<link rel="stylesheet" href="styles.cf390c6bfbe7555f.css">

學術出版;;Publications

Permanent URI for this communityhdl:11536/1

收集所有交通大學研究人員與學生個人或團體所發表之各項學術著作，涵蓋期刊論文、教師專書、學位論文等項。;;Collections of Publications of NCTU Researchers and Students Like Journal Papers and Thesis.

Browse

🏛️國立陽明交通大學機構典藏

Author: search.filters.author.Chen, CHSubject: search.filters.subject.flame spread

Search Results

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item type:Item,
    Numerical analyses for radiative autoignition and transition to flame spread over a vertically oriented solid fuel in a gravitational field
    (2000)
    Lin, PH
    ;
    Chen, CH
    ;
    機械工程學系
    ;
    Department of Mechanical Engineering
    This study numerically investigates the ignition behaviors of vertically oriented cellulosic materials subjected to a radiant heat flux in a normal gravitational field. The entire process is delineated into two distinct stages. In the heating up stage, the maximum temperature increases with time but at a decreasing rate because of the pyrolysis reaction. The flame development stage consists of ignition and transition processes. In the ignition process, the maximum temperature in gas phase increases dramatically within a short period of time because a large amount of heat is generated from chemical reaction of the accumulative, flammable mixture. The flame is in a transition from a premixed flame to a diffusion one, except for the small region around the flame front. For the effect of varying the heating duration on ignition behavior, prolonging the imposed radiative heat time leads the ignition from a transition one to a persisting ignition. The effect of varying the solid fuel thickness indicates that the ignition delay time increases with an increase of solid fuel thickness while delta(S)less than or equal to 1.802. For 1.802 less than or equal to delta(S)less than or equal to 3.244, the ignition delay times remain constant. Finally, if the external heating rate is the same order as the heat diffuse rate, the ignition delay time increases with an increase in solid fuel thickness.
  • Thumbnail Image
    Item type:Item,
    Numerical analyses for radiative ignition and transition to flame spread over a horizontally oriented solid fuel in a gravitation field
    (2001)
    Lin, PH
    ;
    Fan, WF
    ;
    Chen, CH
    ;
    機械工程學系
    ;
    Department of Mechanical Engineering
    This study numerically investigates the ignition behaviors of horizontal-oriented cellulosic materials subjected to radiant heat flux under a natural convective environment. This process can be divided into two stages: (1) the heating-up stage, during which the maximum temperature increases with time and (2) the flame development stage, consisting of the ignition and transition processes, The ignition process is marked with a sharp increase in maximum temperature. Meanwhile, the flame is in a transition from a premixed flame into a diffused one. In the transition process, the flame propagates upstream, forming a so-called opposed flame spread. There is a time lag between solid fuel pyrolysis and the gas-phase chemical reaction. The pyrolysis front overtakes the flame front in the initial heating-up process. As soon as the flammable mixture ahead of the flame front is ignited, the flame moves forward quickly, moving ahead of the pyrolysis front. The ignition delay time is shorter for a horizontal solid fuel than for a vertical solid fuel under the same environment, because the resultant high-temperature region is not cooled and the flammable mixture is not diluted by the induced flow in a horizontal solid fuel. For the effect of changing gravity, the ignition delay time decreases with a decrease in gravity level, owing to the smaller induced flow velocity.
  • Thumbnail Image
    Item type:Item,
    Downward flame spread over a thick PMMA slab in an opposed flow environment: experiment and modeling
    (2003-03-01)
    Wu, KK
    ;
    Fan, WF
    ;
    Chen, CH
    ;
    Liou, TM
    ;
    Pan, IJ
    This work investigates experimentally and theoretically the downward spread of a flame over a thick polymethylmethacrylate (PMMA) slab with an opposed flow of air. Simulation results, using an unsteady combustion model with mixed convection, indicate that the ignition delay time increases with a decreasing opposed-flow temperature or increasing velocity. The ignition delay time is nearly constant at a low opposed flow velocity, i.e., (u(&INFIN;)) over bar less than or equal to 30 cm/s. Experiments were conducted at three different opposed flow temperatures and velocities, namely, (T-i) over bar = 313, 333, and 353 K and (u(&INFIN;)) over bar= 40, 70, and 100 cm/s, respectively. Measurements included the flame-spread rate and temperature distributions, using thermocouples and laser-holographic interferometry. The qualitative trends of the flame-spread rate and thermal boundary layer thickness, as obtained experimentally and from numerical predictions, were identical. For a quantitative comparison, the predicted and experimental flame-spread rates correlated well with each other, except at the lowest velocity ((u(&INFIN;)) over bar = 40 cm/s). The discrepancies between the measured and predicted thermal boundary layer thicknesses decreased with an increasing flow velocity. The quantitative agreement with a high velocity indicates that the spread of an opposed flame is mainly controlled by the flame front, whereas the discrepancies at low flow rates demonstrate the importance of radiation, the finite length of the fuel, and also three-dimensional effects, which were not considered in the model. The temperature profiles around the flame front measured by interferometric photographs indicate a recirculation flow there, as predicted by the simulation. (C) 2003 The Combustion Institute. All rights reserved.
  • Thumbnail Image
    Item type:Item,
    Radiation effects for downward flame spread over a thermally thin fuel in a partial-gravity environment
    (2004-11-01)
    Wu, KK
    ;
    Chen, CH
    ;
    機械工程學系
    ;
    Department of Mechanical Engineering
    This study explores the effects of radiation on a downward flame spread over a thermally thin solid fuel in a partial-gravity environment. The radiation effect and gravitational field strength (g) are predicted not to influence the ignition delay time. The flame-spread rate reaches a maximum at g = 0.01. At g > 0.01, the flame stretch effect dominates the behaviors of the flame. Radiation heat transfer and oxygen transport control the flame behaviors for g < 0.01. The predicted quenching limit is g = 5 x 10(-6), close to the value obtained experimentally elsewhere. Radiation has two simultaneous effects. One is to reduce the flame strength by carrying heat to the ambient. The other one is combined with upstream conduction to enhance the total forward heat transfer rate and thus preheat virgin fuel upstream. The solid fuel temperature is low and some fuel is left over in low gravity due to radiation loss. Energy analyses indicate that the conduction heat flux from the flame (<(q(c))over bar>) dominates its behaviors. However, radiation gradually competes with (q(c)) over bar as the gravity is reduced.