Study on fire in a forced ventilated chamber

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Study on fire in a forced ventilated chamber


Author: Yeung, Cho-hung
Title: Study on fire in a forced ventilated chamber
Degree: M.Sc.
Year: 1997
Subject: Fire prevention
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Pages: 1 v. (various pagings) : ill. ; 30 cm
Language: English
Abstract: The occurrence of fire in a forced-ventilated compartment is quite different from that of a natural-ventilated space. While the burning rate of a natural-ventilated fire is related to the ventilation factor of the opening, this is not the case for forced-ventilated fires. Air movement tends to enhance the rate of entrainment of air into a fire flame and promote combustion within the flame. Furthermore, a stable hot smoke layer may not be formed under a forced fire scenario. This work therefore aims to study the smoke layer and temperature characteristics of a forced-ventilated compartmental fire. In this project, 25 full scale burning tests on propan-2-ol were carried out inside the fire chamber at the Department of Building Services Engineering of The Hong Kong Polytechnic University. Three different forced ventilation rates namely; 0.073 m3 s-1 (19.5 times the stoichoimetric ventilation); 0.24 m3 s-1 (ventilation rate about that of an air handling unit for cooling a room of similar configuration to the fire chamber); and 0.37 m3 s-1 (99 times the stoichoimetric ventilation) were adopted to study the fire behaviours under different arrangements of air intake and exhaust vent positions, as well as mechanical/natural - intake/exhaust combinations. A control experiment under natural ventilation condition was also performed.During the course of each test, the temperature profiles inside the chamber were recorded via a set of thermocouple rack and data-logger. The temperature profiles were subsequently utilised to verify the establishment of the smoke layer and the time to quasi steady state. In addition to experimentation, the forced-ventilated fire was also studied theoretically by correlating the measured upper layer temperatures against the predicted temperatures as estimated from the methodologies in the literature. It was found that distinct hot and cool layers can generally be formed for fires with low level natural air supply/high level mechanical exhaust; fires with low level mechanical air supply/high level mechanical exhaust; and fires with low level mechanical air supply/high level natural exhaust respectively. Moreover, with mechanical air supply at low level, the layer interface height tends to increase.The Energy Balance method is shown to be a good approach in estimating the upper layer temperature of a compartmental fire whenever the heat release rate and ventilation rate are known.

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