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|Title: ||Experimental and numerical study on characteristics of premixed propane-air flame in rectangular duct with a 90° bend|
|Other Titles: ||Bing wan-kong qi yu hun huo yan zai 90° wan qu guan dao nei chuan bo te xing de shi yan he mo ni yan jiu|
丙烷-空氣預混火焰在 90° 彎曲管道內傳播特性的實驗和模擬研究
|Authors: ||He, Xuechao (何學超)|
|Department: ||Department of Building and Construction|
|Degree: ||Doctor of Philosophy|
|Issue Date: ||2010|
|Publisher: ||City University of Hong Kong|
|Notes: ||CityU Call Number: QD516 .H4 2010|
xii, 146 leaves : ill. 30 cm.
Thesis (Ph.D.)--City University of Hong Kong, 2010.
Includes bibliographical references (leaves 131-144)
|Abstract: ||Because of accident or man-made causes, combustions or explosions of combustible
hydrocarbon gas occur from time to time in the production, transportation and storage
processes. These always lead to huge losses and damage. Ducts in the industrial duct
networks usually consist of non-straight sections, such as T junctions, 90°bend or
crosses. The understanding of the influence of these configurations on flame
propagation characteristics is important for industrial, operational and personnel
safety. Also flame propagation in the duct is always affected by the flow. The
interaction between flame and flow usually involves flame acceleration, flame
structure variation and flame instability. Accordingly, premixed propane-air flame
propagation in a combustion duct with a 90°bend has been investigated both
numerically and experimentally. The results of this study will offer valuable
information of the designs of hazard prevention systems including the water mist fire
suppression systems and/or inert gas systems, etc.
Firstly, the basic mechanisms of flame propagation in duct were analyzed
Secondly, a series of experiments of propane-air premixed flame in closed and
semi-closed ducts were performed.
(1) Study of the influences of initial conditions on the propagation behavior
The experiments were carried out with premixed propane and air mixture at
atmospheric conditions. High speed camera and Schlieren image technology were
used to record the dynamic process of flame propagation and flame structure variation.
Fine thermocouples, ion probes and PCB pressure transducers were distributed along
the duct to measure the experimental temperature, ion current and overpressure. The
experimental work has provided a unique data set including the effects of equivalence
ratio, pressure relief vent and ignition position which affect the flame propagation and
change of flame structure.
(2) Study of the influences of different opening areas on the propagation behavior
Different opening areas of pressure relief vent were considered when flame
propagated in semi-closed duct. The opening areas were from closed to totally open
with an incremental interval of 10% opening area. The flame propagation velocity
would be influenced by joint effects of the opening area and system pressure. Two
maximum values of flame propagation velocity in horizontal section and bend both
increased with the increase of the opening area. In the process, the flame structure
variation was mainly induced by the interaction between the flame and vortex, the
vortex’s movement and development, Rayleigh-Taylor instability, Kelvin-Helmholtz
instability and thermo-diffusion instability.
Thirdly, numerical studies were performed using the computational fluid dynamics
code - Fluent with Realizable k-ε model. The computational results agreed
qualitatively with the experimental results. The essential characteristics observed in
experiments were well captured in simulation. The primary focus of these simulations
was the interactions among the vortices, reverse flow and flame-induced flow which
directly caused the transformation of the flame structure. The computed results
indicated that for ignition in horizontal section, two developing vortices formed in this
part resulted in the formation of tulip flame, and a big recirculation region existed in
the bend induced the flame tip to move towards the upper side. For ignition in the
vertical section, the flow velocity downstream of the bend remained the same. Also, a
single upward moving vortex caused the inversion of the flame front. After it met the
upper side wall, it decayed and vanished. Fluent can therefore be used to enhance the
understanding of premixed gas flame propagation in ducts.
Key words: premixed flame, flame structure, flame acceleration, ion current, Tulip
flame, vortex effect|
|Online Catalog Link: ||http://lib.cityu.edu.hk/record=b3947503|
|Appears in Collections:||BC - Doctor of Philosophy |
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