Measuring Firebrand Heat Flux with a Thin-Skin Calorimeter.

Area of Science:

• Fire Science
• Heat Transfer
• Wildland-Urban Interface Fires

Background:

• Wildland-urban interface (WUI) fires pose a growing threat, with firebrand exposure being a key, yet poorly understood, factor in fire spread.
• Quantifying the heat transfer from firebrands is essential for understanding their ignition potential and impact on fire spread.

Purpose of the Study:

• To develop and present a novel method for time-resolved heat transfer measurements of individual firebrands.
• To characterize the heat transfer dynamics of glowing firebrands under varying flow conditions.

Main Methods:

• Experiments utilized individual glowing birch disc firebrands placed on a copper thin skin calorimeter.
• Net heat flux was determined by measuring thermal energy storage and conduction losses in the calorimeter.
• Measurements were conducted across a range of air flow velocities from 0.05 m/s to 1.6 m/s.

Main Results:

• The average peak net heat flux from birch firebrands was 45 kW/m², showing no significant dependence on flow velocity.
• Total heating, duration of heating, and consumed mass of firebrands increased with increasing flow velocity.
• Data provides detailed heat transfer characteristics for disc-shaped firebrands.

Conclusions:

• While peak heat flux is independent of flow, increased airflow enhances the overall thermal impact and consumption of firebrands.
• The developed method provides crucial data for modeling firebrand ignition and spread in WUI fire scenarios.
• Findings contribute to a better understanding of fire spread mechanisms in wildland-urban interface environments.