Effect of Flow Turbulence on Evaporation Rate of a Single Droplet PDF Download
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Author: A. V. Eckartsberg
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: A. V. Eckartsberg
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Ferran Marti Duran
Publisher:
ISBN: 9781267815934
Category :
Languages : en
Pages : 104
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In this thesis, we develop and test an experimental apparatus capable of examining the effect of turbulence on the evaporation of droplets when the Kolmogorov scale is smaller than the size of the drop (where size refers to the nominal droplet diameter). Traveling drop and suspended drop cases have been studied experimentally and the evaporation rate has also been predicted based on classical computations of transport rates. Cases involving still air, a mean flow with turbulence, and a mean flow without turbulence have been tested. The experimental data matches the theoretical computations for the case of still air and mean flow with no turbulence. There is no accepted computational model that can account for turbulent flow, but the experimental conditions tested so far do not show any measurable effect of turbulence on the evaporation rate. These findings suggest that turbulence is a much smaller factor in evaporation than is mean flow over the droplet. Hence, one suggestion for future work is to study traveling droplets with zero relative velocity to the air in order to focus the analysis on the effects of turbulence with no mean flow.
Author: Cameron Mark Verwey
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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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: R.G. FLEDDERMAN, A.R. HANSON
Publisher:
ISBN:
Category :
Languages : en
Pages : 112
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Author: Arnold Frohn
Publisher: Springer Science & Business Media
ISBN: 3662040409
Category : Technology & Engineering
Languages : en
Pages : 298
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The book deals with the dynamical behaviour of single droplets and regular droplet systems. It has been written mainly for experimental researchers. After a short description of the theoretical background, the different experimental facilities and methods necessary for the investigation of single droplets are described in detail. A summary of important applications is included.
Author: Richard Gould
Publisher:
ISBN:
Category :
Languages : en
Pages : 8
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Single acetone and heptane droplets were suspended from a hypodermic needle in turbulent airflow, and the Nusselt number was obtained from direct measurements of the droplet diameter and evaporation rate. Acetone was selected because it fluoresces when irradiated with ultraviolet laser radiation while heptane was selected because of its high volatility compared with water, methanol, and ethanol which were used previously. Planar laser induced fluorescence (PLIF) measurements were made to obtain qualitative concentration measurements of gaseous acetone in the boundary layer surrounding the droplet. The goal of these measurements was to give insight as to why the evaporation rate is increased by 50 % when the gas phase turbulence is increased from the laminar flow case to the case where the freestream turbulence is 10%. The use of acetone droplets required that the influence of humidity on droplet evaporation rate be considered. Measurements of the turbulence intensity of heated freestream air were also made. Finally, many modifications to improve the experimental apparatus were made during this research project.
Author: J.-S. Wu
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Sergei S. Sazhin
Publisher: Springer Nature
ISBN: 3030997464
Category : Technology & Engineering
Languages : en
Pages : 603
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This book acts as a guide to simple models that describe some of the complex fluid dynamics, heat/mass transfer and combustion processes in droplets and sprays. Attention is focused mainly on the use of classical hydrodynamics, and a combination of kinetic and hydrodynamic models, to analyse the heating and evaporation of mono- and multi-component droplets. The models were developed for cases when small and large numbers of components are present in droplets. Some of these models are used for the prediction of time to puffing/micro-explosion of composite water/fuel droplets — processes that are widely used in combustion devices to stimulate disintegration of relatively large droplets into smaller ones. The predictions of numerical codes based on these models are validated against experimental results where possible. In most of the models, droplets are assumed to be spherical; some preliminary results of the generalisation of these models to the case of non-spherical droplets, approximating them as spheroids, are presented.
Author:
Publisher:
ISBN:
Category : Thermodynamics
Languages : en
Pages : 462
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Author: United States. Wright Air Development Division
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 1746
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