MODELING OF FIRE EXTINGUISHING WITH METAL GRIDS IN THE FDS PROGRAM

Source abstract

The use of metal grids to extinguish flames is based on the mechanism of intensive heat dissipation in narrow channels, which necessitates the validation of numerical models to predict the effectiveness of grid fire barriers on foci of various scales. The paper presents the results of comparing laboratory experiments on extinguishing a diffusion flame of ethanol in a crucible with a diameter of 2.2 cm with metal grids with different cell sizes (0.1, 1.0 and 6.0 mm) and feed rates (from 0.015 to 1.5 m/s) with numerical simulation data in the Fire Dynamics Simulator (FDS/PyroSim) software environment. It has been experimentally established that for fine-mesh grids (0.1 and 1.0 mm), extinguishing is achieved over the entire studied range of contact times, whereas for a grid with a cell of 6 mm, gorenje stops only at a minimum speed (contact time of at least 0.13 s), which confirms the critical role of the duration of heat removal. The developed numerical model, which implements the method of discrete displacement of solid-state obstacles (OBST) using the logical functions DEVC and CTRL, showed qualitative and quantitative compliance with field data. As a result of the simulation, it was determined that for a grid with a cell of 0.1 mm, gorenje occurs at a heat flux density on its surface of the order of 20 kW/m2. The results obtained demonstrate the fundamental possibility of using CFD modeling in the FDS environment to analyze the thermal effect of metal grids on small flames and create the basis for further validation of the model on larger-diameter foci in order to develop a scientifically sound scaling technique for real objects.