Numerical study on the effect of temperature in the retention time of an inert agent. (July 2020) - Kim, Goonho
Abstract: In a Fire Extinguishing System (FES), it is important to maintain the design concentration of the gaseous agent in the enclosure for a specific time. An inert agent, in particular, can maintain an O2 concentration below 15% by maintaining a gaseous concentration above the threshold value for a specified time, which is called the retention time. However, the current theoretical model for retention time in the inert agent reflects only species diffusion due to differences in gravity and molecular weight but not due to temperature. Therefore, this study analyzed species diffusion with temperature using IG-541, a representative inert agent. A numerical analysis was done with the assumption of a stable flow field (no bias pressure from HVAC systems), and the discharge step was eliminated for a simplified approach. As a result, the retention time of the inert agent was sensitive to species diffusion with temperature. The diffusion flux was used to analyze the influence on the inert agent temperature according to Fick's law and the slope ω according to the interface thickness. The numerical analysis could provide a basis for a new model that takes into account temperature in the future. Highlights: Species diffusivity of the inert agents is sensitive to temperature. The retention time of the inert agent depends on the temperature as well as the density. Species diffusion flux should be added to the governing equation for retention time. It can be the basis for reflecting the effect of temperature on the governing equation for the retention time.