Evolution Behaviors Of Characteristic Parameters Of Fire Plume And Ceiling Jets Driven By Difform Nozzle Jet Fire Sources

Most of the fires occurred in the real world can be approximately divided into three types from the dimensions of fire source:axisymmetric fire, rectangular fire and line fire. It can be considered as axisymmetric fire when the long side is equal to the short side of the fire source while it can be dealt with line fire when the long side is much larger than the short side of the fire source. The fire dimensions fall between these two types are the general rectangular cases. For example:The fire due to gas leakage from a broken valve of pipeline can be considered as a axisymmetric fire; The feeder cable fire can be considered as a line fire; the forest surface fire spreading can also be dealt with the line fire theory; the flame ejecting behavior from a building facade opening can be considered as an axisymmetric fire or a line fire according to different real situations. A lot of research results about axisymmetric fire have been reported in the past years because it is easy to analyze. However, the study on the line fire is relatively rarer than that about axisymmetric fire. In addition, the investigation about the fire driven by rectangular fire sources are also few. So, it is necessary to study the fire characteristics of fires driven by difform nozzle fire sources and give the unified rules of them.Firstly, we study the flame height and axial temperature distribution of jet fires driven by rectangular sources with aspect ratio ranging from1:1to1:71. Secondly, we research the flame extension length and the temperature distribution of ceiling jet flow induced by axisymmetric fire and the temperature distribution of ceiling jet driven by weak line fire flume. Then, we reveal the differences between these two types of ceiling jets. Finally, we expand the research results to the hypobaric hypoxia environment in high altitude. The major findings include:Comprehensive experimental work was carried out to study the flame height of jet fire produced by rectangular equal-area nozzles with different aspect ratios. First of all, we verify the applicability of the theoretical results deduced by Quintiere and Grove using the experimental data of rectangular nozzle with aspect ratio of1:1. Meanwhile, this also can prove the credibility of our experimental results. Then, the value of C1is obtained through the data fitting of experimental data for each rectangular nozzle whose aspect ratio varied from1:2to1:71. Finally, an explicit model is established to predict the flame height based on the implicit correlation. Results show that:For the axisymmetric fire, the value of C1in this work are in good agreement with Quintiere and Grove have proposed; However, the value of C1needs not to transit from0.179to0.444with decreasing of aspect ratio from1:1to1:71. The value of C1can be taken as a constant, which implies that the entrainment coefficient is nearly the same for both axisymmetric fire source and line cases; the flame height can be well collapsed by the proposed explicit model.The axial temperature profiles of buoyant plume driven by fires produced by rectangular sources are investigated in this paper. We assume that the centerline Froude number of a buoyant plume can be presented by source Froude number which is related to the fuel exit velocity. Then, we theoretically deduced the axial temperature profiles correlations based on this assumption. Immediately following, the correlation to predict centerline Froude number as well as the range of its application is given based on experimental data. In the end, the comparison of experimental data and the theoretical correlation shows that the axial temperature profiles of buoyant plume can be well described by the new proposed model.The evolution behaviors of smoke movement of the ceiling jet flow induced by a fire plume impinging upon a ceiling are studied in this thesis. Experiments have been conducted to investigate the ceiling temperature profiles and the flame extension length under the ceiling for ceiling jets driven by strong axisymmetric fire plume. New predictive model for flame extension length is established and a modified model about temperature profiles based on weak plume driven ceiling jets’correlations is proposed. The line source plume driven ceiling jets have also been studied and the temperature distribution profiles are discovered. Finally, the differences between these two kinds of fire sources induced ceiling jets are discussed. It should be noted that the ceiling temperature induced by the line fire is usually lower than that of the axisymmetric fire under the same fire situation. This means that the fire produced by a line source is more difficult to be detected by the traditional fire detectors equipped at the roof of the buildings.At last, we investigate the flame height, the axial temperature and the ceiling flow characteristics of rectangular jet fire under a hypobaric hypoxia environment in plateau (Tibet Lhasa city at a high altitude). The experimental data in both Hefei and Lhasa have been compared. Based on the phenomenon of weakened entrainment in Tibet Lhasa, the correlations about flame heights, centerline temperature profiles and ceiling jets established in normal atmosphere are expanded to this hypobaric hypoxia environment. It is found that the coefficient Cf in the explicit model for flame heights and C/β in temperature correlations are both higher in Lhasa than that in Hefei In addition, this paper gives the value of an important coefficient n (ratio of oxygen entrained into fire and oxygen needed for combustion) in Lhasa. Finally, a global model to predict temperature distribution of ceiling flow driven by line source weak buoyant plume in these two ambient atmospheric pressures are proposed. The conclusions would be significant for the regularity and prevention of fire in high latitudes.