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.