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Title: A spray flame propagating in a nonadiabatic duct with varying cross-sectional area

Abstract

The influence of flame stretch, preferential diffusion, internal heat transfer, and external heat loss on the extinction of dilute spray flames propagating in a nonadiabatic duct with varying cross-sectional area is analyzed using activation energy asymptotics. A completely prevaporized mode and a partially prevaporized mode of flame propagation are identified. Internal heat transfer, resulting from droplets gasifying, varies with the liquid-fuel loading and the initial droplet size in the spray and also provides internal heat loss for rich sprays but heat gain for lean sprays. A spray flame propagating in a divergent (convergent) duct experiences positive (negative) stretch. The results show that the burning intensity of a lean (or rich) spray is enhanced (or reduced) with an increased liquid-fuel loading or smaller initial droplets. The positive stretch coupled with the effects of the Lewis number (Le) weakens a lean methanol-spray flame (Le>1), but intensifies a rich methanol-spray flame (Le<1). For a positively stretched flame with Le<1 or a negatively stretched flame with Le>1, without external heat loss, no extinction occurs by increasing the stretch. However, irrespective of heat loss, a flame with Le>1 experiencing positive stretch or a flame with Le<1 enduring negative stretch can be extinguished by increasing themore » stretch. Flame extinction characterized by a C-shaped curve is dominated by stretch or external heat loss. Note that for a methanol-rich spray flame (Le<1) experiencing positive stretch and enduring a partially prevaporized spray composed of a large enough liquid loading and sufficiently large droplets, an S-shaped extinction curve can be obtained. The S-shaped curve, which differs from the C-shaped one, indicates that flame extinction is governed by internal heat loss.« less

Authors:
 [1];  [2];  [3]
  1. Department of Mechanical Engineering, Hsiuping Institute of Technology, Taichung, Taiwan 412 (Republic of China)
  2. Department of Mechanical Engineering, Kun Shan University, Tainan, Taiwan 71003 (Republic of China)
  3. Department of Mechanical Engineering, National Cheng Kung University, Tainan, Taiwan 70101 (Republic of China)
Publication Date:
OSTI Identifier:
20685992
Resource Type:
Journal Article
Resource Relation:
Journal Name: Combustion and Flame; Journal Volume: 144; Journal Issue: 1-2; Other Information: Elsevier Ltd. All rights reserved
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; FLAME PROPAGATION; DUCTS; SIZE; DIFFUSION; HEAT TRANSFER; HEAT LOSSES; SPRAYS; METHANOL; DROPLETS

Citation Formats

Tsai, Chih-Hsin, Hou, Shuhn-Shyurng, and Lin, Ta-Hui. A spray flame propagating in a nonadiabatic duct with varying cross-sectional area. United States: N. p., 2006. Web. doi:10.1016/j.combustflame.2005.08.006.
Tsai, Chih-Hsin, Hou, Shuhn-Shyurng, & Lin, Ta-Hui. A spray flame propagating in a nonadiabatic duct with varying cross-sectional area. United States. doi:10.1016/j.combustflame.2005.08.006.
Tsai, Chih-Hsin, Hou, Shuhn-Shyurng, and Lin, Ta-Hui. Sun . "A spray flame propagating in a nonadiabatic duct with varying cross-sectional area". United States. doi:10.1016/j.combustflame.2005.08.006.
@article{osti_20685992,
title = {A spray flame propagating in a nonadiabatic duct with varying cross-sectional area},
author = {Tsai, Chih-Hsin and Hou, Shuhn-Shyurng and Lin, Ta-Hui},
abstractNote = {The influence of flame stretch, preferential diffusion, internal heat transfer, and external heat loss on the extinction of dilute spray flames propagating in a nonadiabatic duct with varying cross-sectional area is analyzed using activation energy asymptotics. A completely prevaporized mode and a partially prevaporized mode of flame propagation are identified. Internal heat transfer, resulting from droplets gasifying, varies with the liquid-fuel loading and the initial droplet size in the spray and also provides internal heat loss for rich sprays but heat gain for lean sprays. A spray flame propagating in a divergent (convergent) duct experiences positive (negative) stretch. The results show that the burning intensity of a lean (or rich) spray is enhanced (or reduced) with an increased liquid-fuel loading or smaller initial droplets. The positive stretch coupled with the effects of the Lewis number (Le) weakens a lean methanol-spray flame (Le>1), but intensifies a rich methanol-spray flame (Le<1). For a positively stretched flame with Le<1 or a negatively stretched flame with Le>1, without external heat loss, no extinction occurs by increasing the stretch. However, irrespective of heat loss, a flame with Le>1 experiencing positive stretch or a flame with Le<1 enduring negative stretch can be extinguished by increasing the stretch. Flame extinction characterized by a C-shaped curve is dominated by stretch or external heat loss. Note that for a methanol-rich spray flame (Le<1) experiencing positive stretch and enduring a partially prevaporized spray composed of a large enough liquid loading and sufficiently large droplets, an S-shaped extinction curve can be obtained. The S-shaped curve, which differs from the C-shaped one, indicates that flame extinction is governed by internal heat loss.},
doi = {10.1016/j.combustflame.2005.08.006},
journal = {Combustion and Flame},
number = 1-2,
volume = 144,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • It is shown that the nonadiabatic premixed flame propagating through zero-mean, time-independent, periodic shear flow is quenched provided the flow-field intensity exceeds a certain critical level. In the nearly quenched flame at the points of its highest stretch, where the flame temperature is lowest, the stretch intensity appears to be independent of the flow scale, provided the latter is large enough. It is argued that the results obtained may be relevant to the experimentally known phenomenon of flame quenching by turbulence.
  • We can calculate the heat transfer in ducts of arbitrary cross section with the definition of the equivalent diameter only in turbulent flow. In laminar flow, it is not sufficient to define an equivalent diameter, because the boundary layer of each wall is influenced by another wall. Therefore, one needs additional quantities to describe the heat transfer and pressure drop. This is shown for pressure drop calculations by Yilmaz and heat transfer for constant wall temperature by Yilmaz and Cihan. In these works, by using other quantities, it was possible to obtain general equations for pressure drop and heat transfermore » for constant wall temperature. In the present work, an equation for heat transfer for the boundary condition of constant heat flux at the wall for laminar developed flow in ducts of arbitrary cross-sectional area is given. 14 refs., 1 fig., 4 tabs.« less
  • A computer method that calculates tracheal cross-sectional area by compensating for partial volume averaging was developed and validated in a study with phantoms. The program was then used to determine the tracheal cross-sectional area of 30 normal children who ranged in age from four months to 18 years. CT-derived cross sections were correlated with age, height, weight, and body-surface area, and they were compared with findings of published clinical and post-mortem studies. CT cross-sectional areas ranged from 20 to 275 mm/sup 2/, varied by as much as 22% at the three different tracheal levels studied, and appeared to correlate mostmore » closely with body height. CT-derived tracheal cross-sectional areas are quite similar to those in published reports of postmortem and clinical studies. Measurements of tracheal cross section by CT may prove useful in quantitating tracheal compromise by intrinsic or extrinsic causes.« less