensable components from gas mixtures. One of the key issues for this novel technology is the complex supersonic swirling flow that is not well understood. A swirling device composed of an ellipsoid and several helical blades...

Effect of nozzle geometry for swirl type twin-fluid water mist nozzle on the spray characteristic

Energy Technology Data Exchange (ETDEWEB)

Yoon, Soon Hyun; Kim, Do Yeon; Kim, Dong Keon [Pusan National University, Busan (Korea, Republic of); Kim, Bong Hwan [Jinju National University, Jinju (Korea, Republic of)

2011-07-15

Experimental investigations on the atomization characteristics of twin-fluid water mist nozzle were conducted using particle image velocimetry (PIV) system and particle motion analysis system (PMAS). The twin-fluid water mist nozzles with swirlers designed two types of swirl angles such as 0 .deg. , 90 .deg. and three different size nozzle hole diameters such as 0.5mm, 1mm, 1.5mm were employed. The experiments were carried out by the injection pressure of water and air divided into 1bar, 2bar respectively. The droplet size of the spray was measured using PMAS. The velocity and turbulence intensity were measured using PIV. The velocity, turbulence intensity and SMD distributions of the sprays were measured along the centerline and radial direction. As the experimental results, swirl angle controlled to droplet sizes. It was found that SMD distribution decreases with the increase of swirl angle. The developed twin-fluid water mist nozzle was satisfied to the criteria of NFPA 750, Class 1. It was proven that the developed nozzle under low pressures could be applied to fire protection system.

Effect of nozzle geometry for swirl type twin-fluid water mist nozzle on the spray characteristic

International Nuclear Information System (INIS)

Yoon, Soon Hyun; Kim, Do Yeon; Kim, Dong Keon; Kim, Bong Hwan

2011-01-01

Experimental investigations on the atomization characteristics of twin-fluid water mist nozzle were conducted using particle image velocimetry (PIV) system and particle motion analysis system (PMAS). The twin-fluid water mist nozzles with swirlers designed two types of swirl angles such as 0 .deg. , 90 .deg. and three different size nozzle hole diameters such as 0.5mm, 1mm, 1.5mm were employed. The experiments were carried out by the injection pressure of water and air divided into 1bar, 2bar respectively. The droplet size of the spray was measured using PMAS. The velocity and turbulence intensity were measured using PIV. The velocity, turbulence intensity and SMD distributions of the sprays were measured along the centerline and radial direction. As the experimental results, swirl angle controlled to droplet sizes. It was found that SMD distribution decreases with the increase of swirl angle. The developed twin-fluid water mist nozzle was satisfied to the criteria of NFPA 750, Class 1. It was proven that the developed nozzle under low pressures could be applied to fire protection system

Sheet, ligament and droplet formation in swirling primary atomization

Directory of Open Access Journals (Sweden)

Changxiao Shao

2018-04-01

Full Text Available We report direct numerical simulations of swirling liquid atomization to understand the physical mechanism underlying the sheet breakup of a non-turbulent liquid swirling jet which lacks in-depth investigation. The volume-of-fluid (VOF method coupled with adapted mesh refinement (AMR technique in GERRIS code is employed in the present simulation. The mechanisms of sheet, ligament and droplet formation are investigated. It is observed that the olive-shape sheet structure is similar to the experimental result qualitatively. The numerical results show that surface tension, pressure difference and swirling effect contribute to the contraction and extension of liquid sheet. The ligament formation is partially at the sheet rim or attributed to the extension of liquid hole. Especially, the movement of hairpin vortex exerts by an anti-radial direction force to the sheet surface and leads to the sheet thinness. In addition, droplet formation is attributed to breakup of ligament and central sheet.

Sheet, ligament and droplet formation in swirling primary atomization

Science.gov (United States)

Shao, Changxiao; Luo, Kun; Chai, Min; Fan, Jianren

2018-04-01

We report direct numerical simulations of swirling liquid atomization to understand the physical mechanism underlying the sheet breakup of a non-turbulent liquid swirling jet which lacks in-depth investigation. The volume-of-fluid (VOF) method coupled with adapted mesh refinement (AMR) technique in GERRIS code is employed in the present simulation. The mechanisms of sheet, ligament and droplet formation are investigated. It is observed that the olive-shape sheet structure is similar to the experimental result qualitatively. The numerical results show that surface tension, pressure difference and swirling effect contribute to the contraction and extension of liquid sheet. The ligament formation is partially at the sheet rim or attributed to the extension of liquid hole. Especially, the movement of hairpin vortex exerts by an anti-radial direction force to the sheet surface and leads to the sheet thinness. In addition, droplet formation is attributed to breakup of ligament and central sheet.

Cascade enzymatic reactions for efficient carbon sequestration.

Science.gov (United States)

Xia, Shunxiang; Zhao, Xueyan; Frigo-Vaz, Benjamin; Zheng, Wenyun; Kim, Jungbae; Wang, Ping

2015-04-01

Thermochemical processes developed for carbon capture and storage (CCS) offer high carbon capture capacities, but are generally hampered by low energy efficiency. Reversible cascade enzyme reactions are examined in this work for energy-efficient carbon sequestration. By integrating the reactions of two key enzymes of RTCA cycle, isocitrate dehydrogenase and aconitase, we demonstrate that intensified carbon capture can be realized through such cascade enzymatic reactions. Experiments show that enhanced thermodynamic driving force for carbon conversion can be attained via pH control under ambient conditions, and that the cascade reactions have the potential to capture 0.5 mol carbon at pH 6 for each mole of substrate applied. Overall it manifests that the carbon capture capacity of biocatalytic reactions, in addition to be energy efficient, can also be ultimately intensified to approach those realized with chemical absorbents such as MEA. Copyright © 2015 Elsevier Ltd. All rights reserved.

Energy and exergy analysis of a new ejector enhanced auto-cascade refrigeration cycle

International Nuclear Information System (INIS)

Yan, Gang; Chen, Jiaheng; Yu, Jianlin

2015-01-01

Highlights: • A new ejector enhanced auto-cascade refrigeration cycle using R134a/R23 is proposed. • The performance of new and basic cycles is compared by simulation method. • The new cycle outperforms the basic cycle in both energetic and exergy aspects. • Both cycles have optimum mixture compositions to obtain optimal performance. - Abstract: A new ejector enhanced auto-cascade refrigeration cycle using R134a/R23 refrigerant mixture is proposed in this paper. In the new cycle, an ejector is used to recover part of the work that would otherwise be lost in the throttling processes. The performance comparison between the new cycle and a basic auto-cascade refrigeration cycle is carried out based on the first and second laws of thermodynamics. The simulation results show that both the coefficient of performance and exergy efficiency of the new cycle can be improved by 8.42–18.02% compared with those of the basic cycle at the same operation conditions as the ejector has achieved pressure lift ratios of 1.12–1.23. It is found that in the new cycle, the highest exergy destruction occurs in the compressor followed by the condenser, cascade condenser, expansion valve, ejector and evaporator. The effect of some main parameters on the cycle performance is further investigated. The results show that for the new cycle, the achieved performance improvement over the basic cycle is also dependent on the mixture composition and the vapor quality at the condenser outlet. The coefficient of performance improvement of the new cycle over the basic cycle degrades with increasing vapor quality. In addition, there exists an optimum mixture composition to obtain the maximum coefficient of performance for the new cycle when other operation conditions are given. The optimum mixture composition of both cycles may be fixed at about 0.5 under the given evaporating temperature.

On-chip plasmonic cavity-enhanced spontaneous emission rate at the zero-phonon line

DEFF Research Database (Denmark)

Siampour, Hamidreza; Kumar, Shailesh; Bozhevolnyi, Sergey I.

Highly confined surface plasmon polariton (SPP) modes can be utilized to enhance light-matter interaction at the single emitter level of quantum optical systems [1-4]. Dielectric-loaded SPP waveguides (DLSPPWs) confine SPPs laterally with relatively low propagation loss, enabling to benefit both ...... and an up to 42-fold spontaneous emission rate enhancement at the zero-phonon line (a ∼7-fold resonance enhancement in addition to a ∼6-fold broadband enhancement) is achieved, revealing the potential of our approach for on-chip realization of quantum-optical networks....... from a large Purcell factor and from a large radiative efficiency (low quenching rates) [1, 2]. In this work, we present a DLSPPW-based Bragg cavity resonator to direct emission from a single diamond nitrogen vacancy (NV) center into the zero-phonon line (Fig. 1). A quality factor of ∼70 for the cavity...

Enhancing monochromatic multipole emission by a subwavelength enclosure of degenerate Mie resonances

KAUST Repository

Zhao, Jiajun

2017-07-06

Sound emission is inefficient at low frequencies as limited by source size. This letter presents enhancing emission of monochromatic monopole and multipole sources by enclosing the source with a subwavelength circular enclosure filled of an anisotropic material of a low radial sound speed. The anisotropy is associated with an infinite tangential density along the azimuth. Numerical simulations show that emission gain is produced at frequencies surrounding degenerate Mie resonant frequencies of the enclosure, and meanwhile the radiation directivity pattern is well preserved. The degeneracy is theoretically analyzed. A realization of the material is suggested by using a space-coiling structure.

Experiments and computations on coaxial swirling jets with centerbody in an axisymmetric combustor

International Nuclear Information System (INIS)

Chao, Y.C.; Ho, W.C.; Lin, S.K.

1987-01-01

Experiments and computations of turbulent, confined, coannular swirling flows have been performed in a model combustor. Numerical results are obtained by means of a revised two-equation model of turbulence. The combustor consists of two confined, concentric, swirling jets and a centerbody at the center of the inlet. Results are reported for cold flow conditions under co- and counter-swirl. The numerical results agree with the experimental data under both conditions. The size of the central recirculation zone is dominated by the strength of the outer swirl. A two-cell recirculation zone may be formed due to the presence of the swirler hub. The mechanism of interaction between the separation bubble at the hub of the swirler and the central recirculation zone due to vortex breakdown is also investigated. 18 references

Microscopic cascading of second-order molecular nonlinearity: New design principles for enhancing third-order nonlinearity.

Science.gov (United States)

Baev, Alexander; Autschbach, Jochen; Boyd, Robert W; Prasad, Paras N

2010-04-12

Herein, we develop a phenomenological model for microscopic cascading and substantiate it with ab initio calculations. It is shown that the concept of local microscopic cascading of a second-order nonlinearity can lead to a third-order nonlinearity, without introducing any new loss mechanisms that could limit the usefulness of our approach. This approach provides a new molecular design protocol, in which the current great successes achieved in producing molecules with extremely large second-order nonlinearity can be used in a supra molecular organization in a preferred orientation to generate very large third-order response magnitudes. The results of density functional calculations for a well-known second-order molecule, (para)nitroaniline, show that a head-to-tail dimer configuration exhibits enhanced third-order nonlinearity, in agreement with the phenomenological model which suggests that such an arrangement will produce cascading due to local field effects.

Heat transfer study of water-cooled swirl tubes for neutral beam targets

International Nuclear Information System (INIS)

Kim, J.; Davis, R.C.; Gambill, W.R.; Haselton, H.H.

1977-01-01

Heat transfer considerations of water-cooled swirl-tubes including heat transfer correlations, burnout data, and 2-D considerations are presented in connection with high power neutral beam target applications. We also discuss performance results of several swirl tube targets in use at neutral beam development facilities

Defect production in simulated cascades: Cascade quenching and short-term annealing

International Nuclear Information System (INIS)

Heinisch, H.L.

1983-01-01

Defect production in displacement cascades in copper has been modeled using the MARLOWE code to generate cascades and the stochastic annealing code ALSOME to simulate cascade quenching and short-term annealing of isolated cascades. Quenching is accomplished by using exaggerated values for defect mobilities and for critical reaction distances in ALSOME for a very short time. The quenched cascades are then short-term annealed with normal parameter values. The quenching parameter values were empirically determined by comparison with results of resistivity measurements. Throughout the collisional, quenching and short-term annealing phases of cascade development, the high energy cascades continue to behave as a collection of independent lower energy lobes. For recoils above about 30 keV the total number of defects and the numbers of free defects scale with the damage energy. As the energy decreases from 30 keV, defect production varies with the changing nature of the cascade configuration, resulting in more defects per unit damage energy. The simulated annealing of a low fluence of interacting cascades revealed an interstitial shielding effect on depleted zones during Stage I recovery. (orig.)

Studi Variasi Beab Pendinginan pada Evaporator pada Low Stage Sistem Refrigerasi Cascade R22-404A

Directory of Open Access Journals (Sweden)

Moch. Munirul Ichsan

2013-03-01

Full Text Available Saat ini banyak dibutuhkan sistem pendingingan yang memiliki temperatur rendah dan kapasitas yang besar. Maka dari itu digunakanlah sistem refrigerasi cascade yang disusun atas dua stage yaitu high stage dan low stage. Alat pengujian sistem refrigerasi cascade ini menggunakan refrigerant R-22 di high stage dan R-404A di low stage yang dihubungkan dengan heat exchanger tipe konsentrik untuk memindahkan kalor dari kondensor low stage menuju evaporator high stage. Dalam melakukan pengujian diberikan beban pendinginan sebanyak sepuluh variasi heater. Dengan variasi beban mulai dari tanpa pemberian beban sampai beban heater sebesar 203,72watt. Sehingga setelah melakukan penelitian ini didapatkan hasil yang optimum pada pembebanan 203,72watt berupa COPcascade 1,06213, εeffectiveness 0,78313, temperatur evaporator minimum -26,9 °C. Dan dari hasil ini menunjukkan desain heat exchanger tipe konsentrik sangat menentukan dalam perpindahan panas, sehingga performa dari sistem refrigerasi cascade sangat ditentukan oleh tingkat perpindahan kalor pada heat exchanger yang diketahui melalui nilai εeffectiveness dan NTU.

M3 spectral analysis of lunar swirls and the link between optical maturation and surface hydroxyl formation at magnetic anomalies

Science.gov (United States)

Kramer, G.Y.; Besse, S.; Dhingra, D.; Nettles, J.; Klima, R.; Garrick-Bethell, I.; Clark, Roger N.; Combe, J.-P.; Head, J. W.; Taylor, L.A.; Pieters, C.M.; Boardman, J.; McCord, T.B.

2011-01-01

We examined the lunar swirls using data from the Moon Mineralogy Mapper (M3). The improved spectral and spatial resolution of M3 over previous spectral imaging data facilitates distinction of subtle spectral differences, and provides new information about the nature of these enigmatic features. We characterized spectral features of the swirls, interswirl regions (dark lanes), and surrounding terrain for each of three focus regions: Reiner Gamma, Gerasimovich, and Mare Ingenii. We used Principle Component Analysis to identify spectrally distinct surfaces at each focus region, and characterize the spectral features that distinguish them. We compared spectra from small, recent impact craters with the mature soils into which they penetrated to examine differences in maturation trends on- and off-swirl. Fresh, on-swirl crater spectra are higher albedo, exhibit a wider range in albedos and have well-preserved mafic absorption features compared with fresh off-swirl craters. Albedoand mafic absorptions are still evident in undisturbed, on-swirl surface soils, suggesting the maturation process is retarded. The spectral continuum is more concave compared with off-swirl spectra; a result of the limited spectral reddening being mostly constrained to wavelengths less than ∼1500 nm. Off-swirl spectra show very little reddening or change in continuum shape across the entire M3 spectral range. Off-swirl spectra are dark, have attenuated absorption features, and the narrow range in off-swirl albedos suggests off-swirl regions mature rapidly. Spectral parameter maps depicting the relative OH surface abundance for each of our three swirl focus regions were created using the depth of the hydroxyl absorption feature at 2.82 μm. For each of the studied regions, the 2.82 μm absorption feature is significantly weaker on-swirl than off-swirl, indicating the swirls are depleted in OH relative to their surroundings. The spectral characteristics of the swirls and adjacent terrains

The modified swirl sedimentation tanks for water purification.

Science.gov (United States)

Ochowiak, Marek; Matuszak, Magdalena; Włodarczak, Sylwia; Ancukiewicz, Małgorzata; Krupińska, Andżelika

2017-03-15

This paper discusses design, evaluation, and application for the use of swirl/vortex technologies as liquid purification system. A study was performed using modified swirl sedimentation tanks. The vortex separators (OW, OWK, OWR and OWKR) have been studied under laboratory conditions at liquid flow rate from 2.8⋅10 -5 to 5.1⋅10 -4 [m 3 /s]. The pressure drop and the efficiency of purification of liquid stream were analyzed. The suspended particles of different diameters were successfully removed from liquid with the application of swirl chambers of proposed constructions. It was found that damming of liquid in the tank increases alongside liquid stream at the inlet and depends on the tank construction. The efficiency of the sedimentation tanks increases alongside the diameters of solid particles and decrease in the liquid flow rate. The best construction proved to be the OWR sedimentation tank due to smallest liquid damming, even at high flow rates, and the highest efficiency of the purification liquid stream for solid particles of the smallest diameter. The proposed solution is an alternative to the classical constructions of sedimentation tanks. Copyright © 2016 Elsevier Ltd. All rights reserved.

Imulation of temperature field in swirl pulverized coal boiler

Science.gov (United States)

Lv, Wei; Wu, Weifeng; Chen, Chen; Chen, Weifeng; Qi, Guoli; Zhang, Songsong

2018-02-01

In order to achieve the goal of energy saving and emission reduction and energy efficient utilization, taking a 58MW swirl pulverized coal boiler as the research object, the three-dimensional model of the rotor is established. According to the principle of CFD, basic assumptions and boundary conditions are selected, the temperature field in the furnace of 6 kinds of working conditions is numerically solved, and the temperature distribution in the furnace is analyzed. The calculation results show that the temperature of the working condition 1 is in good agreement with the experimental data, and the error is less than 10%,the results provide a theoretical basis for the following calculation. Through the comparison of the results of the 6 conditions, it is found that the working condition 3 is the best operating condition of the pulverized coal boiler.

Numerical modelling of swirling diffusive flames

Directory of Open Access Journals (Sweden)

Parra-Santos Teresa

2016-01-01

Full Text Available Computational Fluid Dynamics has been used to study the mixing and combustion of two confined jets whose setup and operating conditions are those of the benchmark of Roback and Johnson. Numerical model solves 3D transient Navier Stokes for turbulent and reactive flows. Averaged velocity profiles using RNG swirl dominated k-epsilon model have been validated with experimental measurements from other sources for the non reactive case. The combustion model is Probability Density Function. Bearing in mind the annular jet has swirl number over 0.5, a vortex breakdown appears in the axis of the burner. Besides, the sudden expansion with a ratio of 2 in diameter between nozzle exits and the test chamber produces the boundary layer separation with the corresponding torus shape recirculation. Contrasting the mixing and combustion models, the last one produces the reduction of the vortex breakdown.

Influence of piston displacement on the scavenging and swirling flow in two-stroke diesel engines

DEFF Research Database (Denmark)

Obeidat, Anas; Haider, Sajjad; Ingvorsen, Kristian Mark

We study the effect of piston motion on the in-cylinder swirling flow in a low speed, large two-stroke marine diesel engine. The work involves experimental, and numerical simulation using OpenFOAM platform, Large Eddy Simulation was used with three different models, One equation Eddy, Dynamic One...

Large eddy simulations of flow and mixing in jets and swirl flows: application to a gas turbine

Energy Technology Data Exchange (ETDEWEB)

Schluter, J.U.

2000-07-01

Large Eddy Simulations (LES) are an accepted tool in turbulence research. Most LES investigations deal with low Reynolds-number flows and have a high spatial discretization, which results in high computational costs. To make LES applicable to industrial purposes, the possibilities of LES to deliver results with low computational costs on high Reynolds-number flows have to be investigated. As an example, the cold flow through the Siemens V64.3A.HR gas turbine burner shall be examined. It is a gas turbine burner of swirl type, where the fuel is injected on the surface of vanes perpendicular to the main air flow. The flow regime of an industrial gas turbine is governed by several flow phenomena. The most important are the fuel injection in form of a jet in cross flow (JICF) and the swirl flow issuing into a combustion chamber. In order to prove the ability of LES to deal with these flow phenomena, two numerical investigations were made in order to reproduce the results of experimental studies. The first one deals with JICF. It will be shown that the reproduction of three different JICF is possible with LES on meshes with a low number of mesh points. The results are used to investigate the flow physics of the JICF, especially the merging of two adjacent JICFs. The second fundamental investigation deals with swirl flows. Here, the accuracy of an axisymmetric assumption is examined in detail by comparing it to full 3D LES computations and experimental data. Having demonstrated the ability of LES and the flow solver to deal with such complex flows with low computational efforts, the LES approach is used to examine some details of the burner. First, the investigation of the fuel injection on a vane reveals that the vane flow tends to separate. Furthermore the tendency of the fuel jets to merge is shown. Second, the swirl flow in the combustion chamber is computed. For this investigation the vanes are removed from the burner and swirl is imposed as a boundary condition. As

Geophysical applicability of aerosol size distribution measurements using cascade impactors and proton induced X-ray emission

International Nuclear Information System (INIS)

Van Grieken, R.E.; Johansson, T.B.; Akselsson, K.R.; Winchester, J.W.; Nelson, J.W.; Chapman, K.R.

1976-01-01

Proton Induced X-ray Emission, (PIXE), is capable of high precision analysis for trace element components of aerosol particle size fractions sampled by cascade impactor. A statistical evaluation of data quality has been carried out in order to distinguish between analytical uncertainties in the PIXE procedure, errors caused by cascade impactor performance and by other factors in the sampling procedure, and geophysical causes of differences in composition and particle size distributions of the elements in aerosols. Replicate analyses and simultaneous samplings taken in north Florida and St. Louis have been used for the data evaluation. In addition to the analytical error the sampling procedure contributes an error of approximately 10% to be added quadratically. The resulting precision is sufficient to evaluate the data in geophysical terms. This is illustrated by means of sample sets taken simultaneously in an urban, forest and coastal environment of the same region. (author)

Basic characteristics of a low uranium enrichment cascade by centrifugation, (2)

International Nuclear Information System (INIS)

Kai, Tsunetoshi

1975-01-01

The theory for a cascade of centrifuges described in the preceding report of the same general title is further developed. First, equations describing the distributions of the flow and the mole concentration are derived from the material balance relations for a square cascade. Corresponding equations are next obtained to cover a squared-off cascade consisting of a series of square cascades. A computer program is outlined which makes it possible to obtain the shape of the most efficient squared-off cascade. The efficiency of the current form of squared-off centrifuge cascade with reflux pipes is found to be lower than obtainable with gaseous diffusion. The efficiency can be improved by the adoption of a tapered squared-off cascade with centrifuges provided with eccentric cuts to take the place of reflux pipes. The dynamic characteristics are also discussed. Analysis of the start-up behavior reveals that the equilibrium time of the centrifuge cascade is much shorter than for a coresponding gaseous diffusion cascade, and that the mole concentration of the product rapidly rises to attain steady state condition. It is also found that even when the feed flow rate fluctuates, the mole concentration of the product is relatively stable. The effect of a centrifuge failure in the cascade is examined. The optimum mole concentration for the waste effluent discarded from the cascade is calculated from the viewpoint of cost. (auth.)

Spray structure of a pressure-swirl atomizer for combustion applications

OpenAIRE

Jicha Miroslav; Jedelsky Jan; Durdina Lukas

2012-01-01

In the present work, global as well as spatially resolved parameters of a spray produced by a pressure-swirl atomizer are obtained. Small pressure-swirl atomizer for aircraft combustion chambers was run on a newly designed test bench with Jet A-1 kerosene type aviation fuel. The atomizer was tested in four regimes based on typical operation conditions of the engine. Spray characteristics were studied using two optical measurement systems, Particle Image velocimetry (PIV) and Phase-Doppler Par...

Analysis of Effect of Inlet Swirl In Four Stroke Single Cylinder Diesel Engine With Different Inlet Valve Geometries Using CFD

Science.gov (United States)

Gobinath, R.; Mathiselvan, G.; Kumarasubramanian, R.

2017-05-01

Flow patterns are essential to ensure that the engine can produce high performance with the presence of swirl and tumble effect inside the engine cylinder. This paper provides the simulation of air is simulated in the software to predict the flow pattern. The flow pattern is simulated by using the steady state pressure based solver. The domain used for the simulations predicated on the particular engine parameters. Mistreatment the CFD problem solver ANSYS FLUENT, the CFD simulation is earned for four totally different geometries of the valve. The geometries consist of Horizontal, Vertical, curve and arc springs. In this simulation, only the intake strokes are simulated. From this results show that the velocity of the air flow is high during the sweeps the intake stroke takes place. This situation is produced more swirls and tumble effect during the compression, hence enhancing the combustion rate in a whole region of the clearance volume of the engine cylinder. This will initiate to the production of tumble and swirl in the engine cylinder.

Photon enhanced thermionic emission

Science.gov (United States)

Schwede, Jared; Melosh, Nicholas; Shen, Zhixun

2014-10-07

Photon Enhanced Thermionic Emission (PETE) is exploited to provide improved efficiency for radiant energy conversion. A hot (greater than 200.degree. C.) semiconductor cathode is illuminated such that it emits electrons. Because the cathode is hot, significantly more electrons are emitted than would be emitted from a room temperature (or colder) cathode under the same illumination conditions. As a result of this increased electron emission, the energy conversion efficiency can be significantly increased relative to a conventional photovoltaic device. In PETE, the cathode electrons can be (and typically are) thermalized with respect to the cathode. As a result, PETE does not rely on emission of non-thermalized electrons, and is significantly easier to implement than hot-carrier emission approaches.

Anisotropic Characteristics of Turbulence Dissipation in Swirling Flow: A Direct Numerical Simulation Study

Directory of Open Access Journals (Sweden)

Xingtuan Yang

2015-01-01

Full Text Available This study investigates the anisotropic characteristics of turbulent energy dissipation rate in a rotating jet flow via direct numerical simulation. The turbulent energy dissipation tensor, including its eigenvalues in the swirling flows with different rotating velocities, is analyzed to investigate the anisotropic characteristics of turbulence and dissipation. In addition, the probability density function of the eigenvalues of turbulence dissipation tensor is presented. The isotropic subrange of PDF always exists in swirling flows relevant to small-scale vortex structure. Thus, with remarkable large-scale vortex breakdown, the isotropic subrange of PDF is reduced in strongly swirling flows, and anisotropic energy dissipation is proven to exist in the core region of the vortex breakdown. More specifically, strong anisotropic turbulence dissipation occurs concentratively in the vortex breakdown region, whereas nearly isotropic turbulence dissipation occurs dispersively in the peripheral region of the strong swirling flows.

Impact of Vitiation on a Swirl-Stabilized and Premixed Methane Flame

Directory of Open Access Journals (Sweden)

Mao Li

2017-10-01

Full Text Available Vitiation refers to the condition where the oxygen concentration in the air is reduced due to the mix of dilution gas. The vitiation effects on a premixed methane flame were investigated on a swirl-stabilized gas turbine model combustor under atmospheric pressure. The main purpose is to analyze the combustion stability and CO emission performance in vitiated air and compare the results with the flame without vitiation. The N2, CO2, and H2O (steam were used as the dilution gas. Measurements were conducted in a combustor inlet temperature of 384 K and 484 K. The equivalence ratio was varied from stoichiometric conditions to the LBO (Lean Blowout limits where the flame was physically blown out from the combustor. The chemical kinetics calculation was performed with Chemkin software to analyze the vitiation effects on the flame reaction zone. Based on the calculation results, the changes in the temperature gradient, CO concentration, and active radicals across the flame reaction zone were identified. The time-averaged CH chemiluminescence images were recorded and the results indicated the features of the flame shape and location. The CH signal intensity provided the information about the heat-release zone in the combustor. The combustion LBO limits were measured and the vitiation of CO2 and H2O were found to have a stronger impact to elevate the LBO limits than N2. Near the LBO limits, the instability of the flame reaction was revealed by the high-speed chemiluminescence imaging and the results were analyzed by FFT (Fast Fourier Transfer. CO emission was measured with a water-cooled probe which is located at the exit of the combustor. The combustion vitiation has been found to have the compression effect on the operation range for low CO emission. However, this compression effect could be compensated by improving the combustor inlet temperature.

Experimental study of gas entrainment from surface swirl

Energy Technology Data Exchange (ETDEWEB)

Moudjed, B., E-mail: brahim.moudjed@cea.fr; Excoffon, J.; Riva, R.; Rossi, L., E-mail: lionel.rossi@cea.fr

2016-12-15

Gas entrainment from surface swirls is characterized using water experiments. A free surface shear flow is generated in an open channel flow. A suction nozzle is set at the bottom of the test section to induce a downward flow and provoke gas entrainment. An important originality of these experiments is the possibility to change the inlet condition so as to generate different turbulent shear flows. This is done by adding obstacles of different sizes and shapes at the end of a flat plate separating the inlet flow from a “stagnant” water area. Velocity fields and profiles, measured with the PIV technique, are provided both to describe the inlet conditions corresponding to various geometries and flow rates, and to characterize the temporal average shear flow generated within the centre part of the channel. Gas entrainment mappings are established from direct observations of the different flow configurations. These new results show that the threshold for the suction velocities required to entrain gas are similar for the configurations with small obstacles and the flat plate configuration triggering a standard shear flow. Increasing the size of the obstacles promotes gas entrainment and reduces the threshold values of the suction velocity to trigger gas entrainment. Shadowgraphy with image processing is used to present new results characterizing the geometrical properties of surface swirls and the quantity of gas entrained. Inlet configurations with obstacles generate larger surface swirls which move upstream from the suction nozzle centre whereas they are situated downstream with the flat plate configuration. Moreover, dimensionless power laws are found to be good approximations for the surface swirl width and the quantity of gas entrained. In addition to provide new insights about gas entrainment in analytical configurations relevant to Sodium cooled fast nuclear reactor, these results should provide different test cases for the validation of MCFD codes.

Investigation of turbulent swirling jet-flames by PIV / OH PLIF / HCHO PLIF

Science.gov (United States)

Lobasov, A. S.; Chikishev, L. M.

2018-03-01

The present paper reports on the investigation of fuel-lean and fuel-rich turbulent combustion in a high-swirl jet. Swirl rate of the flow exceeded a critical value for breakdown of the swirling jet’s vortex core and formation of the recirculation zone at the jet axis. The measurements were performed by the stereo PIV, OH PLIF and HCHO PLIF techniques, simultaneously. The Reynolds number based on the flow rate and viscosity of the air was fixed as 5 000 (the bulk velocity was U 0 = 5 m/s). Three cases of the equivalence ratio ϕ of the mixture issuing from the nozzle-burner were considered, viz., 0.7, 1.4 and 2.5. The latter case corresponded to a lifted flame of fuel-rich swirling jet flow, partially premixed with the surrounding air. In all cases the flame front was subjected to deformations due to large-scale vortices, which rolled-up in the inner (around the central recirculation zone) and outer (between the annular jet core and surrounding air) mixing layers.

Influence of piston position on the scavenging and swirling flow in two-stoke diesel engines

DEFF Research Database (Denmark)

Obeidat, Anas; Haider, Sajjad; Meyer, Knud Erik

2011-01-01

We study the eect of piston position on the in-cylinder swirling flow in a low speed large two-stroke marine diesel engine model. We are using Large Eddy Simulations in OpenFOAM, with three different models for the turbulent flow: a one equation model (OEM), a dynamic one equation model (DOEM...

The capacity of the cascaded fading channel in the low power regime

KAUST Repository

Benkhelifa, Fatma

2014-04-01

In this paper, we present a simple way to compute the ergodic capacity of cascaded channels with perfect channel state information at both the transmitter and the receiver. We apply our generic results to the Rayleigh-double fading channel, and to the free-space optical channel in the presence of pointing errors and we express their low signal-to-noise ratio capacities. We mainly focus on the low signal-to-noise ratio range.

Analysis of residual swirl in tangentially-fired natural gas-boiler

International Nuclear Information System (INIS)

Hasril Hasini; Muhammad Azlan Muad; Mohd Zamri Yusoff; Norshah Hafeez Shuaib

2010-01-01

This paper describes the investigation on residual swirl flow in a 120 MW natural gas, full-scale, tangential-fired boiler. Emphasis is given towards the understanding of the behavior of the combustion gas flow pattern and temperature distribution as a result of the tangential firing system of the boiler. The analysis was carried out based on three-dimensional computational modeling on full scale boiler with validation from key design parameter as well as practical observation. Actual operating parameters of the actual boiler are taken as the boundary conditions for this modeling. The prediction of total heat flux was found to be in agreement with the key design parameter while the residual swirl predicted at the upper furnace agrees qualitatively with the practical observation. Based on this comparison, detail analysis was carried out for comprehensive understanding on the generation and destruction of the residual swirl behavior in boiler especially those with high capacity. (author)

Spontaneous emission enhancement of colloidal perovskite nanocrystals

Science.gov (United States)

Yang, Zhili; Waks, Edo

Halide perovskite semiconductors have emerged as prominent photovoltaic materials since their high conversion efficiency and promising light emitting materials in optoelectronics. In particular, easy-to-fabricated colloidal perovskite nanocrystals based on CsPbX3 quantum dots has been intensively investigated recently. Their luminescent wavelength could be tuned precisely by their chemical composition and size of growth. This opens new applications including light-emitting diodes, optical amplifiers and lasing since their promising performance as emitters. However, this potentially high-efficient emitter and gain material has not been fully investigated and realized in integrated photonic structures. Here we demonstrate Purcell enhancement effect of CsPbBr3 perovskite nanocrystals by coupling to an optimized photonic crystal nanobeam cavity as a first crucial step towards realization of integrated on-chip coherent light source with low energy consumption. We show clearly highly-enhanced photoluminescent spectrum and an averaged Purcell enhancement factor of 2.9 is achieved when they are coupled to nanobeam photonic crystal cavities compared to the ones on unpatterned surface in our lifetime measurement. Our success in enhancement of emission from CsPbX3 perovskite nanocrystals paves the way towards the realization of efficient light sources for integrated optoelectronic devices with low energy consumption.

Numerical investigation on the regression rate of hybrid rocket motor with star swirl fuel grain

Science.gov (United States)

Zhang, Shuai; Hu, Fan; Zhang, Weihua

2016-10-01

Although hybrid rocket motor is prospected to have distinct advantages over liquid and solid rocket motor, low regression rate and insufficient efficiency are two major disadvantages which have prevented it from being commercially viable. In recent years, complex fuel grain configurations are attractive in overcoming the disadvantages with the help of Rapid Prototyping technology. In this work, an attempt has been made to numerically investigate the flow field characteristics and local regression rate distribution inside the hybrid rocket motor with complex star swirl grain. A propellant combination with GOX and HTPB has been chosen. The numerical model is established based on the three dimensional Navier-Stokes equations with turbulence, combustion, and coupled gas/solid phase formulations. The calculated fuel regression rate is compared with the experimental data to validate the accuracy of numerical model. The results indicate that, comparing the star swirl grain with the tube grain under the conditions of the same port area and the same grain length, the burning surface area rises about 200%, the spatially averaged regression rate rises as high as about 60%, and the oxidizer can combust sufficiently due to the big vortex around the axis in the aft-mixing chamber. The combustion efficiency of star swirl grain is better and more stable than that of tube grain.

Near-infrared H2 emission from Herbig-Haro objects. I. A survey of low excitation objects

International Nuclear Information System (INIS)

Schwartz, R.D.; Cohen, M.; Williams, P.M.

1987-01-01

A survey for H 2 1-0 S(1) emission in 16 Herbig-Haro (HH) objects and three exciting stars for HH objects is reported. Eleven HH objects which show low-excitation optical spectra exhibit H 2 emission. One object (HH 43) is more than twice as bright as any previously reported HH object. In addition, spectra in the range 1.6-2.55 microns are reported for HH 43 and HH 120, and a 2.0-2.55 micron spectrum is presented for HH 26. The spectra yield estimates of the H 2 density and temperature ranges in these objects. The role of ultraviolet H 2 emission-line fluorescence in HH 43 with respect to cascading among excited vibrational states of the ground electronic state is discussed. Models which may account for the combined ultraviolet, optical, and near-IR spectra of HHs are briefly analyzed. 35 references

Modeling of classical swirl injector dynamics

Science.gov (United States)

Ismailov, Maksud M.

The knowledge of the dynamics of a swirl injector is crucial in designing a stable liquid rocket engine. Since the swirl injector is a complex fluid flow device in itself, not much work has been conducted to describe its dynamics either analytically or by using computational fluid dynamics techniques. Even the experimental observation is limited up to date. Thus far, there exists an analytical linear theory by Bazarov [1], which is based on long-wave disturbances traveling on the free surface of the injector core. This theory does not account for variation of the nozzle reflection coefficient as a function of disturbance frequency, and yields a response function which is strongly dependent on the so called artificial viscosity factor. This causes an uncertainty in designing an injector for the given operational combustion instability frequencies in the rocket engine. In this work, the author has studied alternative techniques to describe the swirl injector response, both analytically and computationally. In the analytical part, by using the linear small perturbation analysis, the entire phenomenon of unsteady flow in swirl injectors is dissected into fundamental components, which are the phenomena of disturbance wave refraction and reflection, and vortex chamber resonance. This reveals the nature of flow instability and the driving factors leading to maximum injector response. In the computational part, by employing the nonlinear boundary element method (BEM), the author sets the boundary conditions such that they closely simulate those in the analytical part. The simulation results then show distinct peak responses at frequencies that are coincident with those resonant frequencies predicted in the analytical part. Moreover, a cold flow test of the injector related to this study also shows a clear growth of instability with its maximum amplitude at the first fundamental frequency predicted both by analytical methods and BEM. It shall be noted however that Bazarov

Investigation of Swirling Flow in Rod Bundle Subchannels Using Computational Fluid Dynamics

International Nuclear Information System (INIS)

Holloway, Mary V.; Beasley, Donald E.; Conner, Michael E.

2006-01-01

The fluid dynamics for turbulent flow through rod bundles representative of those used in pressurized water reactors is examined using computational fluid dynamics (CFD). The rod bundles of the pressurized water reactor examined in this study consist of a square array of parallel rods that are held on a constant pitch by support grids spaced axially along the rod bundle. Split-vane pair support grids are often used to create swirling flow in the rod bundle in an effort to improve the heat transfer characteristics for the rod bundle during both normal operating conditions and in accident condition scenarios. Computational fluid dynamics simulations for a two subchannel portion of the rod bundle were used to model the flow downstream of a split-vane pair support grid. A high quality computational mesh was used to investigate the choice of turbulence model appropriate for the complex swirling flow in the rod bundle subchannels. Results document a central swirling flow structure in each of the subchannels downstream of the split-vane pairs. Strong lateral flows along the surface of the rods, as well as impingement regions of lateral flow on the rods are documented. In addition, regions of lateral flow separation and low axial velocity are documented next to the rods. Results of the CFD are compared to experimental particle image velocimetry (PIV) measurements documenting the lateral flow structures downstream of the split-vane pairs. Good agreement is found between the computational simulation and experimental measurements for locations close to the support grid. (authors)

Defect production in simulated cascades: cascade quenching and short-term annealing

International Nuclear Information System (INIS)

Heinisch, H.L.

1982-01-01

Defect production in high energy displacement cascades has been modeled using the computer code MARLOWE to generate the cascades and the stochastic computer code ALSOME to simulate the cascade quenching and short-term annealing of isolated cascades. The quenching is accomplished by using ALSOME with exaggerated values for defect mobilities and critical reaction distanes for recombination and clustering, which are in effect until the number of defect pairs is equal to the value determined from resistivity experiments at 4K. Then normal mobilities and reaction distances are used during short-term annealing to a point representative of Stage III recovery. Effects of cascade interactions at low fluences are also being investigated. The quenching parameter values were empirically determined for 30 keV cascades. The results agree well with experimental information throughout the range from 1 keV to 100 keV. Even after quenching and short-term annealing the high energy cascades behave as a collection of lower energy subcascades and lobes. Cascades generated in a crystal having thermal displacements were found to be in better agreement with experiments after quenching and annealing than those generated in a non-thermal crystal

Atom-atom collision cascades localization

International Nuclear Information System (INIS)

Kirsanov, V.V.

1980-01-01

The presence of an impurity and thermal vibration influence on the atom-atom collision cascade development is analysed by the computer simulation method (the modificated dynamic model). It is discovered that the relatively low energetic cascades are localized with the temperature increase of an irradiated crystal. On the basis of the given effect the mechanism of splitting of the high energetic cascades into subcascades is proposed. It accounts for two factors: the primary knocked atom energy and the irradiated crystal temperature. Introduction of an impurity also localizes the cascades independently from the impurity atom mass. The cascades localization leads to intensification of the process of annealing in the cascades and reduction of the post-cascade vacancy cluster sizes. (author)

LES of the interaction between a premixed flame and complex turbulent swirling flow

International Nuclear Information System (INIS)

Iudiciani, P; Duwig, C; Szasz, R Z; Fuchs, L; Gutmark, E

2011-01-01

In this paper the Triple Annular Research Swirler, a fuel injector characterized by complex design with three concentric air passages, has been studied numerically. A swirl-stabilized lean premixed flame has been simulated by means of Large Eddy Simulation. The computations characterize successfully the dynamics of the flame and their interactions with the complex swirling flow. The flame is stabilized upstream the fuel injector exit, and the dynamics are led by a Precessing Vortex Core which seems to originate in the inner air passage. The results obtained by Proper Orthogonal Decomposition analysis are in agreement with previous findings in the context of swirling flows/flames.

Fast automotive diesel exhaust measurement using quantum cascade lasers

Science.gov (United States)

Herbst, J.; Brunner, R.; Lambrecht, A.

2013-12-01

Step by step, US and European legislations enforce the further reduction of atmospheric pollution caused by automotive exhaust emissions. This is pushing automotive development worldwide. Fuel efficient diesel engines with SCRtechnology can impede NO2-emission by reduction with NH3 down to the ppm range. To meet the very low emission limits of the Euro6 resp. US NLEV (National Low Emission Vehicle) regulations, automotive manufacturers have to optimize continuously all phases of engine operation and corresponding catalytic converters. Especially nonstationary operation holds a high potential for optimizing gasoline consumption and further reducing of pollutant emissions. Test equipment has to cope with demanding sensitivity and speed requirements. In the past Fraunhofer IPM has developed a fast emission analyzer called DEGAS (Dynamic Exhaust Gas Analyzer System), based on cryogenically cooled lead salt lasers. These systems have been used at Volkswagen AG`s test benches for a decade. Recently, IPM has developed DEGAS-Next which is based on cw quantum cascade lasers and thermoelectrically cooled detectors. The system is capable to measure three gas components (i.e. NO, NO2, NH3) in two channels with a time resolution of 20 ms and 1 ppm detection limits. We shall present test data and a comparison with fast FTIR measurements.

Experimental assessment of fluorescence microscopy signal enhancement by stimulated emission

Science.gov (United States)

Dake, Fumihiro; Yazawa, Hiroki

2017-10-01

The quantity of photons generated during fluorescence microscopy is principally determined by the quantum yield of the fluorescence dyes and the optical power of the excitation beam. However, even though low quantum yields can produce poor images, it is challenging to tune this parameter, while increasing the power of the excitation beam often results in photodamage. Here, we propose the use of stimulated emission (SE) as a means of enhancing both the signal intensity and signal-to-noise ratio during confocal fluorescence microscopy. This work experimentally confirmed that both these factors can be enhanced by SE radiation, through generating a greater number of photons than are associated with the standard fluorescence signal. We also propose the concept of stimulated emission enhancing fluorescence (SEEF) microscopy, which employs both the SE and fluorescence signals, and demonstrate that the intensity of an SEEF signal is greater than those of the individual SE and fluorescence signals.

Experimental Study of Hydrogen Addition Effects on a Swirl-Stabilized Methane-Air Flame

Directory of Open Access Journals (Sweden)

Mao Li

2017-11-01

Full Text Available The effects of H2 addition on a premixed methane-air flame was studied experimentally with a swirl-stabilized gas turbine model combustor. Experiments with 0%, 25%, and 50% H2 molar fraction in the fuel mixture were conducted under atmospheric pressure. The primary objectives are to study the impacts of H2 addition on flame lean blowout (LBO limits, flame shapes and anchored locations, flow field characteristics, precessing vortex core (PVC instability, as well as the CO emission performance. The flame LBO limits were identified by gradually reducing the equivalence ratio until the condition where the flame physically disappeared. The time-averaged CH chemiluminescence was used to reveal the characteristics of flame stabilization, e.g., flame structure and stabilized locations. In addition, the inverse Abel transform was applied to the time-averaged CH results so that the distribution of CH signal on the symmetric plane of the flame was obtained. The particle image velocimetry (PIV was used to detect the characteristics of the flow field with a frequency of 2 kHz. The snapshot method of POD (proper orthogonal decomposition and fast Fourier transform (FFT were adopted to capture the most prominent coherent structures in the turbulent flow field. CO emission was monitored with an exhaust probe that was installed close to the combustor exit. The experimental results indicated that the H2 addition extended the flame LBO limits and the operation range of low CO emission. The influence of H2 addition on the flame shape, location, and flow field was observed. With the assistance of POD and FFT, the combustion suppression impacts on PVC was found.

The spray characteristic of gas-liquid coaxial swirl injector by experiment

OpenAIRE

Chen Chen; Zhihui Yan; Yang Yang; Hongli Gao; Shunhua Yang; Lei Zhang

2017-01-01

Using the laser phase Doppler particle analyzer (PDPA), the spray characteristics of gas-liquid coaxial swirl injector were studied. The Sauter mean diameter (SMD), axial velocity and size data rate were measured under different gas injecting pressure drop and liquid injecting pressure drop. Comparing to a single liquid injection, SMD with gas presence is obviously improved. So the gas presence has a significant effect on the atomization of the swirl injector. What’s more, the atomization eff...

The swirl turbine

Science.gov (United States)

Haluza, M.; Pochylý, F.; Rudolf, P.

2012-11-01

In the article is introduced the new type of the turbine - swirl turbine. This turbine is based on opposite principle than Kaplan turbine. Euler equation is satisfied in the form gHηh = -u2vu2. From this equation is seen, that inflow of liquid into the runner is without rotation and on the outflow is a rotation of liquid opposite of rotation of runner. This turbine is suitable for small head and large discharge. Some constructional variants of this turbine are introduced in the article and theoretical aspects regarding losses in the draft tube. The theory is followed by computational simulations in Fluent and experiments using laser Doppler anemometry.

Turbulent swirling flow in a model of a uniflow-scavenged two-stroke engine

DEFF Research Database (Denmark)

Ingvorsen, Kristian Mark; Meyer, Knud Erik; Walther, Jens Honore

2013-01-01

The turbulent and swirling flow of a uniflow-scavenged two-stroke engine cylinder is investigated using a scale model with a static geometry and a transparent cylinder. The swirl is generated by 30 equally spaced ports with angles of 0°, 10°, 20°, and 30°. A detailed characterization of the flow...

Experimental investigation of atomization characteristics of swirling spray by ADN gelled propellant

Science.gov (United States)

Guan, Hao-Sen; Li, Guo-Xiu; Zhang, Nai-Yuan

2018-03-01

Due to the current global energy shortage and increasingly serious environmental issues, green propellants are attracting more attention. In particular, the ammonium dinitramide (ADN)-based monopropellant thruster is gaining world-wide attention as a green, non-polluting and high specific impulse propellant. Gel propellants combine the advantages of liquid and solid propellants, and are becoming popular in the field of spaceflight. In this paper, a swirling atomization experimental study was carried out using an ADN aqueous gel propellant under different injection pressures. A high-speed camera and a Malvern laser particle size analyzer were used to study the spray process. The flow coefficient, cone angle of swirl atomizing spray, breakup length of spray membrane, and droplet size distribution were analyzed. Furthermore, the effects of different injection pressures on the swirling atomization characteristics were studied.

Regimes of spray formation in gas-centered swirl coaxial atomizers

Energy Technology Data Exchange (ETDEWEB)

Sivakumar, D.; Kulkarni, V. [Indian Institute of Science, Department of Aerospace Engineering, Bangalore (India)

2011-09-15

Spray formation in ambient atmosphere from gas-centered swirl coaxial atomizers is described by carrying out experiments in a spray test facility. The atomizer discharges a circular air jet and an axisymmetric swirling water sheet from its coaxially arranged inner and outer orifices. A high-speed digital imaging system along with a backlight illumination arrangement is employed to record the details of liquid sheet breakup and spray development. Spray regimes exhibiting different sheet breakup mechanisms are identified and their characteristic features presented. The identified spray regimes are wave-assisted sheet breakup, perforated sheet breakup, segmented sheet breakup, and pulsation spray regime. In the regime of wave-assisted sheet breakup, the sheet breakup shows features similar to the breakup of two-dimensional planar air-blasted liquid sheets. At high air-to-liquid momentum ratios, the interaction process between the axisymmetric swirling liquid sheet and the circular air jet develops spray processes which are more specific to the atomizer studied here. The spray exhibits a periodic ejection of liquid masses whose features are dominantly controlled by the central air jet. (orig.)

Unified model of secondary electron cascades in diamond

International Nuclear Information System (INIS)

Ziaja, Beata; London, Richard A.; Hajdu, Janos

2005-01-01

In this article we present a detailed and unified theoretical treatment of secondary electron cascades that follow the absorption of x-ray photons. A Monte Carlo model has been constructed that treats in detail the evolution of electron cascades induced by photoelectrons and by Auger electrons following inner shell ionizations. Detailed calculations are presented for cascades initiated by electron energies between 0.1 and 10 keV. The present article expands our earlier work [B. Ziaja, D. van der Spoel, A. Szoeke, and J. Hajdu, Phys. Rev. B 64, 214104 (2001), Phys. Rev. B 66, 024116 (2002)] by extending the primary energy range, by improving the treatment of secondary electrons, especially at low electron energies, by including ionization by holes, and by taking into account their coupling to the crystal lattice. The calculations describe the three-dimensional evolution of the electron cloud, and monitor the equivalent instantaneous temperature of the free electron gas as the system cools. The dissipation of the impact energy proceeds predominantly through the production of secondary electrons whose energies are comparable to the binding energies of the valence (40-50 eV) and of the core electrons (300 eV). The electron cloud generated by a 10 keV electron is strongly anisotropic in the early phases of the cascade (t≤1 fs). At later times, the sample is dominated by low energy electrons, and these are scattered more isotropically by atoms in the sample. Our results for the total number of secondary electrons agree with available experimental data, and show that the emission of secondary electrons approaches saturation within about 100 fs following the primary impact

Measurement of electron density and electron temperature of a cascaded arc plasma using laser Thomson scattering compared to an optical emission spectroscopic approach

Science.gov (United States)

Yong, WANG; Cong, LI; Jielin, SHI; Xingwei, WU; Hongbin, DING

2017-11-01

As advanced linear plasma sources, cascaded arc plasma devices have been used to generate steady plasma with high electron density, high particle flux and low electron temperature. To measure electron density and electron temperature of the plasma device accurately, a laser Thomson scattering (LTS) system, which is generally recognized as the most precise plasma diagnostic method, has been established in our lab in Dalian University of Technology. The electron density has been measured successfully in the region of 4.5 × 1019 m-3 to 7.1 × 1020 m-3 and electron temperature in the region of 0.18 eV to 0.58 eV. For comparison, an optical emission spectroscopy (OES) system was established as well. The results showed that the electron excitation temperature (configuration temperature) measured by OES is significantly higher than the electron temperature (kinetic electron temperature) measured by LTS by up to 40% in the given discharge conditions. The results indicate that the cascaded arc plasma is recombining plasma and it is not in local thermodynamic equilibrium (LTE). This leads to significant error using OES when characterizing the electron temperature in a non-LTE plasma.

Investigation of noise radiation from a swirl stabilized diffusion flame with an array of microphones

International Nuclear Information System (INIS)

Singh, A.V.; Yu, M.; Gupta, A.K.; Bryden, K.M.

2013-01-01

Highlights: • Acoustic spectral characteristics independent of equivalence ratio and flow velocity. • Combustion noise dependent on global equivalence ratio and flow velocity. • Increased global equivalence ratio decreased the frequency of peak. • Decay and growth coefficients largely independent of different flow conditions. • Acoustic radiation coherent up to 1.5 kHz for spatially separated microphones. - Abstract: Next generation of combustors are expected to provide significant improvement on efficiency and reduced pollutants emission. In such combustors, the challenges of local flow, pressure, chemical composition and thermal signatures as well as their interactions will require detailed investigation for seeking optimum performance. Sensor networks with a large number of sensors will be employed in future smart combustors, which will allow one to obtain fast and comprehensive information on the various ongoing processes within the system. In this paper sensor networks with specific focus on an array of homogeneous microphones are used examine the spectral characteristics of combustion noise from a non-premixed combustor. A non-premixed double concentric swirl-flame burner was used. Noise spectra were determined experimentally for the non-premixed swirl flame at various fuel–air ratios using an array of homogeneous condenser microphones. Multiple microphones positioned at discrete locations around the turbulent diffusion flame, provided an understanding of the total sound power and their spectral characteristics. The growth and decay coefficients of total sound power were investigated at different test conditions. The signal coherence between different microphone pairs was also carried out to determine the acoustic behavior of a swirl stabilized turbulent diffusion flame. The localization of acoustic sources from the multiple microphones was examined using the noise spectra. The results revealed that integration of multiple sensors in combustors

Stability of swirling annular flow

Czech Academy of Sciences Publication Activity Database

Maršík, František; Trávníček, Zdeněk; Novotný, Pavel; Werner, E.

2010-01-01

Roč. 17, č. 3 (2010), s. 267-279 ISSN 1065-3090 R&D Projects: GA AV ČR(CZ) IAA200760801; GA MŠk(CZ) 1M06031 Institutional research plan: CEZ:AV0Z20760514 Keywords : swirling jet * hydrodynamic stability * impinging jet Subject RIV: BK - Fluid Dynamics http://www.begellhouse.com/journals/52b74bd3689ab10b,6bfbd93509947e2e,03fca4e77476857d.html

Study on Droplet Size and Velocity Distributions of a Pressure Swirl Atomizer Based on the Maximum Entropy Formalism

Directory of Open Access Journals (Sweden)

Kai Yan

2015-01-01

Full Text Available A predictive model for droplet size and velocity distributions of a pressure swirl atomizer has been proposed based on the maximum entropy formalism (MEF. The constraint conditions of the MEF model include the conservation laws of mass, momentum, and energy. The effects of liquid swirling strength, Weber number, gas-to-liquid axial velocity ratio and gas-to-liquid density ratio on the droplet size and velocity distributions of a pressure swirl atomizer are investigated. Results show that model based on maximum entropy formalism works well to predict droplet size and velocity distributions under different spray conditions. Liquid swirling strength, Weber number, gas-to-liquid axial velocity ratio and gas-to-liquid density ratio have different effects on droplet size and velocity distributions of a pressure swirl atomizer.

Swirl flow analysis in a helical wire inserted tube using CFD code

International Nuclear Information System (INIS)

Park, Yusun; Chang, Soon Heung

2010-01-01

An analysis on the two-phase flow in a helical wire inserted tube using commercial CFD code, CFX11.0, was performed in bubbly flow and annular flow regions. The analysis method was validated with the experimental results of Takeshima. Bubbly and annular flows in a 10 mm inner diameter tube with varying pitch lengths and inserted wire diameters were simulated using the same analysis methods after validation. The geometry range of p/D was 1-4 and e/D was 0.08-0.12. The results show that the inserted wire with a larger diameter increased swirl flow generation. An increasing swirl flow was seen as the pitch length increased. Regarding pressure loss, smaller pitch lengths and inserted wires with larger diameters resulted in larger pressure loss. The average liquid film thickness increased as the pitch length and the diameter of the inserted wire increased in the annular flow region. Both in the bubbly flow and annular flow regions, the effect of pitch length on swirl flow generation and pressure loss was more significant than that of the inserted wire diameters. Pitch length is a more dominant factor than inserted wire diameter for the design of the swirl flow generator in small diameter tubes.

Conical quarl swirl stabilized non-premixed flames: flame and flow field interaction

KAUST Repository

Elbaz, Ayman M.; Roberts, William L.

2017-01-01

The flame-flow field interaction is studied in non-premixed methane swirl flames stabilized in quartz quarl via simultaneous measurements of the flow field using a stereo PIV and OH-PLIF at 5 KHz repetition rate. Under the same swirl intensity, two flames with different fuel jet velocity were investigated. The time-averaged flow field shows a unique flow pattern at the quarl exit, where two recirculation vortices are formed; a strong recirculation zone formed far from the quarl exit and a larger recirculation zone extending inside the quarl. However, the instantaneous images show that, the flow pattern near the quarl exit plays a vital role in the spatial location and structure of the reaction zone. In the low fuel jet velocity flame, a pair of vortical structures, located precisely at the corners of the quarl exit, cause the flame to roll up into the central region of low speed flow, where the flame sheet then tracks the axial velocity fluctuations. The vorticity field reveals a vortical structure surrounding the reaction zones, which reside on a layer of low compressive strain adjacent to that vortical structure. In the high fuel jet velocity flame, initially a laminar flame sheet resides at the inner shear layer of the main jet, along the interface between incoming fresh gas and high temperature recirculating gas. Further downstream, vortex breakdown alters the flame sheet path toward the central flame region. The lower reaction zones show good correlation to the regions of maximum vorticity and track the regions of low compressive strain associated with the inner shear layer of the jet flow. In both flames the reactions zones conform the passage of the large structure while remaining inside the low speed regions or at the inner shear layer.

Conical quarl swirl stabilized non-premixed flames: flame and flow field interaction

KAUST Repository

Elbaz, Ayman M.

2017-09-19

The flame-flow field interaction is studied in non-premixed methane swirl flames stabilized in quartz quarl via simultaneous measurements of the flow field using a stereo PIV and OH-PLIF at 5 KHz repetition rate. Under the same swirl intensity, two flames with different fuel jet velocity were investigated. The time-averaged flow field shows a unique flow pattern at the quarl exit, where two recirculation vortices are formed; a strong recirculation zone formed far from the quarl exit and a larger recirculation zone extending inside the quarl. However, the instantaneous images show that, the flow pattern near the quarl exit plays a vital role in the spatial location and structure of the reaction zone. In the low fuel jet velocity flame, a pair of vortical structures, located precisely at the corners of the quarl exit, cause the flame to roll up into the central region of low speed flow, where the flame sheet then tracks the axial velocity fluctuations. The vorticity field reveals a vortical structure surrounding the reaction zones, which reside on a layer of low compressive strain adjacent to that vortical structure. In the high fuel jet velocity flame, initially a laminar flame sheet resides at the inner shear layer of the main jet, along the interface between incoming fresh gas and high temperature recirculating gas. Further downstream, vortex breakdown alters the flame sheet path toward the central flame region. The lower reaction zones show good correlation to the regions of maximum vorticity and track the regions of low compressive strain associated with the inner shear layer of the jet flow. In both flames the reactions zones conform the passage of the large structure while remaining inside the low speed regions or at the inner shear layer.

Hysteresis and transition in swirling nonpremixed flames

NARCIS (Netherlands)

Tummers, M.J.; Hübner, A.W.; van Veen, E.H.; Hanjalic, K.; van der Meer, Theodorus H.

2009-01-01

Strongly swirling nonpremixed flames are known to exhibit a hysteresis when transiting from an attached long, sooty, yellow flame to a short lifted blue flame, and vice versa. The upward transition (by increasing the air and fuel flow rates) corresponds to a vortex breakdown, i.e. an abrupt change

Effect of adding a swirl on flow pattern and recirculation zone in ADS windowless spallation target

Energy Technology Data Exchange (ETDEWEB)

Liu, Jie, E-mail: nauty@ucas.ac.cn [School of Physics, University of Chinese Academy of Sciences, Beijing (China); Gao, Lei [School of Physics, University of Chinese Academy of Sciences, Beijing (China); Yang, Lei [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou (China); Lu, Wen-qiang [School of Physics, University of Chinese Academy of Sciences, Beijing (China)

2014-09-15

Highlights: • The reduction of the recirculation zone and the stability of the free surface are key issues in the target. • A swirl is numerically added in the target to make the recirculation zone small and stable. • Numerical simulation with different boundary conditions is carried out. • Physical analysis is presented to explain the numerical results. - Abstract: Aiming the key issues in the accelerator driven system (ADS), windowless spallation target focus on the minimization of the recirculation zone and on the stability of the free surface, an innovation has been made by numerically adding swirl to the fluid at the inlet. At first, two phase flow pattern in the simulation is compared with the experiments and numerical method is employed correctly. The results reveal that the recirculation zone and the flow pattern are greatly influenced when the swirl strength is changed from 1.0 rad/s to 2.5 rad/s. The height of the recirculation zone decreases with increase in swirl strength and completely disappears when the swirl strength reaches 2.0 rad/s. In addition, larger swirl strength leads to different flow pattern and a new cavitation zone is generated under the recirculation zone. The Bernoulli's equation and angular momentum conservation are applied to make it clear that this phenomena is due to the decrease of the axial pressure caused by the radial velocity. Moreover, the new cavitation zone totally links to the vapor area above the recirculation zone when the swirl strength is 2.5 rad/s. The results are very helpful to the design and optimization of the ADS windowless spallation target.

Effect of adding a swirl on flow pattern and recirculation zone in ADS windowless spallation target

International Nuclear Information System (INIS)

Liu, Jie; Gao, Lei; Yang, Lei; Lu, Wen-qiang

2014-01-01

Highlights: • The reduction of the recirculation zone and the stability of the free surface are key issues in the target. • A swirl is numerically added in the target to make the recirculation zone small and stable. • Numerical simulation with different boundary conditions is carried out. • Physical analysis is presented to explain the numerical results. - Abstract: Aiming the key issues in the accelerator driven system (ADS), windowless spallation target focus on the minimization of the recirculation zone and on the stability of the free surface, an innovation has been made by numerically adding swirl to the fluid at the inlet. At first, two phase flow pattern in the simulation is compared with the experiments and numerical method is employed correctly. The results reveal that the recirculation zone and the flow pattern are greatly influenced when the swirl strength is changed from 1.0 rad/s to 2.5 rad/s. The height of the recirculation zone decreases with increase in swirl strength and completely disappears when the swirl strength reaches 2.0 rad/s. In addition, larger swirl strength leads to different flow pattern and a new cavitation zone is generated under the recirculation zone. The Bernoulli's equation and angular momentum conservation are applied to make it clear that this phenomena is due to the decrease of the axial pressure caused by the radial velocity. Moreover, the new cavitation zone totally links to the vapor area above the recirculation zone when the swirl strength is 2.5 rad/s. The results are very helpful to the design and optimization of the ADS windowless spallation target

The swirl turbine

International Nuclear Information System (INIS)

Haluza, M; Pochylý, F; Rudolf, P

2012-01-01

In the article is introduced the new type of the turbine - swirl turbine. This turbine is based on opposite principle than Kaplan turbine. Euler equation is satisfied in the form gHη h = −u 2 v u2 . From this equation is seen, that inflow of liquid into the runner is without rotation and on the outflow is a rotation of liquid opposite of rotation of runner. This turbine is suitable for small head and large discharge. Some constructional variants of this turbine are introduced in the article and theoretical aspects regarding losses in the draft tube. The theory is followed by computational simulations in Fluent and experiments using laser Doppler anemometry.

Direct observation of cascade defect formation at low temperatures in ion-irradiated metals

International Nuclear Information System (INIS)

Muroga, T.; Hirooka, K.; Ishino, S.

1984-01-01

Direct transmission electron microscopy observations of cascade defect formation have been carried out in gold, Type 316 stainless steel, and aluminum irradiated by Al + , Ar - , and Xe + ions with energies between 80 and 400 keV. By utilizing a link of an ion accelerator to an electron microscope, in situ observations at low temperature (-150 0 C) have become possible. In gold, subcascade structures are clearly observed in all cases. Obvious dependence on projectile mass and energy is observed for cascade structure and vacancy clustering efficiency in gold and for defect visibility in aluminum and Type 316 stainless steel. A computer simulation calculation using MARLOWE shows subcascade distributions a little smaller in size and larger in number than the present observation

Development of novel micro swirl mixer for producing fine metal oxide nanoparticles by continuous supercritical hydrothermal method.

Science.gov (United States)

Kawasaki, Shin-ichiro; Sue, Kiwamu; Ookawara, Ryuto; Wakashima, Yuichiro; Suzuki, Akira

2010-01-01

Novel micro swirl mixers were developed to synthesize nanoparticles, and the effect of their mixing performance on the characteristics of the synthesized nanoparticles was determined. The results were compared with those obtained using simple T-shaped mixers under the same reaction conditions. The synthesis of NiO, whose characteristics depend on the mixing performance of the mixer, was chosen as a model reaction. Initial investigations highlighted that the average particle size decreased from 32 to 23 to 20 nm as the inner diameter of the swirl mixers was decreased from 3.2 mm (Swirl mixer, SM-3.2) to 0.8 mm (Micro swirl mixer, MSM-0.8) to 0.5 mm (Micro swirl mixer, MSM-0.5), respectively. On the other hand, a similar decrease in the average particle size from 34 to 20 nm was observed with a decrease in the inner diameter of the T-shaped mixers from 1.3 mm (Tee union, T-1.3) to 0.3 mm (Micro tee union, T-0.3), respectively. Further, narrow particle size distributions were observed with a decrease in the inner diameter of each mixer. Furthermore, a computational fluid dynamics (CFD) simulation indicated an excellent mixing mechanism, which contributed to the improvement in the heating rate and the formation of nanoparticles of smaller size with a narrow particle size distribution. The result presented here indicates that the micro swirl mixers produce high-quality metal oxide nanoparticles. The size of the obtained particles with improved size distributions was comparable to that of the particles obtained using the T-shaped mixers, although the inner diameter of the swirl mixers was larger. Therefore, preliminary evidence suggests that the swirl flow mixers have the ability to produce rapid and homogeneous fluid mixing, thus controlling the particle size.

Low NOx combustion and SCR flow field optimization in a low volatile coal fired boiler.

Science.gov (United States)

Liu, Xing; Tan, Houzhang; Wang, Yibin; Yang, Fuxin; Mikulčić, Hrvoje; Vujanović, Milan; Duić, Neven

2018-08-15

Low NO x burner redesign and deep air staging have been carried out to optimize the poor ignition and reduce the NO x emissions in a low volatile coal fired 330 MW e boiler. Residual swirling flow in the tangentially-fired furnace caused flue gas velocity deviations at furnace exit, leading to flow field unevenness in the SCR (selective catalytic reduction) system and poor denitrification efficiency. Numerical simulations on the velocity field in the SCR system were carried out to determine the optimal flow deflector arrangement to improve flow field uniformity of SCR system. Full-scale experiment was performed to investigate the effect of low NO x combustion and SCR flow field optimization. Compared with the results before the optimization, the NO x emissions at furnace exit decreased from 550 to 650 mg/Nm³ to 330-430 mg/Nm³. The sample standard deviation of the NO x emissions at the outlet section of SCR decreased from 34.8 mg/Nm³ to 7.8 mg/Nm³. The consumption of liquid ammonia reduced from 150 to 200 kg/h to 100-150 kg/h after optimization. Copyright © 2018. Published by Elsevier Ltd.

Modeling of atomization and distribution of drop-liquid fuel in unsteady swirling flows in a combustion chamber and free space

Science.gov (United States)

Sviridenkov, A. A.; Toktaliev, P. D.; Tretyakov, V. V.

2018-03-01

Numerical and experimental research of atomization and propagation of drop-liquid phase in swirling flow behind the frontal device of combustion chamber was performed. Numerical procedure was based on steady and unsteady Reynolds equations solution. It's shown that better agreement with experimental data could be obtained with unsteady approach. Fractional time step method was implemented to solve Reynolds equations. Models of primary and secondary breakup of liquid fuel jet in swirling flows are formulated and tested. Typical mean sizes of fuel droplets for base operational regime of swirling device and combustion chamber were calculated. Comparison of main features of internal swirling flow in combustion chamber with unbounded swirling flow was made.

Characterizing G-Loading, Swirl Direction, and Rayleigh Losses in an Ultra Compact Combustor

Science.gov (United States)

2013-07-01

low Mach numbers to avoid these pressure losses while burning. Radtke [25] used a modified version of the Anthenien et al. [9] rig to study pressure...losses in the combustor due to Rayleigh effects. Radtke saw this increase in Mach number when comparing reacting and non-reacting cases, seen in...Anderson, W., Radtke , J., King, P., Thornburg, H., Zelina, J., Sekar, B., “Effects of Main Swirl Direction on High-g Combustion,” 44th AIAA/ASME/SAE

Instability Suppression in a Swirl-Stabilized Combustor Using Microjet Air Injection

KAUST Repository

LaBry, Zachary

2010-01-04

In this study, we examine the effectiveness of microjet air injection as a means of suppressing thermoacoustic instabilities in a swirl-stabilized, lean-premixed propane/air combustor. High-speed stereo PIV measurements, taken to explore the mechanism of combustion instability, reveal that the inner recirculation zone plays a dominant role in the coupling of acoustics and heat release that leads to combustion instability. Six microjet injector configurations were designed to modify the inner and outer recirculation zones with the intent of decoupling the mechanism leading to instability. Microjets that injected air into the inner recirculation zone, swirling in the opposite sense to the primary swirl were effective in suppressing combustion instability, reducing the overall sound pressure level by up to 17 dB within a certain window of operating conditions. Stabilization was achieved near an equivalence ratio of 0.65, corresponding to the region where the combustor transitions from a 40 Hz instability mode to a 110 Hz instability mode. PIV measurements made of the stabilized flow revealed significant modification of the inner recirculation zone and substantial weakening of the outer recirculation zone.

A hybrid nanoantenna for highly enhanced directional spontaneous emission

Energy Technology Data Exchange (ETDEWEB)

Chou, R. Yuanying; Lu, Guowei, E-mail: guowei.lu@pku.edu.cn; Shen, Hongming; He, Yingbo; Cheng, Yuqing [State Key Laboratory for Mesoscopic Physics, Department of Physics, Peking University, Beijing 100871 (China); Perriat, Pascal [MATEIS, UMR 5510 CNRS, INSA-Lyon, Université de Lyon, Villeurbanne Cedex 69621 (France); Martini, Matteo; Tillement, Olivier [ILM, UMR 5306 CNRS, Université de Lyon, Villeurbanne Cedex 69622 (France); Gong, Qihuang [State Key Laboratory for Mesoscopic Physics, Department of Physics, Peking University, Beijing 100871 (China); Collaborative Innovation Center of Quantum Matter, Beijing 100871 (China)

2014-06-28

Spontaneous emission modulated by a hybrid plasmonic nanoantenna has been investigated by employing finite-difference time-domain method. The hybrid nanoantenna configurations constituted by a gap hot-spot and of a plasmonic corrugated grating and a metal reflector sandwiching a SiO{sub 2} thin layer which appears promising for high spontaneous emission enhancement devices. Simulation assays show that the coupling between the gap-antenna and plasmonic corrugations reaches an ultra-high near-field enhancement factor in the excitation process. Moreover, concerning the emission process, the corrugations concentrate the far-field radiated power within a tiny angular volume, offering unprecedented collection efficiency. In the past decades, many kinds of optical antennas have been proposed and optimized to enhance single molecule detection. However, the excitation enhancement effect for single individual or dimmer plasmonic nanostructure is limited due to intrinsic nonradiative decay of the nanoparticle plasmon and quantum tunneling effect. The proposed hybrid configuration overwhelms the enhancement limit of single individual plasmonic structure. The findings provide an insight into spontaneous emission high enhancement through integrating the functions of different metallic nanostructures.

A hybrid nanoantenna for highly enhanced directional spontaneous emission

International Nuclear Information System (INIS)

Chou, R. Yuanying; Lu, Guowei; Shen, Hongming; He, Yingbo; Cheng, Yuqing; Perriat, Pascal; Martini, Matteo; Tillement, Olivier; Gong, Qihuang

2014-01-01

Spontaneous emission modulated by a hybrid plasmonic nanoantenna has been investigated by employing finite-difference time-domain method. The hybrid nanoantenna configurations constituted by a gap hot-spot and of a plasmonic corrugated grating and a metal reflector sandwiching a SiO 2 thin layer which appears promising for high spontaneous emission enhancement devices. Simulation assays show that the coupling between the gap-antenna and plasmonic corrugations reaches an ultra-high near-field enhancement factor in the excitation process. Moreover, concerning the emission process, the corrugations concentrate the far-field radiated power within a tiny angular volume, offering unprecedented collection efficiency. In the past decades, many kinds of optical antennas have been proposed and optimized to enhance single molecule detection. However, the excitation enhancement effect for single individual or dimmer plasmonic nanostructure is limited due to intrinsic nonradiative decay of the nanoparticle plasmon and quantum tunneling effect. The proposed hybrid configuration overwhelms the enhancement limit of single individual plasmonic structure. The findings provide an insight into spontaneous emission high enhancement through integrating the functions of different metallic nanostructures.

Twisted Vanes Would Enhance Fuel/Air Mixing In Turbines

Science.gov (United States)

Nguyen, H. Lee; Micklow, Gerald J.; Dogra, Anju S.

1994-01-01

Computations of flow show performance of high-shear airblast fuel injector in gas-turbine engine enhanced by use of appropriately proportioned twisted (instead of flat) dome swirl vanes. Resultant more nearly uniform fuel/air mixture burns more efficiently, emitting smaller amounts of nitrogen oxides. Twisted-vane high-shear airblast injectors also incorporated into paint sprayers, providing advantages of low pressure drop characteristic of airblast injectors in general and finer atomization of advanced twisted-blade design.

Large-eddy simulations of the non-reactive flow in the Sydney swirl burner

International Nuclear Information System (INIS)

Yang Yang; Kær, Søren Knudsen

2012-01-01

Highlights: ► Rational mesh and grid system for LES are discussed. ► Validated results are provided and discrepancy of mean radial velocity component is discussed. ► Flow structures are identified using vorticity field. ► We performed POD on cross sections to assist in understanding of coherent structures. - Abstract: This paper presents a numerical investigation using large-eddy simulation. Two isothermal cases from the Sydney swirling flame database with different swirl numbers were tested. Rational grid system and mesh details were presented firstly. Validations showed overall good agreement in time averaged results. In medium swirling case, there are two reverse-flow regions with a collar-like structure between them. The existence of strong unsteady structure, precessing vortex core, was proven. Coherent structures are detached from the instantaneous field. Q-criterion was used to visualize vorticity field with distinct clear structure of vortice tubes. Dominating spatial–temporal structures contained in different cross sections were extracted using proper orthogonal decomposition. In high swirling case, there is only one long reverse-flow region. In this paper, we proved the capability of a commercial CFD package in predicting complex flow field and presented the potential of large eddy simulation in understanding dynamics.

Thermoeconomic Optimization of Cascade Refrigeration System Using Mixed Carbon Dioxide and Hydrocarbons at Low Temperature Circuit

Directory of Open Access Journals (Sweden)

Nasruddin Nasruddin

2016-12-01

Full Text Available Many applications and industrial processes require very low cooling temperature, such as cold storage in the biomedical field, requiring temperature below -80 °C. However,single-cycle refrigeration systems can only achieve the effective cooling temperature of -40 °C and, also, the performance of the cycle will decrease drastically for cooling temperatures lower than -35°C. Currently, most of cascade refrigeration systems use refrigerants that have ozone depletion potential (ODP and global warming potential (GWP, therefore, in this study, a cascade system is simulated using a mixture of environmentally friendly refrigerants, namely, carbon dioxide and a hydrocarbon (propane, ethane or ethylene as the refrigerant of the low temperature circuit. A thermodynamic analysis is performed to determine the optimal composition of the mixture of carbon dioxide and hydrocarbons in the scope of certain operating parameters. In addition, an economic analysis was also performed to determine the annual cost to be incurred from the cascade refrigeration system. The multi-objective/thermoeconomic optimization points out optimal operating parameter values of the system, to addressing both exergy efficiency and its relation to the costs to be incurred.

Combustion behaviors of GO2/GH2 swirl-coaxial injector using non-intrusive optical diagnostics

Science.gov (United States)

GuoBiao, Cai; Jian, Dai; Yang, Zhang; NanJia, Yu

2016-06-01

This research evaluates the combustion behaviors of a single-element, swirl-coaxial injector in an atmospheric combustion chamber with gaseous oxygen and gaseous hydrogen (GO2/GH2) as the propellants. A brief simulated flow field schematic comparison between a shear-coaxial injector and the swirl-coaxial injector reveals the distribution characteristics of the temperature field and streamline patterns. Advanced optical diagnostics, i.e., OH planar laser-induced fluorescence and high-speed imaging, are simultaneously employed to determine the OH radical spatial distribution and flame fluctuations, respectively. The present study focuses on the flame structures under varying O/F mixing ratios and center oxygen swirl intensities. The combined use of several image-processing methods aimed at OH instantaneous images, including time-averaged, root-mean-square, and gradient transformation, provides detailed information regarding the distribution of the flow field. The results indicate that the shear layers anchored on the oxygen injector lip are the main zones of chemical heat release and that the O/F mixing ratio significantly affects the flame shape. Furthermore, with high-speed imaging, an intuitionistic ignition process and several consecutive steady-state images reveal that lean conditions make it easy to drive the combustion instabilities and that the center swirl intensity has a moderate influence on the flame oscillation strength. The results of this study provide a visualized analysis for future optimal swirl-coaxial injector designs.

Energy considerations in spraying process of a spill-return pressure-swirl atomizer

International Nuclear Information System (INIS)

Jedelsky, Jan; Jicha, Miroslav

2014-01-01

Graphical abstract: - Highlights: • We analyse energy conversion in simplex and spill-return pressure-swirl atomizer. • Inlet (pressure) energy converts into liquid motion with nozzle efficiency ∼58%. • Kinetic energy of developed spray at closed spill line is ∼33% of the inlet energy. • It consists of energy of droplets (∼2/3) and entrained air (1/3). • Atomization efficiency is <0.3%; it declines with inlet pressure and spill opening. - Abstract: The work focuses on energy conversion during the internal flow, discharge and formation of the spray from a pressure-swirl (PS) atomizer in the simplex as well as spill-return mode. Individual energy forms are described in general and assessed experimentally for a particular PS atomizer and light heating oil as a medium. The PS spray was observed at various loads to investigate the liquid breakup process and the spray characteristics. Spatially resolved diameters and droplet velocities, measured by means of phase-Doppler anemometry, served for estimation of the energy characteristics in the PS spray. The input energy given by the potential energy of the supplied liquid partially converts into the kinetic energy (KE) in the swirling ports with hydraulic loss in per cent scale. Most of the pressure drop is associated with rotational motion in the swirl chamber with total conversion efficiency at the exit orifice ∼58%. The rest of the input energy ends up as friction loss, leaving room for improvement. The overall value (ID 32 ) of the Sauter mean diameter of droplets in the spray, D 32 , varies with pressure drop Δp l powered to −0.1. The radial profiles of D 32 widen with the increase in spill/feed ratio (SFR), but the ID 32 remain almost constant within the studied SFR range. The spray KE at closed spill line covers the droplet KE (21–26%) and that of entrained air (10–13%), both moderately varying with Δp l . The specific KEs of both the liquid and air markedly drop down with the spill line

Energetic Charged Particle Emission from Hydrogen-Loaded pd and ti Cathodes and its Enhancement by He-4 Implantation

Science.gov (United States)

Lipson, A. G.; Miley, G. H.; Lipson, A. G.; Lyakhov, B. F.; Roussetski, A. S.

2006-02-01

In this paper, we demonstrate reproducible emissions of energetic alphas and protons appearing in an energy range where both cosmic ray interference and possible alpha emissions from contamination (e.g., radon) is assumed to be negligible. We also show that He4 doping of Pd and Ti cathodes leads to a significant enhancement of the energetic charged particles emission (ECPE). This measurement of the emissions of energetic (MeV) particles, in a region of low background interference plus their enhancement by He4 doping provides very strong support for the existence of LENR processes in the crystalline lattice of deuterated metals.

Energetic charged particle emission from hydrogen-loaded Pd and Ti cathodes and its enhancement by He-4 implantation

International Nuclear Information System (INIS)

Lipson, A.G.; Miley, G.H.; Lipson, A.G.; Lyakhov, B.F.; Roussetski, A.S.

2006-01-01

In this paper, we demonstrate reproducible emissions of energetic alphas and protons appearing in an energy range where both cosmic ray interference and possible alpha emissions from contamination (e.g., radon) is assumed to be negligible. We also show that, 4 He doping of Pd and Ti cathodes leads to a significant enhancement of the energetic charged particles emission (ECPE). This measurement of the emissions of energetic (MeV) particles, in a region of low background interference plus their enhancement by 4 He doping provides very strong support for the existence of LENR processes in the crystalline lattice of deuterated metals. (authors)

Effect of free swirl flow on the rate of mass and heat transfer at the bottom of a vertical cylindrical container and possible applications

International Nuclear Information System (INIS)

Konsowa, A.H.; Abdel-Aziz, M.H.; Abdo, M.S.E.; Hassan, M.S.; Sedahmed, G.H.

2017-01-01

Highlights: • Mass transfer at the bottom of a cylindrical container was studied under decaying swirl flow. • Parameters studied are swirl flow velocity, diameter of the inlet nozzle and solution properties. • A dimensionless equation was obtained using the significant parameters. • The present results were compared with the results obtained using perpendicular inlet nozzle. • Relevance of study to the design of membrane processes was highlighted. - Abstract: Rates of mass transfer at the base of a vertical cylindrical container were determined under decaying swirl flow by the electrochemical technique. Variables studied were swirl flow solution velocity, diameter of the tangential inlet nozzle and physical properties of the solution. The data were correlated by a dimensionless mass transfer equation. The equation can be used to predict the rate of heat loss from the bottom of swirl flow equipment as well as the rate of diffusion controlled corrosion of the bottom. The importance of the derived equation in the design and scale up of a cylindrical batch recirculating catalytic or electrochemical reactor with a catalyst layer or electrode at the bottom and a cooling jacket around the vertical wall suitable for conducting exothermic liquid – solid diffusion controlled reactions which need rapid temperature control to avoid the loss of heat sensitive catalysts or heat sensitive products was pointed out. Comparison of the present results with the results obtained using perpendicular inlet nozzle which generates parallel flow at the bottom and axial flow along the cylindrical container revealed the fact that although swirl flow produces higher rates of heat and mass transfer at the cylindrical wall than axial flow and the reverse is true at the container base. Relevance of the present study to the design and operation of membrane processes and heat recovery from hot pools of liquid metals and low melting alloys in the production stage was highlighted.

Numerical investigation on liquid sheets interaction characteristics of liquid-liquid coaxial swirling jets in bipropellant thruster

International Nuclear Information System (INIS)

Ding, Jia-Wei; Li, Guo-Xiu; Yu, Yu-Song

2016-01-01

Highlights: • A LES-VOF model is conducted to simulate atomization of coaxial swirling jets. • Structure and flow field of coaxial swirling jets are investigated. • Merging process occurs at the nozzle exit and generates additional perturbation. • The Rayleigh mode instability dominates the breakup of ligaments. - Abstract: Spray atomization process of a liquid-liquid coaxial swirl injector in bipropellant thruster has been investigated using volume of fluid (VOF) method coupled with large eddy simulation methodology. With fine grid resolution, detailed flow field of interacted liquid sheet has been captured and analyzed. For coaxial swirling jet, static pressure drop in the region between the liquid sheets makes two liquid sheets to approach each other and merge. A strong pressure, velocity and turbulent fluctuations are calculated near the contact position of two coaxial jets. Simulation results indicate that additional perturbations are generated due to strong radial and axial shear effects between coaxial jets. Observation of droplet formation process reveals that the Rayleigh mode instability dominates the breakup of the ligament. Droplet diameter and distribution have been investigated quantitatively. The mean diameter of the coaxial jets is between that of the inner and the outer jets. Compared with the individual swirling jets, wider size distributions of droplets are produced in the coaxial jets.

Coherent quantum cascade laser micro-stripe arrays

Directory of Open Access Journals (Sweden)

G. M. de Naurois

2011-09-01

Full Text Available We have fabricated InP-based coherent quantum cascade laser micro-stripe arrays. Phase-locking is provided by evanescent coupling between adjacent stripes. Stripes are buried into semi-insulating iron doped InP. Lasing at room temperature is obtained at 8.4μm for stripe arrays comprising up to 16 emitters. Pure supermode emission is demonstrated via farfield measurements and simulations. The farfield pattern shows a dual-lobe emission, corroborating the predicted phase-locked antisymmetric supermode emission.

Dependence of energy characteristics of ascending swirling air flow on velocity of vertical blowing

Science.gov (United States)

Volkov, R. E.; Obukhov, A. G.; Kutrunov, V. N.

2018-05-01

In the model of a compressible continuous medium, for the complete Navier-Stokes system of equations, an initial boundary problem is proposed that corresponds to the conducted and planned experiments and describes complex three-dimensional flows of a viscous compressible heat-conducting gas in ascending swirling flows that are initiated by a vertical cold blowing. Using parallelization methods, three-dimensional nonstationary flows of a polytropic viscous compressible heat-conducting gas are constructed numerically in different scaled ascending swirling flows under the condition when gravity and Coriolis forces act. With the help of explicit difference schemes and the proposed initial boundary conditions, approximate solutions of the complete system of Navier-Stokes equations are constructed as well as the velocity and energy characteristics of three-dimensional nonstationary gas flows in ascending swirling flows are determined.

Fully Premixed Low Emission, High Pressure Multi-Fuel Burner

Science.gov (United States)

Nguyen, Quang-Viet (Inventor)

2012-01-01

A low-emissions high-pressure multi-fuel burner includes a fuel inlet, for receiving a fuel, an oxidizer inlet, for receiving an oxidizer gas, an injector plate, having a plurality of nozzles that are aligned with premix face of the injector plate, the plurality of nozzles in communication with the fuel and oxidizer inlets and each nozzle providing flow for one of the fuel and the oxidizer gas and an impingement-cooled face, parallel to the premix face of the injector plate and forming a micro-premix chamber between the impingement-cooled face and the in injector face. The fuel and the oxidizer gas are mixed in the micro-premix chamber through impingement-enhanced mixing of flows of the fuel and the oxidizer gas. The burner can be used for low-emissions fuel-lean fully-premixed, or fuel-rich fully-premixed hydrogen-air combustion, or for combustion with other gases such as methane or other hydrocarbons, or even liquid fuels.

Band-to-Band Tunneling-Dominated Thermo-Enhanced Field Electron Emission from p-Si/ZnO Nanoemitters.

Science.gov (United States)

Huang, Zhizhen; Huang, Yifeng; Xu, Ningsheng; Chen, Jun; She, Juncong; Deng, Shaozhi

2018-06-13

Thermo-enhancement is an effective way to achieve high performance field electron emitters, and enables the individually tuning on the emission current by temperature and the electron energy by voltage. The field emission current from metal or n-doped semiconductor emitter at a relatively lower temperature (i.e., current saturation was observed in the thermo-enhanced field emission measurements. The emission current density showed about ten-time enhancement (from 1.31 to 12.11 mA/cm 2 at 60.6 MV/m) by increasing the temperature from 323 to 623 K. The distinctive performance did not agree with the interband excitation mechanism but well-fit to the band-to-band tunneling model. The strong thermo-enhancement was proposed to be benefit from the increase of band-to-band tunneling probability at the surface portion of the p-Si/ZnO nanojunction. This work provides promising cathode for portable X-ray tubes/panel, ionization vacuum gauges and low energy electron beam lithography, in where electron-dose control at a fixed energy is needed.

Swirl and blade wakes in the interaction between gas turbines and exhaust diffusers investigated by endoscopic particle image velocimetry

Energy Technology Data Exchange (ETDEWEB)

Opilat, Victor

2011-10-21

Exhaust diffusers studied in this thesis are installed behind the last turbine stage of gas turbines, including those used in combined cycle power plants. Extensive research made in recent years proved that effects caused by an upstream turbine need to be taken into account when designing efficient diffusers. Under certain conditions these effects can stabilize the boundary layer in diffusers and prevent separation. In this research the impact of multiple parameters, such as tip leakage flow, swirl, and rotating blade wakes, on the performance of a diffuser is studied. Experiments were conducted using a diffuser test rig with a rotating bladed wheel as a turbine effect generator and with an additional tip leakage flow insert. The major advantages of this test rig are modularity and easy variation of the main parameters. To capture the complexity and understand the physics of diffuser flow, and to clarify the phenomenon of the flow stabilisation, the 2D endoscopic laser optical measurement technique Partide Image Velocimetry (PIV) was adopted to the closed ''rotating'' diffuser test rig. Intensity and distribution of vortices in the blade tip area are decisive for diffuser performance. Large vortices in the annular diffuser inlet behind the blade tips interact with the boundary layer in diffusers. At design point these vortices are very early suppressed by the main flow. For the operating point with a low value of the flow coefficient (negative swirl), vortices are ab out two tim es stronger than for design point and the boundary layer is destabilized. V mtices develop in the direction contrary to swirl in the main flow and just cause flow destabilization. Coherent back flow zones are induced and reduction of diffuser performance occurs. For the operating point with positive swirl (for a high flow coefficient value), these vortices are also strong but do not counteract the main flow because they develop in the same direction with the swirl in the

Energy sharing and sputtering in low-energy collision cascades

International Nuclear Information System (INIS)

Weller, R.A.; Weller, M.R.

1982-01-01

Using a non-linear transport equation to describe the energy-sharing process in an isotropic collision cascade, we have numerically calculated sputtered particle velocity spectra for several very low energy (=< 10 eV) primary recoil distributions. Our formulation of the sputtering process is essentially that used in the linear model and our equations yield the familiar linear model results in the appropriate limit. Discrepancies between our calculations and the linear model results in other cases may be understood by considering the effects of the linear model assumptions on the sputtering yield at very low energies. Our calculations are also compared with recent experimental results investigating ion-explosion sputtering. The results of this comparison support the conclusion that in insulators sputtering is initiated by very low energy recoil atoms when the energy of the incident beam is high enough that the stopping power is dominated by the electronic contribution. The calculations also suggest that energy spectra similar to those for evaporation may result from non-equilibrium processes but that the apparent temperatures of evaporation are not related in a simple way to any real temperature within the target. (author)

Enhanced flashover strength in polyethylene nanodielectrics by secondary electron emission modification

Directory of Open Access Journals (Sweden)

Weiwang Wang

2016-04-01

Full Text Available This work studies the correlation between secondary electron emission (SEE characteristics and impulse surface flashover in polyethylene nanodielectrics both theoretically and experimentally, and illustrates the enhancement of flashover voltage in low-density polyethylene (LDPE through incorporating Al2O3 nanoparticles. SEE characteristics play key roles in surface charging and gas desorption during surface flashover. This work demonstrates that the presence of Al2O3 nanoparticles decreases the SEE coefficient of LDPE and enhances the impact energy at the equilibrium state of surface charging. These changes can be explained by the increase of surface roughness and of surface ionization energy, and the strong interaction between nanoparticles and the polymer dielectric matrix. The surface charge and flashover voltage are calculated according to the secondary electron emission avalanche (SEEA model, which reveals that the positive surface charges are reduced near the cathode triple point, while the presence of more nanoparticles in high loading samples enhances the gas desorption. Consequently, the surface flashover performance of LDPE/Al2O3 nanodielectrics is improved.

Combustion and emissions control in diesel-methane dual fuel engines: The effects of methane supply method combined with variable in-cylinder charge bulk motion

International Nuclear Information System (INIS)

Carlucci, Antonio P.; Laforgia, Domenico; Saracino, Roberto; Toto, Giuseppe

2011-01-01

Highlights: → We studied dual fuel combustion in diesel engines. → Bulk flow structure of in-cylinder charge and methane supply method were investigated. → Swirl charge motion is capable to enhance air-methane mixture oxidation at low loads. → Methane port injection is capable to reduce unburned hydrocarbons and nitric oxides. - Abstract: In this paper, the results of an extensive experimental campaign about dual fuel combustion development and the related pollutant emissions are reported, paying particular attention to the effect of both the in-cylinder charge bulk motion and methane supply method. A diesel common rail research engine was converted to operate in dual fuel mode and, by activating/deactivating the two different inlet valves of the engine (i.e. swirl and tumble), three different bulk flow structures of the charge were induced inside the cylinder. A methane port injection method was proposed, in which the gaseous fuel was injected into the inlet duct very close to the intake valves, in order to obtain a stratified-like air-fuel mixture up to the end of the compression stroke. For comparison purposes, a homogeneous-like air-fuel mixture was obtained injecting methane more upstream the intake line. Combining the different positions of the methane injector and the three possible bulk flow structures, seven different engine inlet setup were tested. In this way, it was possible to evaluate the effects on dual fuel combustion due to the interaction between methane injector position and charge bulk motion. In addition, methane injection pressure and diesel pilot injection parameters were varied setting the engine at two operating conditions. For some interesting low load tests, the combustion development was studied more in detail by means of direct observation of the process, using an in-cylinder endoscope and a digital CCD camera. Each combustion image was post-processed by a dedicated software, in order to extract only those portions with flame

Enhanced Combustion Low NOx Pulverized Coal Burner

Energy Technology Data Exchange (ETDEWEB)

David Towle; Richard Donais; Todd Hellewell; Robert Lewis; Robert Schrecengost

2007-06-30

For more than two decades, Alstom Power Inc. (Alstom) has developed a range of low cost, infurnace technologies for NOx emissions control for the domestic U.S. pulverized coal fired boiler market. This includes Alstom's internally developed TFS 2000{trademark} firing system, and various enhancements to it developed in concert with the U.S. Department of Energy. As of the date of this report, more than 270 units representing approximately 80,000 MWe of domestic coal fired capacity have been retrofit with Alstom low NOx technology. Best of class emissions range from 0.18 lb/MMBtu for bituminous coal to 0.10 lb/MMBtu for subbituminous coal, with typical levels at 0.24 lb/MMBtu and 0.13 lb/MMBtu, respectively. Despite these gains, NOx emissions limits in the U.S. continue to ratchet down for new and existing boiler equipment. On March 10, 2005, the Environmental Protection Agency (EPA) announced the Clean Air Interstate Rule (CAIR). CAIR requires 25 Eastern states to reduce NOx emissions from the power generation sector by 1.7 million tons in 2009 and 2.0 million tons by 2015. Low cost solutions to meet such regulations, and in particular those that can avoid the need for a costly selective catalytic reduction system (SCR), provide a strong incentive to continue to improve low NOx firing system technology to meet current and anticipated NOx control regulations. The overall objective of the work is to develop an enhanced combustion, low NOx pulverized coal burner, which, when integrated with Alstom's state-of-the-art, globally air staged low NOx firing systems will provide a means to achieve: Less than 0.15 lb/MMBtu NOx emissions when firing a high volatile Eastern or Western bituminous coal, Less than 0.10 lb/MMBtu NOx emissions when firing a subbituminous coal, NOx reduction costs at least 25% lower than the costs of an SCR, Validation of the NOx control technology developed through large (15 MWt) pilot scale demonstration, and Documentation required for

Freely-migrating defects: Their production and interaction with cascade remnants

International Nuclear Information System (INIS)

Rehn, L.E.; Wiedersich, H.

1991-05-01

Many microstructural changes that occur during irradiation are driven primarily by freely-migrating defects, i.e. those defects which escape from nascent cascades to migrate over distances that are large relative to typical cascade dimensions. Several measurements during irradiation at elevated temperatures have shown that the survival rate of freely-migrating defects decreases much more strongly with increasing primary recoil energy than does the survival rate for defects generated at liquid helium temperatures. For typical fission or fusion recoil spectra, and for heavy-ion bombardment, the fraction of defects that migrate long-distances is apparently only ∼1% of the calculated dpa. This small surviving fraction of freely-migrating defects results at least partially from additional intracascade recombination at elevated temperatures. However, cascade remnants, e.g., vacancy and interstitial clusters, also contribute by enhancing intercascade defect annihilation. A recently developed rate-theory approach is used to discuss the relative importance of intra- and intercascade recombination to the survival rate of freely-migrating defects. Within the validity of certain simplifying assumptions, the additional sink density provided by defect clusters produced directly within individual cascades can explain the difference between a defect survival rate of about 30% for low dose, low temperature irradiations with heavy ions, and a survival rate of only ∼1% for freely-migrating defects at elevated temperatures. The status of our current understanding of freely-migrating defects, including remaining unanswered questions, is also discussed. 33 refs., 5 figs

Numerical model for swirl flow cooling in high-heat-flux particle beam targets and the design of a swirl-flow-based plasma limiter

International Nuclear Information System (INIS)

Milora, S.L.; Combs, S.K.; Foster, C.A.

1984-11-01

An unsteady, two-dimensional heat conduction code has been used to study the performance of swirl-flow-based neutral particle beam targets. The model includes the effects of two-phase heat transfer and asymmetric heating of tubular elements. The calorimeter installed in the Medium Energy Test Facility, which has been subjected to 30-s neutral beam pulses with incident heat flux intensities of greater than or equal to 5 kW/cm 2 , has been modeled. The numerical results indicate that local heat fluxes in excess of 7 kW/cm 2 occur at the water-cooled surface on the side exposed to the beam. This exceeds critical heat flux limits for uniformly heated tubes wih straight flow by approximately a factor of 5. The design of a plasma limiter based on swirl flow heat transfer is presented

Enhancing the sensitivity of mid-IR quantum cascade laser-based cavity-enhanced absorption spectroscopy using RF current perturbation.

Science.gov (United States)

Manfred, Katherine M; Kirkbride, James M R; Ciaffoni, Luca; Peverall, Robert; Ritchie, Grant A D

2014-12-15

The sensitivity of mid-IR quantum cascade laser (QCL) off-axis cavity-enhanced absorption spectroscopy (CEAS), often limited by cavity mode structure and diffraction losses, was enhanced by applying a broadband RF noise to the laser current. A pump-probe measurement demonstrated that the addition of bandwidth-limited white noise effectively increased the laser linewidth, thereby reducing mode structure associated with CEAS. The broadband noise source offers a more sensitive, more robust alternative to applying single-frequency noise to the laser. Analysis of CEAS measurements of a CO(2) absorption feature at 1890  cm(-1) averaged over 100 ms yielded a minimum detectable absorption of 5.5×10(-3)  Hz(-1/2) in the presence of broadband RF perturbation, nearly a tenfold improvement over the unperturbed regime. The short acquisition time makes this technique suitable for breath applications requiring breath-by-breath gas concentration information.

Energetic charged particle emission from hydrogen-loaded Pd and Ti cathodes and its enhancement by He-4 implantation

Energy Technology Data Exchange (ETDEWEB)

Lipson, A.G.; Miley, G.H. [University of Illinois at Urbana - Champaign, lL (United States); Lipson, A.G.; Lyakhov, B.F. [lnstitute of Physical Chemistry, The Russian Academy of Sciences, Moscow (Russian Federation); Roussetski, A.S. [P. N. Lebedev Physics Institute, The Russian Academy of Sciences Moscow (Russian Federation)

2006-07-01

In this paper, we demonstrate reproducible emissions of energetic alphas and protons appearing in an energy range where both cosmic ray interference and possible alpha emissions from contamination (e.g., radon) is assumed to be negligible. We also show that, {sup 4}He doping of Pd and Ti cathodes leads to a significant enhancement of the energetic charged particles emission (ECPE). This measurement of the emissions of energetic (MeV) particles, in a region of low background interference plus their enhancement by {sup 4}He doping provides very strong support for the existence of LENR processes in the crystalline lattice of deuterated metals. (authors)

Species coexistence and the superior ability of an invasive species to exploit a facilitation cascade habitat

Directory of Open Access Journals (Sweden)

Andrew H. Altieri

2017-02-01

Full Text Available Facilitation cascades generated by co-occurring foundation species can enhance the abundance and diversity of associated organisms. However, it remains poorly understood how differences among native and invasive species in their ability to exploit these positive interactions contribute to emergent patterns of community structure and biotic acceptance. On intertidal shorelines in New England, we examined the patterns of coexistence between the native mud crabs and the invasive Asian shore crab in and out of a facilitation cascade habitat generated by mid intertidal cordgrass and ribbed mussels. These crab species co-occurred in low intertidal cobbles adjacent to the cordgrass–mussel beds, despite experimental findings that the dominant mud crabs can kill and displace Asian shore crabs and thereby limit their successful recruitment to their shared habitat. A difference between the native and invasive species in their utilization of the facilitation cascade likely contributes to this pattern. Only the Asian shore crabs inhabit the cordgrass–mussel beds, despite experimental evidence that both species can similarly benefit from stress amelioration in the beds. Moreover, only Asian shore crabs settle in the beds, which function as a nursery habitat free of lethal mud crabs, and where their recruitment rates are particularly high (nearly an order of magnitude higher than outside beds. Persistence of invasive adult Asian shore crabs among the dominant native mud crabs in the low cobble zone is likely enhanced by a spillover effect of the facilitation cascade in which recruitment-limited Asian shore crabs settle in the mid intertidal cordgrass–mussel beds and subsidize their vulnerable populations in the adjacent low cobble zone. This would explain why the abundances of Asian shore crabs in cobbles are doubled when adjacent to facilitation cascade habitats. The propensity for this exotic species to utilize habitats created by facilitation cascades

Comparison of reynolds averaged navier stokes based simulation and large eddy simulation for one isothermal swirling flow

DEFF Research Database (Denmark)

Yang, Yang; Kær, Søren Knudsen

2012-01-01

The flow structure of one isothermal swirling case in the Sydney swirl flame database was studied using two numerical methods. Results from the Reynolds-averaged Navier-Stokes (RANS) approach and large eddy simulation (LES) were compared with experimental measurements. The simulations were applied...

Cascade theory in isotopic separation processes; Theorie des cascades en separation isotopique

Energy Technology Data Exchange (ETDEWEB)

Agostini, J P

1994-06-01

Three main areas are developed within the scope of this work: - the first one is devoted to fundamentals: separative power, value function, ideal cascade and square cascade. Applications to two main cases are carried out, namely: Study of binary isotopic mix, Study of processes with a small enrichment coefficient. - The second one is devoted to cascade coupling -high-flux coupling (more widely used and better known) as well as low-flux coupling are presented and compared to one another. - The third one is an outlook on problems linked to cascade transients. Those problem are somewhat intricate and their interest lies mainly into two areas: economics where the start-up time may have a large influence on the interests paid during the construction and start-up period, military productions where the start-up time has a direct bearing on the production schedule. (author). 50 figs. 3 annexes. 12 refs. 6 tabs.

Magnetic swirls and associated fast magnetoacoustic kink waves in a solar chromospheric flux tube

Science.gov (United States)

Murawski, K.; Kayshap, P.; Srivastava, A. K.; Pascoe, D. J.; Jelínek, P.; Kuźma, B.; Fedun, V.

2018-02-01

We perform numerical simulations of impulsively generated magnetic swirls in an isolated flux tube that is rooted in the solar photosphere. These swirls are triggered by an initial pulse in a horizontal component of the velocity. The initial pulse is launched either (a) centrally, within the localized magnetic flux tube or (b) off-central, in the ambient medium. The evolution and dynamics of the flux tube are described by three-dimensional, ideal magnetohydrodynamic equations. These equations are numerically solved to reveal that in case (a) dipole-like swirls associated with the fast magnetoacoustic kink and m = 1 Alfvén waves are generated. In case (b), the fast magnetoacoustic kink and m = 0 Alfvén modes are excited. In both these cases, the excited fast magnetoacoustic kink and Alfvén waves consist of a similar flow pattern and magnetic shells are also generated with clockwise and counter-clockwise rotating plasma within them, which can be the proxy of dipole-shaped chromospheric swirls. The complex dynamics of vortices and wave perturbations reveals the channelling of sufficient amount of energy to fulfil energy losses in the chromosphere (˜104 W m-1) and in the corona (˜102 W m-1). Some of these numerical findings are reminiscent of signatures in recent observational data.

Electron and photon emissions from gold nanoparticles irradiated by X-ray photons

Energy Technology Data Exchange (ETDEWEB)

Casta, R., E-mail: castaromain@gmail.com, E-mail: romain.casta@irsamc.ups-tlse.fr; Champeaux, J.-P.; Moretto-Capelle, P.; Sence, M.; Cafarelli, P. [Université de Toulouse, UPS, Laboratoire Collisions Agrégats Réactivité, IRSAMC, CNRS, UMR 5589 (France)

2015-01-15

In this paper, we develop a totally new probabilistic model for the electron and photon emission of gold nanoparticles irradiated by X-ray photons. This model allows direct applications to recent researches about the radiotherapy enhancement by gold nanoparticles in the context of cancer treatment. Our model uses, in a complete original way, simulated Auger cascade and stopping power to compute electron emission spectra, photon emission spectra and released energy inside the material of gold nanoparticles. It allows us to present new results about the electron and photon emission of gold nanoparticle irradiated by hard X-rays.

Method of calculation of new cyclone-type separator with swirling baffle and bottom take off of clean gas - part II: experimental verification

Energy Technology Data Exchange (ETDEWEB)

Chmielniak, T.; Bryczkowski, A. [Inst. for Chemical Processing of Coal, Zabrze (Poland)

2001-05-01

The results of tests and experimental verification of the derived model to predict collection efficiency and pressure drop of the Institute for Chemical Processing of Coal (IChPW) design of a cyclone-type separator with a swirling baffle are presented. The experimental work contains the testing of the effect of gas flow rate and rotational speed of the rotor on separation efficiency and pressure drop. The effect of sealing flow on dedusting efficiency was also tested. The separator with a swirling baffle is characterized by high efficiency and low pressure drop. Higher dedusting efficiency and lower pressure drop can be obtained by extension of the baffle height. The calculational method shows good agreement with the experiments.

Cosmic-ray and neutrino emission from Gamma-Ray Bursts with a nuclear cascade

Energy Technology Data Exchange (ETDEWEB)

Biehl, Daniel; Boncioli, Denise; Fedynitch, Anatoli; Winter, Walter

2017-05-24

We discuss neutrino and cosmic-ray emission from Gamma-Ray Bursts (GRBs) with the injection of nuclei, where we take into account that a nuclear cascade from photo-disintegration can fully develop in the source. One of our main objectives is to test if recent results from the IceCube and the Pierre Auger Observatory can be accommodated with the paradigm that GRBs are the sources of Ultra-High Energy Cosmic Rays (UHECRs). While our key results are obtained using an internal shock model, we discuss how the secondary emission from a GRB shell can be interpreted in terms of other astrophysical models. It is demonstrated that the expected neutrino flux from GRBs weakly depends on the injection composition, which implies that prompt neutrinos from GRBs can efficiently test the GRB-UHECR paradigm even if the UHECRs are nuclei. We show that the UHECR spectrum and composition, as measured by the Pierre Auger Observatory, can be self-consistently reproduced in a combined source-propagation model. In an attempt to describe the energy range including the ankle, we find tension with the IceCube bounds from the GRB stacking analyses. In an alternative scenario, where only the UHECRs beyond the ankle originate from GRBs, the requirement for a joint description of cosmic-ray and neutrino observations favors lower luminosities, which does not correspond to the typical expectation from γ-ray observations.

Cosmic-ray and neutrino emission from Gamma-Ray Bursts with a nuclear cascade

International Nuclear Information System (INIS)

Biehl, Daniel; Boncioli, Denise; Fedynitch, Anatoli; Winter, Walter

2017-01-01

We discuss neutrino and cosmic-ray emission from Gamma-Ray Bursts (GRBs) with the injection of nuclei, where we take into account that a nuclear cascade from photo-disintegration can fully develop in the source. One of our main objectives is to test if recent results from the IceCube and the Pierre Auger Observatory can be accommodated with the paradigm that GRBs are the sources of Ultra-High Energy Cosmic Rays (UHECRs). While our key results are obtained using an internal shock model, we discuss how the secondary emission from a GRB shell can be interpreted in terms of other astrophysical models. It is demonstrated that the expected neutrino flux from GRBs weakly depends on the injection composition, which implies that prompt neutrinos from GRBs can efficiently test the GRB-UHECR paradigm even if the UHECRs are nuclei. We show that the UHECR spectrum and composition, as measured by the Pierre Auger Observatory, can be self-consistently reproduced in a combined source-propagation model. In an attempt to describe the energy range including the ankle, we find tension with the IceCube bounds from the GRB stacking analyses. In an alternative scenario, where only the UHECRs beyond the ankle originate from GRBs, the requirement for a joint description of cosmic-ray and neutrino observations favors lower luminosities, which does not correspond to the typical expectation from γ-ray observations.

Energy cascades in Canada

Energy Technology Data Exchange (ETDEWEB)

Hayden, A. C.; Brown, T. D.

1979-03-15

Combining energy uses in a cascade can result in significant overall reductions in fuel requirements. The simplest applications for a cascade are in the recovery of waste heat from existing processes using special boilers or turbines. Specific applications of more-complex energy cascades for Canada are discussed. A combined-cycle plant at a chemical refinery in Ontario is world leader in energy efficiency. Total-energy systems for commercial buildings, such as one installed in a school in Western Canada, offer attractive energy and operating cost benefits. A cogeneration plant proposed for the National Capital Region, generating electricity as well as steam for district heating, allows the use of a low-grade fossil fuel (coal), greatly improves energy-transformation efficiency, and also utilizes an effectively renewable resource (municipal garbage). Despite the widespread availability of equipment and technology of energy cascades, the sale of steam and electricity across plant boundaries presents a barrier. More widespread use of cascades will require increased cooperation among industry, electric utilities and the various levels of government if Canada is to realize the high levels of energy efficiency potential available.

Cascade Organic Solar Cells

KAUST Repository

Schlenker, Cody W.

2011-09-27

We demonstrate planar organic solar cells consisting of a series of complementary donor materials with cascading exciton energies, incorporated in the following structure: glass/indium-tin-oxide/donor cascade/C 60/bathocuproine/Al. Using a tetracene layer grown in a descending energy cascade on 5,6-diphenyl-tetracene and capped with 5,6,11,12-tetraphenyl- tetracene, where the accessibility of the π-system in each material is expected to influence the rate of parasitic carrier leakage and charge recombination at the donor/acceptor interface, we observe an increase in open circuit voltage (Voc) of approximately 40% (corresponding to a change of +200 mV) compared to that of a single tetracene donor. Little change is observed in other parameters such as fill factor and short circuit current density (FF = 0.50 ± 0.02 and Jsc = 2.55 ± 0.23 mA/cm2) compared to those of the control tetracene-C60 solar cells (FF = 0.54 ± 0.02 and Jsc = 2.86 ± 0.23 mA/cm2). We demonstrate that this cascade architecture is effective in reducing losses due to polaron pair recombination at donor-acceptor interfaces, while enhancing spectral coverage, resulting in a substantial increase in the power conversion efficiency for cascade organic photovoltaic cells compared to tetracene and pentacene based devices with a single donor layer. © 2011 American Chemical Society.

Cascade Organic Solar Cells

KAUST Repository

Schlenker, Cody W.; Barlier, Vincent S.; Chin, Stephanie W.; Whited, Matthew T.; McAnally, R. Eric; Forrest, Stephen R.; Thompson, Mark E.

2011-01-01

We demonstrate planar organic solar cells consisting of a series of complementary donor materials with cascading exciton energies, incorporated in the following structure: glass/indium-tin-oxide/donor cascade/C 60/bathocuproine/Al. Using a tetracene layer grown in a descending energy cascade on 5,6-diphenyl-tetracene and capped with 5,6,11,12-tetraphenyl- tetracene, where the accessibility of the π-system in each material is expected to influence the rate of parasitic carrier leakage and charge recombination at the donor/acceptor interface, we observe an increase in open circuit voltage (Voc) of approximately 40% (corresponding to a change of +200 mV) compared to that of a single tetracene donor. Little change is observed in other parameters such as fill factor and short circuit current density (FF = 0.50 ± 0.02 and Jsc = 2.55 ± 0.23 mA/cm2) compared to those of the control tetracene-C60 solar cells (FF = 0.54 ± 0.02 and Jsc = 2.86 ± 0.23 mA/cm2). We demonstrate that this cascade architecture is effective in reducing losses due to polaron pair recombination at donor-acceptor interfaces, while enhancing spectral coverage, resulting in a substantial increase in the power conversion efficiency for cascade organic photovoltaic cells compared to tetracene and pentacene based devices with a single donor layer. © 2011 American Chemical Society.

Analysis of the Impact Caused by Coherent Structures in Swirling Flow Combustion Systems

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Valera-Medina A.

2012-04-01

Full Text Available Amongst the technologies used in the energy and propulsion generation for the reduction of emissions, the use of swirling flows has demonstrated its high performance in anchoring the flame inside of the combustion systems. This, added to the use of premixing in the pre-chambers, has created one of the most innovative methods for the reduction of highly polluting particles such as NOx. However, the lack of understanding of these flows makes it necessary to increase the research on the topic in order to clarify themes as complex as the role of the coherent structures inside of the system. This paper explains some of the phenomena produced by some of the coherent structures observed in the system. The results showed the existence of complex Recirculation Zones (RZ, Precessing Vortex Core (PVC and Combustion Induced Vortex Breakdown (CIVB.

Prediction of soot and thermal radiation in a model gas turbine combustor burning kerosene fuel spray at different swirl levels

Science.gov (United States)

Ghose, Prakash; Patra, Jitendra; Datta, Amitava; Mukhopadhyay, Achintya

2016-05-01

Combustion of kerosene fuel spray has been numerically simulated in a laboratory scale combustor geometry to predict soot and the effects of thermal radiation at different swirl levels of primary air flow. The two-phase motion in the combustor is simulated using an Eulerian-Lagragian formulation considering the stochastic separated flow model. The Favre-averaged governing equations are solved for the gas phase with the turbulent quantities simulated by realisable k-ɛ model. The injection of the fuel is considered through a pressure swirl atomiser and the combustion is simulated by a laminar flamelet model with detailed kinetics of kerosene combustion. Soot formation in the flame is predicted using an empirical model with the model parameters adjusted for kerosene fuel. Contributions of gas phase and soot towards thermal radiation have been considered to predict the incident heat flux on the combustor wall and fuel injector. Swirl in the primary flow significantly influences the flow and flame structures in the combustor. The stronger recirculation at high swirl draws more air into the flame region, reduces the flame length and peak flame temperature and also brings the soot laden zone closer to the inlet plane. As a result, the radiative heat flux on the peripheral wall decreases at high swirl and also shifts closer to the inlet plane. However, increased swirl increases the combustor wall temperature due to radial spreading of the flame. The high incident radiative heat flux and the high surface temperature make the fuel injector a critical item in the combustor. The injector peak temperature increases with the increase in swirl flow mainly because the flame is located closer to the inlet plane. On the other hand, a more uniform temperature distribution in the exhaust gas can be attained at the combustor exit at high swirl condition.

Studi Variasi Beban Pendinginan Di Evaporator Low Stage Sistem Refrigerasi Cascade Menggunakan Heat Exchanger Tipe Concentric Tube Dengan Fluida Kerja Refrigeran Musicool-22 Di High Stage Dan R-404a Di Low Stage

Directory of Open Access Journals (Sweden)

Arrad Ghani Safitra

2013-03-01

Full Text Available Salah satu aplikasi dalam refrigerasi makanan adalah pembekuan daging dalam cold storage. Dimana temperaturnya dijaga konstan dalam standar tertentu untuk mempertahankan kesegaran, memperpanjang masa simpan dan memberikan tekstur daging yang lebih baik. Penggunaan refrigeran Musicool-22 dan R-404A dengan compact heat exchanger pada sistem refrigerasi cascade masih kurang bagus. Sebagai solusi maka akan digunakan sistem refrigerasi cascade dengan refrigeran yang sama dan menggunakan concentric tube sebagai heat exchanger. Penelitian dilakukan dengan merancang alat sistem refrigerasi cascade dengan refrigeran Musicool-22 di High Stage dan R-404A di Low Stage. Kemudian dilakukan eksperimen pada sistem tersebut dengan variasi beban pendinginan di evaporator Low Stage menggunakan electric heater. Variasi mulai dari 0 (tanpa beban, 11, 35, 70, 95, 140, 210, dan 300 Watt. Hasil dari studi eksperimen ini menunjukkan nilai-nilai optimum untuk proses pembekuan daging yaitu pada pembebanan 35 Watt dengan Qevap = 0,327 kW, COPcas = 0,935 dan temperatur di dalam cooling box sebesar -26,2°C. Pada beban 300 Wat diperoleh kapasitas pendinginan maksimum pada sistem Low Stage sebesar 0,622 kW. Kerja maksimum kompresor pada sistem High Stage 0,148 kW dan Low Stage 0,461 kW, nilai COP cascade maksimum 1,020, efek refrigerasi maksimum pada Low Stage 135,865 kJ/kg, HRR maksimum pada Low Stage 1,742 Kemudian diperoleh nilai effectiveness cascade heat exchanger tertinggi 0,93 dan terendah 0,89 serta nilai NTU tertinggi 7,06 dan terendah 4,76 pada saat beban 300Watt.

Coherent Lagrangian swirls among submesoscale motions.

Science.gov (United States)

Beron-Vera, F J; Hadjighasem, A; Xia, Q; Olascoaga, M J; Haller, G

2018-03-05

The emergence of coherent Lagrangian swirls (CLSs) among submesoscale motions in the ocean is illustrated. This is done by applying recent nonlinear dynamics tools for Lagrangian coherence detection on a surface flow realization produced by a data-assimilative submesoscale-permitting ocean general circulation model simulation of the Gulf of Mexico. Both mesoscale and submesoscale CLSs are extracted. These extractions prove the relevance of coherent Lagrangian eddies detected in satellite-altimetry-based geostrophic flow data for the arguably more realistic ageostrophic multiscale flow.

Improving the limits of detection of low background alpha emission measurements

Science.gov (United States)

McNally, Brendan D.; Coleman, Stuart; Harris, Jack T.; Warburton, William K.

2018-01-01

Alpha particle emission - even at extremely low levels - is a significant issue in the search for rare events (e.g., double beta decay, dark matter detection). Traditional measurement techniques require long counting times to measure low sample rates in the presence of much larger instrumental backgrounds. To address this, a commercially available instrument developed by XIA uses pulse shape analysis to discriminate alpha emissions produced by the sample from those produced by other surfaces of the instrument itself. Experience with this system has uncovered two residual sources of background: cosmogenics and radon emanation from internal components. An R&D program is underway to enhance the system and extend the pulse shape analysis technique further, so that these residual sources can be identified and rejected as well. In this paper, we review the theory of operation and pulse shape analysis techniques used in XIA's alpha counter, and briefly explore data suggesting the origin of the residual background terms. We will then present our approach to enhance the system's ability to identify and reject these terms. Finally, we will describe a prototype system that incorporates our concepts and demonstrates their feasibility.

KEWPIE2: A cascade code for the study of dynamical decay of excited nuclei

OpenAIRE

Lu , H.; Marchix , A.; Abe , Y.; Boilley , D.

2016-01-01

Submitted to Computer Physics Communications; International audience; KEWPIE — a cascade code devoted to investigating the dynamical decay of excited nuclei, specially designed for treating very low probability events related to the synthesis of super-heavy nuclei formed in fusion-evaporation reactions — has been improved and rewritten in C++ programing language to become KEWPIE2. The current version of the code comprises various nuclear models concerning the light-particle emission, fission ...

A Computational Fluid Dynamics Study of Swirling Flow Reduction by Using Anti-Vortex Baffle

Science.gov (United States)

Yang, H. Q.; Peugeot, John W.; West, Jeff S.

2017-01-01

An anti-vortex baffle is a liquid propellant management device placed adjacent to an outlet of the propellant tank. Its purpose is to substantially reduce or eliminate the formation of free surface dip and vortex, as well as prevent vapor ingestion into the outlet, as the liquid drains out through the flight. To design an effective anti-vortex baffle, Computational Fluid Dynamic (CFD) simulations were undertaken for the NASA Ares I vehicle LOX tank subjected to the simulated flight loads with and without the anti-vortex baffle. The Six Degree-Of-Freedom (6-DOF) dynamics experienced by the Crew Launch Vehicle (CLV) during ascent were modeled by modifying the momentum equations in a CFD code to accommodate the extra body forces from the maneuvering in a non-inertial frame. The present analysis found that due to large moments, the CLV maneuvering has a significant impact on the vortical flow generation inside the tank. Roll maneuvering and side loading due to pitch and yaw are shown to induce swirling flow. The vortical flow due to roll is symmetrical with respect to the tank centerline, while those induced by pitch and yaw maneuverings showed two vortices side by side. The study found that without the anti-vortex baffle, the swirling flow caused surface dip during the late stage of drainage and hence early vapor ingestion. The flow can also be non-uniform in the drainage pipe as the secondary swirling flow velocity component can be as high as 10% of the draining velocity. An analysis of the vortex dynamics shows that the swirling flow in the drainage pipe during the Upper Stage burn is mainly the result of residual vortices inside the tank due to the conservation of angular momentum. The study demonstrated that the swirling flow in the drainage pipe can be effectively suppressed by employing the anti-vortex baffle.

Broadband enhancement of spontaneous emission in a photonic-plasmonic structure

DEFF Research Database (Denmark)

Zhu, Xiaolong; Xie, Fengxian; Shi, Lei

2012-01-01

We demonstrate that a broadband enhancement of spontaneous emission can be achieved within a photonic-plasmonic structure. The structure can strongly modify the spontaneous emission by exciting plasmonic modes. Because of the excited plasmonic modes, an enhancement up to 30 times is observed, lea......, leading to a 4 times broader emission spectrum. The reflectance measurement and the finite-difference time-domain simulation are carried out to support these results....

Low emission internal combustion engine

Science.gov (United States)

Karaba, Albert M.

1979-01-01

A low emission, internal combustion compression ignition engine having a cylinder, a piston movable in the cylinder and a pre-combustion chamber communicating with the cylinder near the top thereof and in which low emissions of NO.sub.x are achieved by constructing the pre-combustion chamber to have a volume of between 70% and 85% of the combined pre-chamber and main combustion chamber volume when the piston is at top dead center and by variably controlling the initiation of fuel injection into the pre-combustion chamber.

Experimental investigation of combustion instabilities in lean swirl-stabilized partially-premixed flames in single- and multiple-burner setup

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Christian Kraus

2016-03-01

Full Text Available In the present work, combustion instabilities of a modular combustor are investigated. The combustor operates with partially premixed, swirl-stabilized flames and can be operated in single- and different multiple-burner setups. The design parameters of the combustor prevent large-scale flame–flame interactions in the multiple-burner arrangements. The objective is to investigate how the interaction of the swirl jets affects the thermoacoustic stability of the combustor. Results of measurements of pressure oscillations and high-speed OH*-chemiluminescence imaging for the single-burner setup and two multiple-burner setups are discussed. Additionally, results of investigations with different flame characteristics are presented. These are achieved by varying the ratio of the mass flow rates through the swirlers of the double-concentric swirl nozzle. Several unstable modes with high pressure amplitudes are observed in the single-burner setup as well as in the multiple-burner setups. Numerical studies of the acoustic behavior of the combustor setups were performed that indicate that the different geometries show similar acoustic behaviors. The results lead to the conclusion that the interaction of the swirl jets in the multiple-burner setups affects the thermoacoustic response spectrum of the flame even in the absence of large-scale flame–flame interactions. Based on the findings in earlier studies, it is concluded that the differences in the flame response characteristics are induced by the reduction of the swirl intensity in the multiple-burner arrangements, which is caused by the exchange of momentum between the adjacent swirl jets.

Large Eddy Simulation of Flow Structures in the Sydney Swirl Burner

DEFF Research Database (Denmark)

Yang, Yang

. The theories of LES and the corresponding closure models have been well developed. This research focuses on statistical analysing flow field and characteristic features. Validation studies show good agreement in the isothermal cases, while for the reacting case, the LES predictions are less satisfactory...... zone which starts at the burner surface. As for the medium swirling isothermal case, there are two reverse flow zones in the reacting case. Due to the low stoichiometric mixture fraction in the methane flame, only the outer layer of the bluff‐body induced reverse zone is reactive. The main reactive...... method strategy has limitations concerning wall bounded flows, especially for complex geometries typically found in industry. Multi‐phase flows need special treatment....

Numerical Study of Correlation of Fluid Particle Acceleration and Turbulence Intensity in Swirling Flow

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Nan Gui

2015-01-01

Full Text Available Numerical investigation of correlation between the fluid particle acceleration and the intensity of turbulence in swirling flows at a large Reynolds number is carried out via direct numerical simulation. A weak power-law form correlation ur.m.sE~C(aLφ between the Lagrangian acceleration and the Eulerian turbulence intensity is derived. It is found that the increase of the swirl level leads to the increase of the exponent φ and the trajectory-conditioned correlation coefficient ρ(aL,uE and results in a weak power-law augmentation of the acceleration intermittency. The trajectory-conditioned convection of turbulence fluctuation in the Eulerian viewpoint is generally linearly proportional to the fluctuation of Lagrangian accelerations, indicating a weak but clear relation between the Lagrangian intermittency and Eulerian intermittency effects. Moreover, except the case with vortex breakdown, the weak linear dependency is maintained when the swirl levels change, only with the coefficient of slope varied.

International Assistance for Low-Emission Development Planning: Coordinated Low Emissions Assistance Network (CLEAN) Inventory of Activities and Tools--Preliminary Trends

Energy Technology Data Exchange (ETDEWEB)

Cox, S.; Benioff, R.

2011-05-01

The Coordinated Low Emissions Assistance Network (CLEAN) is a voluntary network of international practitioners supporting low-emission planning in developing countries. The network seeks to improve quality of support through sharing project information, tools, best practices and lessons, and by fostering harmonized assistance. CLEAN has developed an inventory to track and analyze international technical support and tools for low-carbon planning activities in developing countries. This paper presents a preliminary analysis of the inventory to help identify trends in assistance activities and tools available to support developing countries with low-emission planning.

Enhanced radiative Auger emission from lithiumlike 20Ca17+

International Nuclear Information System (INIS)

Bernstein, E.M.; Clark, M.W.; Tanis, J.A.; Graham, W.G.; Morgan, T.J.; Stoeckli, M.P.; Berkner, K.H.; Schlachter, A.S.; Stearns, J.W.

1991-01-01

Radiative Auger emission (RAE) from lithiumlike 20 Ca 17+ projectiles excited in collisions with He has been measured. The intensity of RAE photons relative to K α X-ray emission is enhanced by a factor of 10-17 compared with theoretical calculations for ions with few electron vacancies. The enhancement of RAE for Ca 17+ is consistent with the results reported previously for lithiumlike 16 S 13+ and 23 V 20+ and indicates a systematic dependence on Z. Both the enhancement and the relative RAE transition rate increase with Z. (orig.)

Collisional cascading - The limits of population growth in low earth orbit

Science.gov (United States)

Kessler, Donald J.

1991-01-01

Random collisions between made-made objects in earth orbit will lead to a significant source of orbital debris, but there are a number of uncertainties in these models, and additional analysis and data are required to fully characterize the future environment. However, the nature of these uncertainties are such that while the future environment is uncertain, the fact that collisions will control the future environment is less uncertain. The data that already exist is sufficient to show that cascading collisions will control the future debris environment with no, or very minor increases in the current low-earth-orbit population. Two populations control this process: explosion fragments and expended rocket bodies and payloads. Practices are already changing to limit explosions in low earth orbit; it is necessary to begin limiting the number of expended rocket bodies and payloads in orbit.

Stationary rotary force waves on the liquid-air core interface of a swirl atomizer

Science.gov (United States)

Chinn, J. J.; Cooper, D.; Yule, A. J.; Nasr, G. G.

2016-10-01

A one-dimensional wave equation, applicable to the waves on the surface of the air-core of a swirl atomizer is derived analytically, by analogy to the similar one-dimensional wave equation derivation for shallow-water gravity waves. In addition an analogy to the flow of water over a weir is used to produce an analytical derivation of the flow over the lip of the outlet of a swirl atomizer using the principle of maximum flow. The principle of maximum flow is substantiated by reference to continuity of the discharge in the direction of streaming. For shallow-water gravity waves, the phase velocity is the same expression as for the critical velocity over the weir. Similarly, in the present work, the wave phase velocity on the surface of the air-core is shown to be the same expression as for the critical velocity for the flow at the outlet. In addition, this wave phase velocity is shown to be the square root of the product of the radial acceleration and the liquid thickness, as analogous with the wave phase velocity for shallow water gravity waves, which is the square root of the product of the acceleration due to gravity and the water depth. The work revisits the weirs and flumes work of Binnie et al. but using a different methodology. The results corroborate with the work of Binnie. High speed video, Laser Doppler Anemometry and deflected laser beam experimental work has been carried out on an oversize Perspex (Plexiglas) swirl atomizer. Three distinctive types of waves were detected: helical striations, low amplitude random ripples and low frequency stationary waves. It is the latter wave type that is considered further in this article. The experimentally observed waves appear to be stationary upon the axially moving flow. The mathematical analysis allows for the possibility of a negative value for the phase velocity expression. Therefore the critical velocity and the wave phase velocity do indeed lead to stationary waves in the atomizer. A quantitative comparison

Cascaded Emission Regions in 2.4 μm GaInAsSb Light Emitting Diode's for Improved Current Efficiency

Science.gov (United States)

Prineas, John; Yager, Jeff; Olesberg, Jonathon; Cao, Chuanshun; Reddy, Madhu; Coretsopoulos, Chris

2008-03-01

Infrared optoelectronics play an important role in sensing of molecules through characteristic vibrational resonances that occur at those wavelengths. For molecules in aqueous and at room temperature, where optical transistions tend to be broad, the broadband emission of light emitting diodes (LEDs) are well suited for obtaining molecular absorption spectra. The 2-2.6 μm range is an advantageous range for sensing of glucose. Voltages available in batteries and control electronics are limited to much higher voltages than those required to turn on an infrared LED, and moreover have limited current supply. Here, we demonstrate room temperature operature of 5-stage cascaded emission regions in 2-2.6 μm GaInAsSb LEDs. We report three times higher turn on voltage, and nine times improved current efficiency compared to a single stage device.

Interband cascade lasers

International Nuclear Information System (INIS)

Vurgaftman, I; Meyer, J R; Canedy, C L; Kim, C S; Bewley, W W; Merritt, C D; Abell, J; Weih, R; Kamp, M; Kim, M; Höfling, S

2015-01-01

We review the current status of interband cascade lasers (ICLs) emitting in the midwave infrared (IR). The ICL may be considered the hybrid of a conventional diode laser that generates photons via electron–hole recombination, and an intersubband-based quantum cascade laser (QCL) that stacks multiple stages for enhanced current efficiency. Following a brief historical overview, we discuss theoretical aspects of the active region and core designs, growth by molecular beam epitaxy, and the processing of broad-area, narrow-ridge, and distributed feedback (DFB) devices. We then review the experimental performance of pulsed broad area ICLs, as well as the continuous-wave (cw) characteristics of narrow ridges having good beam quality and DFBs producing output in a single spectral mode. Because the threshold drive powers are far lower than those of QCLs throughout the λ = 3–6 µm spectral band, ICLs are increasingly viewed as the laser of choice for mid-IR laser spectroscopy applications that do not require high output power but need to be hand-portable and/or battery operated. Demonstrated ICL performance characteristics to date include threshold current densities as low as 106 A cm −2 at room temperature (RT), cw threshold drive powers as low as 29 mW at RT, maximum cw operating temperatures as high as 118 °C, maximum cw output powers exceeding 400 mW at RT, maximum cw wallplug efficiencies as high as 18% at RT, maximum cw single-mode output powers as high as 55 mW at RT, and single-mode output at λ = 5.2 µm with a cw drive power of only 138 mW at RT. (topical review)

Test Results for Rotordynamic Coefficients of the SSME HPOTP Turbine Interstage Seal with Two Swirl Brakes

Science.gov (United States)

Childs, Dara W.; Baskharone, Erian; Ramsey, Christopher

1991-01-01

Test results are presented for the HPOTP Turbine Interstage Seal with both the current and an alternate, aerodynamically designed, swirl brake. Tests were conducted at speeds out to 16,000 rpm, supply pressures up to 18.3 bars, and the following three inlet tangential velocity conditions: (1) no preswirl; (2) intermediate preswirl in the direction of rotation; and (3) high preswirl in the direction of rotation. The back pressure can be controlled independently and was varied to yield the following four pressure ratios: 0.4, 0.45, 0.56, and 0.67. The central and simplest conclusion to be obtained from the test series is that the alternate swirl brake consistently outperforms the current swirl brake in terms of stability performance. The alternate swirl brake's whirl frequency ratio was generally about one half or less than corresponding values for the current design. In many cases, the alternate design yielded negative whirl frequency ratio values in comparison to positive values for the current design. The alternate design can be directly substituted into the space currently occupied by the current design. There is no change in leakage performance.

Cosmic ray and neutrino emission from gamma-ray bursts with a nuclear cascade

Science.gov (United States)

Biehl, D.; Boncioli, D.; Fedynitch, A.; Winter, W.

2018-04-01

Aim. We discuss neutrino and cosmic ray emission from gamma-ray bursts (GRBs) with the injection of nuclei, where we take into account that a nuclear cascade from photodisintegration can fully develop in the source. Our main objective is to test whether recent results from the IceCube and the Pierre Auger Observatory can be accommodated within the paradigm that GRBs are the sources of ultra-high-energy cosmic rays (UHECRs). Methods: We simulate this scenario in a combined source-propagation model. While our key results are obtained using an internal shock model of the source, we discuss how the secondary emission from a GRB shell can be interpreted in terms of other astrophysical models. Results: We demonstrate that the expected neutrino flux from GRBs weakly depends on the injection composition for the same injection spectra and luminosities, which implies that prompt neutrinos from GRBs can efficiently test the GRB-UHECR paradigm even if the UHECRs are nuclei. We show that the UHECR spectrum and composition, as measured by the Pierre Auger Observatory, can be self-consistently reproduced. In an attempt to describe the energy range including the ankle, we find tension with the IceCube bounds from the GRB stacking analyses. In an alternative scenario, where only the UHECRs beyond the ankle originate from GRBs, the requirement for a joint description of cosmic ray and neutrino observations favors lower luminosities, which does not correspond to the typical expectation from γ-ray observations.

Field emission properties of low-density carbon nanotubes prepared on anodic aluminum-oxide template

Energy Technology Data Exchange (ETDEWEB)

Jeong, Soo-Hwan [Samsung Advanced Institute of Technology, Suwon (Korea, Republic of); Lee, Kun-Hong [Pohang University of Science and Technology, Pohang (Korea, Republic of)

2004-08-15

Anodic aluminum-oxide (AAO) templates were fabricated by two-step anodizing an Al film. After the Co catalyst had been electrochemically deposited onto the bottom of the AAO template, carbon nanotubes (CNTs) were grown by using catalytic pyrolysis of C{sub 2}H{sub 2} and H{sub 2} at 650 .deg. C. Overgrowth of CNTs with low density on the AAO templates was observed. The field-emission measurements on the samples showed a turn-on field of 2.17 V/mum and a field enhancement factor of 5700. The emission pattern on a phosphor screen was quite homogeneous over the area at a relatively low electric field.

Swirling Combustor Energy Converter: H2/Air Simulations of Separated Chambers

Directory of Open Access Journals (Sweden)

Angelo Minotti

2015-09-01

Full Text Available This work reports results related to the “EU-FP7-HRC-Power” project aiming at developing micro-meso hybrid sources of power. One of the goals of the project is to achieve surface temperatures up to more than 1000 K, with a ∆T ≤ 100 K, in order to be compatible with a thermal/electrical conversion by thermo-photovoltaic cells. The authors investigate how to reach that goal adopting swirling chambers integrated in a thermally-conductive and emitting element. The converter consists of a small parallelepiped brick inside two separated swirling meso-combustion chambers, which heat up the parallelepiped, emitting material by the combustion of H2 and air at ambient pressure. The overall dimension is of the order of cm. Nine combustion simulations have been carried out assuming detailed chemistry, several length/diameter ratios (Z/D = 3, 5 and 11 and equivalence ratios (0.4, 0.7 and 1; all are at 400 W of injected chemical power. Among the most important results are the converter surfaces temperatures, the heat loads, provided to the environment, and the chemical efficiency. The high chemical efficiency, h > 99.9%, is due to the relatively long average gas residence time coupled with the fairly good mixing due to the swirl motion and the impinging air/fuel jets that provide heat and radicals to the flame.

Low-Loss Hollow Waveguide Fibers for Mid-Infrared Quantum Cascade Laser Sensing Applications

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James A. Harrington

2013-01-01

Full Text Available We report on single mode optical transmission of hollow core glass waveguides (HWG coupled with an external cavity mid-IR quantum cascade lasers (QCLs. The QCL mode results perfectly matched to the hybrid HE11 waveguide mode and the higher losses TE-like modes have efficiently suppressed by the deposited inner dielectric coating. Optical losses down to 0.44 dB/m and output beam divergence of ~5 mrad were measured. Using a HGW fiber with internal core size of 300 µm we obtained single mode laser transmission at 10.54 µm and successful employed it in a quartz enhanced photoacoustic gas sensor setup.

Making of Croatian Low-Emission Development Strategy

International Nuclear Information System (INIS)

Bartle, B.; Herencic, L.; Kordic, Z.; Pasicko, R.; Vlasic, S.

2012-01-01

A Low-Emission Development Strategy (LEDS) is a national, high-level, comprehensive, long-term strategy, developed by domestic stakeholders, which aims at decoupling economic growth and social development from greenhouse gas (GHG) emissions growth. Croatia has begun to join the growing list of countries in the world that have already developed a long-term strategy for low-emissions development and thereby take the road of sustainable development. The 16th Conference of the Parties'' (COP), held in Cancun in December 2010, adopted the Cancun Agreements - a historic set of decisions laying the foundation to tackle climate change through a new post-2012 regime. The Cancun Agreements ''encourages governments to prepare low-carbon development strategies in the context of sustainable development.'' and ''realizes that addressing climate change requires a paradigm shift towards building a low-carbon society that offers substantial opportunities and ensures continued high growth and sustainable development''. Recently the European Commission adopted a Roadmap for transforming the European Union into a competitive low carbon economy by 2050. The Roadmap describes the cost-effective pathway to reach the EU's objective of cutting greenhouse gas emissions by 80-95% of 1990 levels by 2050. On the domestic level, the LEDS is a country-driven policy instrument for national decision making. The LEDS supports sector transformation through a national, economy-wide approach. On the international level, LEDS support the global goal of GHG emission reduction. The Croatian Ministry of Environmental and Nature Protection in cooperation with United Nations Development Programme (UNDP) Croatia will design and implement the Low-Emissions Development Strategy (LEDS) under project titled ''Supporting RBEC countries transition to low-emission development''. The LEDS merges climate change action with national sustainable development and helps to identify and prioritize nationally appropriate

Has spring snowpack declined in the Washington Cascades?

Directory of Open Access Journals (Sweden)

P. Mote

2008-02-01

Full Text Available Our best estimates of 1 April snow water equivalent (SWE in the Cascade Mountains of Washington State indicate a substantial (roughly 15–35% decline from mid-century to 2006, with larger declines at low elevations and smaller declines or increases at high elevations. This range of values includes estimates from observations and hydrologic modeling, reflects a range of starting points between about 1930 and 1970 and also reflects uncertainties about sampling. The most important sampling issue springs from the fact that half the 1 April SWE in the Cascades is found below about 1240 m, altitudes at which sampling was poor before 1945. Separating the influences of temperature and precipitation on 1 April SWE in several ways, it is clear that long-term trends are dominated by trends in temperature, whereas variability in precipitation adds "noise" to the time series. Consideration of spatial and temporal patterns of change rules out natural variations like the Pacific Decadal Oscillation as the sole cause of the decline. Regional warming has clearly played a role, but it is not yet possible to quantify how much of that regional warming is related to greenhouse gas emissions.

Biochar helps enhance maize productivity and reduce greenhouse gas emissions under balanced fertilization in a rainfed low fertility inceptisol.

Science.gov (United States)

Zhang, Dengxiao; Pan, Genxing; Wu, Gang; Kibue, Grace Wanjiru; Li, Lianqing; Zhang, Xuhui; Zheng, Jinwei; Zheng, Jufeng; Cheng, Kun; Joseph, Stephen; Liu, Xiaoyu

2016-01-01

Maize production plays an important role in global food security, especially in arid and poor-soil regions. Its production is also increasing in China in terms of both planting area and yield. However, maize productivity in rainfed croplands is constrained by low soil fertility and moisture insufficiency. To increase the maize yield, local farmers use NPK fertilizer. However, the fertilization regime (CF) they practice is unbalanced with too much nitrogen in proportion to both phosphorus and potassium, which has led to low fertilizer use efficiency and excessive greenhouse gases emissions. A two-year field experiment was conducted to assess whether a high yielding but low greenhouse gases emission system could be developed by the combination of balanced fertilization (BF) and biochar amendment in a rainfed farmland located in the Northern region of China. Biochar was applied at rates of 0, 20, and 40 t/ha. Results show that BF and biochar increased maize yield and partial nutrient productivity and decreased nitrous oxide (N2O) emission. Under BF the maize yield was 23.7% greater than under CF. N2O emissions under BF were less than half that under CF due to a reduced N fertilizer application rate. Biochar amendment decreased N2O by more than 31% under CF, while it had no effect on N2O emissions under BF. Thus BF was effective at maintaining a high maize yield and reducing greenhouse gases emissions. If combined with biochar amendment, BF would be a good way of sustaining low carbon agriculture in rainfed areas. Copyright © 2015 Elsevier Ltd. All rights reserved.

Photothermal Effect Enhanced Cascade-Targeting Strategy for Improved Pancreatic Cancer Therapy by Gold Nanoshell@Mesoporous Silica Nanorod.

Science.gov (United States)

Zhao, Ruifang; Han, Xuexiang; Li, Yiye; Wang, Hai; Ji, Tianjiao; Zhao, Yuliang; Nie, Guangjun

2017-08-22

Pancreatic cancer, one of the leading causes of cancer-related mortality, is characterized by desmoplasia and hypovascular cancerous tissue, with a 5 year survival rate of targeting (mediated by photothermal effect and molecular receptor binding) and photothermal treatment-enhanced gemcitabine chemotherapy, under mild near-infrared laser irradiation condition. GNRS significantly improved gemcitabine penetration and accumulation in tumor tissues, thus destroying the dense stroma barrier of pancreatic cancer and reinforcing chemosensitivity in mice. Our current findings strongly support the notion that further development of this integrated plasmonic photothermal strategy may represent a promising translational nanoformulation for effective treatment of pancreatic cancer with integral cascade tumor targeting strategy and enhanced drug delivery efficacy.

Implementation of an integrating sphere for the enhancement of noninvasive glucose detection using quantum cascade laser spectroscopy

Science.gov (United States)

Werth, Alexandra; Liakat, Sabbir; Dong, Anqi; Woods, Callie M.; Gmachl, Claire F.

2018-05-01

An integrating sphere is used to enhance the collection of backscattered light in a noninvasive glucose sensor based on quantum cascade laser spectroscopy. The sphere enhances signal stability by roughly an order of magnitude, allowing us to use a thermoelectrically (TE) cooled detector while maintaining comparable glucose prediction accuracy levels. Using a smaller TE-cooled detector reduces form factor, creating a mobile sensor. Principal component analysis has predicted principal components of spectra taken from human subjects that closely match the absorption peaks of glucose. These principal components are used as regressors in a linear regression algorithm to make glucose concentration predictions, over 75% of which are clinically accurate.

Turbulent swirling flow in a dynamic model of a uniflow-scavenged two-stroke engine

DEFF Research Database (Denmark)

Ingvorsen, Kristian Mark; Meyer, Knud Erik; Walther, Jens Honore

2014-01-01

turbulence models. In the present work, the flow in a dynamic scale model of a uniflowscavenged cylinder is investigated experimentally. The model has a transparent cylinder and a moving piston driven by a linear motor. The flow is investigated using phase-locked stereoscopic particle image velocimetry (PIV...... cannot be assumed to be quasi-steady. The temporal development of the swirl strength is investigated by computing the angular momentum. The swirl strength shows an exponential decay from scavenge port closing to scavenge port opening corresponding to a reduction of 34 %, which is in good agreement...

Cascaded Photoenhancement: Implications for Photonic Chemical and Biological Sensors

Science.gov (United States)

Fuller, Kirk A.; Smith, David D.

2006-01-01

Our analysis shows that coupling of gold nanoparticles to microspheres will evoke a cascading effect from the respective photoenhancement mechanisms. We refer to this amplification process as cascaded photoenhancement, and the resulting cavity amplification of surface-enhanced Raman scattering (SERS) and fluorescence as CASERS and CAF, respectively. Calculations, based on modal analysis of scattering and absorption by compound spheres, presented herein indicate that the absorption cross sections of metal nanoparticles immobilized onto dielectric microspheres can be greatly enhanced by cavity resonances in the microspheres without significant degradation of the resonators. Gain factors associated with CSP of 10(exp 3) - 10(exp 4) are predicted for realistic experimental conditions using homogenous microspheres. Cascaded surface photoenhancement thus has the potential of dramatically increasing the sensitivities of fluorescence and vibrational spectroscopies.

Scaling laws for gas–liquid flow in swirl vane separators

International Nuclear Information System (INIS)

Liu, Li; Bai, Bofeng

2016-01-01

Highlights: • Model for swirl vane separator performance is established with similarity criteria. • Scaling laws are developed to correlate downscale test with prototype separator. • Effects of key similarity criteria on separation performance are studied. • The vital role of droplet size distribution on separation performance is discussed. - Abstract: Laboratory tests on gas–liquid flow in swirl vane separators are usually carried out to help establish an experimental database for separator design and performance improvement. Such model tests are generally performed in the reduced scale and not on the actual working conditions. Though great efficiency is often obtainable in the reduced model, the performance of the full-sized prototype usually cannot be well predicted. To design downscale model tests and apply the experimental results to predict the prototype, a general relationship to correlate them is required. In this paper, the relation of the similitude-criterion concerning the pressure loss is presented by using the dimensionless analysis, and mathematical models for critical droplet diameter, grade efficiency and overall separation efficiency are established by analyzing the features of the droplet trajectory in gas swirling flow field. The essential similarity criteria accounting for pressure loss and separation efficiency are obtained, respectively. On this basis, the scaling laws which enable a comparison between the reduced model and the full-sized prototype under similar conditions are also developed. It is found that the overall separation efficiency is significantly affected by the size distribution of the small droplets, especially when the mean diameter is smaller than the critical droplet diameter.

Novel swirl-flow reactor for kinetic studies of semiconductor photocatalysis

NARCIS (Netherlands)

Ray, A.K; Beenackers, A.A C M

1997-01-01

A new two-phase swirl-flow monolithic-type reactor was designed to study the kinetics of heterogeneous photocatalytic processes on immobilized semiconductor catalysts. True kinetic rate constants for destruction of a textile dye were measured as a function of wavelength of light intensity and angle

Volatile emissions from Cascade cinder cone eruptions: Implications for future hazard assessments in the Central and Southern Cascades

Science.gov (United States)

Walsh, L. K.; Wallace, P. J.; Cashman, K. V.

2012-12-01

An abundance of hazardous effects including ash fall out, basaltic lava flows and poisonous volcanic gas have been documented at active volcanic centers (e.g. Auckland Volcanic Field, New Zealand; Bebbington and Cronin 2011) and have been inferred using tools such as geologic mapping and geochemical analyses for prehistoric eruptions (e.g. Cerro Negro, Nicaragua; Hill et al. 1995; McKnight and Williams 1997). The Cascades volcanic history is also dominated by prehistoric eruptions; however the associated hazards have yet to be studied in-depth. Short recurrence rates of cinder cone volcanism (1x10-5 to 5x10-4 events/yr; Smid et al. 2009) likely intensify the probability of human experience with cinder cone hazards. Hence, it is important to understand the effects that cinder cone volcanism can have on communities near the Cascades. In this study, we estimate volatile fluxes of prehistoric Cascade cinder cone eruptions by analyzing olivine-hosted melt inclusions and rapidly quenched tephra matrix glass. The melt inclusions provide pre-eruptive volatile concentrations whereas tephra groundmass glass provides post-eruptive volatile concentrations. By comparing initial and final concentrations we can determine the amounts of sulfur, chlorine and fluorine released into the atmosphere. We have analyzed S, Cl and F concentrations in melt inclusions from cinder cones in the Central Oregon Cascades (Collier Cone, Yapoah Crater, Four-in-One Fissure, Garrison Butte) and in Northern California near Mt. Lassen (Cinder Cone, Basalt of Old Railroad Grade, Basalt of Highway 44). Analyses of volatiles in melt inclusions and matrix glasses were done using the Cameca SX100 electron microprobe at the University of Oregon. Melt inclusions and matrix glass were run under 15kV, 50nA, and 10μm-beam conditions. For F analyses, a use of an LTAP crystal and relatively long counting times (160 sec. on peak) resulted in good analytical precision. Preliminary results for melt inclusions from

Non-spill control squared cascade

International Nuclear Information System (INIS)

Kai, Tsunetoshi; Inoue, Yoshiya; Oya, Akio; Suemori, Nobuo.

1974-01-01

Object: To reduce a mixed loss thus enhancing separating efficiency by the provision of a simple arrangement wherein a reflux portion in a conventional spill control squared cascade is replaced by a special stage including centrifugal separators. Structure: Steps in the form of a square cascade, in which a plurality of centrifugal separators are connected by pipe lines, are accumulated in multistage fashion to form a squared cascade. Between the adjoining steps is disposed a special stage including a centrifugal separator which receives both lean flow from the upper step and rich flow from the lower step. The centrifugal separator in the special stage has its rich side connected to the upper step and its lean side connected to the lower step. Special stages are each disposed at the upper side of the uppermost step and at the lower side of the lowermost step. (Kamimura, M.)

The High-Temperature Resistance Properties of Polysiloxane/Al Coatings with Low Infrared Emissivity

Directory of Open Access Journals (Sweden)

Jun Zhao

2018-03-01

Full Text Available High-temperature-resistant coatings with low infrared emissivity were prepared using polysiloxane resin and flake aluminum as the adhesive and pigment, respectively. The heat resistance mechanisms of the polysiloxane/Al coating were systematically investigated. The composition, surface morphology, infrared reflectance spectra, and thermal expansion dimension (ΔL of the coatings were characterized by X-ray photoelectron spectroscopy (XPS, field emission scanning electron microscopy (FE-SEM, Fourier transform infrared spectroscopy, and thermal mechanical analysis (TMA, respectively. The results show that thermal decomposition of the resin and mismatch of ΔL between the coating and the substrate facilitate the high temperature failure of the coating. A suitable amount of flake aluminum pigments could restrain the thermal decomposition of the resin and could increase the match degree of ΔL between the coating and substrate, leading to an enhanced thermal resistance of the coating. Our results find that a coating with a pigment to binder ratio (P/B ratio of 1.0 could maintain integrity until 600 °C, and the infrared emissivity was as low as 0.27. Hence, a coating with high-temperature resistance and low emissivity was obtained. Such coatings can be used for infrared stealth technology or energy savings in high-temperature equipment.

PIV Study of the Effect of Piston Motion on the Confined Swirling Flow in the Scavenging Process in 2-Stroke Marine Diesel Engines

DEFF Research Database (Denmark)

Haider, Sajjad; Meyer, Knud Erik; Schramm, Jesper

2010-01-01

The effect of piston motion on the incylinder swirling flow for a low speed, large two-stroke marine diesel engine is studies using the stereoscopic PIV technique. The measuremenrs are conducted at 5 cross sectional planes along the cylinder length and at piston positions covering the air intake...

Effects of Enhanced Eathode Electron Emission on Hall Thruster Operation

International Nuclear Information System (INIS)

Raitses, Y.; Smirnov, A.; Fisch, N.J.

2009-01-01

Interesting discharge phenomena are observed that have to do with the interaction between the magnetized Hall thruster plasma and the neutralizing cathode. The steadystate parameters of a highly ionized thruster discharge are strongly influenced by the electron supply from the cathode. The enhancement of the cathode electron emission above its self-sustained level affects the discharge current and leads to a dramatic reduction of the plasma divergence and a suppression of large amplitude, low frequency discharge current oscillations usually related to an ionization instability. These effects correlate strongly with the reduction of the voltage drop in the region with the fringing magnetic field between the thruster channel and the cathode. The measured changes of the plasma properties suggest that the electron emission affects the electron cross-field transport in the thruster discharge. These trends are generalized for Hall thrusters of various configurations.

Analysis of the pressure fields in a swirling annular jet flow

Science.gov (United States)

Percin, M.; Vanierschot, M.; Oudheusden, B. W. van

2017-12-01

In this paper, we investigate the flow structures and pressure fields of a free annular swirling jet flow undergoing vortex breakdown. The flow field is analyzed by means of time-resolved tomographic particle image velocimetry measurements, which enable the reconstruction of the three-dimensional time-resolved pressure fields using the governing flow equations. Both time-averaged and instantaneous flow structures are discussed, including a characterization of the first- and second-order statistical moments. A Reynolds decomposition of the flow field shows that the time-averaged flow is axisymmetric with regions of high anisotropic Reynolds stresses. Two recirculation zones exist that are surrounded by regions of very intense mixing. Notwithstanding the axisymmetric nature of the time-averaged flow, a non-axisymmetric structure of the instantaneous flow is revealed, comprising a central vortex core which breaks up into a precessing vortex core. The winding sense of this helical structure is opposite to the swirl direction and it is wrapped around the vortex breakdown bubble. It precesses around the central axis of the flow at a frequency corresponding to a Strouhal number of 0.27. The precessing vortex core is associated with a low-pressure region along the central axis of the jet and the maximum pressure fluctuations occur upstream of the vortex breakdown location, where the azimuthal velocity component also reaches peak values as a result of the inward motion of the fluid and the conservation of angular momentum. The POD analysis of the pressure fields suggests that the precessing helical vortex formation is the dominant coherent structure in the instantaneous flow.

Enhancement of electroplex emission by using multi-layer device structure

International Nuclear Information System (INIS)

Wang Yuanmin; Teng Feng; Xu Zheng; Hou Yanbing; Wang Yongsheng; Xu Xurong

2005-01-01

Electroplex emission based on poly(N-vinylcarbazole) (PVK) and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) has been improved dramatically by using a multi-layer device structure indium-tin oxide (ITO)/poly(3,4-ethylenedioxythiophene): poly(styrenesulphonic acid) (PEDOT:PSS)/PVK/BCP/PVK/BCP/LiF/Al. Electroplex emission at 595 nm has been improved about 10 times under low voltage and four times under high voltage compared to the double layer device ITO/PVK/BCP/Al. The maximum brightness of the device also has been improved about eight times. Bright white emission via electroplex formation can be obtained with Commission International d'Eclairage (CIE) coordinates (0.336, 0.320) at 26 V with a brightness of 123 cd/m 2 . Based on the analysis of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the materials, we suggest the enhancement is mainly ascribed to the confinement effect of the quantum-well-like multi-layer device structure. Every hole and electron has more possibilities to cross recombination at the PVK/BCP interface

Enhancement of electroplex emission by using multi-layer device structure

Energy Technology Data Exchange (ETDEWEB)

Wang Yuanmin [Institute of Optoelectronic Technology, Beijing Jiaotong University, Beijing 100044 (China); Key Laboratory for Information Storage, Displays and Materials, Beijing 100044 (China); Teng Feng [Institute of Optoelectronic Technology, Beijing Jiaotong University, Beijing 100044 (China) and Key Laboratory for Information Storage, Displays and Materials, Beijing 100044 (China)]. E-mail: advanced9898@126.com; Xu Zheng [Institute of Optoelectronic Technology, Beijing Jiaotong University, Beijing 100044 (China); Key Laboratory for Information Storage, Displays and Materials, Beijing 100044 (China); Hou Yanbing [Institute of Optoelectronic Technology, Beijing Jiaotong University, Beijing 100044 (China); Key Laboratory for Information Storage, Displays and Materials, Beijing 100044 (China); Wang Yongsheng [Institute of Optoelectronic Technology, Beijing Jiaotong University, Beijing 100044 (China); Key Laboratory for Information Storage, Displays and Materials, Beijing 100044 (China); Xu Xurong [Institute of Optoelectronic Technology, Beijing Jiaotong University, Beijing 100044 (China); Key Laboratory for Information Storage, Displays and Materials, Beijing 100044 (China)

2005-04-30

Electroplex emission based on poly(N-vinylcarbazole) (PVK) and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) has been improved dramatically by using a multi-layer device structure indium-tin oxide (ITO)/poly(3,4-ethylenedioxythiophene): poly(styrenesulphonic acid) (PEDOT:PSS)/PVK/BCP/PVK/BCP/LiF/Al. Electroplex emission at 595 nm has been improved about 10 times under low voltage and four times under high voltage compared to the double layer device ITO/PVK/BCP/Al. The maximum brightness of the device also has been improved about eight times. Bright white emission via electroplex formation can be obtained with Commission International d'Eclairage (CIE) coordinates (0.336, 0.320) at 26 V with a brightness of 123 cd/m{sup 2}. Based on the analysis of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the materials, we suggest the enhancement is mainly ascribed to the confinement effect of the quantum-well-like multi-layer device structure. Every hole and electron has more possibilities to cross recombination at the PVK/BCP interface.

Large-eddy simulations of the non-reactive flow in the Sydney swirl burner

DEFF Research Database (Denmark)

Yang, Yang; Kær, Søren Knudsen

2012-01-01

results. In medium swirling case, there are two reverse-flow regions with a collar-like structure between them. The existence of strong unsteady structure, precessing vortex core, was proven. Coherent structures are detached from the instantaneous field. Q-criterion was used to visualize vorticity field...... with distinct clear structure of vortice tubes. Dominating spatial–temporal structures contained in different cross sections were extracted using proper orthogonal decomposition. In high swirling case, there is only one long reverse-flow region. In this paper, we proved the capability of a commercial CFD...... package in predicting complex flow field and presented the potential of large eddy simulation in understanding dynamics....

PIV study of the effect of piston position on the in-cylinder swirling flow during the scavenging process in large two-stroke marine diesel engines

DEFF Research Database (Denmark)

Haider, Sajjad; Schnipper, Teis; Obeidat, Anas

2013-01-01

A simplified model of a low speed large twostroke marine diesel engine cylinder is developed. The effect of piston position on the in-cylinder swirling flow during the scavenging process is studied using the stereoscopic particle image velocimetry technique. The measurements are conducted...

Effect of inlect swirl on the convergence behavior of a combustor flow computation algorithm

International Nuclear Information System (INIS)

Shyy, W.; Braaten, M.E.; Hwang, T.H.

1987-01-01

The flow in a single sector of gas-turbine combustor with dilution holes has been studied numerically. It is found that there are some distinctive differences between the numerical behavior of the solution algorithm for combusting and noncombusting flows in a single-cup gas turbine combustor enclosed by four-sided solid walls. With the use of an iterative solution procedure and the standard κ-ε turbulence model, converged steady-state solutions are obtained for noncombusting flows with or without the presence of swirl of dilution jets. However, for the combusting flows, the interaction between the strength of the swirl ratio and the jet-to-main flow velocity ratio affects the ability of the algorithm to achieve a converged steady-state solution. Increasing inlet swirl causes the flow field to oscillate as the iterations progress, and to fail to reach a steady-state solution, while increasing the flow through the dilution jets helps achieve a steady-state solution. The above phenomena are not observed for the flows with periodic boundary conditions along two side planes

Enhancement on field emission characteristics of pulsed laser deposited diamondlike carbon films using Au precoatings

International Nuclear Information System (INIS)

Chuang, F.Y.; Sun, C.Y.; Cheng, H.F.; Lin, I.N.

1997-01-01

Using Au precoatings has been observed to significantly enhance the field emission properties of diamondlike carbon (DLC) films deposited on Si substrates. The electron emission can be turned on at a low field as 7 V/μm and a large emission current density as 2000 μA/cm 2 can be obtained at 20 V/μm applied field. However, preannealing the Au-coated Si substrates at 500 degree C for 30 min is necessary to achieve such a performance. Microscopic examination on surface and cross-sectional morphologies of the DLC/Au/Si films using atomic force microscopy and scanning electron microscopy, respectively, in conjunction with the elemental depth profile examination of these films using secondary ion mass spectroscopy, indicated that substantial interdiffusion between DLC, Au, and Si layers has occurred. Such kind of reaction is proposed to lower the resistance for electrons to transport across the interfaces and, thereafter, enhances the field emission properties of the DLC/Au/Si films. copyright 1997 American Institute of Physics

Changes in Sea Salt Emissions Enhance ENSO Variability

Energy Technology Data Exchange (ETDEWEB)

Yang, Yang; Russell, Lynn M.; Lou, Sijia; Lamjiri, Maryam A.; Liu, Ying; Singh, Balwinder; Ghan, Steven J.

2016-11-15

Two 150-year pre-industrial simulations with and without interactive sea salt emissions from the Community Earth System Model (CESM) are performed to quantify the interactions between sea salt emissions and El Niño–Southern Oscillation (ENSO). Variations in sea salt emissions over the tropical Pacific Ocean are affected by changing wind speed associated with ENSO variability. ENSO-induced interannual variations in sea salt emissions result in decreasing (increasing) aerosol optical depth (AOD) by 0.03 over the equatorial central-eastern (western) Pacific Ocean during El Niño events compared to those during La Niña events. These changes in AOD further increase (decrease) radiative fluxes into the atmosphere by +0.2 W m^-2 (-0.4 W m^-2) over the tropical eastern (western) Pacific. Thereby, sea surface temperature increases (decreases) by 0.2–0.4 K over the tropical eastern (western) Pacific Ocean during El Niño compared to La Niña events and enhances ENSO variability by 10%. The increase in ENSO amplitude is a result of systematic heating (cooling) during the warm (cold) phase, of ENSO in the eastern Pacific. Interannual variations in sea salt emissions then produce the anomalous ascent (subsidence) over the equatorial eastern (western) Pacific between El Niño and La Niña events, which is a result of heating anomalies. Due to variations in sea salt emissions, the convective precipitation is enhanced by 0.6–1.2 mm day^-1 over the tropical central-eastern Pacific Ocean and weakened by 0.9–1.5 mm day^-1 over the Maritime Continent during El Niño compared to La Niña events, enhancing the precipitation variability over the tropical Pacific.

Improvement of the intranuclear cascade code of Bruyeres-le-Chatel (BRIC) at low intermediate energy

International Nuclear Information System (INIS)

Duarte, H.

2003-01-01

The IntraNuclear cascade code of Bruyeres-le-Chatel called BRIC has been extended to low intermediate energy by taking in account some medium effects that are included in other nuclear dynamics models such as BUU or QMD. The results of BRIC 1.4 with the medium effects are in better agreement with experimental data than those of the first version on a wide range of incident energy, especially at low intermediate energy. We may conclude that no preequilibrium model is necessary between our INC and the deexcitation step. (orig.)

Self-organized vortex multiplets in swirling flow

DEFF Research Database (Denmark)

Okulov, Valery; Naumov, Igor; Sørensen, Jens Nørkær

2008-01-01

The possibility of double vortex multiplet formation at the center of an intensively swirling cocurrent flow generated in a cylindrical container by its rotating lid is reported for the first time. The boundary of the transition to unsteady flow regimes, which arise as a result of the equilibrium...... rotation of self-organized vortex multiplets (triplet, double triplet, double doublet, and quadruplet), has been experimentally determined for cylinders with the aspect (height to radius) ratios in a wider interval than that studied previously....

A comparative study of the enhancement of molecular emission in a spatially confined plume through optical emission spectroscopy and probe beam deflection measurements

Energy Technology Data Exchange (ETDEWEB)

Ding, Dayu; Liang, Peipei; Wu, Jiada; Xu, Ning; Ying, Zhifeng; Sun, Jian, E-mail: jsun@fudan.edu.cn

2013-01-01

The spatial confinement effects of shock wave on the expansion of a carbon plume induced by pulsed laser ablation of graphite in air and the enhancement of the plume emission were studied by optical emission spectroscopy and probe beam deflection measurements. A metal disk was set in the way of the ablation-generated shock wave to block and reflect the supersonically propagating shock wave. The reflected shock wave propagated backwards and confined the expanding plume. The optical emission of CN molecules was enhanced in contrast to the case without the block disk and the emission enhancement was dependent on the position of the disk. Based on the results of time-integrated and -resolved optical emission spectroscopy, and the time- and space-resolved probe beam deflection measurements, the processes occurring in the plume were discussed and the mechanisms responsible for the enhancement of molecular emission in the spatially confined plume were investigated. - Highlights: ► Spatial confinement and optical emission enhancement of carbon plume were studied. ► Ablation-generated shockwave propagating in air was reflected by a block disk. ► The effects of reflected shockwave on the emission enhancement were confirmed. ► The reflect shockwave confined the carbon plume and enhanced the plume emission.

A comparative study of the enhancement of molecular emission in a spatially confined plume through optical emission spectroscopy and probe beam deflection measurements

International Nuclear Information System (INIS)

Ding, Dayu; Liang, Peipei; Wu, Jiada; Xu, Ning; Ying, Zhifeng; Sun, Jian

2013-01-01

The spatial confinement effects of shock wave on the expansion of a carbon plume induced by pulsed laser ablation of graphite in air and the enhancement of the plume emission were studied by optical emission spectroscopy and probe beam deflection measurements. A metal disk was set in the way of the ablation-generated shock wave to block and reflect the supersonically propagating shock wave. The reflected shock wave propagated backwards and confined the expanding plume. The optical emission of CN molecules was enhanced in contrast to the case without the block disk and the emission enhancement was dependent on the position of the disk. Based on the results of time-integrated and -resolved optical emission spectroscopy, and the time- and space-resolved probe beam deflection measurements, the processes occurring in the plume were discussed and the mechanisms responsible for the enhancement of molecular emission in the spatially confined plume were investigated. - Highlights: ► Spatial confinement and optical emission enhancement of carbon plume were studied. ► Ablation-generated shockwave propagating in air was reflected by a block disk. ► The effects of reflected shockwave on the emission enhancement were confirmed. ► The reflect shockwave confined the carbon plume and enhanced the plume emission

Fuel Flexible, Low Emission Catalytic Combustor for Opportunity Fuel Applications

Energy Technology Data Exchange (ETDEWEB)

Eteman, Shahrokh

2013-06-30

Limited fuel resources, increasing energy demand and stringent emission regulations are drivers to evaluate process off-gases or process waste streams as fuels for power generation. Often these process waste streams have low energy content and/or highly reactive components. Operability of low energy content fuels in gas turbines leads to issues such as unstable and incomplete combustion. On the other hand, fuels containing higher-order hydrocarbons lead to flashback and auto-ignition issues. Due to above reasons, these fuels cannot be used directly without modifications or efficiency penalties in gas turbine engines. To enable the use of these wide variety of fuels in gas turbine engines a rich catalytic lean burn (RCL®) combustion system was developed and tested in a subscale high pressure (10 atm.) rig. The RCL® injector provided stability and extended turndown to low Btu fuels due to catalytic pre-reaction. Previous work has shown promise with fuels such as blast furnace gas (BFG) with LHV of 85 Btu/ft3 successfully combusted. This program extends on this work by further modifying the combustor to achieve greater catalytic stability enhancement. Fuels containing low energy content such as weak natural gas with a Lower Heating Value (LHV) of 6.5 MJ/m3 (180 Btu/ft3 to natural gas fuels containing higher hydrocarbon (e.g ethane) with LHV of 37.6 MJ/m3 (1010 Btu/ft3) were demonstrated with improved combustion stability; an extended turndown (defined as the difference between catalytic and non-catalytic lean blow out) of greater than 250oF was achieved with CO and NOx emissions lower than 5 ppm corrected to 15% O2. In addition, for highly reactive fuels the catalytic region preferentially pre-reacted the higher order hydrocarbons with no events of flashback or auto-ignition allowing a stable and safe operation with low NOx and CO emissions.

Mid-infrared quantum cascade laser spectroscopy probing of the ...

Indian Academy of Sciences (India)

Aparajeo Chattopadhyay

2018-05-07

May 7, 2018 ... cm3 molecule. −1 s. −1 ... Quantum cascade laser; time-resolved mid-infrared spectroscopy; transient absorption; peroxy radicals .... peak of the laser emission profile. .... cal with O2 is a termolecular reaction (Eq. 3) and the.

Interface control: A modified rooting technique for enhancing field emission from multiwall carbon nanotube based bulk emitters

Energy Technology Data Exchange (ETDEWEB)

Lahiri, Indranil [Nanomaterials and Device Lab, Department of Mechanical and Materials Engineering, Florida International University, 10555 West Flagler Street, Miami, FL 33174 (United States); Choi, Wonbong, E-mail: choiw@fiu.edu [Nanomaterials and Device Lab, Department of Mechanical and Materials Engineering, Florida International University, 10555 West Flagler Street, Miami, FL 33174 (United States)

2011-08-15

The unique properties of carbon nanotubes (CNTs) have raised hopes that these materials might find wide application as cold cathodes in various electron sources. The excellent field emission properties shown by CNT-based field emitters has further stimulated this expectation. However, efficient performance of a practical field emitter, which comprises a large number of randomly or regularly oriented CNTs, is restricted primarily due to poor junctions formed between CNTs and substrates. This study is aimed at enhancing the junction performance by way of a modified 'rooting' technique-interface control. In this process, the interface between CNTs and substrate has been tailored with different metals in an attempt to improve the CNT-substrate junction performance. Multiwall carbon nanotubes (MWCNTs) were synthesized on different interface-controlled substrates, i.e. Cu, Al, W, Si and low-temperature co-fired ceramic. All the samples produced mat-type, randomly oriented MWCNT structures. Among the four different substrates studied, MWCNT-based field emitters on Cu substrate demonstrated the best field emission response, in terms of low turn-on field, high emission current, good field enhancement factor and excellent stability in long-term operation. Emitter structures and their field emission behavior were correlated and it was shown that interface control, as an advanced 'rooting' process, plays an important role in determining the emission response from a bulk field emitter.

Interface control: A modified rooting technique for enhancing field emission from multiwall carbon nanotube based bulk emitters

International Nuclear Information System (INIS)

Lahiri, Indranil; Choi, Wonbong

2011-01-01

The unique properties of carbon nanotubes (CNTs) have raised hopes that these materials might find wide application as cold cathodes in various electron sources. The excellent field emission properties shown by CNT-based field emitters has further stimulated this expectation. However, efficient performance of a practical field emitter, which comprises a large number of randomly or regularly oriented CNTs, is restricted primarily due to poor junctions formed between CNTs and substrates. This study is aimed at enhancing the junction performance by way of a modified 'rooting' technique-interface control. In this process, the interface between CNTs and substrate has been tailored with different metals in an attempt to improve the CNT-substrate junction performance. Multiwall carbon nanotubes (MWCNTs) were synthesized on different interface-controlled substrates, i.e. Cu, Al, W, Si and low-temperature co-fired ceramic. All the samples produced mat-type, randomly oriented MWCNT structures. Among the four different substrates studied, MWCNT-based field emitters on Cu substrate demonstrated the best field emission response, in terms of low turn-on field, high emission current, good field enhancement factor and excellent stability in long-term operation. Emitter structures and their field emission behavior were correlated and it was shown that interface control, as an advanced 'rooting' process, plays an important role in determining the emission response from a bulk field emitter.

Ultrafine particle emissions by in-use diesel buses of various generations at low-load regimes

Science.gov (United States)

Tartakovsky, L.; Baibikov, V.; Comte, P.; Czerwinski, J.; Mayer, A.; Veinblat, M.; Zimmerli, Y.

2015-04-01

Ultrafine particles (UFP) are major contributors to air pollution due to their easy gas-like penetration into the human organism, causing adverse health effects. This study analyzes UFP emissions by buses of different technologies (from Euro II till Euro V EEV - Enhanced Environmentally-friendly Vehicle) at low-load regimes. Additionally, the emission-reduction potential of retrofitting with a diesel particle filter (DPF) is demonstrated. A comparison of the measured, engine-out, particle number concentrations (PNC) for buses of different technological generations shows that no substantial reduction of engine-out emissions at low-load operating modes is observed for newer bus generations. Retrofitting the in-use urban and interurban buses of Euro II till Euro IV technologies by the VERT-certified DPF confirmed its high efficiency in reduction of UFP emissions. Particle-count filtration efficiency values of the retrofit DPF were found to be extremely high - greater than 99.8%, similar to that of the OEM filter in the Euro V bus.

Measuring air core characteristics of a pressure-swirl atomizer via a transparent acrylic nozzle at various Reynolds numbers

Energy Technology Data Exchange (ETDEWEB)

Lee, Eun J.; Oh, Sang Youp; Kim, Ho Y.; Yoon, Sam S. [Dept. of Mechanical, Korea University Anamdong, 5-Ga, Sungbukgu, 136-713 Seoul (Korea); James, Scott C. [Thermal/Fluid Science and Engineering, Sandia National Labs, PO Box 969, Livermore, CA 94551 (United States)

2010-11-15

Because of thermal fluid-property dependence, atomization stability (or flow regime) can change even at fixed operating conditions when subject to temperature change. Particularly at low temperatures, fuel's high viscosity can prevent a pressure-swirl (or simplex) atomizer from sustaining a centrifugal-driven air core within the fuel injector. During disruption of the air core inside an injector, spray characteristics outside the nozzle reflect a highly unstable, nonlinear mode where air core length, Sauter mean diameter (SMD), cone angle, and discharge coefficient variability. To better understand injector performance, these characteristics of the pressure-swirl atomizer were experimentally investigated and data were correlated to Reynolds numbers (Re). Using a transparent acrylic nozzle, the air core length, SMD, cone angle, and discharge coefficient are observed as a function of Re. The critical Reynolds numbers that distinguish the transition from unstable mode to transitional mode and eventually to a stable mode are reported. The working fluids are diesel and a kerosene-based fuel, referred to as bunker-A. (author)

An Investigation on Flame Shape and Size for a High-Pressure Turbulent Non-Premixed Swirl Combustion

Directory of Open Access Journals (Sweden)

Zhongya Xi

2018-04-01

Full Text Available Flame shape and size for a high-pressure turbulent non-premixed swirl combustion were experimentally investigated over a wide range of varying parameters including fuel mass flow rate, combustor pressure, primary-air mass flow rate, and nozzle exit velocity. A CFD simulation was conducted to predict the flame profile. Meanwhile, a theoretical calculation was also performed to estimate flame length. It was observed that flame length increased linearly with increasing fuel mass flow rate but decreased with the increment of combustor pressure in the power function. The flame diminished at a larger primary-air mass flow rate but remained unaffected by the increasing nozzle exit velocity. Considering the global effect of all parameters at a particular pressure, the flame length generally decreased as the primary-air to fuel ratio increased. This was attributed to the reduced air entrainment required to dilute the fuel to stoichiometric proportions. The CFD simulation offered a good prediction of the variation trends of flame length, although some deviations from experimental values were observed. The theoretical calculation estimated the trends of flame length variation particularly well. Nevertheless the difference between the theoretical and experimental results was found to be due to the swirl influence. Hence, a swirl factor was proposed to be added to the original equation for swirl flames.

Large Eddy Simulation of Sydney Swirl Non-Reaction Jets

DEFF Research Database (Denmark)

Yang, Yang; Kær, Søren Knudsen; Yin, Chungen

The Sydney swirl burner non-reaction case was studied using large eddy simulation. The two-point correlation method was introduced and used to estimate grid resolution. Energy spectra and instantaneous pressure and velocity plots were used to identify features in flow field. By using these method......, vortex breakdown and precessing vortex core are identified and different flow zones are shown....

Galvanic displacement synthesis of Al/Ni core–shell pigments and their low infrared emissivity application

Energy Technology Data Exchange (ETDEWEB)

Yuan, Le, E-mail: yuanle.cn@gmail.com [Center for Advanced Materials and Energy, Xihua University, Chengdu, 610039 (China); National Engineering Research Center of Electromagnetic Radiation Control Materials, UESTC, Chengdu, 610054 (China); Hu, Juan [Center for Advanced Materials and Energy, Xihua University, Chengdu, 610039 (China); Weng, Xiaolong [National Engineering Research Center of Electromagnetic Radiation Control Materials, UESTC, Chengdu, 610054 (China); Zhang, Qingyong [Center for Advanced Materials and Energy, Xihua University, Chengdu, 610039 (China); Deng, Longjiang [National Engineering Research Center of Electromagnetic Radiation Control Materials, UESTC, Chengdu, 610054 (China)

2016-06-15

We have successfully developed a magnetic Al/Ni core–shell pigment via a galvanic displacement reaction to obtain low infrared emissivity pigment with low lightness and visible light reflectance. Al/Ni core–shell particles were prepared via a simple one-step synthetic method where Ni was deposited onto the Al surface at the expense of Al atoms. The influence of pH and the amount of NH{sub 4}F complexing agent on phase structure, surface morphology, optical and magnetic properties were studied systematically. The neutral condition and high concentration of NH{sub 4}F forms smooth, flat, uniform and dense Ni shell on the surface of flake Al particles, which can significantly reduce the lightness and visible light reflectance but slightly increase the infrared emissivity. When the core–shell pigments are prepared in neutral pH solution at NH{sub 4}F = 11.2 g/L, the lightness (L{sup *}) and visual light reflectivity can be reduced by 12.6 and 0.46, respectively versus uncoated flake Al pigments, but the infrared emissivity is only increased by 0.02. The color changes from brilliant silver to gray black and the saturation magnetization value is 6.59 emu/g. Therefore, these Al/Ni magnetic composite pigments can be used as a novel low infrared emissivity pigment to improve the multispectral stealth performance of low-E coatings in the visual, IR and Radar wavebands. - Highlights: • Prepared magnetic Al/Ni core–shell pigment with low lightness and low emissivity. • Used one-pot galvanic displacement reaction to form smooth and dense Ni shell. • Show enhanced stealth performance in the visual, IR and Radar wavebands. • The lightness and visible light reflectance was decreased by 12.6 and 0.46. • But the infrared emissivity was only increases by 0.02.

Galvanic displacement synthesis of Al/Ni core–shell pigments and their low infrared emissivity application

International Nuclear Information System (INIS)

Yuan, Le; Hu, Juan; Weng, Xiaolong; Zhang, Qingyong; Deng, Longjiang

2016-01-01

We have successfully developed a magnetic Al/Ni core–shell pigment via a galvanic displacement reaction to obtain low infrared emissivity pigment with low lightness and visible light reflectance. Al/Ni core–shell particles were prepared via a simple one-step synthetic method where Ni was deposited onto the Al surface at the expense of Al atoms. The influence of pH and the amount of NH_4F complexing agent on phase structure, surface morphology, optical and magnetic properties were studied systematically. The neutral condition and high concentration of NH_4F forms smooth, flat, uniform and dense Ni shell on the surface of flake Al particles, which can significantly reduce the lightness and visible light reflectance but slightly increase the infrared emissivity. When the core–shell pigments are prepared in neutral pH solution at NH_4F = 11.2 g/L, the lightness (L"*) and visual light reflectivity can be reduced by 12.6 and 0.46, respectively versus uncoated flake Al pigments, but the infrared emissivity is only increased by 0.02. The color changes from brilliant silver to gray black and the saturation magnetization value is 6.59 emu/g. Therefore, these Al/Ni magnetic composite pigments can be used as a novel low infrared emissivity pigment to improve the multispectral stealth performance of low-E coatings in the visual, IR and Radar wavebands. - Highlights: • Prepared magnetic Al/Ni core–shell pigment with low lightness and low emissivity. • Used one-pot galvanic displacement reaction to form smooth and dense Ni shell. • Show enhanced stealth performance in the visual, IR and Radar wavebands. • The lightness and visible light reflectance was decreased by 12.6 and 0.46. • But the infrared emissivity was only increases by 0.02.

Design and numerical investigation of swirl recovery vanes for the Fokker 29 propeller

Directory of Open Access Journals (Sweden)

Wang Yangang

2014-10-01

Full Text Available Swirl recovery vanes (SRVs are a set of stationary vanes located downstream from a propeller, which may recover some of the residual swirl from the propeller, hoping for an improvement in both thrust and efficiency. The SRV concept design for a scaled version representing the Fokker 29 propeller is performed in this paper, which may give rise to a promotion in propulsive performance of this traditional propeller. Firstly the numerical strategy is validated from two aspects of global quantities and the local flow field of the propeller compared with experimental data, and then the exit flow together with the development of propeller wake is analyzed in detail. Three kinds of SRV are designed with multiple circular airfoils. The numerical results show that the swirl behind the propeller is recovered significantly with Model V3, which is characterized by the highest solidity along spanwise, for various working conditions, and the combination of rotor and vane produced 5.76% extra thrust at the design point. However, a lower efficiency is observed asking for a better vane design and the choice of a working point. The vane position is studied which shows that there is an optimum range for higher thrust and efficiency.

Numerical Calculation of the Swirling Flow in a Centrifugal Compressor Volute

International Nuclear Information System (INIS)

Seong, Seon Mo; Kang, Shin Hyoung; Cho, Kyung Seok; Kim, Woo June

2007-01-01

Flows in the centrifugal compressor volute with circular cross section are numerically investigated. The computational grid for the calculation utilized a multi-block arrangement to form a butterfly grid and flow calculations are performed using commercial CFD software, CFX-TASCflow. The centrifugal compressor of this study has axial diffuser after radial diffuser because of the shape of inlet duct and installation constraints. Due to this feature the swirling flow pattern is different from the other investigations. The flow inside volute is very complex and three dimensional with strong vortex and recirculation through volute tongue. The calculation results show circumferential variations of the swirl and through flow velocity and pressure distribution. The mechanism deciding flow structure is explained by considering the force balance in volute cross section. And static pressure recovery and total pressure loss are estimated from the calculated results and compared with Japikse model

NO kinetics in pulsed low-pressure nitrogen plasmas studied by time resolved quantum cascade laser absorption spectroscopy

NARCIS (Netherlands)

Welzel, S.; Guaitella, O.; Lazzaroni, C.; Pintassilgo, C.; Rousseau, A.; Röpcke, J.

2011-01-01

Time-resolved quantum cascade laser absorption spectroscopy at 1897 cm-1 (5.27 µm) has been applied to study the NO(X) kinetics on the micro- and millisecond time scale in pulsed low-pressure N2/NO dc discharges. Experiments have been performed under flowing and static gas conditions to infer the

Similarity solution of axisymmetric non-Newtonian wall jets with swirl

Czech Academy of Sciences Publication Activity Database

Kolář, Václav

2011-01-01

Roč. 12, č. 6 (2011), s. 3413-3420 ISSN 1468-1218 R&D Projects: GA AV ČR IAA200600801 Institutional research plan: CEZ:AV0Z20600510 Keywords : similarity solution * wall jets * non-Newtonian fluids * power-law fluids * swirl Subject RIV: BK - Fluid Dynamics Impact factor: 2.043, year: 2011

Surface-plasmon-enhanced lasing emission based on polymer distributed feedback laser

Energy Technology Data Exchange (ETDEWEB)

Zhang, Dingke, E-mail: dingke.zhang@gmail.com, E-mail: shijianchen@gmail.com [School of Physics and Electronic Engineering, Chongqing Normal University, Chongqing 401331 (China); Chen, Shijian, E-mail: dingke.zhang@gmail.com, E-mail: shijianchen@gmail.com; Huang, Yingzhou; Zhang, Zhen [School of Physics, Chongqing University, Chongqing 401331 (China); Wang, Yanping; Ma, Dongge [State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China)

2015-01-14

Optical losses associated with the metallic contacts necessary for charge injection are an obstacle to the development of electrically pumped organic lasers. In this work, we show that it is possible to overcome these losses by introducing surface plasmons (SPs) in a distributed feedback laser to enhance the lasing emission. We perform a detailed study of the SPs influence on the lasing emission. We experimentally show that enhanced lasing emission has been successfully achieved in the presence of a metal electrode. The laser emission is strongly dependent on the thickness of Ag layer. By optimizing the thickness of Ag layer, surface-plasmon-enhanced lasing emission has been achieved with much reduced thresholds and higher intensity. When the thickness of the Ag layer increases to 50 nm, the device exhibits ten-fold emission intensity and a fifth of excitation threshold comparing with Ag-free one. The finite-difference time-domain (FDTD) results show that large field intensity is built at the 4-(dicyanomethylene)-2-i-propyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl) -4H-pyran:/poly(9-vinylcarbazole)Ag interface, which could lead to a strong coupling between lasing and SPs, and consequently a much enhanced laser emission at the photon energy of around 2.02 eV (615 nm). Our FDTD simulations gave an explanation of the effects of the SPs on lasing operation in the periodic structures. The use of SPs would lead to a new class of highly efficient solid-state laser sources and provide a new path to achieve electrically pumped organic lasers.

Component Development to Accelerate Commercial Implementation of Ultra-Low Emissions Catalytic Combustion

Energy Technology Data Exchange (ETDEWEB)

McCarty, Jon; Berry, Brian; Lundberg, Kare; Anson, Orris

2003-03-31

This final report describes a 2000-2003 program for the development of components and processes to enhance the commercialization of ultra-low emissions catalytic combustion in industrial gas turbines. The range of project tasks includes: development of more durable, lower-cost catalysts and catalytic combustor components; development and design of a catalytic pre-burner and a catalytic pilot burner for gas turbines, and on-site fuel conversion processing for utilization of liquid fuel.

Analysis of the pressure fields in a swirling annular jet flow

NARCIS (Netherlands)

Perçin, M.; Vanierschot, M.; van Oudheusden, B.W.

2017-01-01

In this paper, we investigate the flow structures and pressure fields of a free annular swirling jet flow undergoing vortex breakdown. The flow field is analyzed by means of time-resolved tomographic particle image velocimetry measurements, which enable the reconstruction of the three-dimensional

Bias-enhanced post-treatment process for enhancing the electron field emission properties of ultrananocrystalline diamond films

International Nuclear Information System (INIS)

Saravanan, A.; Huang, B. R.; Sankaran, K. J.; Tai, N. H.; Dong, C. L.; Lin, I. N.

2015-01-01

The electron field emission (EFE) properties of ultrananocrystalline diamond films were markedly improved via the bias-enhanced plasma post-treatment (bep) process. The bep-process induced the formation of hybrid-granular structure of the diamond (bep-HiD) films with abundant nano-graphitic phase along the grain boundaries that increased the conductivity of the films. Moreover, the utilization of Au-interlayer can effectively suppress the formation of resistive amorphous-carbon (a-C) layer, thereby enhancing the transport of electrons crossing the diamond-to-Si interface. Therefore, bep-HiD/Au/Si films exhibit superior EFE properties with low turn-on field of E 0  = 2.6 V/μm and large EFE current density of J e  = 3.2 mA/cm 2 (at 5.3 V/μm)

Fabrication of a novel cascade high-pressure electro-osmotic pump.

Science.gov (United States)

Zhang, Feifang; Wang, Rong; Han, Tingting; Yang, Bingcheng; Liang, Xinmiao

2011-07-07

A novel cascade electro-osmotic pump (EOP) has been fabricated by alternately connecting a cation monolithic column and anion monolithic column in series. In this manner, the change of electric polarity between each stage of the cascade EOP is easily achieved and the pressure output of the EOP could be greatly enhanced without increase of the applied voltage.

Quantum cascade lasers, systems, and applications in Europe

Science.gov (United States)

Lambrecht, Armin

2005-03-01

Since the invention of the Quantum Cascade Laser (QCL) a decade ago an impressive progress has been achieved from first low temperature pulsed laser emission to continuous wave operation at room temperature. Distributed feedback (DFB) lasers working in pulsed mode at ambient temperatures and covering a broad spectral range in the mid infrared (MIR) are commercially available now. For many industrial applications e.g. automotive exhaust control and process monitoring, laser spectroscopy is an established technique, generally using near infrared (NIR) diode lasers. However, the mid infrared (MIR) spectral region is of special interest because of much stronger absorption lines compared to NIR. The status of QCL devices, system development and applications is reviewed. Special emphasis is given to the situation in Europe where a remarkable growth of QCL related R&D can be observed.

Performance comparison of two low-CO2 emission solar/methanol hybrid combined cycle power systems

International Nuclear Information System (INIS)

Li, Yuanyuan; Zhang, Na; Lior, Noam

2015-01-01

Highlights: • Two novel solar hybrid combined cycle systems have been proposed and analyzed. • The power systems integrate solar-driven thermo-chemical conversion and CO 2 capture. • Exergy efficiency of about 55% and specific CO 2 emissions of 34 g/kW h are predicted. • Systems CO 2 emissions are 36.8% lower compared to a combined cycle with CO 2 capture. • The fossil fuel demand is ∼30% lower with a solar share of ∼20%. - Abstract: Two novel hybrid combined cycle power systems that use solar heat and methanol, and integrate CO 2 capture, are proposed and analyzed, one based on solar-driven methanol decomposition and the other on solar-driven methanol reforming. The high methanol conversion rates at relatively low temperatures offer the advantage of using the solar heat at only 200–300 °C to drive the syngas production by endothermic methanol conversions and its conversion to chemical energy. Pre-combustion decarbonization is employed to produce CO 2 -free fuel from the fully converted syngas, which is then burned to produce heat at the high temperature for power generation in the proposed advanced combined cycle systems. To improve efficiency, the systems’ configurations were based on the principle of cascade use of multiple heat sources of different temperatures. The thermodynamic performance of the hybrid power systems at its design point is simulated and evaluated. The results show that the hybrid systems can attain an exergy efficiency of about 55%, and specific CO 2 emissions as low as 34 g/kW h. Compared to a gas/steam combined cycle with flue gas CO 2 capture, the proposed solar-assisted system CO 2 emissions are 36.8% lower, and a fossil fuel saving ratio of ∼30% is achievable with a solar thermal share of ∼20%. The system integration predicts high efficiency conversion of solar heat and low-energy-penalty CO 2 capture, with the additional advantage that solar heat is at relatively low temperature where its collection is cheaper and

Beta Radiation Enhanced Thermionic Emission from Diamond Thin Films

Directory of Open Access Journals (Sweden)

Alex Croot

2017-11-01

Full Text Available Diamond-based thermionic emission devices could provide a means to produce clean and renewable energy through direct heat-to-electrical energy conversion. Hindering progress of the technology are the thermionic output current and threshold temperature of the emitter cathode. In this report, we study the effects on thermionic emission caused by in situ exposure of the diamond cathode to beta radiation. Nitrogen-doped diamond thin films were grown by microwave plasma chemical vapor deposition on molybdenum substrates. The hydrogen-terminated nanocrystalline diamond was studied using a vacuum diode setup with a 63Ni beta radiation source-embedded anode, which produced a 2.7-fold increase in emission current compared to a 59Ni-embedded control. The emission threshold temperature was also examined to further assess the enhancement of thermionic emission, with 63Ni lowering the threshold temperature by an average of 58 ± 11 °C compared to the 59Ni control. Various mechanisms for the enhancement are discussed, with a satisfactory explanation remaining elusive. Nevertheless, one possibility is discussed involving excitation of preexisting conduction band electrons that may skew their energy distribution toward higher energies.

Role of work function in field emission enhancement of Au island decorated vertically aligned ZnO nanotapers

Energy Technology Data Exchange (ETDEWEB)

Singh, Avanendra [School of Physical Sciences, National Institute of Science Education and Research (NISER), HBNI, Bhubaneswar 752050, Odisha (India); Senapati, Kartik, E-mail: kartik@niser.ac.in [School of Physical Sciences, National Institute of Science Education and Research (NISER), HBNI, Bhubaneswar 752050, Odisha (India); Kumar, Mohit; Som, Tapobrata [SUNAG Laboratory, Institute of Physics, Bhubaneswar 751005, Odisha (India); Sinha, Anil K. [Indus Synchrotrons Utilization Division, Raja Ramanna Centre for Advanced Technology, Indore 452013, M.P. (India); Sahoo, Pratap K., E-mail: pratap.sahoo@niser.ac.in [School of Physical Sciences, National Institute of Science Education and Research (NISER), HBNI, Bhubaneswar 752050, Odisha (India)

2017-07-31

Highlights: • Hydrothermally synthesized nanotapers were decorated by gold corrugation using simple evaporation techniques for large area applications. • A significantly enhanced field emission properties of nanotapers were achieved. • The metal induced midgap states formed at the ZnO-Au interface and the reduced effective work function are responsible for low turn-on field. • TUNA measurements revealed a very uniform spatial emission profile in the Au decorated nanotapers. - Abstract: In this report, we demonstrate significantly enhanced field emission properties of ZnO nanotapers achieved via a corrugated decoration of Au. Field emission experiments on these Au-decorated ZnO nanotapers showed emission current densities comparable to the best results in the literature. Au decoration of 5 nm also reduced the effective turn-on field to ∼0.54 V/μm, compared to the as grown ZnO nanotapers, which showed a turn-on field of ∼1.1 V/μm. Tunneling atomic force microscopy measurements revealed a very uniform spatial emission profile in the 5 nm Au decorated nanotapers, which is a basic requirement for any large scale application. We believe that metal induced mid-gap states formed at the ZnO–Au interface are responsible for the observed low turn-on field because such interface states are known to reduce the effective work function. A direct measurement of effective work function using Kelvin probe force microscopy indeed showed more than 1.1 eV drop in the case of 5 nm Au decorated ZnO nanotapers compared to the pristine nanotapers, supporting the above argument.

Five-hole pitot probe measurements of swirl, confinement and nozzle effects on confined turbulent flow

Science.gov (United States)

Lilley, D. G.; Scharrer, G. L.

1984-01-01

The results of a time-mean flow characterization of nonswirling and swirling inert flows in a combustor are reported. The five-hole pitot probe technique was used in axisymmetric test sections with expansion ratios of 1 and 1.5. A prominent corner recirculation zone identified in nonswirling expanding flows decreased in size with swirling flows. The presence of a downstream nozzle led to an adverse pressure gradient at the wall and a favorable gradient near the centerline. Reducing the expansion ratio reduced the central recirculation length. No significant effect was introduced in the flowfield by a gradual expansion.

Real-time monitoring through the use of technology to enhance performances throughout HIV cascades.

Science.gov (United States)

Avery, Matthew; Mills, Stephen J; Stephan, Eric

2017-09-01

Controlling the HIV epidemic requires strong linkages across a 'cascade' of prevention, testing, and treatment services. Information and communications technology (ICT) offers the potential to monitor and improve the performance of this HIV cascade in real time. We assessed recent (media to expand reach and improve programmatic targeting; technology in healthcare settings to strengthen coordination, guide clinical decision-making and improve clinical interactions; and telephone-based follow-up to improve treatment retention and adherence. With exceptions, publications have tended to be descriptive rather than evaluative, and the evidence-base for the effectiveness of ICT-driven interventions remains mixed. There is widespread recognition of the potential for ICT to improve HIV cascade performance, but with significant challenges. Successful implementation of real-time cascade monitoring will depend upon stakeholder engagement, compatibility with existing workflows, appropriate resource allocation, and managing expectations.

Simulated annealing of displacement cascades in FCC metals. 1. Beeler cascades

International Nuclear Information System (INIS)

Doran, D.G.; Burnett, R.A.

1974-09-01

An important source of damage to structural materials in fast reactors is the displacement of atoms from normal lattice sites. A high energy neutron may impart sufficient energy to an atom to initiate a displacement cascade consisting of a localized high density of hundreds of interstitials and vacancies. These defects subsequently interact to form clusters and to reduce their density by mutual annihilation. This short term annealing of an isolated cascade has been simulated at high and low temperatures using a correlated random walk model. The cascade representations used were developed by Beeler and the point defect properties were based on the model of γ-iron by Johnson. Low temperature anneals, characterized by no vacancy migration and a 104 site annihilation region (AR), resulted in 49 defect pairs at 20 keV and 11 pairs at 5 keV. High temperature anneals, characterized by both interstitial and vacancy migration and a 32 site AR, resulted in 68 pairs at 20 keV and 18 pairs at 5 keV when no cluster dissociation was permitted; most of the vacancies were in immobile clusters. These high temperature values dropped to 40 and 14 upon dissolution of the vacancy clusters. Parameter studies showed that, at a given temperature, the large AR resulted in about one-half as many defects as the small AR. Cluster size distributions and examples of spatial configurations are included. (U.S.)

Enhanced radiative Auger emission from lithiumlike 16S13+

International Nuclear Information System (INIS)

Bernstein, E.M.; Clark, M.W.; Oglesby, C.S.; Tanis, J.A.; Graham, W.G.; McFarland, R.H.; Morgan, T.J.; Johnson, B.M.; Jones, K.W.

1990-01-01

The radiative Auger emission (RAE) from 0.94--6.25-MeV/u 16 S 13+ (lithiumlike) projectiles excited in collisions with He target atoms has been measured. For these highly stripped ions the intensity of RAE photons relative to Kα x-ray emission is enhanced by about a factor of five compared with theoretical calculations and an earlier experimental measurement for S ions with few electron vacancies. The enhancement of RAE for S 13+ is qualitatively similar to results reported previously for lithiumlike 23 V 20+ ; however, some differences between S and V are evident

Molecular dynamics studies of displacement cascades

International Nuclear Information System (INIS)

Averback, R.S.; Hsieh, Horngming; Diaz de la Rubia, T.

1990-02-01

Molecular-dynamics simulations of cascades in Cu and Ni with primary-knock-on energies up to 5 keV and lattice temperatures in the range 0 K--700 K are described. Interatomic forces were represented by either the Gibson II (Cu) or Johnson-Erginsoy (Ni) potentials in most of this work, although some simulations using ''Embedded Atom Method'' potentials, e.g., for threshold events in Ni 3 Al, are also presented. The results indicate that the primary state of damage produced by displacement cascades is controlled by two phenomena, replacement collision sequences during the collisional phase of the cascade and local melting during the thermal spike. As expected, the collisional phase is rather similar in Cu and Ni, however, the thermal spike is of longer duration and has a more pronounced influence in Cu than Ni. When the ambient temperature of the lattice is increased, the melt zones are observed to both increase in size and cool more slowly. This has the effect of reducing defect production and enhancing atomic mixing and disordering. The implications of these results for defect production, cascade collapse, atomic disordering will be discussed. 34 refs., 7 figs., 2 tabs

Enhanced PM10 bounded PAHs from shipping emissions

Science.gov (United States)

Pongpiachan, S.; Hattayanone, M.; Choochuay, C.; Mekmok, R.; Wuttijak, N.; Ketratanakul, A.

2015-05-01

Earlier studies have highlighted the importance of maritime transport as a main contributor of air pollutants in port area. The authors intended to investigate the effects of shipping emissions on the enhancement of PM10 bounded polycyclic aromatic hydrocarbons (PAHs) and mutagenic substances in an industrial area of Rayong province, Thailand. Daily PM10 speciation data across two air quality observatory sites in Thailand during 2010-2013 were collected. Diagnostic binary ratios of PAH congeners, analysis of variances (ANOVA), and principal component analysis (PCA) were employed to evaluate the enhanced genotoxicity of PM10 during the docking period. Significant increase of PAHs and mutagenic index (MI) of PM10 were observed during the docking period in both sampling sites. Although stationary sources like coal combustions from power plants and vehicular exhausts from motorway can play a great role in enhancing PAH concentrations, regulating shipping emissions from diesel engine in the port area like Rayong is predominantly crucial.

Methods for reducing pollutant emissions from jet aircraft

Science.gov (United States)

Butze, H. F.

1971-01-01

Pollutant emissions from jet aircraft and combustion research aimed at reducing these emissions are defined. The problem of smoke formation and results achieved in smoke reduction from commercial combustors are discussed. Expermental results of parametric tests performed on both conventional and experimental combustors over a range of combustor-inlet conditions are presented. Combustor design techniques for reducing pollutant emissions are discussed. Improved fuel atomization resulting from the use of air-assist fuel nozzles has brought about significant reductions in hydrocarbon and carbon monoxide emissions at idle. Diffuser tests have shown that the combustor-inlet airflow profile can be controlled through the use of diffuser-wall bleed and that it may thus be possible to reduce emissions by controlling combustor airflow distribution. Emissions of nitric oxide from a shortlength annular swirl-can combustor were significantly lower than those from a conventional combustor operating at similar conditions.

Cascade theory in isotopic separation processes

International Nuclear Information System (INIS)

Agostini, J.P.

1994-06-01

Three main areas are developed within the scope of this work: - the first one is devoted to fundamentals: separative power, value function, ideal cascade and square cascade. Applications to two main cases are carried out, namely: Study of binary isotopic mix, Study of processes with a small enrichment coefficient. - The second one is devoted to cascade coupling -high-flux coupling (more widely used and better known) as well as low-flux coupling are presented and compared to one another. - The third one is an outlook on problems linked to cascade transients. Those problem are somewhat intricate and their interest lies mainly into two areas: economics where the start-up time may have a large influence on the interests paid during the construction and start-up period, military productions where the start-up time has a direct bearing on the production schedule. (author). 50 figs. 3 annexes. 12 refs. 6 tabs

Stability of radial swirl flows

International Nuclear Information System (INIS)

Dou, H S; Khoo, B C

2012-01-01

The energy gradient theory is used to examine the stability of radial swirl flows. It is found that the flow of free vortex is always stable, while the introduction of a radial flow will induce the flow to be unstable. It is also shown that the pure radial flow is stable. Thus, there is a flow angle between the pure circumferential flow and the pure radial flow at which the flow is most unstable. It is demonstrated that the magnitude of this flow angle is related to the Re number based on the radial flow rate, and it is near the pure circumferential flow. The result obtained in this study is useful for the design of vaneless diffusers of centrifugal compressors and pumps as well as other industrial devices.

Experimental investigation of aerodynamics, combustion, and emissions characteristics within the primary zone of a gas turbine combustor

Science.gov (United States)

Elkady, Ahmed M.

2006-04-01

The present work investigates pollutant emissions production, mainly nitric oxides and carbon monoxide, within the primary zone of a highly swirling combustion and methods with which to reduce their formation. A baseline study was executed at different equivalence ratios and different inlet air temperatures. The study was then extended to investigate the effects of utilizing transverse air jets on pollutant emission characteristics at different jet locations, jet mass ratio, and overall equivalence ratio as well as to investigate the jets' overall interactions with the recirculation zone. A Fourier Transform Infrared (FTIR) spectrometer was employed to measure emissions concentrations generated during combustion of Jet-A fuel in a swirl-cup assembly. Laser Doppler Velocimetry (LDV) was employed to investigate the mean flow aerodynamics within the combustor. Particle Image Velocimetry (PIV) was utilized to capture the instantaneous aerodynamic behavior of the non-reacting primary zone. Results illustrate that NOx production is a function of both the recirculation zone and the flame length. At low overall equivalence ratios, the recirculation zone is found to be the main producer of NOx. At near stoichiometric conditions, the post recirculation zone appears to be responsible for the majority of NOx produced. Results reveal the possibility of injecting air into the recirculation zone without altering flame stability to improve emission characteristics. Depending on the jet location and strength, nitric oxides as well as carbon monoxide can be reduced simultaneously. Placing the primary air jet just downstream of the fuel rich recirculation zone can lead to a significant reduction in both nitric oxides and carbon monoxide. In the case of fuel lean recirculation zone, reduction of nitric oxides can occur by placing the jets below the location of maximum radius of the recirculation zone.

Double helix vortex breakdown in a turbulent swirling annular jet flow

NARCIS (Netherlands)

Vanierschot, M.; Perçin, M.; van Oudheusden, B.W.

2018-01-01

In this paper, we report on the structure and dynamics of double helix vortex breakdown in a turbulent annular swirling jet. Double helix breakdown has been reported previously for the laminar flow regime, but this structure has rarely been observed in turbulent flow. The flow field is

Two different mechanisms on UV emission enhancement in Ag-doped ZnO thin films

International Nuclear Information System (INIS)

Xu, Linhua; Zheng, Gaige; Zhao, Lilong; Pei, Shixin

2015-01-01

Ag-doped ZnO thin films were prepared by a sol–gel method. The structural, morphological and optical properties of the samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV–vis and photoluminescence spectra. The results show that the Ag in the ZnO thin films annealed at 500 °C for 1 h substitutes for Zn and exists in the form of Ag + ion (Ag Zn ) while the Ag in the ZnO thin films without a post-annealing mainly exists in the form of simple substance (Ag 0 ). The incorporation of Ag indeed can improve the ultraviolet emission of ZnO thin films and suppress the visible emissions at the same time. However, the mechanisms on the ultraviolet emission enhancement in the annealed and unannealed Ag-doped ZnO thin films are very different. As for the post-annealed Ag-doped ZnO thin films, the UV emission enhancement maybe mainly results from more electron–hole pairs (excitons) due to Ag-doping while for the unannealed Ag-doped ZnO thin films; the UV emission enhancement is attributed to the resonant coupling between exciton emission in ZnO and localized surface plasmon in Ag nanoparticles. - Highlights: • Ag-doped ZnO thin films have been prepared by the sol–gel method. • Ag-doping can enhance ultraviolet emission of ZnO thin films and depress the visible emissions at the same time. • There are two different mechanisms on UV emission enhancement in Ag-doped ZnO thin films. • The UV emission enhancement from the resonant coupling between excitonic emissions and localized surface plasmon in Ag nanoparticle is very attractive

Response of forest soil Acari to prescribed fire following stand structure manipulation in the southern Cascade Range.Can

Science.gov (United States)

Michael A. Camann; Nancy E. Gillette; Karen L. Lamoncha; Sylvia R. Mori

2008-01-01

We studied responses of Acari, especially oribatid mites, to prescribed low-intensity fire in an east side pine site in the southern Cascade Range in California. We compared oribatid population and assemblage responses to prescribed fire in stands that had been selectively logged to enhance old growth characteristics, in logged stands to minimize old growth...

Geometrical optimization of a swirling Savonius wind turbine using an open jet wind tun

Directory of Open Access Journals (Sweden)

Abdullah Al-Faruk

2016-09-01

Full Text Available It has been suggested that waste heats or naturally available heat sources can be utilized to produce swirling flow by a design similar to that of split channels which is currently used to initiate fire whirls in laboratories. The new design combines the conventional Savonius wind turbine and split channel mechanisms. Previous computational and preliminary experimental works indicate a performance improvement in the new design (named as swirling Savonius turbine compared to the conventional Savonius design. In this study, wind tunnel experiments have been carried out to optimize the swirling Savonius turbine geometry in terms of maximum power coefficient by considering several design parameters. The results indicate that the blade overlap ratio, hot air inlet diameter and the condition of the top end plate have significant influence on power and torque coefficients, while a larger aspect ratio and closed top end plate have some favourable effects on the performance. The optimum configuration has been tested in four different wind velocities to determine its influence on the performance, and power coefficients were found to be higher in high wind velocities. The performance comparison of optimum configuration with conventional Savonius rotor showed an increase of 24.12% in the coefficient of power.

Spontaneous Emission Enhancement at Finite-length Metal

DEFF Research Database (Denmark)

Filonenko, K.; Willatzen, Morten; Bordo, V.

2013-01-01

We study spontaneous emission enhancement of a two-level atomic emitter placed in a dielectric medium near a finite-length cylindrical metal nanowire. We calculate the dependence of the Purcell factor and the normalized decay rate to a continuous spectrum on the nanowire radius for several emitter...

The Of emission lines near 4650 A

International Nuclear Information System (INIS)

Underhill, A.B.; Gilroy, K.K.; Hill, G.M.

1989-01-01

Rectified, normalized, high S/N intensity tracings of nine Of stars were obtained from Reticon spectra in the 4550-4800-A region. The well-known relatively sharp Of emission lines are seen to stand on pedestals of broad weak emission somewhat like the broad emission lines from WR stars. It is suggested that cascades following dielectronic recombination may be an important process driving some lines of N III, C III, and C IV into the emission of Of stars, and that the sharp Of lines come from plasma that is stationary with respect to the star. The broad emission features show an extensive low-density wind from each star. The results imply that the detection of two, more or less equal, broad jumps in the rest spectra of galaxies at about 4640 and 4686 A is more indicative of Of stars than of WR stars. 32 refs

Tunable signal processing in synthetic MAP kinase cascades.

Science.gov (United States)

O'Shaughnessy, Ellen C; Palani, Santhosh; Collins, James J; Sarkar, Casim A

2011-01-07

The flexibility of MAPK cascade responses enables regulation of a vast array of cell fate decisions, but elucidating the mechanisms underlying this plasticity is difficult in endogenous signaling networks. We constructed insulated mammalian MAPK cascades in yeast to explore how intrinsic and extrinsic perturbations affect the flexibility of these synthetic signaling modules. Contrary to biphasic dependence on scaffold concentration, we observe monotonic decreases in signal strength as scaffold concentration increases. We find that augmenting the concentration of sequential kinases can enhance ultrasensitivity and lower the activation threshold. Further, integrating negative regulation and concentration variation can decouple ultrasensitivity and threshold from the strength of the response. Computational analyses show that cascading can generate ultrasensitivity and that natural cascades with different kinase concentrations are innately biased toward their distinct activation profiles. This work demonstrates that tunable signal processing is inherent to minimal MAPK modules and elucidates principles for rational design of synthetic signaling systems. Copyright © 2011 Elsevier Inc. All rights reserved.

Thermodynamic analysis of a novel ejector expansion transcritical CO_2/N_2O cascade refrigeration (NEETCR) system for cooling applications at low temperatures

International Nuclear Information System (INIS)

Megdouli, K.; Ejemni, N.; Nahdi, E.; Mhimid, A.; Kairouani, L.

2017-01-01

Natural substances are becoming very promising for long term alternative for refrigeration purposes. In this paper, two natural refrigerants have been proposed and analyzed for a novel ejector expansion transcritical cascade refrigeration (NEETCR) system. Nitrous oxide (N_2O) is used in the low temperature circuit (LTC) whereas carbon dioxide (CO_2) is used in the high temperature circuit (HTC) of the NEETCR system. The reject of refrigerant vapor heat in the HTC is carried out through the use of transcritical carbon dioxide Rankine cycle. This produces work, which will be used to reduce the consumption work of compressors and feed pump thereby resulting in the improvement of the energy efficiency of the whole system. The simulation results were obtained by a computer FORTRAN program, where REFPROP 9 database was used to get the refrigerant thermodynamic properties. The simulation results showed that the (NEETCR) system had higher coefficient of performance and higher system second law efficiency compared to the EETCR system. An enhancement more than 9% in the COP and exergy efficiency of NEETCR system was found in comparison with EETCR system, when the cooling capacity and operating conditions of the two systems were the same. The increase of COP of NEETCR system and its efficiency along with the reduction of power consumption make it more practical for the use in cooling applications. - Highlights: • Exergy-energy analysis of two cascade refrigeration systems is conducted. • The input power of the NEETCR system is lower than that of the EETCR system. • The COP of the NEETCR system is higher than that of the EETCR system. • The NEETCR system is promise in cascade refrigeration system.

Visualization of the structure of vortex breakdown in free swirling jet flow

NARCIS (Netherlands)

Vanierschot, M.; Perçin, M.; van Oudheusden, B.W.

2016-01-01

In this paper we investigate the three dimensional flow structures in a free annular swirling jet flow undergoing vortex breakdown. The flow field is analyzed by means of time-resolved Tomographic Particle Image Velocimetry measurements. Both time-averaged and instantaneous flow structures are

Geothermal segmentation of the Cascade Range in the USA

Science.gov (United States)

Guffanti, Marianne; Muffler, L.J.; Mariner, R.H.; Sherrod, D.R.; Smith, James G.; Blackwell, D.D.; Weaver, C.S.

1990-01-01

Characteristics of the crustal thermal regime of the Quaternary Cascades vary systematically along the range. Spatially congruent changes in volcanic vent distribution, volcanic extrusion rate, hydrothermal discharge rate, and regional conductive heat flow define 5 geothermal segments. These segments are, from north to south: (1) the Washington Cascades north of Mount Rainier, (2) the Cascades from Mount Rainier to Mount Hood, (3) the Oregon Cascades from south of Mount Hood to the California border, (4) northernmost California, including Mount Shasta and Medicine Lake volcano, and (5) the Lassen region of northern California. This segmentation indicates that geothermal resource potential is not uniform in the Cascade Range. Potential varies from high in parts of Oregon to low in Washington north of Mount Rainier.

Experimental study of a high-efficiency low-emission surface combustor-heater

International Nuclear Information System (INIS)

Xiong, Tian-yu; Khinkis, M.J.; Fish, F.F.

1991-01-01

The surface combustor-heater is a combined combustion/heat-transfer device in which the heat-exchange surfaces are embedded in a stationary bed of refractory material where gaseous fuel is burned. Because of intensive heat radiation from the hot solid particles and enhanced heat convection from the gas flow to the heat-exchange tubes, heat transfer is significantly intensified. Removing heat simultaneously with the combustion process has the benefit of reducing the combustion temperature, which suppresses NO x formation. A basic experimental study was conducted on a 60-kW bench-scale surface combustor-heater with two rows of water-cooled tube coils to evaluate its performance and explore the mechanism of combined convective-radiative heat transfer and its interaction with combustion in the porous matrix. Combustion stability in the porous matrix, heat-transfer rates, emissions, and pressure drop through the unit have been investigated for the variable parameters of operation and unit configurations. Experimental results have demonstrated that high combustion intensity (up to 2.5 MW/m 2 ), high heat-transfer rates (up to 310 kW/m 2 ), high density of energy conversion (up to 8 MW/m 3 ), as well as ultra-low emissions (NO x and CO as low as 15 vppm*) have been achieved. The excellent performance of the test unit and the extensive data obtained from the present experimental study provide the basis for further development of high-efficiency and ultra low-emission water heaters, boilers, and process heaters based on the surface combustor-heater concept. 4 refs., 16 figs

Rotating polygon instability of a swirling free surface flow

DEFF Research Database (Denmark)

Tophøj, Laust Emil Hjerrild; Bohr, Tomas; Mougel, J.

2013-01-01

We explain the rotating polygon instability on a swirling fluid surface [G. H. Vatistas, J. Fluid Mech. 217, 241 (1990)JFLSA70022-1120 and Jansson et al., Phys. Rev. Lett. 96, 174502 (2006)PRLTAO0031-9007] in terms of resonant interactions between gravity waves on the outer part of the surface...... behavior near the corners), and indeed we show that we can obtain the polygons transiently by violently stirring liquid nitrogen in a hot container....

Global Search of a Three-dimensional Low Solidity Circular Cascade Diffuser for Centrifugal Blowers by Meta-model Assisted Optimization

Science.gov (United States)

Sakaguchi, Daisaku; Sakue, Daiki; Tun, Min Thaw

2018-04-01

A three-dimensional blade of a low solidity circular cascade diffuser in centrifugal blowers is designed by means of a multi-point optimization technique. The optimization aims at improving static pressure coefficient at a design point and at a small flow rate condition. Moreover, a clear definition of secondary flow expressed by positive radial velocity at hub side is taken into consideration in constraints. The number of design parameters for three-dimensional blade reaches to 10 in this study, such as a radial gap, a radial chord length and mean camber angle distribution of the LSD blade with five control points, control point between hub and shroud with two design freedom. Optimization results show clear Pareto front and selected optimum design shows good improvement of pressure rise in diffuser at small flow rate conditions. It is found that three-dimensional blade has advantage to stabilize the secondary flow effect with improving pressure recovery of the low solidity circular cascade diffuser.

Water-processed carbon nanotube/graphene hybrids with enhanced field emission properties

International Nuclear Information System (INIS)

Song, Meng; Xu, Peng; Wang, Xu; Wu, Huizhen; Wang, Miao; Song, Yenan; Li, Zhenhua; Zhao, Pei; Shang, Xuefu

2015-01-01

Integrating carbon nanotubes (CNTs) and graphene into hybrid structures provides a novel approach to three dimensional (3D) materials with advantageous properties. Here we present a water-processing method to create integrated CNT/graphene hybrids and test their field emission properties. With an optimized mass ratio of CNTs to graphene, the hybrid shows a significantly enhanced field emission performance, such as turn-on electric field of 0.79 V/μm, threshold electric field of 1.05 V/μm, maximum current density of 0.1 mA/cm 2 , and field enhancement factor of ∼1.3 × 10 4 . The optimized mass ratio for field emission emphasizes the importance of both CNTs and graphene in the hybrid. We also hypothesize a possible mechanism for this enhanced field emission performance from the CNT/graphene hybrid. During the solution treatment, graphene oxide behaves as surfactant sheets for CNTs to form a well dispersed solution, which leads to a better organized 3D structure with more conducting channels for electron transport

Water-processed carbon nanotube/graphene hybrids with enhanced field emission properties

Energy Technology Data Exchange (ETDEWEB)

Song, Meng; Xu, Peng; Wang, Xu; Wu, Huizhen; Wang, Miao, E-mail: peizhao@zju.edu.cn, E-mail: miaowang@css.zju.edu.cn [Department of Physics, Zhejiang University, Hangzhou 310027 (China); Song, Yenan; Li, Zhenhua; Zhao, Pei, E-mail: peizhao@zju.edu.cn, E-mail: miaowang@css.zju.edu.cn [Institute of Applied Mechanics, Zhejiang University, Hangzhou 310027 (China); Shang, Xuefu [Department of Physics, Faculty of Science, Jiangsu University, Zhenjiang 212013 (China)

2015-09-15

Integrating carbon nanotubes (CNTs) and graphene into hybrid structures provides a novel approach to three dimensional (3D) materials with advantageous properties. Here we present a water-processing method to create integrated CNT/graphene hybrids and test their field emission properties. With an optimized mass ratio of CNTs to graphene, the hybrid shows a significantly enhanced field emission performance, such as turn-on electric field of 0.79 V/μm, threshold electric field of 1.05 V/μm, maximum current density of 0.1 mA/cm{sup 2}, and field enhancement factor of ∼1.3 × 10{sup 4}. The optimized mass ratio for field emission emphasizes the importance of both CNTs and graphene in the hybrid. We also hypothesize a possible mechanism for this enhanced field emission performance from the CNT/graphene hybrid. During the solution treatment, graphene oxide behaves as surfactant sheets for CNTs to form a well dispersed solution, which leads to a better organized 3D structure with more conducting channels for electron transport.

Distortion-product otoacoustic emission at low frequencies in humans

DEFF Research Database (Denmark)

Christensen, Anders Tornvig

-frequency hearing has not yet been characterized by measurement of low-frequency emissions from the cochlea. Low-frequency emissions are expected to be covered in sounds of breathing, blood circulation, and so on, if they exist at all at measurable levels. The present study shows, in essence, that the human ear...... emits distortion at least 1-2 octaves lower in frequency than has previously been shown. The emission is promising for further exploratory and clinical assessment of cochlear activity associated with low-frequency hearing. Anders received his M.Sc. degree in acoustics in 2012 from Aalborg University...

A non-conventional isotope separation cascade without any mixing: net cascade

International Nuclear Information System (INIS)

Zeng Shi; Jiang Dongjun; Ying Zhengen

2012-01-01

A component has different concentrations in the incoming flows at a confluent point in all existing isotope separations cascades for multi-component isotope separation and mixing is inevitable, which results in deterioration of separation performance of the separation cascade. However, realization of no-mixing at a confluent point is impossible with a conventional cascade. A non-conventional isotope separation cascade, net cascade, is found to be able to realize no mixings for all components at confluent points, and its concept is further developed here. No-mixing is fulfilled by requiring symmetrical separation of two specified key components at every stage, and the procedure of realizing no-mixing is presented in detail. Some properties of net cascade are investigated preliminarily, and the results demonstrated the no-mixing property is indeed realized. Net cascade is the only separation cascade that so far possesses the no-mixing property. (authors)

SHI induced enhancement in green emission from nanocrystalline CdS thin films for photonic applications

International Nuclear Information System (INIS)

Kumar, Pragati; Saxena, Nupur; Chandra, Ramesh; Gao, Kun; Zhou, Shengqiang; Agarwal, Avinash; Singh, Fouran; Gupta, Vinay; Kanjilal, D.

2014-01-01

Intense green emission is reported from nanocrystalline CdS thin films grown by pulsed laser deposition. The effect of ion beam induced dense electronic excitation on luminescence property of CdS films is explored under irradiation using 70 MeV 58 Ni 6+ ions. It is found that swift heavy ion beam irradiation enhances the emission intensity by an order of 1 and broadens the emission range. This feature is extremely useful to enhance the performance of different photonic devices like light emitting diodes and lasers, as well as luminescence based sensors. To examine the role of energy relaxation process of swift heavy ions in creation/annihilation of different defect levels, multi-peaks are fitted in photoluminescence spectra using a Gaussian function. The variation of contribution of different emissions in green emission with ion fluence is studied. Origin of enhancement in green emission is supported by various characterization techniques like UV–visible absorption spectroscopy, glancing angle X-ray diffraction, micro-Raman spectroscopy and transmission electron microscopy. A possible mechanism of enhanced GE due to ion beam irradiation is proposed on the basis of existing models. -- Highlights: • Room temperature green luminescence nanocrystalline CdS thin films grown by pulsed laser deposition. • Enhanced green emission by means of swift heavy ion irradiation. • Multipeak fitting of photoluminescence spectra using a Gaussian function. • Variation of area contributed by different emissions in green emission is studied with respect to ion fluence. • Mechanism of enhanced green emission is discussed based on creation/annihilation of defects due to ion beam irradiation

SHI induced enhancement in green emission from nanocrystalline CdS thin films for photonic applications

Energy Technology Data Exchange (ETDEWEB)

Kumar, Pragati, E-mail: pkumar.phy@gmail.com [Department of Physics, Bareilly College, Shahmat Ganj Road, Bareilly 243005, Uttar Pradesh (India); Saxena, Nupur [Inter University Accelerator Centre, Aruna Asaf Ali Marg, P.O. Box 10502, New Delhi 110067 (India); Chandra, Ramesh [Institute Instrumentation Centre, Indian Institute of Technology, Roorkee 247667 (India); Gao, Kun; Zhou, Shengqiang [Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf (HZDR), P.O. Box 510119, 01314 Dresden (Germany); Agarwal, Avinash [Department of Physics, Bareilly College, Shahmat Ganj Road, Bareilly 243005, Uttar Pradesh (India); Singh, Fouran [Inter University Accelerator Centre, Aruna Asaf Ali Marg, P.O. Box 10502, New Delhi 110067 (India); Gupta, Vinay [Department of Physics and Astrophysics, Delhi University, Delhi 110007 (India); Kanjilal, D. [Inter University Accelerator Centre, Aruna Asaf Ali Marg, P.O. Box 10502, New Delhi 110067 (India)

2014-03-15

Intense green emission is reported from nanocrystalline CdS thin films grown by pulsed laser deposition. The effect of ion beam induced dense electronic excitation on luminescence property of CdS films is explored under irradiation using 70 MeV {sup 58}Ni{sup 6+} ions. It is found that swift heavy ion beam irradiation enhances the emission intensity by an order of 1 and broadens the emission range. This feature is extremely useful to enhance the performance of different photonic devices like light emitting diodes and lasers, as well as luminescence based sensors. To examine the role of energy relaxation process of swift heavy ions in creation/annihilation of different defect levels, multi-peaks are fitted in photoluminescence spectra using a Gaussian function. The variation of contribution of different emissions in green emission with ion fluence is studied. Origin of enhancement in green emission is supported by various characterization techniques like UV–visible absorption spectroscopy, glancing angle X-ray diffraction, micro-Raman spectroscopy and transmission electron microscopy. A possible mechanism of enhanced GE due to ion beam irradiation is proposed on the basis of existing models. -- Highlights: • Room temperature green luminescence nanocrystalline CdS thin films grown by pulsed laser deposition. • Enhanced green emission by means of swift heavy ion irradiation. • Multipeak fitting of photoluminescence spectra using a Gaussian function. • Variation of area contributed by different emissions in green emission is studied with respect to ion fluence. • Mechanism of enhanced green emission is discussed based on creation/annihilation of defects due to ion beam irradiation.

Primary pulmonary low-grade angiosarcoma characterized by mismatch between {sup 18}F-FDG FET and dynamic contrast-enhanced CT

Energy Technology Data Exchange (ETDEWEB)

KIm, Eun Young; Lee, Ho Yun; Han, Joung Ho; Choi, Joon Young [Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul (Korea, Republic of)

2015-10-15

We report a rare case of primary pulmonary low-grade angiosarcoma on dynamic contrast-enhanced CT and {sup 18}F-fluorodeoxyglucose (FDG) positron emission tomography (PET)/CT imaging. A 38-year-old, asymptomatic woman was hospitalized because of an abnormality on chest radiography. A dynamic contrast-enhanced chest CT showed a 1.2 cm-sized irregular-margined nodule with strong and persistent enhancement in the right lower lobe. The lesion had low metabolic activity on an {sup 18}F-FDG PET/CT scan. The patient underwent a wedge resection for the lesion, and pathology revealed a primary pulmonary low-grade angiosarcoma.

Photoacoustic emission from fluorescent nanodiamonds enhanced with gold nanoparticles

Science.gov (United States)

Zhang, Bailin; Fang, Chia-Yi; Chang, Cheng-Chun; Peterson, Ralph; Maswadi, Saher; Glickman, Randolph D.; Chang, Huan-Cheng; Ye, Jing Yong

2012-01-01

Fluorescent nanodiamonds (FNDs) have drawn much attention in recent years for biomedical imaging applications due to their desired physical properties including excellent photostability, high biocompatibility, extended far-red fluorescence emission, and ease of surface functionalization. Here we explore a new feature of FNDs, i.e. their photoacoustic emission capability, which may lead to potential applications of using FNDs as a dual imaging contrast agent for combined fluorescence and photoacoustic imaging modalities. We observed significant enhancement of photoacoustic emission from FNDs when they were conjugated with gold nanoparticles (GNPs). PMID:22808436

Photoacoustic emission from fluorescent nanodiamonds enhanced with gold nanoparticles.

Science.gov (United States)

Zhang, Bailin; Fang, Chia-Yi; Chang, Cheng-Chun; Peterson, Ralph; Maswadi, Saher; Glickman, Randolph D; Chang, Huan-Cheng; Ye, Jing Yong

2012-07-01

Fluorescent nanodiamonds (FNDs) have drawn much attention in recent years for biomedical imaging applications due to their desired physical properties including excellent photostability, high biocompatibility, extended far-red fluorescence emission, and ease of surface functionalization. Here we explore a new feature of FNDs, i.e. their photoacoustic emission capability, which may lead to potential applications of using FNDs as a dual imaging contrast agent for combined fluorescence and photoacoustic imaging modalities. We observed significant enhancement of photoacoustic emission from FNDs when they were conjugated with gold nanoparticles (GNPs).

Evolution and transition mechanisms of internal swirling flows with tangential entry

Science.gov (United States)

Wang, Yanxing; Wang, Xingjian; Yang, Vigor

2018-01-01

The characteristics and transition mechanisms of different states of swirling flow in a cylindrical chamber have been numerically investigated using the Galerkin finite element method. The effects of the Reynolds number and swirl level were examined, and a unified theory connecting different flow states was established. The development of each flow state is considered as a result of the interaction and competition between basic mechanisms: (1) the centrifugal effect, which drives an axisymmetric central recirculation zone (CRZ); (2) flow instabilities, which develop at the free shear layer and the central solid-body rotating flow; (3) the bouncing and restoring effects of the injected flow, which facilitate the convergence of flow on the centerline and the formation of bubble-type vortex breakdown; and (4) the damping effect of the end-induced flow, which suppresses the development of the instability waves. The results show that the CRZ, together with the free shear layer on its surface, composes the basic structure of swirling flow. The development of instability waves produces a number of discrete vortex cores enclosing the CRZ. The azimuthal wave number is primarily determined by the injection angle. Generally, the wave number is smaller at a higher injection angle, due to the reduction of the perimeter of the free shear layer. At the same time, the increase in the Reynolds number facilitates the growth of the wave number. The end-induced flow tends to reduce the wave number near the head end and causes a change in wave number from the head end to the downstream region. Spiral-type vortex breakdown can be considered as a limiting case at a high injection angle, with a wave number equal to 0 near the head end and equal to 1 downstream. At lower Reynolds numbers, the bouncing and restoring effect of the injected flow generates bubble-type vortex breakdown.

Quantifying alkane emissions in the Eagle Ford Shale using boundary layer enhancement

Science.gov (United States)

Roest, Geoffrey; Schade, Gunnar

2017-09-01

The Eagle Ford Shale in southern Texas is home to a booming unconventional oil and gas industry, the climate and air quality impacts of which remain poorly quantified due to uncertain emission estimates. We used the atmospheric enhancement of alkanes from Texas Commission on Environmental Quality volatile organic compound monitors across the shale, in combination with back trajectory and dispersion modeling, to quantify C2-C4 alkane emissions for a region in southern Texas, including the core of the Eagle Ford, for a set of 68 days from July 2013 to December 2015. Emissions were partitioned into raw natural gas and liquid storage tank sources using gas and headspace composition data, respectively, and observed enhancement ratios. We also estimate methane emissions based on typical ethane-to-methane ratios in gaseous emissions. The median emission rate from raw natural gas sources in the shale, calculated as a percentage of the total produced natural gas in the upwind region, was 0.7 % with an interquartile range (IQR) of 0.5-1.3 %, below the US Environmental Protection Agency's (EPA) current estimates. However, storage tanks contributed 17 % of methane emissions, 55 % of ethane, 82 % percent of propane, 90 % of n-butane, and 83 % of isobutane emissions. The inclusion of liquid storage tank emissions results in a median emission rate of 1.0 % (IQR of 0.7-1.6 %) relative to produced natural gas, overlapping the current EPA estimate of roughly 1.6 %. We conclude that emissions from liquid storage tanks are likely a major source for the observed non-methane hydrocarbon enhancements in the Northern Hemisphere.

Enhanced Plasmonic Wavelength Selective Infrared Emission Combined with Microheater

Directory of Open Access Journals (Sweden)

Hiroki Ishihara

2017-09-01

Full Text Available The indirect wavelength selective thermal emitter that we have proposed is constructed using a new microheater, demonstrating the enhancement of the emission peak generated by the surface plasmon polariton. The thermal isolation is improved using a 2 μm-thick Si membrane having 3.6 and 5.4 mm outer diameter. The emission at around the wavelength of the absorption band of CO2 gas is enhanced. The absorption signal increases, confirming the suitability for gas sensing. Against input power, the intensity at the peak wavelength shows a steeper increasing ratio than the background intensity. The microheater with higher thermal isolation gives larger peak intensity and its increasing ratio against the input power.

Enhanced EGFP Fluorescence Emission in Presence of PEG Aqueous Solutions and PIB1000-PEG6000-PIB1000 Copolymer Vesicles

Directory of Open Access Journals (Sweden)

Noor Muhammad

2013-01-01

Full Text Available An EGFP construct interacting with the PIB1000-PEG6000-PIB1000 vesicles surface reported a ~2-fold fluorescence emission enhancement. Because of the constructs nature with the amphiphilic peptide inserted into the PIB core, EGFP is expected to experience a “pure” PEG environment. To unravel this phenomenon PEG/water solutions at different molecular weights and concentrations were used. Already at ~1 : 10 protein/PEG molar ratio the increase in fluorescence emission is observed reaching a plateau correlating with the PEG molecular weight. Parallel experiments in presence of glycerol aqueous solutions did show a slight fluorescence enhancement however starting at much higher concentrations. Molecular dynamics simulations of EGFP in neat water, glycerol, and PEG aqueous solutions were performed showing that PEG molecules tend to “wrap” the protein creating a microenvironment where the local PEG concentration is higher compared to its bulk concentration. Because the fluorescent emission can be perturbed by the refractive index surrounding the protein, the clustering of PEG molecules induces an enhanced fluorescence emission already at extremely low concentrations. These findings can be important when related to the use of EGFP as reported in molecular biology experiments.

Pengaruh Modifikasi Heat Exchanger Tipe Concentric Tube Terhadap Performance Sistem Refrigerasi Cascade

Directory of Open Access Journals (Sweden)

Jhona Purnama Putra

2014-03-01

Full Text Available Dalam beberapa bidang industri seperti pengawetan makanan, perminyakan, pengolahan bahan-bahan kimia dan pendinginan setempat (spot cooling pada industri baja dibutuhkan kondisi ruangan yang sangat rendah berkisar antara -30°C hingga -60°C. Maka dari itu digunakanlah sistem refrigerasi cascade yang disusun atas dua stage yaitu high dan low. Dimana kedua stage ini digabungkan menjadi satu oleh sebuah heat exchanger yang melakukan perpindahan kalor dari kondensor low stage menuju evaporator high stage. pada penelitian terdahulu alat penukar panas yang digunakan yaitu alat penukar panas tipe concentric tube masih menunjukan performa yang belum baik kepada sistem refrigerasi cascade. Penelitian dilakukan dengan memodifikasi alat penukar panas dan menganalisa performa sistem setelah dilakukannya modifikasi penambahan panjang pada alat penukar panas, dengan fluida kerja refrigeran Musicool-22 di High Stage dan R-404A di Low Stage. Setelah perancangan alat selesai, dilakukan eksperimen pada sistem tersebut dengan variasi beban pendinginan menggunakan electric heater di evaporator Low Stage sebesar 0 (tanpa beban, 6, 16, 40, 60, dan 98 Watt.. Hasil dari studi eksperimen ini menunjukkan nilai-nilai optimum yang didapatkan yaitu pada pembebanan 60 Watt dengan Qevap = 0,599 kW, COP cascade = 0,968 dan temperatur di dalam cooling box sebesar -30,1°C serta nilai-nilai maksimum dari performa sistem refrigerasi cascade pada beban 98 Watt yaitu kapasitas pendinginan maksimum pada sistem Low Stage adalah 0,60654 kW, kerja maksimum kompresor pada sistem High Stage 0,1711 kW dan Low Stage 0,4432 kW, nilai COP cascade maksimum 0,9969, efek refrigerasi maksimum pada Low Stage 137,85 kJ/kg, HRR maksimum pada Low Stage 1,731. Kemudian diperoleh nilai effectiveness cascade heat exchanger tertinggi 0,922 dan terendah 0,912 serta nilai NTU tertinggi 7,1800 dan terendah 6,4121.

Double helix vortex breakdown in a turbulent swirling annular jet flow

Science.gov (United States)

Vanierschot, M.; Percin, M.; van Oudheusden, B. W.

2018-03-01

In this paper, we report on the structure and dynamics of double helix vortex breakdown in a turbulent annular swirling jet. Double helix breakdown has been reported previously for the laminar flow regime, but this structure has rarely been observed in turbulent flow. The flow field is investigated experimentally by means of time-resolved tomographic particle image velocimetry. Notwithstanding the axisymmetric nature of the time-averaged flow, analysis of the instantaneous three-dimensional (3D) vortical structures shows the existence of a vortex core along the central axis which breaks up into a double helix downstream. The winding sense of this double helix is opposite to the swirl direction (m =-2 ) and it is wrapped around a central vortex breakdown bubble. This structure is quite different from double helix breakdown found in laminar flows where the helix is formed in the wake of the bubble and not upstream. The double helix precesses around the central axis of the jet with a precessing frequency corresponding to a Strouhal number of 0.27.

Evaluation of design factors for a cascade aerator to enhance the efficiency of an oxidation pond for ferruginous mine drainage.

Science.gov (United States)

Oh, Chamteut; Ji, Sangwoo; Cheong, Youngwook; Yim, Giljae; Hong, Ji-Hye

2016-10-01

This research focused on the optimum design of a cascade aerator to enhance the efficiency of an oxidation pond in a passive treatment system for remediating ferruginous mine drainage. For this purpose, various aeration experiments with aerators of different drop heights (0-4 m) and formations (types A and B) were executed on mine drainage. Type A simply drops the mine drainage into the oxidation pond while type B sprays the mine drainage and retains it for 8 min in each step. The efficiency enhancement of the oxidation pond was strongly dependent on the increase in pH and DO of the mine drainage discharged into the pond. The water quality improved with the increase in drop height but especially showed better effect with type B. The reasons for this result were attributed to the increase of contact surface and retention time of the mine drainage. The cascade aerator, therefore, should be designed to be as high as possible with the assistance of spraying form and retention time of the mine drainage to maximize the efficiency of the oxidation pond. These effects could be evaluated by calculating required areas of the oxidation pond for 95% of Fe(2+) oxidation.

Vortex breakdown control by adding near-axis swirl and temperature gradients.

Science.gov (United States)

Herrada, Miguel Angel; Shtern, Vladimir

2003-10-01

Vortex breakdown (VB) is an intriguing effect of practical and fundamental interest, occurring, e.g., in tornadoes, above delta-wing aircraft, and in vortex devices. Depending on application, VB is either beneficiary or harmful and therefore requires a proper control. This study shows that VB can be efficiently controlled by a combination of additional near-axis swirl and heat. To explore the underlying mechanism, we address a flow in a cylindrical container driven by a rotating bottom disk. This model flow has been extensively studied being well suited for understanding both the VB mechanism and its control. Our numerical analysis explains experimentally observed effects of control corotation and counter-rotation (with no temperature gradient) and reveals some flaws of dye visualization. An important feature found is that a moderate negative (positive) axial gradient of temperature can significantly enforce (diminish) the VB enhancement by the counter-rotation. A strong positive temperature gradient stimulates the centrifugal instability and time oscillations in the flow with counter-rotation. An efficient time-evolution code for axisymmetric compressible flows has facilitated the numerical study.

The development of an ultra-low-emission gas-fired cyclonic combustor

International Nuclear Information System (INIS)

Xiong, Tian-yu; Khinkis, M.J.; Coppin, W.P.

1991-01-01

A gas-fired cyclonic combustor has been developed for relatively low-temperature direct-air heating applications that require ultra-low pollutant emissions. High-lean premixed combustion with a flame stabilizer is adopted to achieve ultra-low emissions and high turndown operation. On the basis of analytical studies and cold modeling, a 350-kW test combustor was designed and successfully tested. Experimental results obtained using natural gas and ambient air demonstrated that the test combustor can operate steadily at high excess air up to 80% to 100% over a large turndown range up to 40:1. At design operating conditions, NO x emissions as low as 0.6 vppm and CO and total hydrocarbon (THC) emissions below 3 vppm were achieved. Over the full operating range, NO x emissions from 0.3 to 1.0 vppm and CO and THC emissions below 4 vppm were demonstrated. In all tests, concentrations of NO 2 were less than 40% of the total NO x emissions -- lower than the level of NO 2 emissions from combustion processes required for good indoor air quality (0.5 vppm). This paper presents the concept of high-lean premixed ultra-low-emission cyclonic combustion, design specifications for the combustion system, and the major experimental results, including flame stability, emissions, and turndown performance. 13 refs., 12 figs., 1 tab

Quantum-dot nano-cavity lasers with Purcell-enhanced stimulated emission

DEFF Research Database (Denmark)

Gregersen, Niels; Skovgård, Troels Suhr; Lorke, Michael

2012-01-01

We present a rate equation model for quantum-dot light-emitting devices that take into account Purcell enhancement of both spontaneous emission and stimulated emission as well as the spectral profile of the optical and electronic density-of-states. We find that below threshold the b-factor in a q...

Development of combined low-emissions burner devices for low-power boilers

Science.gov (United States)

Roslyakov, P. V.; Proskurin, Yu. V.; Khokhlov, D. A.

2017-08-01

Low-power water boilers are widely used for autonomous heat supply in various industries. Firetube and water-tube boilers of domestic and foreign manufacturers are widely represented on the Russian market. However, even Russian boilers are supplied with licensed foreign burner devices, which reduce their competitiveness and complicate operating conditions. A task of developing efficient domestic low-emissions burner devices for low-power boilers is quite acute. A characteristic property of ignition and fuel combustion in such boilers is their flowing in constrained conditions due to small dimensions of combustion chambers and flame tubes. These processes differ significantly from those in open combustion chambers of high-duty power boilers, and they have not been sufficiently studied yet. The goals of this paper are studying the processes of ignition and combustion of gaseous and liquid fuels, heat and mass transfer and NO x emissions in constrained conditions, and the development of a modern combined low-emissions 2.2 MW burner device that provides efficient fuel combustion. A burner device computer model is developed and numerical studies of its operation on different types of fuel in a working load range from 40 to 100% of the nominal are carried out. The main features of ignition and combustion of gaseous and liquid fuels in constrained conditions of the flame tube at nominal and decreased loads are determined, which differ fundamentally from the similar processes in steam boiler furnaces. The influence of the burner devices design and operating conditions on the fuel underburning and NO x formation is determined. Based on the results of the design studies, a design of the new combined low-emissions burner device is proposed, which has several advantages over the prototype.

Characterization of In-Flight Processing of Alumina Powder Using a DC-RF Hybrid Plasma Flow System at Constant Low Operating Power

Science.gov (United States)

Nishiyama, H.; Onodera, M.; Igawa, J.; Nakajima, T.

2009-12-01

The aim of this study is to provide the optimum operating conditions for enhancing in-flight alumina particle heating as much as possible for particle spheroidization and aggregation of melted particles using a DC-RF hybrid plasma flow system even at constant low operating power based on the thermofluid considerations. It is clarified that the swirl flow and higher operating pressure enhance the particle melting and aggregation of melted particles coupled with increasing gas temperature downstream of a plasma uniformly in the radial direction at constant electrical discharge conditions.

Krakow conference on low emissions sources: Proceedings

Energy Technology Data Exchange (ETDEWEB)

Pierce, B.L.; Butcher, T.A. [eds.

1995-12-31

The Krakow Conference on Low Emission Sources presented the information produced and analytical tools developed in the first phase of the Krakow Clean Fossil Fuels and Energy Efficiency Program. This phase included: field testing to provide quantitative data on missions and efficiencies as well as on opportunities for building energy conservation; engineering analysis to determine the costs of implementing pollution control; and incentives analysis to identify actions required to create a market for equipment, fuels, and services needed to reduce pollution. Collectively, these Proceedings contain reports that summarize the above phase one information, present the status of energy system management in Krakow, provide information on financing pollution control projects in Krakow and elsewhere, and highlight the capabilities and technologies of Polish and American companies that are working to reduce pollution from low emission sources. It is intended that the US reader will find in these Proceedings useful results and plans for control of pollution from low emission sources that are representative of heating systems in central and Eastern Europe. Selected papers are indexed separately for inclusion in the Energy Science and Technology Database.

Cascade conical refraction for annular pumping of a vortex Nd:YAG laser and selective excitation of low- and high-order Laguerre–Gaussian modes

Science.gov (United States)

Wu, Yongxiao; Wang, Zhongyang; Chen, Sanbin; Shirakwa, Akira; Ueda, Ken-ichi; Li, Jianlang

2018-05-01

We proposed an efficient and vortex Nd:YAG laser for selective lasing of low- and high-order vortex modes, in which multiple-ring pump light was originated from cascaded conical refraction of multiple biaxial crystals. In our proof of concept demonstration, we used two-crystal cascade conical refraction to generate two-ring pump light; the mutual intensity ratio and relative separation of the inner ring and outer ring were controlled by rotating the second biaxial crystal and by moving the imaging lens, respectively. As a result, we obtained selective excitation of Laguerre–Gaussian (LG01 and LG03) vortex modes in the end-pump Nd:YAG laser. For LG01-mode output, the laser power reached 439 mW with 52.5% slope efficiency; for LG03-mode output, the laser power reached 160 mW with 41.3% slope efficiency. Our results revealed that the multiple-ring pumping technique based on cascaded conical refraction would pave the way for realization of the efficient and switchable excitation of low- and high-order LG modes in an end-pumped solid-state laser.

Thermodynamics of photon-enhanced thermionic emission solar cells

International Nuclear Information System (INIS)

Reck, Kasper; Hansen, Ole

2014-01-01

Photon-enhanced thermionic emission (PETE) cells in which direct photon energy as well as thermal energy can be harvested have recently been suggested as a new candidate for high efficiency solar cells. Here, we present an analytic thermodynamical model for evaluation of the efficiency of PETE solar cells including an analysis of the entropy production due to thermionic emission of general validity. The model is applied to find the maximum efficiency of a PETE cell for given cathode and anode work functions and temperatures

Post Cyclone (PoC) : An innovative way to reduce the emission of fines from industrial cyclones

NARCIS (Netherlands)

Ray - Bhowmick, Madhumita; Luning, P.E.; Hoffmann, A.C; Plomp, A.; Beumer, M.I.L.

A novel approach for reducing the emission of industrial-scale cyclones of particles smaller than 10 mu m is presented. Utilizing the strong swirl already present in the vortex finder of a conventional cyclone, the escaped dust from the cyclone is collected in a so-called ''Post Cyclone'' (PoC),

Engineering models for low-NO{sub x} burners

Energy Technology Data Exchange (ETDEWEB)

Storm Pedersen, Lars

1997-08-01

The present Ph.D. thesis describes a theoretical investigation of NO formation in pulverised coal combustion and an experimental investigation of co-combustion of straw and pulverised coal. The theoretical work has resulted in a simplified mathematical model of a swirling pulverised coal flame able to predict the NO emission and the burnout of coal. In order to simplify the flow pattern of a confined swirling flame, the residence time distribution (RTD) in a swirling pulverised coal flame was determined. This was done by using the solution of a detailed fluid dynamic mathematical model for a 2.2 MW{sub th} and a 12 MW{sub th} pulverised coal flame. From the mathematical solution the RTD was simulated by tracing a number of fluid particles or inert particles. The RTD in the near burner zone was investigated by use of the mathematical model for the 2.2 MW{sub th} and 12 MW{sub th} flame. Results showed that the gas phase in the near burner zone may be approximated as a CSTR and that the mean residence time increased with particle size. In pulverised coal flames, the most important volatile nitrogen component forming NO{sub x} is HCN. To be able to model the nitrogen chemistry in coal flames it is necessary to have an adequate model for HCN oxidation. In order to develop a model for HCN/NH{sub 3}/NO conversion, a systematic reduction of a detailed chemical kinetic model was performed. Based on the simplification of the flow pattern for a swirling flame and the reduced chemistry developed, a chemical engineering model of pulverised coal flame was established. The objectives were to predict the NO emission, the CO emission, and the burnout of char. The effects of co-firing straw and pulverised coal was investigated in a 2.5 MW{sub th} pilot-scale burner and a 250 MW{sub e} utility boiler. In the 2.5 MW{sub th} trial the straw was chopped and fed separately to the burner, whereas in the full-scale experiment the straw was pre-processed as pellets and pulverised with the

Experimental Study of the Swirling Oxidizer Flow in HTPB/N2O Hybrid Rocket Motor

Directory of Open Access Journals (Sweden)

Mohammad Mahdi Heydari

2017-01-01

Full Text Available Effects of swirling oxidizer flow on the performance of a HTPB/N2O Hybrid rocket motor were studied. A hybrid propulsion laboratory has been developed, to characterize internal ballistics characteristics of swirl flow hybrid motors and to define the operating parameters, like fuel regression rate, specific impulse, and characteristics velocity and combustion efficiency. Primitive variables, like pressure, thrust, temperature, and the oxidizer mass flow rate, were logged. A modular motor with 70 mm outer diameter and variable chamber length is designed for experimental analysis. The injector module has four tangential injectors and one axial injector. Liquid nitrous oxide (N2O as an oxidizer is injected at the head of combustion chamber into the motor. The feed system uses pressurized air as the pressurant. Two sets of tests have been performed. Some tests with axial and tangential oxidizer injection and a test with axial oxidizer injection were done. The test results show that the fuel grain regression rate has been improved by applying tangential oxidizer injection at the head of the motor. Besides, it was seen that combustion efficiency of motors with the swirl flow was about 10 percent more than motors with axial flow.

Quantifying alkane emissions in the Eagle Ford Shale using boundary layer enhancement

Directory of Open Access Journals (Sweden)

G. Roest

2017-09-01

Full Text Available The Eagle Ford Shale in southern Texas is home to a booming unconventional oil and gas industry, the climate and air quality impacts of which remain poorly quantified due to uncertain emission estimates. We used the atmospheric enhancement of alkanes from Texas Commission on Environmental Quality volatile organic compound monitors across the shale, in combination with back trajectory and dispersion modeling, to quantify C2–C4 alkane emissions for a region in southern Texas, including the core of the Eagle Ford, for a set of 68 days from July 2013 to December 2015. Emissions were partitioned into raw natural gas and liquid storage tank sources using gas and headspace composition data, respectively, and observed enhancement ratios. We also estimate methane emissions based on typical ethane-to-methane ratios in gaseous emissions. The median emission rate from raw natural gas sources in the shale, calculated as a percentage of the total produced natural gas in the upwind region, was 0.7 % with an interquartile range (IQR of 0.5–1.3 %, below the US Environmental Protection Agency's (EPA current estimates. However, storage tanks contributed 17 % of methane emissions, 55 % of ethane, 82 % percent of propane, 90 % of n-butane, and 83 % of isobutane emissions. The inclusion of liquid storage tank emissions results in a median emission rate of 1.0 % (IQR of 0.7–1.6 % relative to produced natural gas, overlapping the current EPA estimate of roughly 1.6 %. We conclude that emissions from liquid storage tanks are likely a major source for the observed non-methane hydrocarbon enhancements in the Northern Hemisphere.

High Efficiency, Low Emission Refrigeration System

Energy Technology Data Exchange (ETDEWEB)

Fricke, Brian A [ORNL; Sharma, Vishaldeep [ORNL

2016-08-01

Supermarket refrigeration systems account for approximately 50% of supermarket energy use, placing this class of equipment among the highest energy consumers in the commercial building domain. In addition, the commonly used refrigeration system in supermarket applications is the multiplex direct expansion (DX) system, which is prone to refrigerant leaks due to its long lengths of refrigerant piping. This leakage reduces the efficiency of the system and increases the impact of the system on the environment. The high Global Warming Potential (GWP) of the hydrofluorocarbon (HFC) refrigerants commonly used in these systems, coupled with the large refrigerant charge and the high refrigerant leakage rates leads to significant direct emissions of greenhouse gases into the atmosphere. Methods for reducing refrigerant leakage and energy consumption are available, but underutilized. Further work needs to be done to reduce costs of advanced system designs to improve market utilization. In addition, refrigeration system retrofits that result in reduced energy consumption are needed since the majority of applications address retrofits rather than new stores. The retrofit market is also of most concern since it involves large-volume refrigerant systems with high leak rates. Finally, alternative refrigerants for new and retrofit applications are needed to reduce emissions and reduce the impact on the environment. The objective of this Collaborative Research and Development Agreement (CRADA) between the Oak Ridge National Laboratory and Hill Phoenix is to develop a supermarket refrigeration system that reduces greenhouse gas emissions and has 25 to 30 percent lower energy consumption than existing systems. The outcomes of this project will include the design of a low emission, high efficiency commercial refrigeration system suitable for use in current U.S. supermarkets. In addition, a prototype low emission, high efficiency supermarket refrigeration system will be produced for

A comparison of three turbulence models for axisymmetric isothermal swirling flows in the near burner zone

Energy Technology Data Exchange (ETDEWEB)

Ahlstedt, H [Tampere Univ. of Technology (Finland). Energy and Process Engineering

1998-12-31

In this work three different turbulence models, the k - {epsilon}, RNG k - {epsilon} and Reynolds stress model, have been compared in the case of confined swirling flow. The flow geometries are the isothermal swirling flows measured by International Flame Research Foundation (IFRF). The inlet boundary profiles have been taken from the measurements. At the outlet the effect of furnace end contraction has been studied. The k - {epsilon} model falls to predict the correct flow field. The RNG k - {epsilon} model can provide improvements, although it has problems near the symmetry axis. The Reynolds stress model produces the best agreement with measured data. (author) 13 refs.

A comparison of three turbulence models for axisymmetric isothermal swirling flows in the near burner zone

Energy Technology Data Exchange (ETDEWEB)

Ahlstedt, H. [Tampere Univ. of Technology (Finland). Energy and Process Engineering

1997-12-31

In this work three different turbulence models, the k - {epsilon}, RNG k - {epsilon} and Reynolds stress model, have been compared in the case of confined swirling flow. The flow geometries are the isothermal swirling flows measured by International Flame Research Foundation (IFRF). The inlet boundary profiles have been taken from the measurements. At the outlet the effect of furnace end contraction has been studied. The k - {epsilon} model falls to predict the correct flow field. The RNG k - {epsilon} model can provide improvements, although it has problems near the symmetry axis. The Reynolds stress model produces the best agreement with measured data. (author) 13 refs.

Cooperative Enhancement Mechanisms of Low Energy Nuclear Reactions Using Superlow Energy External Fields

OpenAIRE

Gareev, F. A.; Zhidkova, I. E.

2006-01-01

We proposed a new mechanism of LENR: cooperative processes in whole system - nuclei+atoms+condensed matter can occur at smaller threshold energies then corresponding ones on free constituents. The cooperative processes can be induced and enhanced by low energy external fields. The excess heat is the emission of internal energy and transmutations at LENR are the result of redistribution inner energy of whole system.

A future role for cascade hydropower in the electricity system of China

International Nuclear Information System (INIS)

Tang, Xinhua; Zhou, Jianjun

2012-01-01

Due to the dominance of coal power, the electricity sector is the primary contributor of greenhouse gas emissions in China. The increase of peak-load and intermittent renewable power requires significant resources of regulation facilities. Comprehensively utilizing large-scale cascade hydropower plants (CHPPs), which are being rapidly developed in China, as renewable regulating facilities would be a strategic decision, considering the flexibility of hydropower. Jointly modeling a set of CHPP in the upstream Yangtze River indicated that the CHPP can regulate peak-load up to 30–40 GW and intermittent renewables to scales of nearly 15 GW from wind and solar sources with the help of ±800 KV ultra-high voltage direct current (UHVDC) transmissions. The present study shows that the hydraulic stability of the concerned river reaches can be preserved easily and the comprehensive efficiency of regulation and transmission by CHPPs is much higher than that of pumped hydro energy storage (PHES) stations. As increasingly more giant CHPPs emerge in west China, using them primarily as regulating facilities can enhance the structure of power grids, promote the development of renewables, save energy and reduce emissions. Thus we propose to shift the CHPPs that were originally projected mainly for electricity to facility primarily for power improvement. - Highlights: ► Large cascade hydropower plant (CHPP) is efficient and renewable peaking facility (PF). ► CHPPs can easily anti-regulate the hydro-fluctuations caused by power regulations. ► Remote CHPPs with UHVDC transmission can massively replace the traditional PFs.► Shift China's CHPPs mainly as PF to promote intermittent renewables are proposed.

Enhancement of single particle rare earth doped NaYF4: Yb, Er emission with a gold shell

International Nuclear Information System (INIS)

Li, Ling; Green, Kory; Hallen, Hans; Lim, Shuang Fang

2015-01-01

Upconversion of infrared light to visible light has important implications for bioimaging. However, the small absorption cross-section of rare earth dopants has limited the efficiency of these anti-Stokes nanomaterials. We present enhanced excitation absorption and single particle fluorescent emission of sodium yttrium fluoride, NaYF 4 : Yb, Er based upconverting nanoparticles coated with a gold nanoshell through surface plasmon resonance. The single gold-shell coated nanoparticles show enhanced absorption in the near infrared, enhanced total emission intensity, and increased green relative to red emission. We also show differences in enhancement between single and aggregated gold shell nanoparticles. The surface plasmon resonance of the gold-shell coated nanoparticle is shown to be dependent on the shell thickness. In contrast to other reported results, our single particle experimental observations are corroborated by finite element calculations that show where the green/red emission enhancement occurs, and what portion of the enhancement is due to electromagnetic effects. We find that the excitation enhancement and green/red emission ratio enhancement occurs at the corners and edges of the doped emissive core. (paper)

Coupling of Ag Nanoparticle with Inverse Opal Photonic Crystals as a Novel Strategy for Upconversion Emission Enhancement of NaYF4: Yb(3+), Er(3+) Nanoparticles.

Science.gov (United States)

Shao, Bo; Yang, Zhengwen; Wang, Yida; Li, Jun; Yang, Jianzhi; Qiu, Jianbei; Song, Zhiguo

2015-11-18

Rare-earth-ion-doped upconversion (UC) nanoparticles have generated considerable interest because of their potential application in solar cells, biological labeling, therapeutics, and imaging. However, the applications of UC nanoparticles were still limited because of their low emission efficiency. Photonic crystals and noble metal nanoparticles are applied extensively to enhance the UC emission of rare earth ions. In the present work, a novel substrate consisting of inverse opal photonic crystals and Ag nanoparticles was prepared by the template-assisted method, which was used to enhance the UC emission of NaYF4: Yb(3+), Er(3+) nanoparticles. The red or green UC emissions of NaYF4: Yb(3+), Er(3+) nanoparticles were selectively enhanced on the inverse opal substrates because of the Bragg reflection of the photonic band gap. Additionally, the UC emission enhancement of NaYF4: Yb(3+), Er(3+) nanoparticles induced by the coupling of metal nanoparticle plasmons and photonic crystal effects was realized on the Ag nanoparticles included in the inverse opal substrate. The present results demonstrated that coupling of Ag nanoparticle with inverse opal photonic crystals provides a useful strategy to enhance UC emission of rare-earth-ion-doped nanoparticles.

Technical and Economic Aspects of Low Emission Reduction in Poland

Science.gov (United States)

Dzikuć, M.; Łasiński, K.

2017-12-01

The paper presents the problem of excessive air pollution in Poland caused mainly by low emission. The emission arises in result of heating flats by means of old and energetically inefficient heating installations. In Poland and Bulgaria the inhaled air is of the worst quality out of all EU countries. The paper presents economic and technical problems related to low emission occurring during the combustion of solid fuels in local boiler houses. Furthermore, the most significant economic issues, connected with the reduction of low emission are discussed, as well as technological possibilities of efficient reduction of the amount of pollution in the atmosphere. Conclusions are presented at the end of the article.

Enhanced Transmissions Through Three-dimensional Cascade Sharp Waveguide Bends Using C-slit Diaphragms.

Science.gov (United States)

Yang, Rui; Hu, Bowei; Zhang, Aofang; Gao, Dongxing; Wang, Hui; Shi, Ayuan; Lei, Zhenya; Yang, Pei

2017-03-21

Transmission properties through sharp rectangular waveguide bends are investigated to determine the cut-off bending angles of the wave propagation. We show that a simple metallic diaphragm at the bending corner with properly devised sub-wavelength defect apertures of C-slits would be readily to turn on the transmissions with scarce reflections of the propagating modes, while preserving the integrity of the transmitting fields soon after the bends. In particularly, our design also demonstrates the capability of eliminating all the unwanted cavity resonant transmissions that exist in the three-dimensional cascade sharp waveguide bends, and solely let the desired signals travel along the whole passage of the waveguide. The present approach, using C-slit diaphragms to support the sharp bending behaviors of the guided waves with greatly enhanced transmissions, would be especially effective in constructing novel waveguides and pave the way for the development of more compact and miniaturized electromagnetic systems that exploit these waveguide bends.

Consideration of the Change of Material Emission Signatures due to Longterm Emissions for Enhancing VOC Source Identification

DEFF Research Database (Denmark)

Han, K. H.; Zhang, J. S.; Knudsen, Henrik Nellemose

2011-01-01

The objectives of this study were to characterize the changes of VOC material emission profiles over time and develop a method to account for such changes in order to enhance a source identification technique that is based on the measurements of mixed air samples and the emission signatures of in...

Large Eddy Simulations and Experimental Investigation of Flow in a Swirl Stabilized Combustor

KAUST Repository

Kewlani, Gaurav

2012-01-09

Swirling flows are the preferred mode of flame stabilization in lean premixed gas turbine engine combustors. Developing a fundamental understanding of combustion dynamics and flame stability in such systems requires a detailed investigation of the complex interactions between fluid mechanics and combustion. The turbulent reacting flow in a sudden expansion swirl combustor is studied using compressible large eddy simulations (LES) and compared with experimental data measured using PIV. Different vortex breakdown structures are observed, as the mixture equivalence ratio is reduced, that progressively diminish the stability of the flame. Sub-grid scale combustion models such as the artificially thickened flame method and the partially stirred reactor approach, along with appropriate chemical schemes, are implemented to describe the flame. The numerical predictions for average velocity correspond well with experimental results, and higher accuracy is obtained using the more detailed reaction mechanism. Copyright © 2012 American Institute of Aeronautics and Astronautics, Inc.

Enhanced biogenic emissions of nitric oxide and nitrous oxide following surface biomass burning

Science.gov (United States)

Anderson, Iris C.; Levine, Joel S.; Poth, Mark A.; Riggan, Philip J.

1988-01-01

Recent measurements indicate significantly enhanced biogenic soil emissions of both nitric oxide (NO) and nitrous oxide (N2O) following surface burning. These enhanced fluxes persisted for at least six months following the burn. Simultaneous measurements indicate enhanced levels of exchangeable ammonium in the soil following the burn. Biomass burning is known to be an instantaneous source of NO and N2O resulting from high-temperature combustion. Now it is found that biomass burning also results in significantly enhanced biogenic emissions of these gases, which persist for months following the burn.

Dispersion compensated mid-infrared quantum cascade laser frequency comb with high power output

Directory of Open Access Journals (Sweden)

Q. Y. Lu

2017-04-01

Full Text Available Chromatic dispersion control plays an underlying role in optoelectronics and spectroscopy owing to its enhancement to nonlinear interactions by reducing the phase mismatching. This is particularly important to optical frequency combs based on quantum cascade lasers which require negligible dispersions for efficient mode locking of the dispersed modes into equally spaced comb modes. Here, we demonstrated a dispersion compensated mid-IR quantum cascade laser frequency comb with high power output at room temperature. A low-loss dispersive mirror has been engineered to compensate the device’s dispersion residue for frequency comb generation. Narrow intermode beating linewidths of 40 Hz in the comb-working currents were identified with a high power output of 460 mW and a broad spectral coverage of 80 cm-1. This dispersion compensation technique will enable fast spectroscopy and high-resolution metrology based on QCL combs with controlled dispersion and suppressed noise.

Supercritical droplet dynamics and emission in low speed cross-flows

International Nuclear Information System (INIS)

Chae, J. W.; Yang, H. S.; Yoon, W. S.

2008-01-01

Droplet dynamics and emission of a supercritical droplet in crossing gas stream are numerically investigated. Effects of ambient pressure and velocity of nitrogen gas on the dynamics of the supercritical oxygen droplet are parametrically examined. Unsteady conservative axisymmetric Navier-Stokes equations in curvilinear coordinates are preconditioned and solved by dual-time stepping method. A unified property evaluation scheme based on a fundamental equation of state and extended corresponding-state principle is established to deal with thermodynamic non-idealities and transport anomalies. At lower pressures and velocities of nitrogen cross flows, both the diffusion and the convection are important in determining the droplet dynamics. Relative flow motion causes a secondary breakup and cascading vortices, and the droplet lifetime is reduced with increasing in ambient pressure. At higher ambient pressures and velocities, however, the droplet dynamics become convection-controlled while the secondary breakup is hindered by reduced diffusivity of the oxygen. Gas-phase mixing depends on the convection and diffusion velocities in conjunction with corresponding droplet deformation and flow interaction. Supercritical droplet dynamics and emission is not similar with respect to the pressure and velocity of the ambient gas and thus provides no scale

Flame structure, spectroscopy and emissions quantification of rapeseed biodiesel under model gas turbine conditions

International Nuclear Information System (INIS)

Chong, Cheng Tung; Hochgreb, Simone

2017-01-01

Highlights: • Rapeseed biodiesel shows extended flame reaction zone with no soot formation. • RME spray flame shows higher droplet number density and volume flux than diesel. • RME droplet size and velocity distribution are similar to diesel. • Blending 50% RME with diesel reduces soot formation non-linearly. • RME shows lower NO_x and higher CO emissions level compared to diesel. - Abstract: The spray combustion characteristics of rapeseed biodiesel/methyl esters (RME) and 50% RME/diesel blend were investigated and compared with conventional diesel fuel, using a model swirl flame burner. The detailed database with well-characterised boundary conditions can be used as validation targets for flame modelling. An airblast, swirl-atomized liquid fuel spray was surrounded by air preheated to 350 °C at atmospheric pressure. The reacting droplet distribution within the flame was determined using phase Doppler particle anemometry. For both diesel and RME, peak droplet concentrations are found on the outside of the flame region, with large droplets migrating to the outside via swirl, and smaller droplets located around the centreline region. However, droplet concentrations and sizes are larger for RME, indicating a longer droplet evaporation timescale. This delayed droplet vaporisation leads to a different reaction zone relative to diesel, with an extended core reaction. In spite of the longer reaction zone, RME flames displayed no sign of visible soot radiation, unlike the case of diesel spray flame. Blending 50% RME with diesel results in significant reduction in soot radiation. Finally, RME emits 22% on average lower NO_x emissions compared to diesel under lean burning conditions.

Bursting behaviours in cascaded stimulated Brillouin scattering

International Nuclear Information System (INIS)

Liu Zhan-Jun; He Xian-Tu; Zheng Chun-Yang; Wang Yu-Gang

2012-01-01

Stimulated Brillouin scattering is studied by numerically solving the Vlasov—Maxwell system. A cascade of stimulated Brillouin scattering can occur when a linearly polarized laser pulse propagates in a plasma. It is found that a stimulated Brillouin scattering cascade can reduce the scattering and increase the transmission of light, as well as introduce a bursting behaviour in the evolution of the laser-plasma interaction. The bursting time in the reflectivity is found to be less than half the ion acoustic period. The ion temperature can affect the stimulated Brillouin scattering cascade, which can repeat several times at low ion temperatures and can be completely eliminated at high ion temperatures. For stimulated Brillouin scattering saturation, higher-harmonic generation and wave—wave interaction of the excited ion acoustic waves can restrict the amplitude of the latter. In addition, stimulated Brillouin scattering cascade can restrict the amplitude of the scattered light. (physics of gases, plasmas, and electric discharges)

Cascades on a stochastic pulse-coupled network

Science.gov (United States)

Wray, C. M.; Bishop, S. R.

2014-09-01

While much recent research has focused on understanding isolated cascades of networks, less attention has been given to dynamical processes on networks exhibiting repeated cascades of opposing influence. An example of this is the dynamic behaviour of financial markets where cascades of buying and selling can occur, even over short timescales. To model these phenomena, a stochastic pulse-coupled oscillator network with upper and lower thresholds is described and analysed. Numerical confirmation of asynchronous and synchronous regimes of the system is presented, along with analytical identification of the fixed point state vector of the asynchronous mean field system. A lower bound for the finite system mean field critical value of network coupling probability is found that separates the asynchronous and synchronous regimes. For the low-dimensional mean field system, a closed-form equation is found for cascade size, in terms of the network coupling probability. Finally, a description of how this model can be applied to interacting agents in a financial market is provided.

Enhanced Pedestrian Navigation Based on Course Angle Error Estimation Using Cascaded Kalman Filters.

Science.gov (United States)

Song, Jin Woo; Park, Chan Gook

2018-04-21

An enhanced pedestrian dead reckoning (PDR) based navigation algorithm, which uses two cascaded Kalman filters (TCKF) for the estimation of course angle and navigation errors, is proposed. The proposed algorithm uses a foot-mounted inertial measurement unit (IMU), waist-mounted magnetic sensors, and a zero velocity update (ZUPT) based inertial navigation technique with TCKF. The first stage filter estimates the course angle error of a human, which is closely related to the heading error of the IMU. In order to obtain the course measurements, the filter uses magnetic sensors and a position-trace based course angle. For preventing magnetic disturbance from contaminating the estimation, the magnetic sensors are attached to the waistband. Because the course angle error is mainly due to the heading error of the IMU, and the characteristic error of the heading angle is highly dependent on that of the course angle, the estimated course angle error is used as a measurement for estimating the heading error in the second stage filter. At the second stage, an inertial navigation system-extended Kalman filter-ZUPT (INS-EKF-ZUPT) method is adopted. As the heading error is estimated directly by using course-angle error measurements, the estimation accuracy for the heading and yaw gyro bias can be enhanced, compared with the ZUPT-only case, which eventually enhances the position accuracy more efficiently. The performance enhancements are verified via experiments, and the way-point position error for the proposed method is compared with those for the ZUPT-only case and with other cases that use ZUPT and various types of magnetic heading measurements. The results show that the position errors are reduced by a maximum of 90% compared with the conventional ZUPT based PDR algorithms.

Seal-rotordynamic-coefficient Test Results for a Model SSME ATD-HPFTP Turbine Interstage Seal with and Without a Swirl Brake

Science.gov (United States)

Childs, Dara W.; Ramsey, Christopher

1991-01-01

The predictions of Scharrer's (1988) theory for rotordynamic coefficients of labyrinth gas seals were compared with measurements for a model SSME Alternate Turbopump Development High Pressure Fuel Turbopump with and without swirl brakes. Using the test apparatus described by Childs et al., tests were conducted with supply pressures up to 18.3 bars and speeds up to 16,000 rpm. Seal back pressure was controlled to provide four pressure ratios at all supply pressures. No measurable differences in leakage was detected for the seal with and without the swirl brakes. Comparisons of the measurement results for the seal without a swirl brake with the Scharrer theory showed that the theory can be used only to provide design guidelines; systematic differences were observed between theory and experiment due to changes in running speed, supply pressure, and pressure ratio.

Seal-rotordynamic-coefficient test results for a model SSME ATD-HPFTP turbine interstate seal with and without a swirl brake

Science.gov (United States)

Childs, D. W.; Ramsey, C.

1991-01-01

The predictions of Scharrer's (1988) theory for rotordynamic coefficients of labyrinth gas seals were compared with measurements for a model SSME Alternate Turbopump Development High-Pressure Fuel Turbopump with and without swirl brakes. Using the test apparatus described by Childs et al. (1986, 1990), tests were conducted with supply pressures up to 18.3 bars and speeds up to 16,000 rpm. Seal back pressure was controlled to provide four pressure ratios at all supply pressures. No measurable difference in leakage was detected for the seal with and without the swirl brakes. Comparisons of the measurement results for the seal without a swirl brake with the Scharrer theory showed that the theory can be used only to provide design guidelines; systematic differences were observed between theory and experiment due to changes in running speed, supply pressure, and pressure ratio.

Reduced emissions of greenhouse gases 2050: Technological wedges - Input to the Commission on Low Emissions

International Nuclear Information System (INIS)

Rosenberg, Eva; Espegren, Kari Aamodt; Finden, Per; Hageman, Rolf; Stenersen, Dag

2006-09-01

The Commission on Low Emissions was established in March 2005 and has been charged with the task of describing how Norway can achieve a 50-80 percent reduction in emissions of greenhouse gases by 2050. The commission describes the desired total reduction in emissions to be a set of actions or 'wedges', meaning that the reduction in emissions are linked to an array of technological and behavioural changes. The technological wedges are described here, while the behavioural wedges are treated in a different report. The potentials described are based on the Low Emission's reference line. Possible changes in the reference line will result in changed potentials. The technological wedges studied comprise to a great extent a potential of 50-80 percent reduction in greenhouse gases by 2050. This depends on considerable effort from research and development, and a determination to change external conditions

A Cross-Wavelet Transform Aided Rule Based Approach for Early Prediction of Lean Blow-out in Swirl-Stabilized Dump Combustor

Directory of Open Access Journals (Sweden)

Debangshu Dey

2015-03-01

Full Text Available Lean or ultralean combustion is one of the popular strategies to achieve very low emission levels. However, it is extremely susceptible to lean blow-out (LBO. The present work explores a Cross-wavelet transform (XWT aided rule based scheme for early prediction of lean blowout. XWT can be considered as an advancement of wavelet analysis which gives correlation between two waveforms in time-frequency space. In the present scheme a swirl-stabilized dump combustor is used as a laboratory-scale model of a generic gas turbine combustor with LPG as fuel. Various time series data of CH chemiluminescence signal are recorded for different flame conditions by varying equivalence ratio, flow rate and level of air-fuel premixing. Some features are extracted from the cross-wavelet spectrum of the recorded waveforms and a reference wave. The extracted features are observed to classify the flame condition into three major classes: near LBO, moderate and healthy. Moreover, a Rough Set based technique is also applied on the extracted features to generate a rule base so that it can be fed to a real time controller or expert system to take necessary control action to prevent LBO. Results show that the proposed methodology performs with an acceptable degree of accuracy.

Defining the `negative emission' capacity of global agriculture deployed for enhanced rock weathering

Science.gov (United States)

Beerling, D. J.; Taylor, L.; Banwart, S. A.; Kantzas, E. P.; Lomas, M.; Mueller, C.; Ridgwell, A.; Quegan, S.

2016-12-01

Enhanced rock weathering involves application of crushed silicates (e.g. basalt) to the landscape to accelerate their chemical breakdown to release base cations and form bicarbonate that ultimate sequester CO2 in the oceans. Global croplands cover an area of 12 million km2 and might be deployed for long-term removal of anthropogenic CO2 through enhanced rock weathering with a number of co-benefits for food security. This presentation assesses the potential of this strategy to contribute to `negative emissions' as defined by a suite of simulations coupling a detailed model of rock grain weathering by crop root-microbial processes with a managed land dynamic global vegetation model driven by the `business as usual' future climate change scenarios. We calculate potential atmospheric CO2 drawdown over the next century by introducing a strengthened C-sink term into the global carbon cycle model within an intermediate complexity Earth system model. Our simulations indicate agricultural lands deployed in this way constitute a `low tech' biological negative emissions strategy. As part of a wider portfolio of options, this strategy might contribute to limiting future warming to 2oC, subject to economic costs and energy requirements.

Managing the Diffusion of Low Emission Vehicles

Energy Technology Data Exchange (ETDEWEB)

Van der Vooren, A.; Alkemade, F. [Innovation Studies Group, Copernicus Institute of Sustainable Development, Utrecht University, 3508TC Utrecht (Netherlands)

2012-03-13

There is significant uncertainty among technology providers, governments, and consumers about which technology will be the vehicle technology of the future. Governments try to stimulate the diffusion of low emission vehicles with diverse policy measures such as purchase price subsidies. However, the effect of such support measures on the speed and direction of technological change is unclear as different vehicle technologies might be preferred under different policy conditions. Decision makers, such as firm actors involved in green technology management, are thus strongly dependent on government policy when making strategic decisions. For these firm actors, determining their strategy regarding low emission vehicles is a complex task in a changing environment of coevolving consumer preferences, technology characteristics, and green technology policies. This paper presents an agent-based model of the competition between several emerging and market-ready low emission vehicle technologies and the dominant fossil-fuel-based internal combustion engine vehicles. The simulations illustrate the effects of different policy measures on technological change and their implications for the strategic actions of firm actors. More specifically, collaboration and standardization strategies can lead to synergies that contribute to technological change without risking early lock-in.

Discussion of the origin of secondary photon and secondary ion emission during energetic particle irradiation of solids. I. The collision cascade

International Nuclear Information System (INIS)

Wright, R.B.; Gruen, D.M.

1980-01-01

Secondary photon and secondary ion emission during energetic particle irradiation of solid surfaces is assumed to arise due to excitation and de-excitation of sputtered particles originating from a collision cascade induced by the incident projectile. The excitation is postulated to occur by two alternative mechanisms: path (a), where excitation occurs at or very near the surface of the solid due to atom--atom or atom--electron collisions; and path (b), where excitation occurs as the sputtered particle leaves the solid, but is still under its influence so that electron exchange processes are permitted. Once the excited and/or ionized sputtered particle is formed nonradiative de-excitation processes are then included in the discussion which allow the excited and/or ionized particle to be de-excited and/or neutralized. The result of these nonradiative de-excitation processes is shown to provide a possible channel for the formation of new excited ''daughters'' by the de-excitation of the initial excited ''parent''. Depending on the initial excitation probability of the parent the new excited daughters are shown to contribute to various energy regions of the excited and/or ionized secondary particle energy distribution. A mathematical formalism is developed based on the neutral sputtered atom energy and velocity distributions assuming a collision cascade origin for these sputtered particles. By including various models for the excitation probability, and the survival probability for excited particles once formed to not undergo nonradiative de-excitation the resulting energy and velocity distributions of the sputtered excited and/or ionized secondary particles are calculated. These distributions are found to be a function of the emission angle depending on the model assumed for the initial excitation. From this formalism the total excited secondary particle yield may be calculated

Large eddy simulation of a two-phase reacting swirl flow inside a cement cyclone

International Nuclear Information System (INIS)

Mikulčić, Hrvoje; Vujanović, Milan; Ashhab, Moh'd Sami; Duić, Neven

2014-01-01

This work presents a numerical study of the highly swirled gas–solid flow inside a cement cyclone. The computational fluid dynamics – CFD simulation for continuum fluid flow and heat exchange was used for the investigation. The Eulearian–Lagrangian approach was used to describe the two-phase flow, and the large eddy simulation – LES method was used for correctly obtaining the turbulent fluctuations of the gas phase. A model describing the reaction of the solid phase, e.g. the calcination process, has been developed and implemented within the commercial finite volume CFD code FIRE. Due to the fact that the calcination process has a direct influence on the overall energy efficiency of the cement production, it is of great importance to have a certain degree of limestone degradation at the cyclone's outlet. The heat exchange between the gas and solid phase is of particular importance when studying cement cyclones, as it has a direct effect on the calcination process. In order to study the heat exchange phenomena and the flow characteristics, a three dimensional geometry of a real industrial scroll type cyclone was used for the CFD simulation. The gained numerical results, characteristic for cyclones, such as the pressure drop, and concentration of particles can thus be used for better understanding of the complex swirled two-phase flow inside the cement cyclone and also for improving the heat exchange phenomena. - Highlights: • CFD (computational fluid dynamics) is being increasingly used to enhance efficiency of reacting multi-phase flows. • Numerical model of calcination process was presented. • A detailed industrial geometry was used for the CFD simulation. • Presented model and measurement data are in good agreement

Investigation of Methane Oxy-Fuel Combustion in a Swirl-Stabilised Gas Turbine Model Combustor

Directory of Open Access Journals (Sweden)

Mao Li

2017-05-01

Full Text Available CO2 has a strong impact on both operability and emission behaviours in gas turbine combustors. In the present study, an atmospheric, preheated, swirl-stabilised optical gas turbine model combustor rig was employed. The primary objectives were to analyse the influence of CO2 on the fundamental characteristics of combustion, lean blowout (LBO limits, CO emission and flame structures. CO2 dilution effects were examined with three preheating temperatures (396.15, 431.15, and 466.15 K. The fundamental combustion characteristics were studied utilising chemical kinetic simulations. To study the influence of CO2 on the operational range of the combustor, equivalence ratio (Ф was varied from stoichiometric conditions to the LBO limits. CO emissions were measured at the exit of the combustor using a water-cooled probe over the entire operational range. The flame structures and locations were characterised by performing CH chemiluminescence imaging. The inverse Abel transformation was used to analyse the CH distribution on the axisymmetric plane of the combustor. Chemical kinetic modelling indicated that the CO2 resulted in a lower reaction rate compared with the CH4/air flame. Fundamental combustion properties such as laminar flame speed, ignition delay time and blowout residence time were found to be affected by CO2. The experimental results revealed that CO2 dilution resulted in a narrower operational range for the equivalence ratio. It was also found that CO2 had a strong inhibiting effect on CO burnout, which led to a higher concentration of CO in the combustion exhaust. CH chemiluminescence showed that the CO2 dilution did not have a significant impact on the flame structure.

An Enhanced GINGER Simulation Code with Harmonic Emission and HDF5 IO Capabilities

International Nuclear Information System (INIS)

Fawley, William M.

2006-01-01

GINGER [1] is an axisymmetric, polychromatic (r-z-t) FEL simulation code originally developed in the mid-1980's to model the performance of single-pass amplifiers. Over the past 15 years GINGER's capabilities have been extended to include more complicated configurations such as undulators with drift spaces, dispersive sections, and vacuum chamber wakefield effects; multi-pass oscillators; and multi-stage harmonic cascades. Its coding base has been tuned to permit running effectively on platforms ranging from desktop PC's to massively parallel processors such as the IBM-SP. Recently, we have made significant changes to GINGER by replacing the original predictor-corrector field solver with a new direct implicit algorithm, adding harmonic emission capability, and switching to the HDF5 IO library [2] for output diagnostics. In this paper, we discuss some details regarding these changes and also present simulation results for LCLS SASE emission at λ = 0.15 nm and higher harmonics

Thermodynamics of photon-enhanced thermionic emission solar cells

DEFF Research Database (Denmark)

Reck, Kasper; Hansen, Ole

2014-01-01

Photon-enhanced thermionic emission (PETE) cells in which direct photon energy as well as thermal energy can be harvested have recently been suggested as a new candidate for high efficiency solar cells. Here, we present an analytic thermodynamical model for evaluation of the efficiency of PETE...

Electron emission from materials at low excitation energies

International Nuclear Information System (INIS)

Urma, N.; Kijek, M.; Millar, J.J.

1996-01-01

Full text: An experimental system has been designed and developed with the purpose of measuring the total electron emission yield from materials at low energy excitation. In the first instance the reliability of the system was checked by measuring the total electron emission yield for a well defined surface (aluminium 99.45%). The obtained data was in the expected range given by the literature, and consequently the system will be used further for measuring the total electron yield for a range of materials with interest in the instrumentation industry. We intend to measure the total electron emission yield under electron bombardment as a function of incident electron energy up to 1200 eV, angle of incidence, state of the surface and environment to which the surface has been exposed. Dependence of emission on total electron irradiated dose is also of interest. For many practical application of the 'Secondary Electron Emission', the total electron yield is desired to be as large as possible. The above phenomenon has practical applicability in electron multiplier tube and Scanning electron microscopy - when by means of the variation of the yield of the emitted electrons one may produce visible images of small sample areas. The electron multiplier tube, is a device which utilises the above effect to detect and amplify both single particles and low currents streams of charged particles. The majority of electron tubes use electrons with low energy, hundreds of eV. Not a lot has been published in the literature about this regime and also about the emission when the impinging electrons have small energy, up to 1 KeV. The information obtained from the experimental measurements concerning the total electron emission yield is used to asses the investigated materials as a potential electron emitting surfaces or dynodes in an electron multiplier tube

Strategic information is everyone's business: perspectives from an international stakeholder meeting to enhance strategic information data along the HIV Cascade for people who inject drugs.

Science.gov (United States)

Pierce, Richard D; Hegle, Jennifer; Sabin, Keith; Agustian, Edo; Johnston, Lisa G; Mills, Stephen; Todd, Catherine S

2015-10-16

People who inject drugs (PWID) are at increased HIV transmission risk because of unsafe injecting practices and a host of other individual, network, and structural factors. Thus, PWID have a great need for services within the Cascade of HIV prevention, diagnosis, care, and treatment (HIV Cascade). Yet the systems that monitor their progress through the Cascade are often lacking. Subsequently, fewer reliable data are available to guide programs targeting this key population (KP). Programmatic data, which are helpful in tracking PWID through the Cascade, also are limited because not all countries have harm reduction programming from which to estimate Cascade indicators. Also, due to stigma and the illegal nature of drug use, PWID may not disclose their drug use behavior or HIV status when accessing services. Consequently, PWID appear to have low HIV testing rates and, for those living with HIV, lower access to health services and lower viral suppression rates than do other KP groups. This commentary, based on outcomes from an international stakeholder meeting, identifies data gaps and proposes solutions to strengthen strategic information (SI), the systematic collection, analysis, and dissemination of information, to optimize HIV prevention, care, and treatment programming for PWID.

Analysis of swirl recovery vanes for increased propulsive efficiency in tractor propeller aircraft

NARCIS (Netherlands)

Veldhuis, L.L.M.; Stokkermans, T.C.A.; Sinnige, T.; Eitelberg, G.

2016-01-01

In this paper we address a preliminary assessment of the performance effects of swirl recovery vanes (SRVs) in a installed and uninstalled tractor propeller arrangement. A numerical analysis was performed on a propeller and a propeller-wing configuration after the SRVs were optimized first in a

Cascade Controller Including Back-stepping for Hydraulic-Mechanical Systems

DEFF Research Database (Denmark)

Choux, Martin; Hovland, Geir; Blanke, Mogens

2012-01-01

Development of a cascade controller structure including adaptive backstepping for a nonlinear hydraulic-mechanical system is considered in this paper where a dynamic friction (LuGre) model is included to obtain the necessary accuracy. The paper compares the performance of two variants of an adapt......Development of a cascade controller structure including adaptive backstepping for a nonlinear hydraulic-mechanical system is considered in this paper where a dynamic friction (LuGre) model is included to obtain the necessary accuracy. The paper compares the performance of two variants...... of an adaptive backstepping tracking controller with earlier results. The new control architecture is analysed and enhanced tracking performance is demonstrated when including the extended friction model. The complexity of the backstepping procedure is significantly reduced due to the cascade structure. Hence...

Five-hole pitot probe time-mean velocity measurements in confined swirling flows

Science.gov (United States)

Yoon, H. K.; Lilley, D. G.

1983-01-01

Nonswirling and swirling nonreacting flows in an axisymmetric test section with an expansion ratio D/d = 2, which may be equipped with contraction nozzles of area ratios 2 and 4, are investigated. The effects of a number of geometric parameters on the flow-field are investigated, among them side-wall expansion angles of 90 and 45 deg, swirl vane angles of 0, 38, 45, 60, and 70 deg, and contraction nozzle locations L/D = 1 and 2 (if present). Data are acquired by means of a five-hole pitot probe enabling three time-mean velocity components in the axial, radial, and azimuthal directions to be measured. The velocities are extensively plotted and artistic impressions of recirculation zones are set forth. The presence of a swirler is found to shorten the corner recirculation zone and to generate a central recirculation zone followed by a precessing vortex core. A gradual inlet expansion has the effect of encouraging the flow to remain close to the sidewall and shortening the extent of the corner recirculation zone in all cases investigated.

High operating temperature interband cascade focal plane arrays

Energy Technology Data Exchange (ETDEWEB)

Tian, Z.-B.; Godoy, S. E.; Kim, H. S.; Schuler-Sandy, T.; Montoya, J. A.; Krishna, S. [Center for High Technology Materials, Department of Electrical and Computer Engineering, University of New Mexico, Albuquerque, New Mexico 87106 (United States)

2014-08-04

In this paper, we report the initial demonstration of mid-infrared interband cascade (IC) photodetector focal plane arrays with multiple-stage/junction design. The merits of IC photodetectors include low noise and efficient photocarrier extraction, even for zero-bias operation. By adopting enhanced electron barrier design and a total absorber thickness of 0.7 μm, the 5-stage IC detectors show very low dark current (1.10 × 10{sup −7} A/cm{sup 2} at −5 mV and 150 K). Even with un-optimized fabrication and standard commercial (mis-matched) read-out circuit technology, infrared images are obtained by the 320 × 256 IC focal plane array up to 180 K with f/2.3 optics. The minimum noise equivalent temperature difference of 28 mK is obtained at 120 K. These initial results indicate great potential of IC photodetectors, particularly for high operating temperature applications.

High operating temperature interband cascade focal plane arrays

International Nuclear Information System (INIS)

Tian, Z.-B.; Godoy, S. E.; Kim, H. S.; Schuler-Sandy, T.; Montoya, J. A.; Krishna, S.

2014-01-01

In this paper, we report the initial demonstration of mid-infrared interband cascade (IC) photodetector focal plane arrays with multiple-stage/junction design. The merits of IC photodetectors include low noise and efficient photocarrier extraction, even for zero-bias operation. By adopting enhanced electron barrier design and a total absorber thickness of 0.7 μm, the 5-stage IC detectors show very low dark current (1.10 × 10 −7 A/cm 2 at −5 mV and 150 K). Even with un-optimized fabrication and standard commercial (mis-matched) read-out circuit technology, infrared images are obtained by the 320 × 256 IC focal plane array up to 180 K with f/2.3 optics. The minimum noise equivalent temperature difference of 28 mK is obtained at 120 K. These initial results indicate great potential of IC photodetectors, particularly for high operating temperature applications

Tunable graphene antennas for selective enhancement of THz-emission

KAUST Repository

Filter, Robert; Farhat, Mohamed; Steglich, Mathias; Alaee, Rasoul; Rockstuhl, Carsten; Lederer, Falk L.

2013-01-01

In this paper, we will introduce THz graphene antennas that strongly enhance the emission rate of quantum systems at specific frequencies. The tunability of these antennas can be used to selectively enhance individual spectral features. We will show as an example that any weak transition in the spectrum of coronene can become the dominant contribution. This selective and tunable enhancement establishes a new class of graphene-based THz devices, which will find applications in sensors, novel light sources, spectroscopy, and quantum communication devices. © 2013 Optical Society of America.

Greenhouse Gas Emission Accounting and Management of Low-Carbon Community

Directory of Open Access Journals (Sweden)

Dan Song

2012-01-01

Full Text Available As the major source of greenhouse gas (GHG emission, cities have been under tremendous pressure of energy conservation and emission reduction for decades. Community is the main unit of urban housing, public facilities, transportation, and other properties of city's land use. The construction of low-carbon community is an important pathway to realize carbon emission mitigation in the context of rapid urbanization. Therefore, an efficient carbon accounting framework should be proposed for CO2 emissions mitigation at a subcity level. Based on life-cycle analysis (LCA, a three-tier accounting framework for the carbon emissions of the community is put forward, including emissions from direct fossil fuel combustion, purchased energy (electricity, heat, and water, and supply chain emissions embodied in the consumption of goods. By compiling a detailed CO2 emission inventory, the magnitude of carbon emissions and the mitigation potential in a typical high-quality community in Beijing are quantified within the accounting framework proposed. Results show that emissions from supply chain emissions embodied in the consumption of goods cannot be ignored. Specific suggestions are also provided for the urban decision makers to achieve the optimal resource allocation and further promotion of low-carbon communities.

Multilevel Inverter by Cascading Industrial VSI

DEFF Research Database (Denmark)

Teodorescu, Remus; Blaabjerg, Frede; Pedersen, John Kim

2002-01-01

In this paper the modularity concept applied to medium-voltage adjustable speed drives is addressed. First, the single-phase cascaded voltage-source inverter that uses series connection of IGBT H-bridge modules with isolated dc-buses is presented. Next, a novel three-phase cascaded voltage......-source inverter that uses three IGBT triphase inverter modules along with an output transformer to obtain a 3 p.u. multilevel output voltage is introduced. The system yields in high-quality multistep voltage with up to 4 levels and low dv/dt, balanced operation of the inverter modules, each supplying a third...... of the motor rated kVA. The concept of using cascaded inverters is further extended to a new modular motor-modular inverter system where the motor winding connections are reconnected into several three-phase groups, either six-lead or 12-lead connection according to the voltage level, each powered...

Enhancement of Aggregation-Induced Emission by Introducing Multiple o-Carborane Substitutions into Triphenylamine

Directory of Open Access Journals (Sweden)

Kenta Nishino

2017-11-01

Full Text Available The enhancement of aggregation-induced emission (AIE is presented on the basis of the strategy for improving solid-state luminescence by employing multiple o-carborane substituents. We synthesized the modified triphenylamines with various numbers of o-carborane units and compared their optical properties. From the optical measurements, the emission bands from the twisted intramolecular charge transfer (TICT state were obtained from the modified triphenylamines. It was notable that emission efficiencies of the multi-substituted triphenylamines including two or three o-carborane units were enhanced 6- to 8-fold compared to those of the mono-substituted triphenylamine. According to mechanistic studies, it was proposed that the single o-carborane substitution can load the AIE property via the TICT mechanism. It was revealed that the additional o-carborane units contribute to improving solid-state emission by suppressing aggregation-caused quenching (ACQ. Subsequently, intense AIEs were obtained. This paper presents a new role of the o-carborane substituent in the enhancement of AIEs.

Enhanced Emission of Quantum System in Si-Ge Nanolayer Structure.

Science.gov (United States)

Huang, Zhong-Mei; Huang, Wei-Qi; Dong, Tai-Ge; Wang, Gang; Wu, Xue-Ke

2016-12-01

It is very interesting that the enhanced peaks near 1150 and 1550 nm are observed in the photoluminescence (PL) spectra in the quantum system of Si-Ge nanolayer structure, which have the emission characteristics of a three-level system with quantum dots (QDs) pumping and emission of quasi-direct-gap band, in our experiment. In the preparing process of Si-Ge nanolayer structure by using a pulsed laser deposition method, it is discovered that the nanocrystals of Si and Ge grow in the (100) and (111) directions after annealing or electron beam irradiation. The enhanced PL peaks with multi-longitudinal-mode are measured at room temperature in the super-lattice of Si-Ge nanolayer quantum system on SOI.

THERMIONIC EMISSION ENHANCEMENT FROM CESIUM COATED RHENIUM IN ELECTRIC FIELDS

Energy Technology Data Exchange (ETDEWEB)

de Steese, J. G.; Zollweg, R. J.

1963-04-15

The plasma-anode technique was used to observe anomalously high thermionic emission from a rhenium surface with small cesium coverage, where the work function of the composite surface is greater than the ionization potential of cesium. Data suggest that emission enhancement is caused by increased cesium coverage because of cesiumion trapping near the emitter surface under the influence of an ion-rich sheath. (auth)

An automated Monte-Carlo based method for the calculation of cascade summing factors

Science.gov (United States)

Jackson, M. J.; Britton, R.; Davies, A. V.; McLarty, J. L.; Goodwin, M.

2016-10-01

A versatile method has been developed to calculate cascade summing factors for use in quantitative gamma-spectrometry analysis procedures. The proposed method is based solely on Evaluated Nuclear Structure Data File (ENSDF) nuclear data, an X-ray energy library, and accurate efficiency characterisations for single detector counting geometries. The algorithm, which accounts for γ-γ, γ-X, γ-511 and γ-e- coincidences, can be applied to any design of gamma spectrometer and can be expanded to incorporate any number of nuclides. Efficiency characterisations can be derived from measured or mathematically modelled functions, and can accommodate both point and volumetric source types. The calculated results are shown to be consistent with an industry standard gamma-spectrometry software package. Additional benefits including calculation of cascade summing factors for all gamma and X-ray emissions, not just the major emission lines, are also highlighted.

Large Eddy simulations of flame/acoustics interactions in a swirl flow; Simulation aux grandes echelles des interactions flamme / acoustique dans un ecoulement vrille

Energy Technology Data Exchange (ETDEWEB)

Selle, L.

2004-01-15

Swirl flows exhibit a large variety of topologies, depending on the ratio of the flux axial momentum to the axial flux of tangential momentum: this ratio is called swirl number. Above a given critical value for the swirl number, the pressure gradient reverses the flow on the axis of rotation. This central recirculation zone is used in turbines for flame stabilization. And yet, reacting-swirled flows can exhibit combustion instabilities resulting from the coupling between acoustics and unsteady heat release. Combustion instabilities can lead to loss of control or even complete destruction of the system. Their prediction is impossible with standard engineering tools. The work presented here investigates the capabilities of numerical research tools for the prediction of combustion instabilities. Large-Eddy Simulation (LES) is implemented in a code solving the Navier-Stokes equations for compressible-multi-components fluids (code AVBP developed at CERFACS). This method takes into account for the major ingredients of combustion instabilities such as acoustics and flame / vortex interaction. The LES methodology is validated in the swirled flow from a complex industrial burner (SIEMENS PG). Both reactive and non-reactive regimes are successfully compared with experimental data in terms of mean temperature and mean and RMS velocities. Experimental measurements were performed at the university of Karlsruhe (Germany). A detailed analysis of the acoustics and its interaction with the flame front is performed with the code AVSP, also developed at CERFACS. (author)

Cascade multiplicity inside deuteron in Π d high energy collisions

International Nuclear Information System (INIS)

Kisielewska, D.

1983-01-01

Multiplicity distribution of double scattering events is analysed using the additive quark model including the cascading effect. The mean multiplicity of particles produced in the process of cascading estimated for Π d experiments at 100, 205 and 360 GeV/c is equal to 1.15 ± .31. This value does not depend on the momentum of the incident pion. Some indications are found that the probability of cascading depends on multiplicity of the collision with the first nucleon and is smaller for low multiplicities. (author)

Pair Cascades and Deathlines in Magnetic Fields with Offset Polar Caps

Science.gov (United States)

Harding, Alice K.; Muslimov, Alex G.

2012-01-01

We present results of electron-positron pair cascade simulations in a dipole magnetic field whose polar cap is offset from the dipole axis. In such a field geometry, the polar cap is displaced a small fraction of the neutron star radius from the star symmetry axis and the field line radius of curvature is modified. Using the modified parallel electric field near the offset polar cap, we simulate pair cascades to determine the pair deathlines and pair multiplicities as a function of the offset. We find that the pair multiplicity can change dr;unatically with a modest offset, with a significant increase on one side of the polar cap. Lower pair deathlines allow a larger fraction of the pulsar population, that include old and millisecond pulsars, to produce cascades with high multiplicity. The results have some important implications for pulsar particle production, high-energy emission and cosmic-ray contribution.

Dust emission from wet, low-emission coke quenching process

Science.gov (United States)

Komosiński, Bogusław; Bobik, Bartłomiej; Konieczny, Tomasz; Cieślik, Ewelina

2018-01-01

Coke plants, which produce various types of coke (metallurgical, foundry or heating), at temperatures between 600 and 1200°C, with limited access to oxygen, are major emitters of particulates and gaseous pollutants to air, water and soils. Primarily, the process of wet quenching should be mentioned, as one of the most cumbersome. Atmospheric pollutants include particulates, tar substances, organic pollutants including B(a)P and many others. Pollutants are also formed from the decomposition of water used to quench coke (CO, phenol, HCN, H2S, NH3, cresol) and decomposition of hot coke in the first phase of quenching (CO, H2S, SO2) [1]. The development of the coke oven technology has resulted in the changes made to different types of technological installations, such as the use of baffles in quench towers, the removal of nitrogen oxides by selective NOx reduction, and the introduction of fabric filters for particulates removal. The BAT conclusions for coke plants [2] provide a methodology for the measurement of particulate emission from a wet, low-emission technology using Mohrhauer probes. The conclusions define the emission level for wet quenching process as 25 g/Mgcoke. The conducted research was aimed at verification of the presented method. For two of three quench towers (A and C) the requirements included in the BAT conclusions are not met and emissions amount to 87.34 and 61.35 g/Mgcoke respectively. The lowest particulates emission was recorded on the quench tower B and amounted to 22.5 g/Mgcoke, therefore not exceeding the requirements.

Low emission transport systems. Reduction of emissions with low-pollutant lubricants; Emissionsarmer Verkehr. Emissionsminderung durch schadstoffarme Schmierstoffe

Energy Technology Data Exchange (ETDEWEB)

Keller, D; Boehncke, A; Mangelsdorf, I

2001-07-01

Due to the lower EURO 4 emission limits, exhaust aftertreatment systems for heavy- and light-duty vehicles will be necessary which are more efficient than the today 3-way- or oxidation-type catalysts. Practicable exhaust aftertreatment systems are, for example, particle traps, SCR or NOx- adsorber catalysts, and combinations of these systems. Most of these exhaust control devices require fuels with sulphur contents below 10 ppm. Then the sulphate emissions from lubricants containing about 0.5% sulphur is in the same order of magnitude as sulphate emissions from low sulfur fuels. Measured data on the influence of sulphur from lubricating oils on future exhaust treatment systems are very limited. Conclusions have mostly been drawn from experimental results with low sulphur fuels. It cannot be ruled out, especially for NOx- adsorbers, that sulphur will adversely affect performance, thus making a reduction of sulphur levels in engine oils necessary. As far as diesel exhaust is concerned lubricants contribute approximately 20 - 26% to total particulate matter and more than 50% to the soluble organic fraction (SOF). Ash deposits derived from additives that contain zinc, calcium, sulphur, or phosphorous are likely to block the newly developed particle filter systems. Also for diesel technologies incorporating precious-metal catalysts (e.g. DOC, CDPF, CR-DPF, Urea- SCR) low sulphur levels are advantageous because the mass of sulphate particulate matter formed from fuel or lubricant sulphur is reduced. Conventional three-way catalysts are less sensitive, the light-off temperature being mainly affected. In summary, all available studies suggest that the lower the level of sulphur the lower emissions are. Furthermore phosphorous (associated with the antiwear additive ZDTP) was shown to limit catalyst life and, together with thermal degradation, is responsible for reduced catalyst efficiency over time. Although there is still a lack of quantitative technical information, it

THE EFFECTS OF SWIRL GENERATOR HAVING WINGS WITH HOLES ON HEAT TRANSFER AND PRESSURE DROP IN TUBE HEAT EXCHANGER

Directory of Open Access Journals (Sweden)

Zeki ARGUNHAN

2006-02-01

Full Text Available This paper examines the effect of turbulance creators on heat transfer and pressure drop used in concentric heat exchanger experimentaly. Heat exchanger has an inlet tube with 60 mm in diameter. The angle of swirl generators wings is 55º with each wing which has single, double, three and four holes. Swirl generators is designed to easily set to heat exchanger entrance. Air is passing through inner tube of heat exhanger as hot fluid and water is passing outer of inner tube as cool fluid.

Saturation mechanism of the heat release response of a premixed swirl flame using LES

NARCIS (Netherlands)

Krediet, H.J.; Beck, C. H.; Krebs, W.; Kok, J. B.W.

2013-01-01

The nonlinear heat release response of a premixed swirl flame to velocity perturbations is investigated using Large Eddy Simulation. The nonlinear heat release response is required for the prediction of thermoacoustic limit cycle pressure amplitudes and is represented here by the Flame Describing

Enhanced stimulated emission in ZnO thin films using microdisk top-down structuring

Energy Technology Data Exchange (ETDEWEB)

Nomenyo, K.; Kostcheev, S.; Lérondel, G. [Laboratoire de Nanotechnologie et d' Instrumentation Optique, Institut Charles Delaunay, CNRS UMR 6281, Université de Technologie de Troyes, 12 rue Marie Curie, CS 42060, 10004 Troyes Cedex (France); Gadallah, A.-S. [Laboratoire de Nanotechnologie et d' Instrumentation Optique, Institut Charles Delaunay, CNRS UMR 6281, Université de Technologie de Troyes, 12 rue Marie Curie, CS 42060, 10004 Troyes Cedex (France); Department of Laser Sciences and Interactions, National Institute of Laser Enhanced Sciences, Cairo University, Giza (Egypt); Rogers, D. J. [Nanovation, 8, route de Chevreuse, 78117 Châteaufort (France)

2014-05-05

Microdisks were fabricated in zinc oxide (ZnO) thin films using a top-down approach combining electron beam lithography and reactive ion etching. These microdisk structured thin films exhibit a stimulated surface emission between 3 and 7 times higher than that from a reference film depending on the excitation power density. Emission peak narrowing, reduction in lasing threshold and blue-shifting of the emission wavelength were observed along with enhancement in the emitted intensity. Results indicate that this enhancement is due to an increase in the internal quantum efficiency combined with an amplification of the stimulated emission. An analysis in terms of waveguiding is presented in order to explain these effects. These results demonstrate that very significant gains in emission can be obtained through conventional microstructuration without the need for more onerous top-down nanostructuration techniques.

Experimental investigation on the spray characteristics of power-law fluid in a swirl injector

Energy Technology Data Exchange (ETDEWEB)

Bai, Fuqiang; Chen, Shixing; Guo, Jinpeng; Jiao, Kui; Du, Qing [State Key Laboratory of Engines, Tianjin University, Tianjin, 300072 (China); Chang, Qing, E-mail: duqing@tju.edu.cn [Wuxi Fuel Injection Equipment Research Institute, China FAW CO., Wuxi, 214063 (China)

2017-06-15

High-speed photography and 3D phase Doppler methods are used to obtain the swirl jet images, 3D velocities and size distribution of different droplets (including deionized water and two kinds of power-law fluid). For the power-law fluids, a short circular jet is formed after the nozzle exit at low pressure. Along the X direction, the distributions of axial velocity w and Sauter mean diameter (SMD) are symmetrical and increase from the center to both sides. The effect of injection pressure on the radial velocity u is not obvious. Along the Z axis, the absolute value of 3D velocities decreases to some extent with droplets moving downstream. The SMD decreases apparently with the increment of the distance along the Z axis at 1.0 MPa. (paper)

LES and RANS modeling of pulverized coal combustion in swirl burner for air and oxy-combustion technologies

International Nuclear Information System (INIS)

Warzecha, Piotr; Boguslawski, Andrzej

2014-01-01

Combustion of pulverized coal in oxy-combustion technology is one of the effective ways to reduce the emission of greenhouse gases into the atmosphere. The process of transition from conventional combustion in air to the oxy-combustion technology, however, requires a thorough investigations of the phenomena occurring during the combustion process, that can be greatly supported by numerical modeling. The paper presents the results of numerical simulations of pulverized coal combustion process in swirl burner using RANS (Reynolds-averaged Navier–Stokes equations) and LES (large Eddy simulation) methods for turbulent flow. Numerical simulations have been performed for the oxyfuel test facility located at the Institute of Heat and Mass Transfer at RWTH Aachen University. Detailed analysis of the flow field inside the combustion chamber for cold flow and for the flow with combustion using different numerical methods for turbulent flows have been done. Comparison of the air and oxy-coal combustion process for pulverized coal shows significant differences in temperature, especially close to the burner exit. Additionally the influence of the combustion model on the results has been shown for oxy-combustion test case. - Highlights: • Oxy-coal combustion has been modeled for test facility operating at low oxygen ratio. • Coal combustion process has been modeled with simplified combustion models. • Comparison of oxy and air combustion process of pulverized coal has been done. • RANS (Reynolds-averaged Navier–Stokes equations) and LES (large Eddy simulation) results for pulverized coal combustion process have been compared

Enhanced Thermionic Emission and Low 1/f Noise in Exfoliated Graphene/GaN Schottky Barrier Diode.