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外因火灾通风网络风量风质失效模型与数值解算方法

Model and numerical solution method the failure of air volume and air flow components in the ventilation network during the period of external fire

  • 摘要: 为了尽可能复现火灾时期通风网络内风量波动、风流逆转、风温异常、有毒有害气体蔓延、氧气体积分数降低等灾变过程,构建了外因火灾通风网络风质风量失效物理模型,采用时序化分析方法进行了解耦处理。通过风阻、火风压、风流密度关键通风参量计算模型,将基于质量流量守恒的通风网络回路风压平衡方程、通风网络风流−围岩热量交换−传播控制方程、有毒有害气体弥散−扩散控制方程、氧气消耗−运移控制方程进行联立,构建了外因火灾通风网络“风量风向−风温−有毒有害气体体积分数−氧气体积分数”非稳定多场耦合数学模型。采用回路风量牛顿法求解通风网络风量风向变化,采用迎风离散格式的有限差分法求解通风网络内风流传热−传质过程,建立了火灾时期全风网“节点−分支−网络”风量风质失效多物理场耦合解算方法,构建了多物理场间接耦合解算流程,编写了解算程序。通过在角联结构试验巷道内开展外因火灾试验,初步验证了模型的准确性与适用性,在此基础上分别模拟了进风区分支与用风区分支火源位置情况下复杂通风网络内风量变化、风流逆转、风温异常、有毒有害气体蔓延、氧气体积分数波动的动态变化过程。模拟结果表明:火源位置在进风井条件下风量显著变化分支达到通风网络分支总数的61%,风流逆转分支数量占通风网络分支总数的11%,风温显著变化分支数量达到通风网络分支总数的76%,CO侵入分支数量达到通风网络分支总数的84%,氧气体积分数显著变化分支数量达到通风网络分支总数的41%,进风井分支发生外因火灾造成的灾害影响范围和影响强度均明显大于其他分支。

     

    Abstract: In order to eeproduced as much as possible the disaster processes such as air volume fluctuations, airflow reversal, abnormal airflow temperature, the spread of toxic and harmful smoke, and the decrease in oxygen volume fraction in the ventilation network during the period of fire occurrence, the airflow pressure balance equation of the ventilation network circuit based on the conservation of airflow mass flow rate, the control equations for heat exchange and propagation in ventilation networks, the control equations for the diffusion and dispersion of toxic and harmful gases in ventilation networks, and the control equation of the consumption and transport of oxygen component in ventilation network were constructed. Based on the theory of multi physics field coupling, the above equations were combined using key ventilation parameters such as airflow resistance, fire pressure, and air flow density to construct the multi field coupling mathematical model for an unstable ventilation network during the period of external fire, which included “air volume and airflow direction, airflow temperature, toxic and harmful gases volume fraction, and oxygen volume fraction”. Based on the Newton method of loop air volume, the variation of air volume and airflow direction in the ventilation network was solved. The finite difference method of upwind discrete format was used to solve the heat and mass transfer process of airflow in the ventilation network. The indirect coupled multi physical field solution method based on temporal logic was adopted to construct the solution process. The accuracy and applicability of the model were preliminarily verified by carrying out external fire experiments in the test roadway of the angular structure, and on this basis, the dynamic change process of air volume change, wind flow reversal, abnormal wind temperature, spread of toxic and harmful gases, and oxygen volume fraction fluctuation in the complex ventilation network under the location of the fire source of the branch in the air inlet area and the branch branch in the air consumption area were simulated respectively.The simulation results showed that under the condition that the ignition source was located in the air inlet well, the number of branches with significant changes in air volume reached 61% of the total number of branches in the ventilation network, the number of branches with significant changes in wind flow reached 11% of the total number of branches in the ventilation network, the number of branches with significant changes in wind temperature reached 76% of the total number of branches in the ventilation network, the number of branches with CO intrusion reached 84% of the total number of branches in the ventilation network, and the number of branches with significant changes in oxygen volume fraction reached 41% of the total number of branches in the ventilation network. The impact scope and intensity of disasters caused by fire in the air inlet shaft branch were significantly greater than those in other branches.

     

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