IMPACT OF DISPERSION OF WATER DROPS ON THE EFFICIENCY OF FIRE EXTINGUISHING OF COMBUSTIBLE LIQUID

Depending on the size of water drops, the process of fire extinguishing is focused either on the burned zone, or on the surface of a burning liquid. The water drops that are smaller than 150 µm evaporate completely in the burned zone which lowers the temperature to the critical value called the flash point. Temperature reduction in the burned zone reduces the speed of vapour inflow. The current paper considers two variants of solving heat-balance equation. The first one views temperature reduction of the surface of combustible liquid (CL) to the temperature lower than the fuel flash point at which the burning stops. The second one analyzes the reduction of burnout velocity to the ignorable quantity, at which air-vapor mixture becomes non-combustible. The difference in size of water drops changes its area of influence on a burning object. Finely dispersed water with an average drop size lower than 100 µm predominately influences the burning zone and completely evaporates there. The water drops larger 0.5 mm evaporate only partially in a gas phase and mainly influence the burning surface of solid combustible materials or CL. As a result of solving heat-balance equation, the following conclusion was made: the drops of 100 µm in size will completely evaporate in the burning zone with extent of 1 m if the flying speed is even 16 mps (acc. to Stokes v = 3 mps); whereas the drops of larger size will evaporateonly partially.