A study on fire suppression mechanism in tall halls by long-throw sprinkler

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A study on fire suppression mechanism in tall halls by long-throw sprinkler


Author: Dong, Xue
Title: A study on fire suppression mechanism in tall halls by long-throw sprinkler
Degree: Ph.D.
Year: 2016
Subject: Fire extinction.
Fire sprinklers.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Building Services Engineering
Pages: xv, 238 pages : color illustrations
Language: English
OneSearch: https://www.lib.polyu.edu.hk/bib/b2904148
URI: http://theses.lib.polyu.edu.hk/handle/200/8572
Abstract: Designing fire suppression in tall and large spaces is a challenge. Tall and large spaces typically contain large fire loads that can lead to a rapid increase in temperatures during an accidental fire. Conventional fire suppression systems are not able to extinguish fires in tall and large atria. The water droplets distinguished from sprinkler systems can either be vaporized or carried away by the fire-induced hot air currents in tall and large spaces. In this thesis, the fundamental principles of rapid and effective fire extinguishment, the major findings and limitations of existing sprinkler systems widely used were identified first. A side-wall long-throw sprinkler system is then proposed. The characteristics of the system including their structure, flow coefficient, operating pressure, sprinkler head distance and installation height were then studied. The experimental portion of the study was started by establishing the key experiment parameters for the long-throw sprinkler, including the use of a 10 MW fire. Appropriate wood cribs were selected as the experimental fire in this study. The heat release rate characteristics for different arrangements of wood cribs with different numbers of wood cribs and placements were explored. Tests were conducted on the water distribution qualities of sprinklers in a hall with different installation heights of 6 m, 8 m and 10 m under operating pressures of 0.2 MPa, 0.35 MPa, and 0.5 MPa respectively. The results were used to justify numerical simulations. Experimental results are then correlated with the most desirable water distribution characteristics for proposing design practices. The Computational Fluid Dynamics (CFD) model Fire Dynamics Simulator (FDS) was then used to study the performance of proposed side-wall long-throw sprinkler systems. Two sets of four scenarios on sprinkler fire were adopted for CFD-FDS simulation. The size distribution of water droplets, sprinkler flow effectiveness, sprinkler head design, fire extinguishing system activation time and heat transfer characteristics between smoke and sprinkler water droplets were studied. For medium hazard classes, sprinklers with flow coefficients 115 and 161, installation heights higher than 10 m and operating pressure of 0.5 MPa are found to be appropriate for extinguishing fires. Full-scale experiments were conducted on sprinkler fire for justifying CFD-FDS predictions. Important technical requirements for designing sprinkler for tall and large halls are the proportion of large water droplets discharged from the sprinkler system reaching the fire. The concept of Actual Delivered Density and Required Delivered Density were applied to evaluate the performance of sprinkler systems. Results from full-scale experiments are consistent with those from the mathematical models.

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