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2. PHD Thesis / Tesis PHD
3. Faculty of Engineering and Built Environment / Fakulti Kejuruteraan dan Alam Bina

Title:	Empirical models of smoke behaviours under different experimental conditions
Authors:	Razeih Khaksari Haddad (P89071)
Supervisor:	Zambri Harun, Ir. Dr.
Keywords:	Universiti Kebangsaan Malaysia -- Dissertations Dissertations, Academic -- Malaysia Smoke diffusion Ventilation Backlayering
Issue Date:	12-Dec-2019
Description:	When a fire occurs in a tunnel, controlling the smoke diffusion by accurate ventilation is crucial. The smoke flow traveling against the direction of ventilation is called backlayering. The critical velocity is defined as the longitudinal velocity needed to sufficiently eliminate the backlayering. Large gaps can be recognized in the literature concerning critical velocity, backlayering characteristics and the effective parameters. There is a lack of knowledge on some specific factors such as the influence of fire source location, and vehicles on smoke flow characteristics, which are the targets of this study. The research objectives are: firstly to conduct experimental studies on fire-induced buoyant smoke temperature distribution along the tunnel ceiling, secondly to study the influence of longitudinal fire location on smoke characteristics under the tunnel ceiling and thirdly to study the influence of different vehicle blockages on smoke characteristics. Three experimental measurements were conducted. Measurements were collected at a 1:50 reduced-scale tunnel model size 3 m 0.6 m 0.95 m (L W H). The fire source is a pool filled with n-heptane and gasoline. The main tools were a ventilation fan, eight K-type thermocouples, and an Arduino board. The backlayering length is defined as the maximum distance between thermocouple above the and the thermocouple which recorded quasi-steady ambient temperature. The critical velocity is obtained by extrapolating the backlayering length-velocity curve since the critical velocity provides the backlayering length at 0 m. The fire source was located at five different distances to study the effect of the fire source location. Three vehicle sizes in two or three arrays, occupying 3-15 of tunnel cross-section in six various scenarios were used. A series of experiments were carried out to study the maximum smoke temperature and temperature decay based on a dimensionless analysis. It was found that an increase in ventilation velocity leads to temperature decrease and the fire source with a higher heat release rate causes higher maximum smoke temperature. For example, the smoke flow temperature experiences a drop of 0.4 times degrees for 34.55 kW and 1 m/s when it travels along the ceiling while it shows a decrease of 0.2 times degrees for 4.22 kW and 1 m/s. The critical velocity had a decrease between 5 and 15 when the distance between the fire source and the origin increased every 0.34 m. Furthermore, backlayering length decreased with the distance from the fire source. Based on experimental results, the maximum temperature location was between the fire source and the center of the tunnel. A proposed model for the maximum smoke temperature was finally developed which considers the horizontal gas burner (fire source) locations. This study reveals that critical velocity decreased in the case that ventilation velocity reaches the fire source directly with approximately the same percentage as blockages ratio, which is the ratio of open space to tunnel cross-section area. However, critical velocity increased when the path of ventilation flow is blocked by blockages up to 20-30. Although the backlayering length follows an exponential trend, shorter backlayering length has resulted in the existence of obstacles. For instance, for 8.98 kW and 1.4 m/s, backlayering length was 0.51 m for a scenario without blockages while it is 0.34 m for a scenario with blockages. A corrected model considering the blockage ratio was presented for the maximum temperature. This study greatly enhances the considerations for smoke management especially to aspiring nations like Malaysia where lengthy train tunnels are getting common.,Ph.D.
Pages:	157
Publisher:	UKM, Bangi
Appears in Collections:	Faculty of Engineering and Built Environment / Fakulti Kejuruteraan dan Alam Bina

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