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|Title: ||Investigation on tunnel fire phenomenon under different emergency ventilation systems|
|Other Titles: ||Bu tong jin ji tong feng xi tong dui sui dao huo zai man yan zhi xiang xi yan jiu|
|Authors: ||Se, Mei King (蘇美琼)|
|Department: ||Department of Building and Construction|
|Degree: ||Doctor of Philosophy|
|Issue Date: ||2009|
|Publisher: ||City University of Hong Kong|
|Subjects: ||Tunnels -- Fires and fire prevention.|
|Notes: ||CityU Call Number: TH9445.T8 S4 2009|
viii, 192 leaves : ill. 30 cm.
Thesis (Ph.D.)--City University of Hong Kong, 2009.
Includes bibliographical references (leaves 178-192)
|Abstract: ||In this research study, the ventilating effect on tunnel fire development has been
investigated under 4 ventilation mode throughout the tunnel: natural ventilation,
fully-transverse ventilation, semi-transverse exhaust and longitudinal ventilation
system. The investigation is performed by two means - full-scale fire test and
To investigate the first three ventilation modes, a full-scale experiment was
conducted with two different fire intensities of 0.7 5MW and 1. 5MW as stipulated in
AS4391 (1999) and the spatial temperature was recorded. The data was analyzed and
compared case by case. The experimental results have shown that the ventilation
system plays an important role on both fire development and heat removal.
Interestingly, semi-transverse exhaust ventilation system gave the lowest
temperature profile along the tunnel. To complement the experimental study,
Computational Fluid Dynamics (CFD) techniques were utilized to validate against
the measurements and give more in-depth analysis on the phenomenon. In general,
CFD can successfully capture the trend of fire development and the predicted
temperature profiles were reasonably well-matched with measurements. The mass
loss rate and stability of pressure boundaries at two ends of tunnel were found
deterministic in the accuracy of numerical results.
In the experiment setup, longitudinal ventilation system was not installed, hence, the
flow field under this ventilation mode was investigated by numerical approach.
Attention is paid on the impact of the location of active fan group on the critical
velocity because assuming an evenly distributed airflow at one end of scaled tunnel is unrealistic. The air flow field in a generic 3-lane D-shape tunnel with a fire size of
5MW was analyzed under activation of different fan groups. Highest upstream
velocity was found when the nearest fan group was activated. Moreover, the
upstream velocity exhibits second order polynomial relationship with the distance of
the active fan group from the fire source. On the other hand, sensitivity study on
changes of dimensions, orientations and nature of fire source are also performed.
Solid fire source was found to have significant effect on the upstream velocity; while
the dimensions and orientation of fire were found with minor influence. In solid fire,
the upstream velocity decreased and asymptotes at the distance 200m away from the
fire source. Such levelling-off characteristic of upstream velocity was also found
correlating with the heat release rate. In order to compensate the unexpected
decrement in upstream velocity, fan group located closer to the fire source shall be
activated to overcome backlayering. In summary, this sensitivity test has shown that
the upstream velocity was affected by some commonly neglected parameters which
could contribute to an undesirable ventilation performance. Further investigation on
other parameters in estimating critical velocity is essential in response to any tunnel
fire event in the future.|
|Online Catalog Link: ||http://lib.cityu.edu.hk/record=b2374854|
|Appears in Collections:||BC - Doctor of Philosophy |
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