1.华南理工大学安全科学与工程研究所
2.广东省安全生产协同科技创新中心

A novel weighted multi-point source thermal radiation model based on inversion optimization of heat source weight parameters
ZHOU Zhihang1,2, CHEN Guohua1,2
1. Institute of Safety Science and Engineering, South China University of Technology, Guangzhou, Guangdong 510640, China
2. Guangdong Provincial Science and Technology Collaborative Innovation Center for Work Safety, Guangzhou, Guangdong 510640, China
Abstract

In order to solve the problem of over-simplified weight distribution of heat source in the original weighted multi-point source thermal radiation model (WMPM), a series of medium-scale natural gas jet fire experiments were conducted, in which heat release of 3.5 MW and the flame Froude number of 4.46 were both considered. Based on the experimental data about the length characteristic parameters and near field thermal radiation of jet fire, the Chicken Swarm Optimization (CSO) algorithm was utilized to invert and optimize the weight distribution parameters of heat sources in the WMPM and explore the influence of test conditions on weight parameters. The optimization results showed that with an increase in flame Froude number, the axial position for peak weight of heat source decreases gradually and the weight distribution of heat source at the both sides of the peak weight becomes balanced gradually. In addition, it was found that the weight distribution of heat source along the relative axial position of the flame can be characterized properly by a double exponential function. The constant coefficients in the double exponential function vary linearly with flame Froude number. Furthermore, a correlation describing weight distribution of heat source associating with flame Froude number was proposed. On this basis, a novel WMPM was thus developed. Compared to the original WMPM, the novel WMPM can significantly improve the prediction accuracy of thermal radiation in the near field of jet fire. In this test, the relative average deviation of prediction results was found to be reduced to 7.68% from the previous 12.87%, while the maximum relative deviation was down to 14.69% from the previous 19.83%.

Keyword: Jet fire; Heat source weight; Inversion analysis; Heat radiation; Chicken Swarm Optimization (CSO) algorithm; Flame Froude number; Medium-scale experiment; Mass flow rate
0 引言

1 天然气喷射火实验
1.1 实验系统装置

 Figure Option 图1 天然气喷射火实验系统示意图

1.2 实验工况设计

2 基于CSO算法的热源权重参数反演优化
2.1 热源权重参数反演优化问题描述

Hankinson等[40]提出的权重多点源模型的基本公式为：

2.2 CSO算法及目标函数

3 优化结果分析与新权重多点源模型建立
3.1 喷口质量流速对热源权重的影响规律

 Figure Option 图2 直径10 mm喷头工况下热源权重分布特征图

 Figure Option 图3 常系数a、b、c与质量流速变化规律图

3.2 基于Frf的热源权重分布关系式

Frf是表征火焰受浮力控制与动量控制作用程度的无量纲参数, 其常用于描述火焰几何特征的变化规律。同时, Zhou等[41]通过量纲分析发现Frf与热辐射分数存在直接关联, 并提出了可适用于不同气体燃料和不同混合比例气体燃料的热辐射分数预测关系式, 该预测关系式很好地表征Frf与燃烧过程中热辐射作用特性之间的负相关趋势规律。而热源权重分布特征主要也是受火焰几何特征和热辐射作用特性两个方面的影响。因此, 笔者将探究各工况的Frf与热源权重分布特性之间的影响关系, 以期定量描述其变化规律。

 Figure Option 图4 常系数与Frf之间关系图

3.3 新权重多点源模型的近场热辐射预测结果分析

 Figure Option 图5 新模型、原模型预测结果相对偏差对比图

4 结论

1）随着出口火焰弗劳德数的增大, 热源权重峰值出现的轴向相对位置逐渐下降, 峰值两侧的热源权重分配逐渐变得均衡; 热源权重沿火焰轴向相对位置呈现双指数函数分布特征, 且该双指数函数中常系数与各工况的火焰弗劳德数之间呈现较好的线性变化关系, 提出基于火焰弗劳德数的热源权重分布关系式, 建立基于该热源权重分布关系式的新权重多点源模型。

2）实验测得热辐射值与模型预测值的对比结果表明, 新权重多点源模型预测结果平均相对偏差的平均值由原模型预测结果的12.87%降至7.68%, 新权重多点源模型预测结果最大相对偏差的平均值由原模型预测结果的19.83%降至14.69%。新权重多点源模型的适用范围为浮力主控转动量主控过渡区天然气喷射火, 对于是否适用于其他气体燃料或气液两相燃料、以及完全动量控制喷射火等情形有待进一步探究。