Alena O. Zhdanova

Deformation of liquid drops moving in a gas medium

Deformation of drops (with initial characteristic sizes of 3–6 mm) of widely used liquids (water, kerosene, and ethyl alcohol) moving in air with moderate velocities (up to 5 m/s) is investigated experimentally using a high-speed (105 frames per second) video camera. The characteristic “deformation cycles” for drops are established. The duration, length, and amplitude of variation of the drop sizes in each cycle are determined. It is shown how the initial size and velocity of drops affect these characteristics. The experimental results are processed using the similarity criteria (Weber and Reynolds numbers) adopted for investigating the motion of liquid drops. The features of the processes under investigation are outlined; it is shown that the conditions and characteristics of deformation of drops are determined not only by the effect of viscous, inertial, and surface tension forces.

Thermal conditions for stopping pyrolysis of forest combustible material and applications to firefighting

Five models describing heat transfer during evaporation of the water sprayed over the forest to stop fires and to cool down the pyrolysis of the bio- top layer are established and investigated by a parametric approach. It aims to improve the understanding of the behaviour and the properties of the forest combustible material. A mathematical description of forest combustible material surfaces (needles of pine and fir-tree, leaves of birch) is established. The characteristic time, td, to cool down the forest combustible material layer below the temperature of the onset of the pyrolysis is the important parameter investigated in the present work. The effective conditions were determined allowing to reach the shortest td and the lowest consumption of e. g. water to be dropped.

Numerical Analysis of Effective Conditions of Chemical Reaction Suppression during Typical Forest Fuel Material Combustion

Three typical solution schemes of adjoint problems of heat transfer, phase transformations and chemical reaction at the forest fuel material surface were analyzed in this work. Characteristic times of thermal decomposition reaction suppression of forest fuel materials (needles of pine and fir-tree, leaves of birch) were presented for concerned heat transfer models. Effective heat exchange conditions which are characterized by minimal times of chemical reaction suppression in forest fuel materials and minimal extinguishing agents expenditure were established.

Deformation of Water Droplets at Various Initial Temperatures During Motion Through Cooled Air

Experimental investigations exploring the integral characteristics of the deformation of water droplets at various initial temperatures (280 to 360 K) in air at 275–300 K were conducted. Sizes (diameters) and motion velocities of the droplets were varied between 3 and 6 mm and 0 to 5 m/sec, respectively. High-speed (up to105 frames per second) video cameras, cross-correlation measuring systems, and panoramic optical methods (PIV and IPI) were used. The main characteristics of droplet “deformation cycles,” as well as their shapes and existence times were determined. The influence of droplet sizes and motion velocities on the characteristics of their deformation for the conditions corresponding to operation of modern cooling towers, evaporators, separating machines, irrigators, and other devices typical in gas-vapor-droplet technological cycles was established.