Effect of Vaporization and Turbulence on Spray Drop-Size and Velocity Distributions PDF Download
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Author: RD. Reitz
Publisher:
ISBN:
Category : Drops
Languages : en
Pages : 13
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Book Description
Local drop-size, velocity, and liquid flux profiles were measured within conical steady sprays using a phase/Doppler velocimeter. The coflowing gas mean velocity, gridinduced turbulence intensity and length scale, and its temperature and pressure were each varied using a wind tunnel facility (gas velocity from 3 to 22.2 m/s, turbulence intensity from 2.7 to 8.6%, length scale from 8.4 to 17.8 mm, gas temperature from 300 to 750K, gas pressure from 101 to 610 kPa, and a differential injection pressure of 689 kPa). The results show that the turbulence in the gas influences the drop-size and velocity distributions. Drop mean and fluctuating velocity components were found to be close to the gas mean and turbulence velocities in regions where the drop-size-velocity correlation coefficient was low. The drop-size-velocity correlation decreased with increasing gas density and gas velocity. Drop-size distributions broadened, and the total amount of liquid vaporized increased when the turbulence intensity and scale were increased. At a given gas temperature, the amount of vaporization increased when the gas density was increased and the overall drop size (a flux-weighted Sauter mean over the spray cross-section) also decreased. However, local drop sizes were larger in vaporizing sprays than in nonvaporizing sprays at the same gas density. This interesting result could be due to the fact that the gas viscosity increases with increasing gas temperature and this increases the drop-drag coefficient, leading to reduced radial penetration of the spray. An additional factor is that, although vaporization reduces the size of all drops, smaller drops vaporize faster and drop-size averages are weighted towards larger drops.
Author: RD. Reitz
Publisher:
ISBN:
Category : Drops
Languages : en
Pages : 13
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Book Description
Local drop-size, velocity, and liquid flux profiles were measured within conical steady sprays using a phase/Doppler velocimeter. The coflowing gas mean velocity, gridinduced turbulence intensity and length scale, and its temperature and pressure were each varied using a wind tunnel facility (gas velocity from 3 to 22.2 m/s, turbulence intensity from 2.7 to 8.6%, length scale from 8.4 to 17.8 mm, gas temperature from 300 to 750K, gas pressure from 101 to 610 kPa, and a differential injection pressure of 689 kPa). The results show that the turbulence in the gas influences the drop-size and velocity distributions. Drop mean and fluctuating velocity components were found to be close to the gas mean and turbulence velocities in regions where the drop-size-velocity correlation coefficient was low. The drop-size-velocity correlation decreased with increasing gas density and gas velocity. Drop-size distributions broadened, and the total amount of liquid vaporized increased when the turbulence intensity and scale were increased. At a given gas temperature, the amount of vaporization increased when the gas density was increased and the overall drop size (a flux-weighted Sauter mean over the spray cross-section) also decreased. However, local drop sizes were larger in vaporizing sprays than in nonvaporizing sprays at the same gas density. This interesting result could be due to the fact that the gas viscosity increases with increasing gas temperature and this increases the drop-drag coefficient, leading to reduced radial penetration of the spray. An additional factor is that, although vaporization reduces the size of all drops, smaller drops vaporize faster and drop-size averages are weighted towards larger drops.
Author: E. Dan Hirleman
Publisher: ASTM International
ISBN: 0803114591
Category : Drops
Languages : en
Pages : 259
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Book Description
Author: Cameron Mark Verwey
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
The performance of liquid-fuelled spray combustion systems has a massive impact on the efficiency of energy production in many sectors across the globe. Realistic combustors generate sub 100-μm droplets and operate under high pressure and temperature in strong turbulence. Investigations into droplet evaporation and combustion provide fundamental knowledge and validation data regarding the behaviour of sprays, and although single droplet approaches have been a staple of energy research for many decades, there is little information regarding the effect of turbulence and initial diameter, especially micro-sized, on droplet evaporation rates. The present experimental study develops, interprets, and correlates the results of almost 500 tests performed on isolated heptane and decane droplets. Droplets in the range of 110 - 770 μm (initial diameter) were generated and suspended on small intersecting micro-fibers in a spherical fan-driven chamber and exposed to quasi-zero mean turbulence of intensity up to 1.5 m/s, temperatures ranging from 25 - 100°C, and pressures between 1 and 10 bar. The results indicate that droplet size has a major influence on evaporation rate, as measured by the temporal reduction in droplet surface area, when the environment is turbulent. Evaporation rates increased with both initial diameter and turbulence intensity at all test conditions. The effectiveness of turbulence, defined as the ability of turbulence to improve the evaporation rate over the rate of a stagnant droplet at identical ambient conditions, increased with pressure but decreased with temperature. Both the ratio of Kolmogorov length scale to droplet diameter and the theoretical molar concentration gradient of fuel at the droplet surface are found to be excellent predictors of turbulence effectiveness. Correlation approaches utilizing a turbulent Reynolds number or a vaporization Damköhler number are suggested to predict the evaporation rate of a single droplet exposed to a purely turbulent flow field.
Author: United States. National Advisory Committee for Aeronautics
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 324
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Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 286
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Book Description
![A Prediction of the Droplet Size and Velocity Distribution in a Spray from First Principles [microform] PDF](https://books.google.com/books/content/images/frontcover/sjSXwgEACAAJ?fife=w80-h100)
Author: Richard William Sellens
Publisher: National Library of Canada
ISBN: 9780315295537
Category : Particle size determination
Languages : en
Pages : 147
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Book Description
The maximum entropy formalism is used to predict the droplet size and velocity distribution in a spray resulting from the breakup of a liquid sheet. The physics of the process are described by simple conservation constraints for mass, momentum, surface energy and kinetic energy. The predicted size distribution is compared with four empirical distributions and found very similar to a Rosin - Rammler distribution with the same parameters. The predicted velocity distribution has a Gaussian cross section at any particular droplet diameter. The variance of the Gaussian decreases with increasing droplet diameter, so that the velocity is nearly single valued for large droplets, but varies widely for smaller droplets. This size and velocity distribution is propagated downstream using a simple physical model which assumes a uniform velocity air flow field, no evaporation, and treats the droplets as solid spheres. Although this is a substantial simplification, it shows that, in the absence of fluctuations in the air stream around the droplets, droplet velocity distributions collapse towards single values. This process takes place over distances which are short when compared to the scale of common spray systems.
Author: Lewis Flight Propulsion Laboratory. Propulsion Chemistry Division
Publisher:
ISBN:
Category : Airplanes
Languages : en
Pages : 288
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Author: Marcus F. Heidmann
Publisher:
ISBN:
Category : Chemical engineering
Languages : en
Pages : 38
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Book Description
Sprays produced by two 0.089-inch-diameter jets at impingement angles of 10 to 90 degrees and jet velocities of 30 to 74 feet per second were studied. Drop-size distributions for sprays formed in 100-foot-per-second air are presented. Distributions were bimodal in character, and the effects of test conditions on the bimodal properties are presented. Photographs of the overall spray pattern produced in quiescent air are also shown.
Author: Robert D. Ingebo
Publisher:
ISBN:
Category : Turbulence
Languages : en
Pages : 39
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Book Description
A droplet camera developed at the NACA Lewis laboratory was used to obtain drop-size distribution and drop-velocity data for isooctane injected from a simple orifice directly into a turbulent air stream. From these data and wet-bulb temperature data, vaporization rates and drag coefficients were calculated for isooctane drops accelerating and evaporating in streams having velocities of 140 and 180 feet per second. Spray vaporization rates based on the mean drop diameter D20 were compared with single-drop vaporization rates buy use of the heat transfer equation.
Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 492
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