Numerical investigation of expandable graphite suppression on metal-based fire

Aqueous suppression systems (i.e. fire sprinkler, water mist) have been extensively utilised for compartmental fire suppression due to their significant heat extraction ability. Nevertheless, challenges can be foreseen in suppressing water-reactive chemicals as a violent explosive reaction will be triggered, such as alkali metals (i.e. Na, Li) and alkali metal hydrides (i.e. LiH, LiAlH4). In this study, expandable graphite (EG) is proposed as a potential suppressant against alkaline metal fire due to its advantageous thermal properties and chemical stability. In-house user-defined functions (UDFs) are developed to characterise the particle expansion coupled with the heat and mass transfer process between EG and the fluid mixture. The model is incorporated in the large eddy simulation (LES) framework to study the temporal fire behaviours and the suppression effect of EG against the flame plume. The numerical model was validated by comparison of temperature profiles and expansion rate of EG particles along the suppression event against experimental results. The EG was found to be relatively effective in fire suppression compared to the same amount of natural graphite. Parametric analysis was conducted on a range of EG particle size between 400 mu m-1000 mu m to investigate the suppression mechanisms and the suppression efficiency of EG particles against metal fires. Within the range of the current study (400 mu m-1000 mu m), the EG particle diameter of 400 mu m has achieved the most effective suppression performance and the suppression time of 2 s. It is observed that the smaller size of EG tends to be effective in fire suppression than the larger sizes.

Automated summary

In this study, expandable graphite (EG) is proposed as a potential suppressant against alkaline metal fire. The model developed to study EG's performance was validated by comparing with experimental results, showing relative effectiveness of EG in fire suppression. Parametric analysis on EG particle sizes within 400-1000 μm range revealed that 400 μm EG particles demonstrated the most effective suppression performance and a suppression time of 2 seconds, indicating smaller sizes of EG tend to be more effective in fire suppression.