The stability of flames on flat sprays

1970 ◽  
Vol 320 (1542) ◽  
pp. 309-322 ◽  
Keyword(s):  
Flame Front ◽  
Drop Size ◽  
Ambient Air ◽  
Drop Diameter ◽  
Flame Stability ◽  
Air Velocity ◽  
Mixture Ratio ◽  
Simple Theoretical Model ◽  
Set Up ◽  
The Stability

An investigation into the stabilization of flames on unconfined fuel sprays has been carried out. A simple theoretical model has been set up and analysed on the basis that the controlling fuel/ air mixture ratio for stability is produced by partial drop evaporation in the flame front and air entrained into the spray. The manner in which the conditions for blow-out varied with fuel supply pressure and ambient air velocity was examined and it was found that flame stability increased with drop size. A theoretically derived expression has been used to correlate the position of the flame front with the local air velocity and a characteristic drop diameter.

Effect of Reactant Preheating on the Stability of Non-Premixed Methane/Air Flames

2010 ◽  
Author(s):  
Sylvain Lamige ◽  
Ce´dric Galizzi ◽  
Jiesheng Min ◽  
Julien Perles ◽  
Fre´de´ric Andre´ ◽  
...  
Keyword(s):  
Room Temperature ◽  
Initial Temperature ◽  
Flame Stability ◽  
Air Velocity ◽  
Lifted Flames ◽  
Local Extinctions ◽  
Lift Off ◽  
Temperature Levels ◽  
The Stability ◽  
Jet Velocities

This study details the influence of reactant temperature on the stability of non-premixed CH4/air co-flow jet flames. Flame characteristics have been studied for five temperature levels (from 295 K to 600 K). The hysteresis zone formed by the limits between attached and lifted flame translates towards higher methane jet velocities with an increase of initial temperature, independently of the air velocity range. Moreover, critical velocities vary linearly with initial temperature. In addition, attachment and lift-off heights have been obtained from CH* chemiluminescence visualization. Results point out that the attachment height decreases significantly with temperature. Observations also indicate that the intrinsic process of lifting is modified. Pre-lifting anchored flame local extinctions, not observed at room-temperature, appear at higher initial temperatures; their occurrence increases with temperature. The lift-off height of turbulent lifted flames is also reduced with temperature. Overall, results show that increasing local temperature in the stabilization zone enhances flame stability.

An Analysis of Errors in Drop Size Distribution Retrievals and Rain Bulk Parameters with a UHF Wind Profiling Radar and a Two-Dimensional Video Disdrometer

2008 ◽  
Vol 25 (12) ◽  
pp. 2282-2292 ◽  
Author(s):  
Laura Kanofsky ◽  
Phillip Chilson
Keyword(s):  
Error Analysis ◽  
Size Distribution ◽  
Drop Size ◽  
Ambient Air ◽  
Drop Size Distribution ◽  
Rainfall Rate ◽  
Doppler Velocity ◽  
Drop Diameter ◽  
Fall Speed ◽  
Air Motion

Abstract Vertically pointed wind profiling radars can be used to obtain measurements of the underlying drop size distribution (DSD) for a rain event by means of the Doppler velocity spectrum. Precipitation parameters such as rainfall rate, radar reflectivity factor, liquid water content, mass-weighted mean drop diameter, and median volume drop diameter can then be calculated from the retrieved DSD. The DSD retrieval process is complicated by the presence of atmospheric turbulence, vertical ambient air motion, selection of fall speed relationships, and velocity thresholding. In this note, error analysis is presented to quantify the effect of each of those factors on rainfall rate. The error analysis results are then applied to two precipitation events to better interpret the rainfall-rate retrievals. It was found that a large source of error in rain rate is due to unaccounted-for vertical air motion. For example, in stratiform rain with a rainfall rate of R = 10 mm h−1, a mesoscale downdraft of 0.6 m s−1 can result in a 34% underestimation of the estimated value of R. The fall speed relationship selection and source of air density information both caused negligible errors. Errors due to velocity thresholding become more important in the presence of significant contamination near 0 m s−1, such as ground clutter. If particles having an equivalent volume diameter of 0.8 mm and smaller are rejected, rainfall rate errors from −4% to −10% are possible, although these estimates depend on DSD and rainfall rate.

scholarly journals Energy Considerations in Twin-Fluid Atomization

1990 ◽  
Author(s):  
Arthur H. Lefebvre
Keyword(s):  
Drop Size ◽  
Sheet Thickness ◽  
Ambient Air ◽  
Liquid Sheet ◽  
Air Pressure ◽  
Air Velocity ◽  
Atomization Process ◽  
Flow Situation ◽  
Heating Oil ◽  
Main Factor

With certain types of prefilming airblast atomizers, the manner in which the atomizing air impinges on the liquid sheet prohibits the wave formation that normally precedes the breakup of a liquid sheet into drops. Instead, the liquid is shattered almost instantaneously into drops of various sizes. This prompt atomization process is characterized by a broad range of drop sizes in the spray and by a lack of sensitivity of mean drop size to variations in liquid viscosity, atomizing air pressure, and initial liquid sheet thickness. Evidence is presented to show that which of these two different modes of atomization will occur in any given flow situation is largely dependent on the angle at which the atomizing air impinges on the liquid sheet. An equation for mean drop size, derived from the assumption that the main factor controlling prompt atomization is the ratio of the energy required for atomization to the kinetic energy of the atomizing air, is shown to provide a good fit to experimental data acquired from atomization studies on water and heating oil, carried out over wide ranges of air velocity, air/liquid ratio, and ambient air pressure.

Energy Considerations in Twin-Fluid Atomization

1992 ◽  
Vol 114 (1) ◽  
pp. 89-96 ◽  
Author(s):  
A. H. Lefebvre
Keyword(s):  
Drop Size ◽  
Sheet Thickness ◽  
Ambient Air ◽  
Liquid Sheet ◽  
Air Pressure ◽  
Air Velocity ◽  
Atomization Process ◽  
Flow Situation ◽  
Heating Oil ◽  
Main Factor

With certain types of prefilming airblast atomizers, the manner in which the atomizing air impinges on the liquid sheet prohibits the wave formation that normally precedes the breakup of a liquid sheet into drops. Instead, the liquid is shattered almost instantaneously into drops of various sizes. This prompt atomization process is characterized by a broad range of drop sizes in the spray and by a lack of sensitivity of mean drop size to variations in liquid viscosity, atomizing air pressure, and initial liquid sheet thickness. Evidence is presented to show that which of these two different modes of atomization will occur in any given flow situation is largely dependent on the angle at which the atomizing air impinges on the liquid sheet. An equation for mean drop size, derived from the assumption that the main factor controlling prompt atomization is the ratio of the energy required for atomization to the kinetic energy of the atomizing air, is shown to provide a good fit to experimental data acquired from atomization studies on water and heating oil, carried out over wide ranges of air velocity, air/liquid ratio, and ambient air pressure.

Analysis of LPG diffusion flame in tube type burner

2019 ◽  
Vol 13 (3) ◽  
pp. 5278-5293
Author(s):  
Vipul Patel ◽  
Rupesh Shah
Keyword(s):  
Diffusion Flame ◽  
Emission Characteristic ◽  
Flame Stability ◽  
Liquefied Petroleum Gas ◽  
Air Velocity ◽  
Length Fraction ◽  
Low Emission ◽  
Tube Type ◽  
Stability Limits ◽  
Co Emission

The present research aims to analyse diffusion flame in a tube type burner with Liquefied petroleum gas (LPG) as a fuel. An experimental investigation is performed to study flame appearance, flame stability, Soot free length fraction (SFLF) and CO emission of LPG diffusion flame. Effects of varying air and fuel velocities are analysed to understand the physical process involved in combustion. SFLF is measured to estimate the reduction of soot. Stability limits of the diffusion flame are characterized by the blowoff velocity. Emission characteristic in terms of CO level is measured at different equivalence ratios. Experimental results show that the air and fuel velocity strongly influences the appearance of LPG diffusion flame. At a constant fuel velocity, blue zone increases and the luminous zone decreases with the increase in air velocity. It is observed that the SFLF increases with increasing air velocity at a constant fuel velocity. It is observed that the blowoff velocity of the diffusion flame increases as fuel velocity increases. Comparison of emission for flame with and without swirl indicates that swirl results in low emission of CO and higher flame stability. Swirler with 45° vanes achieved the lowest CO emission of 30 ppm at Φ = 1.3.

scholarly journals Galloping Stability and Wind Tunnel Test of Iced Quad Bundled Conductors considering Wake Effect

2020 ◽  
Vol 2020 ◽  
pp. 1-15
Author(s):  
Xiaohui Liu ◽  
Ming Zou ◽  
Chuan Wu ◽  
Mengqi Cai ◽  
Guangyun Min ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Transmission Lines ◽  
Degrees Of Freedom ◽  
Wind Tunnel Test ◽  
Aerodynamic Coefficients ◽  
Wake Effect ◽  
Aerodynamic Coefficient ◽  
Set Up ◽  
The Stability ◽  
Three Degrees Of Freedom

A new quad bundle conductor galloping model considering wake effect is proposed to solve the problem of different aerodynamic coefficients of each subconductor of iced quad bundle conductor. Based on the quasistatic theory, a new 3-DOF (three degrees of freedom) galloping model of iced quad bundle conductors is established, which can accurately reflect the energy transfer and galloping of quad bundle conductor in three directions. After a series of formula derivations, the conductor stability judgment formula is obtained. In the wind tunnel test, according to the actual engineering situation, different variables are set up to accurately simulate the galloping of iced quad bundle conductor under the wind, and the aerodynamic coefficient is obtained. Finally, according to the stability judgment formula of this paper, calculate the critical wind speed of conductor galloping through programming. The dates of wind tunnel test and calculation in this paper can be used in the antigalloping design of transmission lines.

Second Paper: The Effects of Physical Factors on Ignition Delay

1966 ◽  
Vol 181 (1) ◽  
pp. 34-59 ◽  
Author(s):  
W-T. Lyn ◽  
E. Valdmanis
Keyword(s):  
Ignition Delay ◽  
Drop Size ◽  
Injection Rate ◽  
Published Data ◽  
Physical Factors ◽  
Injection Timing ◽  
Air Velocity ◽  
Spray Form ◽  
Temperature And Pressure ◽  
Compression Temperature

The effects of physical factors on ignition delay have been studied on a motored research engine using a single injection technique. The fuels used included a high cetane number reference fuel, gas oil and M.T. 80 petrol. The primary factors investigated are those pertaining to the fuel spray, such as injection timing, quantity, and pressure (affecting drop size, velocity and injection rate); hole diameter (affecting drop size and injection rate) and spray form (nozzle type); and those pertaining to the engine, such as temperature, pressure and air velocity. Engine operating variables such as speed and load affect the ignition delay because they change the primary factors such as injection pressure, compression temperature, pressure and air velocity. It has been found that under normal running conditions, compression temperature and pressure are the major factors. All other factors have only secondary effects. Under starting conditions, when ignition is marginal, mixture formation becomes as important as compression temperature and pressure. Such factors as air velocity and spray form which affect the mixing pattern can have a very pronounced effect on ignition delay. Published data on ignition delay are compared with those obtained in the present investigation and a generalization of the data is recommended for engine design and computational work.

The Mitigation of the French Nuclear Option: New Industrial Realism and Technical Democracy

2002 ◽  
Vol 13 (2) ◽  
pp. 263-279 ◽  
Author(s):  
Dominique Finon
Keyword(s):  
Waste Management ◽  
Electricity Markets ◽  
Social Preferences ◽  
Public Inquiry ◽  
The Future ◽  
Parliamentary Committee ◽  
Set Up ◽  
The Stability ◽  
The Cost ◽  
Phase Out

Nuclear phase-out policies and the European obligation to liberalise electricity markets could put the French nuclear option dramatically at risk by influencing social preferences or by constraining power producers' investment choices in the future. So far, the particular institutional set-up which has allowed the efficient build-up and operation of several series of standardised reactors preserves the stability of the main elements of the option. However, important adaptations to the evolving industrial and political environment occur and contribute to changing the option. Some institutional changes (such as local public inquiry, creation of a Parliamentary committee, independence of safety authorities) and divergence between industrial interests already allow debates on internal options such as reprocessing, type of waste management deposits, ordering of an advanced PWR. These changes improve the cost transparency, even if internalisation of nuclear externalities (cost of insurance, provisions for waste management) is still incomplete. However, when effective, this internalisation would not affect definitively the competitive position of the nuclear production because of the parallel internalisation of CO2 externalities from fossil fuel power generation in the official rationale. Consequently the real issue for the future of the nuclear option in France remains the preservation of social acceptability in the perception of nuclear risks.

Manufacture of Non-Toxic Lava from Recovery of the Incineration Ash by Plasma Fusing Technology

2011 ◽  
Vol 194-196 ◽  
pp. 2365-2375
Author(s):  
Jai Houng Leu ◽  
Li Fong Wu ◽  
Ay Su
Keyword(s):  
Heavy Metals ◽  
Fly Ash ◽  
Dissolution Rate ◽  
Bottom Ash ◽  
Reduction Ratio ◽  
National Standards ◽  
Toxic Heavy Metals ◽  
Mixture Ratio ◽  
Sustainable Operation ◽  
The Stability

This research investigated and explored the overall technical and legal suggestions on mixed ash (bottom ash + fly ash) from the first BOT(built-operation then transfer) incineration plant in south Taoyuan of Taiwan, with the hope of serving as the reference for treating ash from urban refuse incinerator and making sustainable operation management policies in Taiwan. Both bottom ash and fly ash contain high-content harmful metals like lead, chrome, and cadmium, with the lead content exceeding standard value. Plasma fusing technology may effectively settle toxic heavy metals and reduce their dissolution rate. The results show that the increase in percentage of bottom ash could maintain post-fusing strength and produce solidification effect, but this reduced the stability of toxic heavy metals and raised their dissolution rate. Suitable mixture ratio of bottom ash and fly ash was 2:1, volume reduction ratio 0.349, and weight reduction ratio 0.4936. The mixture was fulvous and dense with gloss and adequate strength. The dissolution test of lava products complied with national standards, and they might be used for recycling aggregates and solidifying cement.

Evaluation of the influence of ambient air temperature and air velocity on mortar cement durability using a forced convection solar dryer

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Younes Bahammou ◽  
Mounir Kouhila ◽  
Haytem Moussaoui ◽  
Hamza Lamsyehe ◽  
Zakaria Tagnamas ◽  
...  
Keyword(s):  
Environmental Factors ◽  
Forced Convection ◽  
Air Temperature ◽  
Building Materials ◽  
Ambient Air ◽  
Physical Significance ◽  
Drying Process ◽  
Air Velocity ◽  
Content Type ◽  
Ambient Air Temperature

PurposeThis work aims to study the hydrothermal behavior of mortar cement toward certain environmental factors (ambient air temperature and air velocity) based on its drying kinetics data. The objective is to provide a better understanding and controlling the stability of mortar structures, which integrate the sorption phenomenon, drying process, air pressure and intrinsic characteristics. This leads to predict the comportment of mortar structures in relation with main environmental factors and minimize the risk of cracking mortar structures at an early age.Design/methodology/approachThermokinetic study was carried out in natural and forced convection solar drying at three temperatures 20, 30 and 40°C and three air velocities (1, 3 and 5 m.s-1). The empirical and semiempirical models tested successfully describe the drying kinetics of mortar. These models simulate the drying process of water absorbed by capillarity, which is the most common humidity transfer mechanism in building materials and contain parameters with physical significance, which integrate the effect of several environmental factors and intrinsic characteristics of mortar structures.FindingsThe models simulate the drying process of water absorbed by capillarity, which is the most common humidity transfer mechanism in building materials and contain parameters with physical significance, which integrate the effect of several environmental factors and intrinsic characteristics of mortar structures. The average activation energy obtained expressed the temperature effect on the mortar diffusivity. The drying constant and the diffusion coefficient can be used to predict the influence of these environmental factors on the drying behavior of various building materials and therefore on their durability.Originality/valueEvaluation of the effect of several environmental factors and intrinsic characteristics of mortar structures on their durability.

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