Flame Characteristics Of Buoyancy-Controlled Turbulent Jet Fires From Inclined Rectangular Nozzles

With the development of natural gas industry in China, the construction of pipe network system is increasingly accelerated. However, the natural gas leakage accidents occur frequently in the transportation as the long transportation distance and poor geographical circumstance, which may cause fire and explosion that will threaten the stability of our society and the security of people's property. Once the gas encounters spark or open flame, it will form jet fires. The research of jet fires has been conducted for decades of years. The researchers have made great progress in some aspects, such as flame temperature, flame height and radiation. These studies are mainly about axisymmetric jet fires in vertical or horizontal direction. There are few researches about the characteristics of jet fires form inclined rectangular nozzles. However, the natural gas pipe break sizes and location are not just axisymmetric or at the top of the pipe. The variable break sizes and location will cause the changes of flame characteristics. So it is important to carry out the studies of jet fires from inclined rectangular nozzles.Firstly, the research about flame length of buoyancy-controlled turbulent jet fires from inclined rectangular nozzles has been conducted. The length-to-width aspect ratio of nozzles is ranging from 1 to 16 with the same area. The validity of the correlation for the flame height of rectangular sources proposed by Quintiere and Grove is verified under different inclined angles. Two different placed ways of the nozzles have been considered. The value of entrainment coefficient parameter C, is obtained and the distribution of C, under two placed ways is compared. An explicit model has been proposed, which can calculate flame length at arbitrary inclined angle for any aspect ratios directly. The practicability of an existing model has been verified. However, the experimental values begin to deviate from the predictions when the flames have a high level of turbulence. Secondly, the flame temperature of buoyancy-controlled turbulent jet fires from inclined rectangular nozzles has been studied. The result shows that the axial temperature can be characterized into three regions based on axial position in the flame. The distribution about the stable stage of axial temperature is studied with the changing of aspect ratios and inclined angles of the rectangular nozzles. The virtual origin has been deduced and it is a function of flame Froude number (Frf). It is also found that the axial temperature against dimensionless height which is modified by virtual origin can be divided into three zones.