高海拔地区低氧压条件下池火相界面传热特性及液相流的动力学机制研究

Liquid pool fires behave differently at high altitude presenting different combustion properties owing to the relative lower pressure and oxygen concentration comparing to regular pressure environment. Indeed, heat flux at the phase interface caused by flame heat feedback and its resulting liquid convection determine the heat transfer into the liquid and thus the burning rate which significantly affects the combustion properties apart from mixing. Therefore, it is worthwhile studying the flame heat feedback, heat transfer at phase interface and liquid convection in order to reveal the mechanism of variation of combustion properties under low pressures. Moreover, the flame heat feedback has strong connection with the soot formation and development in the flame therefore it has to be investigated first. By carrying out low pressure experiments for liquid pool fires, the current project aims to resolve two crucial problems: 1.Radiative heat flux at the phase interface led by soot formation inside the flame structure and, 2. Effects of liquid convection on the heat transfer at phase interface. The outcomes of the current project include several aspects as follows. Trends of soot formation and corresponding radiative heat flux can be identified from the experiments with varying pressure and oxygen concentration. The heat fluxes at the phase interface will be correlated with the ambient pressure, oxygen concentration, pool size and so on with non-linear model developed. Then the liquid convection will be obtained using both experimental and numerical methods while its effects on the overall heat transfer process inside the liquid will be quantified with mathematical models proposed. At the end, the mechanisms of variations of combustion properties under low pressure will be revealed by combining the experimental results and theoretical analysis. The outcomes will be useful to develop engineering numerical model for pool fires.

可燃液体池火因低压低氧气浓度的影响会表现出与常压条件不同的燃烧物化参数。火焰热反馈引起的相界面传热及液相流决定了液体的蒸发特性，是揭示燃烧物化参数变化机制的关键因素，因而，研究相界面传热及液相流的动力学机制具有重要的科学意义与应用价值。火焰辐射热反馈与碳黑演变过程有关，但目前其产生和发展机理尚未得到系统揭示。本项目以池火为研究对象，重点解决两个科学问题：①火焰区碳黑辐射演变的内在动力学机制，②液相流对相界面传热的影响机理。通过本项目的研究，可望得到不同压力和氧浓度下池火火焰碳黑及辐射强度的演变规律；建立相界面热流强度随环境压力、氧浓度和液池尺寸等参数变化的非线性动力学模型，揭示低压对相界面传热的作用机制；明确液相流随环境条件变化的规律，通过理论分析和数值模拟等手段，揭示液相流对热量向液池内部传递过程的影响；揭示燃烧物化参数变化的内在机理，为构建工程化液体燃烧数值模型提供理论基础。

外界环境参数变化，如环境压力和氧气浓度，会影响可燃液体蒸发及燃烧池火特征，通常会表现出与常压条件不同的物化及燃烧参数。环境参数变化引起火焰热反馈变化，进而引起的相界面传热及液相流变化，决定了液体的蒸发特性变化，这一系列的变化是揭示燃烧物化参数变化机制的关键，因此本项目开展可燃液体相界面传热及液相流的动力学机制研究具有重要的科学意义与应用价值。. 项目通过开展了高海拔地区低氧压条件下可燃液体闪点实验研究，揭示环境压力和添加水对可燃液体燃烧危险性及蒸发的影响规律；开展了高海拔地区低氧压条件下可燃液体扬沸特性实验研究，认识水-可燃液体交界面蒸发规律；开展了典型可燃液体混合池火实验研究，认识可燃液体燃烧气液相界面的蒸发特点；开展了变环境压力条件下可燃液体燃烧碳烟分布实验研究，认识可燃液体燃烧碳烟颗粒生成规律。通过以上研究内容，阐明了高海拔低压环境对可燃液体燃烧相界面传热的作用机制，揭示了环境压力对可燃液体燃烧物化参数变化的内在机理，为构建工程化液体燃烧数值模型提供理论基础。