Movement of water drops in a forest fuel layer in the course of its thermal decomposition

Abstract

In this paper, we conducted an experimental investigation on water droplets gravitating in a layer of typical forest fuel (as illustrated by pine needle litter) in the course of its thermal decomposition. We used a high-speed (200 fps) video recording system, Tema Automotive software with continuous tracking of a moving object as well as a set of low-inertia (no more than 0.1 second) thermocouples. Similar experiments were performed at moderate temperatures (below the onset temperature of forest fuel pyrolysis, i. e. about 300 K). Two approaches were used: continuous tracking of a moving water droplet using high-speed video recording and registration of a droplet path using the readings of thermocouples placed at different levels in a forest fuel layer. We determined the typical depths of an forest fuel layer that water droplets reach with the initial volume of these droplets ranging from 90 to 900 µL. The typical velocities of water droplets were calculated at different depths of the forest fuel layer. We also determined the share of the mass of water spent in an forest fuel layer on evaporation and cooling of the material down to the temperatures below those of thermal decomposition. Finally, we identified the physical processes influencing water droplets moving through the layers of forest fuel heated up to the high temperatures similar to those of thermal decomposition.

Determination of The Minimal Amount of Water for Effective Suppression of The Thermal Decomposition of Forest Combustible Materials

“…The water droplet sizes were controled by the optical diagnostic system [7] using "Shadow Photography" (SP) method. The droplet velocities were measured by the same system using "Particle Tracking Velocimetry" (PTV) method [8].…”

Features of propagation of droplets of water and special water-based compositions in a sample of forest fuel material

“…As a consequence, it is important to carry out the processes of promotion of typical fire extinguishing liquids through the layers of typical forest combustible materials. The results of experiments with water are given in [13]. It is advisable to develop this work on the most typical fire-extinguishing compositions with specialized additives.…”

Development of the mathematical model of heat and mass transfer for researching the processes of evaporation of inhomogeneous water droplets

“…This approach contributes the development of a large range of practical applications (for example, flame cleaning of liquids [3] and polydisperse firefighting [4]). …”

“…The results of investigations [3,4] are shown that the introduction of carbon particles into water droplets intensifies several times the phase transformations of the latter in a hightemperature (more than 700 K). It is established [3] that the evaporation of a liquid droplet containing a commensurate opaque inclusion in high-temperature gases is realized according to one of two schemes: 1) evaporation only from the free (external) surface of the drop; 2) evaporation from a free surface and intensive vaporization at internal interfaces.…”