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ENCIT 2016
16th Brazilian Congress of Thermal Sciences and Engineering
STUDY OF EXPERIMENTAL TECHINIQUES OF VISIBLE FLAME LENGTH MEASUREMENT OF TURBULENT DIFFUSION FLAMES
Submission Author:
LUIS QUEZADA , RS , Brazil
Co-Authors:
Fernando Pereira, Isaias Machado, Orion Costa
Presenter: LUIS QUEZADA
doi://10.26678/ABCM.ENCIT2016.CIT2016-0418
Abstract
Abstract There are many definitions and measurement techniques for determining the visible length of turbulent diffusion flames. In this work Optical visualizations of turbulent diffusion flames are used to estimate the visible flame length (VFL). Methods such as average of a sample of images obtained in high and low exposure time, measurements through identification of percentage area on the flame and film recorder on high velocity are applied to obtain a VFL. There is no study in the literature with an analysis of these techniques, providing the methodology and the validity of the use of the specific parameters to capture images of the flames. Turbulent non premixed natural gas flames were stabilized in a 7.5 mm i.d. nozzle, with Reynolds number varying from 360 to 41000. The flames were confined in a metallic screen enclosure of 1.5 x 1.0 x 3.6 m to eliminate the disturbance of external flows. It is presented a study of three different techniques to determine the VFL using optical techniques. Two photographic cameras of high performance are used to capture the flame geometry. The effects of the principal optics parameters such as: focus, exposure time and sensibility ISO are analyzed. The VFL obtained with imagens of low and high exposure time are compared with a third optical technique that is based on the luminous light intensity. For the two techniques is used an algorithm that is applied in a commercial software to measure the length for several images. The third technique uses a Software specialized (DaVis 8.2 ®) in analysis of flames. It is shown that the two principal techniques presents a maximum difference of 10%. The technique with high exposure time presents an advantage of needing a short time of process data for VFL. The technique with low exposure time is applicable when the observation of the flame stability is required. With DaVis 8.2 it is obtained VFL about 20% smaller than the previous.
Keywords
turbulent flames, flame length, optical visualization
