By Rashid ALIMOV, Dr. Cs. (Tech.), Kazan State Technical University; Guzel MINGALEYEVA, Cand. Sc. (Tech.), Kazan State University of Power Engineering
The progress of human civilization is inseparable from mounting energy consumption. And as we all know, the reserves of our traditional energy sources (wood, combustible shales, turf, coal, gas and oil, atmospheric wind, solar radiation, etc.) are limited due to various causes, to say nothing of their very uneven distribution around the face of this planet. New and dazzing vistas in this field were opened up with the advent of nuclear power engineering. But a really boundless "spead" of nuclear power stations is obstructed by a whole range of unresolved ecological problems and safety considerations involved. This being so, the search for and the introduction of ecologically safe and economically profitable energy sources remains a task of truly paramount importance, facing the international scientific community.
Today, technical experts are boozy trying to assess the efficiency of electricites generating units using the energy of sea and oceanic waves. Within the range of these studies we have to take a really closer look at natural phenomena like atmospheric cyclones (hurricanes, typhoons, tornadoes, etc.) which have always been and remain the indispensable "generators" of sea and oceanic waves. The thing is that having this kind of a whirlwind in what we call the hydrodynamic system, in addition to its common wind "component" and because of the greater angular velocity, it represents a vast reservoir of energy which, unfortunately, has so far been wasted on causing material damage and catastrophic destruction. For an assessment of the energy potential of atmospheric cyclones and obtaining meaningful results and conclusions (by they even of a problematic and debatable nature) one has to take a closer look at the physics of their origin and development.
BIRTH OF CYCLONE
For quite some time already experts have been studying the mechanisms of origin and development of cyclones and the regularities thereof, and quite a lot of data have been accumulated.
The most typical "birth pattern" of cyclones can be described in the following way. As is known, the Sun heats certain parts of the earth surface more than others. Masses of air warmed up by these "hot spots" rize skywards, like columns, and the process is intensified if and when such ascending currents mix up with molecules of water steam, which is lighter than air. And this is exactly the reason why most of the powerful cyclones are born over the oceans.
A low-pressure area produced in this way is "filled in" with masses of air from the surrounding cooler layers. Having reached the heated spot, they warm up in their turn, are saturated with water vapors and "soar up" at an angle of 90. Their rate of ascend in a local air current of this kind can be as high as 100 m/s, and its "crossection" can vary from several meters to hundreds of kilometers. Processes of this kind occur with the limits of the troposphere (10 - 15 km from the earth surface) where most of the air and water vapors are concentrated and clouds are formed producing natural precipitation and such like phenomena.
In other words, at its birth stage a cyclone is like a "thermal machine" which is powered by solar energy. And it is different from a smoke chimney, a furnace or a teapot, operating on the same basic principle, only in terms of its scale, lack of walls which confine and channel the current of air, and also by the fact that the heating is done by solar radiation in the conditions of relatively low temperatures and gradients of their variation.
SELF-SPIN OF CYCLONE
At the next stage of development of this process we observe a spontaneous (self- sustaining) spiral spin of the ascending air column. And we do not yet fully understand the mechanism of this phenomenon. Most of the specialists, however, are in favour of a theory according to which the main cause responsible for the spin of all cyclone formations-including also anticyclones (the difference between the two being that in the former there is reduced atmospheric pressure within the whirlwind, and an increased pressure in the latter), tornadoes (sand-storms, snowstorms etc.) and
Radial-ascending air flow with the formation of a vertical air column at the moment of birth of atmospheric cyclone.
waterspouts - is the impact of the Coriolis force* (which experts blame, among other things, for an excessive wear of one of the two rails of a level railway track, and greater erosion of one of the banks of a river). This force impacts all objects moving along the surface of a rotating body, which in this case is the Earth. Accordingly, cyclones, self-regulating in the Northern hemisphere, are rotating anticlockwise, according to the rule of signs, and anticyclones-in the opposite direction, and just the opposite picture is observed in the Southern hemisphere. As a matter of fact, however, the behavior of whirlwinds, especially waterspouts, deviates con-
* Inertial force introduced for the effect of the spin of a mobile system count on a body's relative motion. - Ed .
Diagram of air flow in atmospheric cyclone with a spiral twist
siderably from this rule. The latter, for example, spin with the same probability in both directions irrespective of the hemisphere where they are born.
These facts make many experts doubt the authenticity of the hypothesis which assumes the Coriolis force to be the primary cause of the initial spin momentum of cyclonic formations. In our own view, it only provides a certain contribution to the development of what we call directional asymmetry of the field of force in the surrounding background, which either boosts or weakens the spin of the air which originates spontaneously and due to a different reason.
And let us stress at this point that the self-spin of cyclones has not been convincingly explained by any of the existing hydromechanical theories or by the known hypotheses of thermo-dynamic, electric, electromagnetic or other kinds.
The way we see it, it would be most reasonable to consider the mechanism, which triggers off the spontaneous spiralling of a column of air, as a result of a loss of stability, occurring in certain conditions, of the basic movement of liquid and gas with its bifurcations into several structural variants, after which the process continues along one of these patterns which, as a rule, requires less energy. The aforesaid assumptions can be supported by the following reasoning. A specific feature of all cyclonic formations, when the torrent changes its direction from the horizontal to the vertical, is the appearance in each of them of a sharp turn at the right angle, like a pipe bend. As has been established by specialists, hydraulic
Diagram of a "cyclonic" power station. (For better view only one jet, or stream of cyclon-storm is shown).
resistance in such places is sufficiently high. And it becomes even greater if such turn of the flow "hits" currents moving into the opposite direction so that their sizes and forms of crossections are changed, as is the case in the above example.
In such a situation of flow, or current of liquid or gas is "offered a choice" (bifurcation point) of the mode of its subsequent movement: keep moving on (at great energy losses) straight onto the obstruction, while remaining in an unstable condition, or seek other "ways out". It is obvious that for liquids or gases, capable of "self- organization" of their structure, and fully in keeping with the common laws of mechanics, it "pays" to choose a more energy-saving route or mode-passing the trajectory bend in a smooth spiral motion (let us recall that coil pipes, or spiral tubes, have no steep bends with high local hydraulic resistance thanks to which relatively low energy losses occur in them in overcoming friction). As proved by experiments, the probability of such a situation is greater, the greater is the asymmetry of the surrounding background which triggers off the ultimate loss of stability of a system which had already become unstable.
What is important-the same picture of a loss of stability of an axis-symmetric (symmetric relative to the central axis) flow is observed in all of the known natural phenomena, and also in technical devices which have inside sharp turns of flow- cyclonic formations at sharp river bends, in pipe knee bends at right angle, in plugged stretches of pipelines with the liquid passing through holls in the walls, etc. So, it turns out that the principle of a stream of gas or liquid passing through a sharp bend with minimal energy losses thanks to a spiral flow or with the formation of a set of spiral micro-cortexes-is a universal phenomenon which does not depend on the scale of a system.
On the strength of the above, the mechanism of generation of atmospheric cyclones with spiral "twist" can be construed in the following way.
The lift forces of floatation, which are constantly at play on a patch of the earth surface heated by the Sun (lift forces produced by different specific weights of certain sections of gas or liquid) "speed up" the right- or left-hand spin of the air current originating therein. And the radius (arm) is gradually increasing which is promoted by the centrifugal forces involved in the process, and the growing rate of discharge occurring in hydraulic systems with a dropping drag (at constant pressure in a system a reduction of its drag, or resistance, leads to growing discharge of the gas or liquid flowing through it, in keeping with the law of the conservation of energy). All of these factors taken together boost the momentum of flow and, as a consequence, involve huge masses of air into a powerful, and rapidly accelerating movement which continues until a gas-dynamic barrier is achieved in the core of cyclone, which is determined by the speed of sound in the air (in pipes without any special fittings the gas velocity can keep growing only to the speed of sound, the so-called gas-dynamic barrier).
The initially obtained torque, with equally probable directions of rotation (clock- or anticlockwise) are influenced by other factors of different physical nature as the cyclone moves away from its place of origin, and these include the Coriolis force. And should the resulting effect weaken the acquired momentum, the cyclone will "fade away" all by itself. In the opposite case it, picking up strength, will embark on its mission of destruction along its route until its energy is exhausted.
"CYCLONIC" POWER STATIONS
All of the above makes it possible to prognosticate the possibilities of "practical uses" of cyclones, say for building power stations.
The key problem involved includes the search for and the selection of a patch of land, intensively heated by the Sun or hot currents and abundantly moistened, which is surrounded by a cooler "environment", and "organizing" there an ascending-rotating flow of a powerful column of humid air. A hydrodynamic system of this kind will differ from a commonly known sandstorm only by the fixed (relative to the location) position of its axis of rotation-something which can be achieved by appropriate engineering solutions. The air torrent generated in this way can set into motion a gas turbine installed in its path. A long high-strength steel shaft, attached to the turbine, will drive an electric generator. And the way we see it, engineering problems will not be of any decisive importance in translating this project into reality.
According to calculations, the energy capacity of the heated stretch of about 1 km in diameter of what we call an "ordinary" stationary cyclone-storm, when the rate of lift and rotation of air amounts to 100 and 300 m/s respectively, should be roughly 5 10 11 Wt - an equivalent of one of the biggest generating stations. And, as compared with fuel and atomic power stations, "cyclone" stations have a lot to offer in terms of ecological advantages.
Summing up the above, it is necessary to point out that these are not mere freaks of imagination, but one of the avenues of development of the power engineering of the future. All that has to be done in this field is to step up research into the problems involved, covering the appropriate engineering provisions and bearing in mind various adverse factors obstructing the process of what we call stationary cyclone formation in real conditions (cyclic seasonal-daily nature of warming up, formation of clouds, natural precipitation, the chance "selection" of directions of rotation, radical relocation of mass under the effect of centrifugal forces, the impact of horizontal gradient forces, etc.).
Illustrations supplied by the authors and ITAR-TASS
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