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УДК 551.557.59
Gekkieva S.
High-mountain Geophysical Institute, Nalchik, Russia
THEORETICAL STUDIES OF INCREASING THE EFFICIENCY OF REAGENTS FOR THE IMPACT ON CLOUDS AND FOG
Abstract
More than 80 countries are conducting research on artificial weather change, among which the most advanced are Russia, China, Australia, France, Israel, the United States, Thailand and India. In the last century, based on the analysis of field and laboratory experimental data, as well as the results of theoretical calculations, the concept of impact on hail processes was developed, which later became the basis for the development of means and methods for protecting crops from hail damage. In this regard, the question of conducting experimental and theoretical studies of the effectiveness of various classes of reagents when they are used in newly developed technical means of actively influencing cloud processes becomes extremely relevant.
Keywords:
active influences, reagent, nanoparticles, ice-forming nuclei.
At present, having reliable information about the current state of the natural environment, forecasts and warnings about adverse natural phenomena, it is possible to prevent or reduce the losses caused by these phenomena, and with the correct and early use of this information, to achieve a great economic effect. Also, the problem of active influence on clouds and fogs is of great interest from the point of view of ensuring the safety of aviation, increasing the amount of precipitation artificially in areas of insufficient moisture, and in order to prevent hail. However, the thing is that atmospheric phenomena and processes have enormous energy [1]. It follows that the direct way of influencing atmospheric phenomena and processes cannot lead to positive results. But taking into account that these phenomena and processes have one feature - there may be cases of their unstable state, when a relatively small (in terms of energy) push is enough to direct the development of the process along the path we need, when a self-developing reaction occurs. Thus, the introduction of a certain amount of special substances into a supercooled cloud leads to a self-developing reaction, ending with the scattering of the cloud and precipitation [1].
In 1946, American chemist Vincent J. Schaefer used a Fair Child monoplane to seed dry ice (solid carbon dioxide) on top of clouds to form snow due to supercooling, and thus performed the first scientific experiment with supercooled clouds. In the same year, another American scientist, Bernard Vonnegut, discovered that silver iodide (AgI) could produce large amounts of ice crystals in a cloud of supercooled water. The discoveries of Schaefer and Vonnegut gave rise to a new era of scientific activity on artificial weather modification. The basis of modern scientific ideas about the physical processes leading to precipitation from supercooled clouds is currently based on the theory developed by A. Wegener, T. Bergeron and V. Findeisen. The theory is based on the fact known from physics that the elasticity of saturated vapors over ice is less than over water at the same negative temperature. It is known that the difference between the saturation elasticities over water and ice reaches a maximum at -12°C and decreases again with a further decrease in temperature [2]. Due to the difference in saturation elasticity over water and ice, ice crystals in a supercooled cloud are in a state of supersaturation, which contributes to their growth. The supply of water vapor in the space surrounding the crystals decreases, the droplets are in a state of undersaturation and begin to evaporate. There is a peculiar mechanism of "distillation" of water vapor from drops to crystals. As a result of "distillation", the crystals grow rapidly and, upon reaching the size of the particles of precipitation, begin to fall under the influence of gravity, continuing to grow in the process of their fall due to coagulation. Falling below the zero isotherm, ice particles begin to melt and fall to the ground in the form of rain, snow, grains or hail. The process of "distillation" of water vapor in the cloud continues
until all the droplets evaporate or until all the crystals grow to the size of precipitation particles and fall out of the cloud. Thus, the provisions formulated by A. Wegener - T. Bergeron - V. Findeisen are the physical basis for modern methods of active influence on supercooled clouds. Indeed, taking into account that in most natural clouds there is a lack of natural ice cloud cores, by creating additional crystals in supercooled clouds, it is possible, depending on their number and place of introduction, to control the development of clouds, i.e. either increase the efficiency of precipitation processes and thereby obtain additional precipitation, or carry out intensive seeding of the cloud with crystallizing reagents and, due to powerful glaciation of the cloud, reduce or completely stop precipitation from it, or redistribute precipitation zones, their intensity and quantity.
A large class of organic compounds (pollen of plants and flowers in the composition of resins, steroids and essential oils) that do not have such a crystal structure, as well as particles of any substances, if they are artificially brought to deep cooling, have a high crystallizing ability (for example, particles of ice, quartz sand, dust). For example, the bacteria Pseudomonas siringae and Ervina herbicola, which multiply on plant leaves, are active centers of ice crystallization starting from a temperature of -2°C [3]. The basis on which water molecules are stacked, forming ice crystals, is a special phospholipid protein found on the surface of bacterial cells. The phospholipid molecule consists of a polar hydrophilic (soluble) head of the phosphate group and two tails (Fig. 1), the soluble surface of the phospholipid protein favors the precipitation of H2O molecules and the formation of a crystal-like surface film of water.
Figure 1 - The structure of phospholipid molecules, explaining the formation of a water film on their surface
Silver iodide and phospholipid proteins belong to completely different classes of substances, but their particles exhibit a high crystallizing ability. This, apparently, is due to two common properties - the low solubility of particles and the hydrophilicity of their surface, which promotes the adsorption of water molecules, the formation of several (up to 20 or more) monolayers of molecules, and the formation of a water film that freezes at low temperatures. That is, the main mechanism of crystal formation on AgI particles and phospholipid molecules is condensation-freezing [3].
Figure 2 - Crystal structure of ice and AgI
Recall that ice-forming reagents include substances whose aerosol particles are capable of creating ice crystals on themselves in a supercooled cloudy environment. In particular, most of the identified organic ice-forming substances cannot in principle be transferred to a highly dispersed aerosol state without decomposition, since the main method for obtaining such aerosols is thermal condensation, in which the substance is first transferred to a vapor state, followed by its sharp cooling. Usually in practice this is achieved by burning a pyrotechnic composition or a solution of a flammable liquid containing an ice-forming substance. To date, a number of technological limitations have led to the fact that in the practice of active influences, only the most active reagent, silver iodide, is used. At the same time, the effectiveness of silver iodide when interacting with a supercooled cloudy environment at a temperature of minus 6°C and above falls. Therefore, in recent years, the efforts of researchers have been directed to studying the possibilities of increasing the ice-forming properties of AgI. The presence of such possibilities is indicated, for example, by the fact that the ice-forming efficiency of pyrotechnic compositions based on silver iodide strongly depends on the production technology of the compositions, on the dispersion of the components included in the composition, on the terms and conditions of storage of pyrotechnic products, etc. It should be noted that at present it is extremely difficult to theoretically reveal the influence of such factors on the ice-forming efficiency of compositions. Therefore, increasing the efficiency of pyrotechnic compositions is mainly achieved by experimental selection of components for each particular pyrotechnic product. So, in particular, in recent years, laboratory experiments have been carried out, where finely dispersed zinc powder with particle sizes from 0.01 - 0.05 mm is introduced into the initial pyrotechnic composition AD-1 in relation to its total mass - respectively 3%, 6% and 9 %.
In works [6,7] it is presented that the presence of finely dispersed zinc powder in the composition of the initial ice-forming fuel in relation to the total mass of the composition of 6% sharply increases the yield of ice-forming particles in the entire range of accepted temperatures, ranging from zero to minus 14 °C Such an increase in the yield of active ice-forming particles in the temperature range under study is explained by the fact that at a high combustion temperature of the pyrotechnic composition, zinc oxide nanoclusters of various modifications and sizes are formed, which actively interact with a supercooled cloudy medium in the accepted temperature range. Due to their phenomenal properties and their combinations, the use of zinc oxide nanoclusters will improve the ice-forming properties of reagents and reach a higher technical level in the development of new reagents.
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© Gekkieva S., 2023
