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Heat and mass transfer resulting in eruptive jetting from stems and leaves during distillation stage of forest fire

Author(s): W. Zhang, E. Zussman, A. L. Yarin
Year Published: 2020
Description:

Forest fires are common large-scale environmental disasters with annual death toll and damages on the scale of tens of billions of dollars. They leave scars visible from space. In the context of climate change, forest fire severity is predicted to increase. Not only forest fires release significant amounts of carbon dioxide and ash to the atmosphere, but the diminishing forest area facilitates the greenhouse effect and climate change. However, the internal mechanisms of forest fires are not fully understood, which complicates their prediction, prevention and quenching. We explore a novel mechanism responsible for fuel and water vapor supply into flame in the form of volatiles-water vapor jets erupting from plants engulfed in fire. This mechanism is significantly accelerated in comparison with the ordinary-implied evaporation/sublimation and diffusion characteristic of the diffusion flames. The eruptive jets accelerate fuel supply into the flame zone and plant drying before burning, which facilitates forest fire. They also ballast the flame zone with water vapor, i.e. provide a counter-acting flame-quenching path. Epipremnum aureum stems and oak (Quercus calliprinos) leaves are used in the experiments to study volatiles and water vapor eruption from biomass burning at the distillation stage of forest fire. The eruptive jets are observed in the experiments with horizontal stems and leaves subjected to the engulfing flame, and the results are explained and predicted theoretically. As a model system, a horizontal syringe needle filled with liquids and subjected to the surrounding flame is used as a stem substitute to separate the effect of water vapor from that of combustible volatiles modeled by ethanol. The velocity and temperature of the jets erupting from the horizontal stems or needles subjected to flame are measured and predicted, with the velocity being on the scale of 10 m/s. The theory is in good agreement with the experimental data.

Citation: Zhang, W.; Zussman, E.; Yarin, A.L. 2020. Heat and mass transfer resulting in eruptive jetting from stems and leaves during distillation stage of forest fire. Experimental Thermal and Fluid Science 116:110112. https://doi.org/10.1016/j.expthermflusci.2020.110112
Topic(s): Fire Behavior, Fuels
Ecosystem(s): None
Document Type: Book or Chapter or Journal Article
NRFSN number: 21776
FRAMES RCS number: 60972
Record updated: Sep 3, 2020