WO2005053379A1

WO2005053379A1 - Apparatus for controlling atmospheric conditions

Info

Publication number: WO2005053379A1
Application number: PCT/IL2004/001033
Authority: WO
Inventors: Alexander Khain; Mark Pinsky; Vladimir Arkhipov; Yaroslav Ryabov; Alexander Puzenko; Ferdus Gubaidullin; Eduard Mastov
Original assignee: Yissum Research Development Company Of The Hebrew University Of Jerusalem; Feldman, Yuri
Priority date: 2003-12-04
Filing date: 2004-11-11
Publication date: 2005-06-16

Abstract

An apparatus (40A) is described for controlling atmospheric conditions in a portion of the atmosphere containing microscopic water droplets (49) dispersed therein. The apparatus (40A) comprises two apparatus portions (40AP, 40AN) for controllable producing negatively and positively charged seeding elements (440), respectively; an electrical power source for providing electrical power required for operation of the apparatus (40A); and a control module (200) for controlling operation of the apparatus (40A) on the basis of a collision model describing collisions between the charged seeding elements and the microscopic water droplets. Each apparatus portion (40AP, 40AN) includes a chamber (41) for providing an element flow stream (43) of a seeding material containing uncharged seeding elements having a predetermined size; a charger (42) downstream of or associated with the chamber (42) and in communication therewith for charging the uncharged seeding elements in the element flow stream (43) so as to produce charged seeding elements (47) having a predetermined polarity and charge magnitude; and a seeder (45) for controllable scattering the charged seeding elements (47) in the atmosphere.

Description

Apparatus for controlling atmospheric conditions

FIELD OF THE INVENTION This invention relates to an apparatus for weather control and modification, and in particular, for controlling atmospheric conditions by seeding dispersing materials in the atmosphere causing the precipitation of water therein.

BACKGROUND OF THE INVENTION Various techniques are known in the art for treating atmospheric conditions to precipitate atmospheric water. Such techniques are utilized for the regulation and enhancement of rain, prevention and suppression of hail, dispersal of ground mist and abatement of fog. In particular, the regulation and enhancement of rain is especially important in countries that experience water shortage for agriculture and other human activities, for example, while the modifying of unfavorable weather by precipitation of fog or mist is crucial for increasing visibility, for example, on roads and runways of airports. It is known that typically water droplets in clouds and fogs are relatively small. Magnitudes of the radii of majority of the droplets in clouds and fogs are distributed in the ranges of 1-10 microns and 1-5 microns, respectively. However, in order to trigger raindrop formation owing to natural process of droplet collision, the droplet radius should exceed 20-25 microns (see, for example, Khain et al, "Notes on the state-of-the-art numerical modeling of cloud microphysics". Atmos. Res., 2000, v. 55, p. 159-224). Water droplets with a radius of higher than 25 microns have sufficient mass to attain a fall velocity under the force of gravity sufficient to collect smaller droplets and precipitate from clouds or fog owing to their collisions and coalescence. On the other hand, the gravity-induced approach of small droplets does not usually lead to their coalescence, because most of the small droplets move around their counterparts together with the airflow. It should be noted that droplets having a radius of 1 to 25 microns will be referred to hereafter as "microscopic droplets", and droplets having a radius exceeding 25 microns will be referred to hereinafter as drops (or droplet- collectors). All references to the size of droplets or drops refer to their radius. The capability of the droplets to produce collisions and thereby precipitate can, inter alia, be characterized by a collision efficiency. It was shown by the applicant of the present application (see, for example, International Application WO 03/061370) that when the drop collectors have a small radius, i.e. around 10 microns, the value of the collision efficiency is very small (ranging from 10^"4 to 10^" ). In other words, the small droplets, in fact, do not collide over a reasonable period of time. On the other hand, when the droplet-collectors reach a radius exceeding about 20 microns, the collision efficiency E has a value sufficient to produce collisions, i.e. larger than 0.1. This drop-collector size is usually thought of as the minimum drop size necessary for triggering a process of collisions and creating the raindrops, i.e., drops larger than about 50 microns in radius. Therefore, if a cloud does not have a sufficient number of large drop- collectors, it cannot realize fully its precipitation potential. Such a situation in clouds is quite usual, because the time necessary to form large drops in natural conditions often exceeds the time period of the cloud's development. Various techniques have been used to date to accelerate the droplet collisions sufficient for the generation of cloud and fog droplets. One of the methods of treatment of atmospheric conditions for this purpose is the glaciogenic seeding technique, i.e. artificially creating ice freezing nuclei and generating ice crystals in supercooled clouds and fogs. Also known in the art are techniques based on dispersing the particles having the property of absorbing the water from clouds and fog, thereby creating large droplet-collectors. One such technique for triggering raindrop formation through the acceleration of large droplets formation is the hygroscopic seeding technique. The main idea of the hygroscopic seeding is to increase the rate of droplet collisions by an increase in the concentration (or creation) of large droplets in the droplet size distributions (DSD). Also known in the art are electrostatic precipitation techniques employing an electrical field to force liquid particles in the fog together to form large drops of sufficient mass to precipitate. For example, U.S. Pat. No. 1,928,963 to Chaffee describes a technique for dissolving clouds and fogs and producing rain by scattering charged particles in the atmosphere. It was proposed to seed clouds and fogs by charged particles with a sign opposite to that of the moisture particles to induce collisions between the scattered particles and moisture particles of cloud and fog. However, besides the pioneering idea of utilizing charged particles for seeding clouds and fog, U.S. Pat. No. 1,928,963 does not provide any practical solution for controlling atmospheric conditions, owing to the fact that at the time when the patent was filed and prosecuted (1925-1933) there was no correct scientific understanding of the physical processes occurring in clouds and fog. In particular, U.S. Pat. No. 1,928,963 mistakenly assumes that water droplets always repel when the charges of the droplets are all of the same sign. Likewise, U.S. Pat. No. 1,928,963 underestimates the interaction between neutral and electrically charged droplets, which is very important, since the majority of water droplets is usually neutral in natural clouds and fog. Therefore, the proposal of U.S. Pat. No. 1,928,963 first to charge the neutral cloud or fog with electricity of one polarity by treating the cloud or fog by scattering particles having a charge of one sign, and then treat it with particles of the opposite polarity, is not practical. Moreover, U.S. Pat. No. 1,928,963 does not teach to use the basic characteristics of atmospheric conditions, such as concentration, mass and size distribution of the moisture and seeding particles for providing control of the collisions required for droplet precipitation. Therefore, U.S. Pat. No. 1,928,963 cannot provide reliable instructions for the error-free control of atmospheric conditions. It is established that cloud and/or fog droplets can be charged by different mechanisms, such as ion-diffusion, convection charging, inductive charging, thermo-electric effect, contact potential effect etc. (see, for example, Pruppacher and Klett, "Microphysics of Clouds and Precipitation " Kluwer Academic Publishers, Dordrecht/Boston/London, 1997, pp. 811 -827). U.S. Pat. No. 3,600,653 to Hall describes a method for reducing fog density by passing the fog between a pair of electrodes. However, this method may be utilized only with equipment emitting artificial fog, since the installation of electrodes above a runway for water precipitation in natural fogs would be highly impractical. U.S. Pat. No. 4,475,927 to Loos describes a technique for the abatement of fog in a space over an aircraft approach zone and runway. According to this technique, charged droplets of both polarities are introduced in the space by air jets. These positively charged droplets having sufficiently low mobility in order to stay long enough are blown aloft to form a virtual electrode suspended at an appropriate height above the ground. The negatively charged droplets (collector drops) are given high enough mobility for collecting of fog drops in an upward motion in the electric field created between the spaced-apart positively and negatively charged droplets. U.S. Pat. No. 4,671,805 to Gourdine describes an EGD (electro- gas- dynamic) system deployed in an array and used for the precipitation of fog over airports. The patent discloses a technique for producing a cloud of sub-micron size charged water droplets that are sprayed into the atmosphere for creating a space-charge cloud above a runway extending to a height of a few tens of meters. The cloud has a maximum electric field strength at the ground, and a zero field strength at the top of the cloud. The charged water droplets, in their earthward motion under the electric force, attach themselves to any other particles that may be suspended in the space-charge cloud. Precipitation occurs also as wind transports the spaced-charge cloud. It should also be mentioned that U.S. Pat. No. 4,671,805 observes that seeding fog with electrically charged particles from an airplane was contemplated but discarded in favor a ground-based system owing to the many operational difficulties of an airborne system. The patent does not expand on the nature of these operational difficulties, but in any event, is restricted to a discussion of ground based systems for fog precipitation principally for dispersing fogs near airports and the like. Moreover, no suggestion is made as to how this can be achieved controllably. One of the main drawbacks of the electrostatic precipitation prior art techniques is their inefficiency, since these techniques require high energy consumption for producing an electromagnetic field over a large space or territory. Therefore, these techniques cannot be utilized over large areas of fog and clouds. U.S. Pat. No. 4,684,063 to Goudy, Jr. describes a mixer/charger apparatus for a variety of purposes employed simultaneously to mix and to electrically charge a fluid flowing therethrough. In one version, the mixer/charger apparatus includes a liquid supply from which the charged mist ultimately is produced for seeding clouds. In an alternate version, the apparatus employs an air input supply that is delivered to a mixer/charger that produces a charged air output used to effect seeding function. The techniques mentioned above are addressed to seeding clouds and fog for rain enhancement and/or fog abatement. However, uncontrolled seeding may result in phenomena that are opposite from what the users expected. For example, the utilization of many conventional glaciogenic and hygroscopic techniques may result in the production of small droplets that are ineffective for rain formation. WO 03/061370 to the Applicant describes a technique for controlling atmospheric conditions in a cloud or fog for weather modification. The control of atmospheric conditions is carried out by controllably urging the collisions between the water droplets in the atmosphere so as to cause their controllable coalescence. This urging is characterized by adjusting electric attraction forces between the droplets to a predetermined value so as to alter a collision rate between the water droplets to a desired value. The changes of the electric attraction forces between the droplets are achieved by dosed seeding a material (e.g., particular material and/or water droplets) in a portion of a cloud or fog that is electrically charged to a required magnitude and polarity. The required magnitude and polarity of the elements of the seeding material depend on (i) a size distribution of the droplets in the portion of the atmosphere, and on (ii) an element size distribution of the seeding material. The required dose, charge magnitude and polarity of the seeding elements (particles and/or droplets) are determined by utilizing an appropriate droplet collision model that takes into account the size distribution of the droplets in the atmosphere and the size distribution of the seeding elements. The dosed seeding of the charged seeding materials can control the concentration of the charged droplets in the cloud or fog as well as their charge magnitudes, and thereby can tune the electrical attractions between the droplets. The attractions increase the collision efficiency between the droplets and the rate of their collisions, which in turn fosters the formation of large droplets leading to raindrops in clouds. In case of fog, it leads to the elimination of small droplets owing to their collisions and coalescence that results in fog dissipation. The Applicants has shown that, the seeding of a cloud with unipolar elements produces more rain over the same period of time, as compared to the bipolar cases, when the seeding of the cloud is carried out by the elements charged with the opposite polarity charges. Thus, in order to obtain the maximum rain enhancement, the seeding elements are preferably charged with the same polarity charges. On the other hand, in the case of a fog seeding, the situation is drastically different from the situation considered in the cloud seeding, because the bipolar seeding produces better fog elimination than the unipolar seeding. Thus, in order to obtain fast increase of visibility in fog, the seeding elements are preferably charged with the opposite polarity charges. In all the cases, the charge magnitudes of the seeding elements should be calculated by using the collision model, as described in WO 03/061370.

SUMMARY OF THE INVENTION Despite the extensive prior art in the area of apparatuses for seeding various materials for treating atmospheric conditions, there is still a need for further improvements for controlling the precipitation of atmospheric water. The foregoing need is accomplished by providing an apparatus for controlling atmospheric conditions in a portion of the atmosphere containing microscopic water droplets. According to the invention, the apparatus includes two substantially identical portions for controllably producing positively and negatively charged seeding elements, respectively. The apparatus further includes a power source for providing electrical power required for operation of the apparatus, and a control module for controlling the operation of the apparatus. The controllable producing implies providing required concentration of charged elements of each polarity. It should be noted that the concentration and charge value of the positively charged elements may be equal to or different from the concentration and charge value of the negatively charged elements. According to the invention, the optimal values of the concentration and the charge of the seeding elements are calculated by using a collision model describing collisions between the charged seeding elements and the atmospheric water droplets. The collision model establishes a relationship between the following parameters: size distribution, concentration and charge of the atmospheric water droplets, size distribution, concentration and charge of seeding elements by means of the magnitude of the collision efficiency between the atmospheric water droplets and the seeding elements. Each of the portions for producing positive and negative charged elements includes a chamber for providing an element flow stream of uncharged seeding elements, a charger coupled to the chamber for charging the elements in the element flow stream, and a seeder for controllably scattering the charged seeding elements in the atmosphere. According to one embodiment of the invention, the chamber of the apparatus includes a feeder of particulate material for allowing the introduction of raw material into the chamber, a mixer for mixing an air flow stream with a particulate material derived from the raw material and an outlet for releasing an output obtained thereby to the charger. The air flow stream can, for example, be provided by a fan coupled to the chamber. According to another embodiment, the air flow stream is provided by an inlet arranged in the chamber. The inlet is fitted for receiving an input air flow stream containing atmospheric water droplets and transferring this stream to the chamber thereby providing the air flow stream containing atmospheric water droplets. When required, a suction device can be arranged in the inlet for the facilitation of the receiving of the input air flow stream from the atmosphere. According to yet another embodiment, the apparatus includes a feeder that includes a tank containing water and a droplet maker, e.g., an ultrasonic mist generator. The droplet maker can be coupled to the control module and be responsive to a droplet size signal produced by the control module for controlling the size of the droplets. According to yet an embodiment, the apparatus includes a feeder containing water and a manifold configured for providing the water to a spray nozzle for creating water droplets. The manifold can include an electrode coupled to the power source for charging the water passing therethrough with the desired electric potential, thereby creating charged water droplets. In order to control the operation of the apparatus, the control module of the apparatus is equipped with conventional devices for indicating and controlling certain parameters such as the amount and kind of raw material to be used, the strain of the air in the air flow stream, the strain of the element flow stream, the strain of the charged element flow stream, the size, charge and concentration of the seeding elements in the element flow stream, etc. Accordingly, the control module of the apparatus for each apparatus's portions can include a first strain regulator arranged in the inlet for producing a first sensor signal representative of the strain of the air in the air flow stream. The control module is responsive to the first sensor signal for controlling the strain. The control module can also include a second strain regulator arranged in the outlet for producing a second sensor signal representative of the strain of the element flow stream. The control module is responsive to the second sensor signal for controlling the strain. Further, the module can also include a third strain regulator arranged in the seeder for producing a third sensor signal representative of the strain of the charged element flow stream. The control module is responsive to the third sensor signal for controlling the strain. The control module can include a charge regulator arranged in the charger and is responsive to a signal produced thereby for controlling the charge magnitude and/or polarity of the charged particles. The charged seeding elements may, for example, be obtained by passing a particulate material and/or water droplets through an electric discharge, and/or by bringing the seeding material into contact with charged electrodes. When desired, each of the apparatus's portions can also include a burner coupled to the chamber for burning the raw material so as to form the particulate material as a combustion product. In such a case, the control module preferably includes a temperature regulator arranged in the chamber. The temperature regulator is responsive to a signal produced thereby for controlling the temperature in the burner. According to a broad aspect of the present invention, there is provided an apparatus for controlling atmospheric conditions in a portion of the atmosphere containing microscopic water droplets dispersed therein, the apparatus comprising: (a) two apparatus portions for controllable producing negatively and positively charged seeding elements, respectively, where each apparatus portion includes: (i) a chamber for providing an element flow stream of a seeding material containing uncharged seeding elements having a predetermined size; (ii) a charger downstream of or associated with the chamber and in communication therewith for charging said uncharged seeding elements in said element flow stream so as to produce charged seeding elements having a predetermined polarity and charge magnitude; and (iii) a seeder for controllable scattering said charged seeding elements in said portion of the atmosphere; (b) an electrical power source for providing electrical power required for operation of the apparatus; and (c) a control module for controlling operation of the apparatus on the basis of a collision model describing collisions between said charged seeding elements and said microscopic water droplets. There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows hereinafter may be better understood. Additional details and advantages of the invention will be set forth in the detailed description, and in part will be appreciated from the description, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: Fig. 1 illustrates an example of the calculation of the dependence of an electrical attraction force between two differently charged conductive spheres on the distance therebetween; Fig. 2 shows a scheme of collisions of small droplets with electrically charged drop-collector; Fig. 3 illustrates a three-dimensional plot showing an example of the collision efficiency as the function of radii for two differently charged elements; Figs. 4A-4D are schematic block diagrams of various examples of an apparatus, according to the present invention; and Figs. 5A and 5B are schematic views of exemplary configurations of electrodes that can be used with the charger of the apparatus of the present invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS The principles and operation of an apparatus according to the present invention may be better understood with reference to the drawings and the accompanying description, it being understood that these drawings are given for illustrative purposes only and are not meant to be limiting. The present invention provides a novel apparatus for controlling atmospheric conditions in a portion of the atmosphere for weather modification. The portion of the atmosphere may, for example, be a portion of a cloud or fog containing water droplets having different sizes dispersed therein. The control of atmospheric conditions is carried out by controllably urging the collisions between the water droplets in the atmosphere so as to cause their controllable coalescence and precipitation. The urging is characterized by adjusting non-gravitational attraction forces between the droplets to a predetermined value so as to alter a collision rate between the water droplets to a desired value. The collision rate is proportional to the collision efficiency and to the droplet concentration. Therefore, altering the non-gravitational attraction forces between the droplets can result in altering the effective collision rate, thereby causing the enhancement or reduction of coalescence and precipitation of the droplets in their motion under the force of gravity. The apparatus provides the changes of the non-gravitational attraction forces between the droplets by dosed seeding in a portion of a cloud or fog a seeding material that is electrically charged to a required magnitude and polarity. The required magnitude and polarity depend on (i) the size distribution of the droplets in the portion of the atmosphere, and on (ii) the size distribution of the elements of the seeding material. According to the present invention, the required magnitude and polarity of the electrically charged seeding elements (particulate material and/or water droplets) are calculated by the apparatus by means of an appropriate droplet collision model. The droplet collision model utilized for the purpose of the present invention will be described herein below. This model takes, inter alia, into account the size distribution of the droplets in the portion of the atmosphere, and the size distribution of the seeding elements. Accordingly, the size distribution of the droplets in the portion of the atmosphere should be determined advance. According to one embodiment of the invention, the seeding material contains such seeding elements as fine particles of a particulate material having a predetermined particle size distribution. According to another embodiment of the invention, the seeding material contains such seeding elements as water droplets. According to one example, the seeding water droplets are collected from the cloud or fog, and then electrically charged to a predetermined magnitude and polarity. According to another example, the seeding water droplets having a predetermined droplet size distribution are generated by a droplet generating device, e.g., an ultrasonic fog generator. According to yet embodiment of the invention, the seeding material contains particles of a particulate material together with seeding water droplets. The size distributions of the seeding particles and droplets have predetermined values. The ratio between the concentrations of the particles and the water droplets has a required predetermined value. The dosed seeding of the charged seeding materials (charged particles and/or water droplets) can control the concentration of the charged droplets in the cloud or fog as well as the charge magnitudes, and thereby can tune the electrical interaction between the droplets. It should be noted that the electrical interaction can take place both between the charged droplets themselves as well as between the charged droplets and the neutral droplets. The charging of the elements of the seeding material (fine particles and/or water droplets) can be obtained, for example, by passing a particulate material and/or water droplets through an electric discharge, and/or by bringing the seeding material into contact with charged electrodes. The droplets in natural clouds and fogs are usually electrically neutral and represent weak salt solutions. It means that the droplets contain a sufficient number of ions to be regarded as conductive particles. Upon the approach of a charged element (particle and/or water droplet) of the charged seeding material to an electrically neutral droplet at a distance sufficient for electrical interaction, a charge with a polarity opposite to the charge of the element is induced on the side of the droplet that is facing the particle. This induced charge causes an electrical attraction between the element and droplet. According to one example, the magnitude of the attraction force in air can be derived from the general approach of interaction of two conductive insulated spheres, which uses the method of electrical images and the potential and the capacitance coefficients corresponding to these spheres (see, for example, Batygin V. V., Toptygin I. N., Problems in Electrodynamics. London, Academic Press, 1978, 574 pp.). According to this approach, the magnitude of the attraction force in air between two conductive insulated spheres can be obtained by

where gj and q₂ are the charges of the conductive insulated spheres, rj and r₂ are the radii of the spheres correspondingly; R is the distance between the spheres' centers; and ε₀ = 8.854 • 10^"12 F/m is the universal dielectric constant. It should be noted that the first term in Eq. (1) represents the Coulomb forces that decaying with the distance R between the spheres as a function of R^~2. The second and third terms in Eq. (1) represent the interaction forces between the point charges and the dipole. These forces decay with the distance between the spheres as a function of R . The three remaining terms describe the interaction forces between the induced charges, and these terms decay with the distance between the spheres as a function of R^~4. Fig. 1 illustrates examples of the dependency of the charged-induced force

(calculated by using Eq. (1)) between the differently charged conductive spheres on the distance R there between. For this example, magnitudes of the spheres' radii were set to r_} = 10 micrometers and r₂ ⁼ 5 micrometers, correspondingly. The magnitudes of the charges of the spheres are shown in the inset in Fig. 1. It can be seen that when the both spheres are charged with the charge of the same sign, not only a repulsion (curve 11), but also attraction (curve 12) of the spheres can be observed, depending on the absolute values of the charges. It is important to mention here that these observations are different from the prior art assumptions. For example, U.S. Pat. No. 1,928,963 erroneously states that when the particles are all of the same sign, whether positive or negative, the particles are always kept apart by repulsion. The present invention utilizes the fact that the attraction between the charged spheres can take place not only for the case when the elements are charged with the charges having the opposite polarity (curve 14), but also for the cases when one of the droplets is neutral (curve 13), or when the both droplets are charged with the charge of the same sign (curve 12). Since the water droplets in natural clouds and fog are usually neutral, the attraction force between neutral and charged droplets turns out to be very significant. The attraction between neutral and charged droplets is attributed to the fact that one of the droplets, within an electrical field induced by its counterpart droplet, becomes a dipole. It should be noted that for the sizes of the spheres different from those shown in this example, the magnitudes of the charges, for which the attraction of the spheres is observed, can be also different. Therefore, in practice, the droplet size distribution of clouds or fog must be determined and taken into account when the charge magnitudes of the seeding elements are selected. This attraction between the charged element and the droplet results in a close approach and capture of the charged element by the droplet. The droplet that received the charge from the charged element can, in its turn, attract another electrically neutral droplet with consequent approach and coalescence that would not be possible in the case of pure gravity-induced attraction. These attractions increase the collision efficiency between the droplets and the rate of their collisions, which in turn foster the formation of large droplets leading to raindrops in clouds. In case of fog, it leads to the elimination of small droplets, due to their collisions and coalescence, which results in fog dissipation. The maximal value to which a seeding element should be electrically charged must also be taken into account in calculating collision efficiency and collision rate. In particular, a cloud droplet located in the air cannot be charged more than with a certain maximum value q_max, that is determined by the air breakdown electrostatic intensity _E₆. It is known for corona discharge that the air breakdown electrostatic intensity Ej, is about 3-10⁶ V/m (see, for example Meek and Craggs, 1953 Electrical Breakdown of Gases. Clarendon Press, Oxford, 507 p.). The electrostatic intensity in the vicinity of a charged spherical particle can, for example, be calculated by using the well-known relationship E = q/4πε₀r². The magnitude of the maximal possible charge of a cloud droplet can be evaluated from the condition E=E_b, which gives tf_ma_x = ^E_bε₀r² (6) wherein r is the droplet' s radius. For example, for a droplet having the radius of 1 micrometer the maximal possible charge has the magnitude of q_ma> 3-10^"14 Coulomb, while a droplet with the radius of 10 micrometers has q_m3X= 3-10 Coulomb. It should be appreciated that when the charge of a cloud droplet is higher than q_max, the electrostatic intensity in the vicinity of the surface of this charged droplet exceeds E_b value, thus a corona discharge immediately appears. This corona discharge process reduces the charge of the droplet to the value q_max, at which the corona discharge stops. Likewise, it should be taken into account that even in case when the droplet's charge Q is less than q_max, the charge may sink owing to the conductivity of air, provided by the mobility of free ions in the air. In this case, a charged droplet slowly loses its charge according to the exponential law Q-Q₀exp(-t/τ), where is the relaxation time, σ is the conductivity of air and Q₀ is the initial charge of the droplet (see, for example, Pruppacher and Klett, 1997 "Microphysics of Clouds and Precipitation. Kluwer Academic Publishers," Dordrecht/Boston/ London, chapter 18, p. 794). For example, for the fair weather conductivity at the sea level was estimated to be about 10^~14 Sm/m that for the relaxation time gives the value of about 6.5 min. However, the conductivity inside a cloud can be significantly lower than the fair weather sea level conductivity, because the concentration of free ions inside a cloud can be significantly lower than that of ions in the air. Thus, Pruppacher and Klett (1997 Chapter 18, p. 802) estimated that the conductivity inside a cloud is in the range of 1/40 up to 1/3 of the fair weather sea level conductivity, which leads to the values of the relaxation time between 20 min and 4 hours. In other words, the time period of droplet discharge can be much longer than the time scale of the coagulation processes leading to the raindrop formation, which are typically about 10 min for cumulus clouds. In general, for the purpose of the invention, the elements utilized for seeding may have a spread of sizes ranging from sub-micron to several microns size, e.g., between 0.1 and 20 microns. The charge may have negative or positive polarity, and maximum magnitude of such charged elements may, e.g., range from about +10^-16 Coulomb to about +10^"12 Coulomb. A calculation of the collision efficiency required for the controllable charging of the seeding elements is described in detail in WO 03/061370, and therefore it will be only briefly explain herebelow. As shown in Fig. 2, the collision efficiency is defined as the ratio between an area of the apparent collision cross- section S_c and an area of the geometrical cross-section S_g. A calculation of S_c can be carried out by numerical simulation experiments of the approach of the small droplets to the large charged drop. For the purpose of the numerical experiments, various state-of the-art mathematical models can be used for a hydrodynamic description of the droplet motions. For example, a known per se superposition method can be considered, according to which each droplet is assumed to move under the gravitational, electric, buoyancy and drag forces in the flow induced by its counterpart moving alone. According to the superposition method, the equation of motion of elements

1 and 2 during their hydrodynamic interaction can, for example, be represented by dt τ_x m_x dx\ _τ7 — dt = π, dV, 1 ^→ _r dt τ₂ fc - Fi - fi,)-- m^₂ , (2) ^ = V₂ , dt ² where x_x and x₂ are the radius-vectors of the elements 1 and 2, V_x and V₂ are the velocity of the elements 1 and 2, V_xι V_2t are the terminal velocity of the elements 1 and 2 in calm atmosphere, xi_x is the perturbed velocities induced by the element 1 at the location of the element 2, u₂ is the perturbed velocities induced by the element 2 at the location of the element 1, e_z is the unit vector directed downward, ^τ _\ = V_\t 18 ^an^ ₂ = V_lt I g are the characteristic relaxation time of the elements 1 and 2, which are the measure of the inertia of the elements 1 and 2, mj and m₂ are the masses of the elements 1 and 2, F_eι is the electrostatic force that can be derived by using Eq. (5), and g = 9&m/s is the free fall acceleration. The system of equations (2) can, for example be used for the calculations of the collision efficiency between the drop and the small droplet as described in WO

03/061370. Fig. 3 is a three-dimensional plot showing a general example of the collision efficiency as the function of radii for two elements having the charges of Qι —2- 10^""13 Coulomb and Q₂ = 1 - 10^-18 Coulomb. As can be seen, the collision efficiencies may reach rather high values exceeding 1000, i.e., several thousand times higher than the collision efficiencies associated with the pure gravitational interaction between the elements. As can be appreciated by a person versed in the art, the controllable variation of the size and electrical charge of the seeding elements enables to alter the collision efficiency in a broad range to a desired value, and thereby to control the atmospheric conditions. Referring now to Figs. 4A-4D, there are illustrated various embodiments of an apparatus for controlling atmospheric conditions in a portion of the atmosphere. It should be noted that the blocks in Fig. 4A-4D are intended as functional entities only, such that the functional relationships between the entities are shown, rather than any physical connections and/or physical relationships. Referring now to Fig. 4A, there is illustrated a schematic block diagram of an apparatus 40A for controlling atmospheric conditions in the portion of the atmosphere, according to one embodiment of the present invention. The apparatus

40A includes two substantially identical apparatus portions 40AP and 40AN for controllable producing positively and negatively charged seeding elements, respectively. The controllable producing of both positively and negatively charged seeding elements is required because for obtain the maximum rain enhancement, the seeding elements are preferably charged with the same polarity charges, while for obtaining fast increase of visibility in fog, the seeding elements are preferably charged with the opposite polarity charges. The apparatus 40A further includes a power source 100 and a control module 200 for controlling the operation of the apparatus 40A. The controllable producing implies providing required concentration of charged elements 440 of each polarity. It should be noted that the concentration and charge value of the positively charged elements may be equal to or different from the concentration and charge value of the negatively charged elements. According to the invention, the optimal values of the concentration and the charge of the seeding elements are calculated by using a collision model describing collisions between the charged seeding elements and the atmospheric water droplets. Since the configuration and operation of the apparatus portions 40AP and

40AN are similar, only one of such portions (i.e., the apparatus portion 40AP) will be described hereinbelow in detail. The apparatus portion 40AP includes a chamber 41 for providing an element flow stream 43, a charger 42 coupled to the chamber 41 for charging the elements 44 in the element flow stream 43, a seeder 45 for releasing a charged element flow stream 46 and controllably scattering charged elements 47 of the charged element flow stream 46 in the portion of the atmosphere. The chamber 41 of the apparatus includes an inlet 411 fitted for receiving an input air flow stream 48 containing atmospheric water droplets 49 and transferring this stream to the chamber 41, thereby providing element flow stream 43 within the chamber 41 containing, inter alia, the water droplets. The element flow stream 43 is fed to the charger 42 coupled to the chamber 41 via an outlet 412 for charging the elements 44 (e.g., the water droplets 49). When required, each of the apparatus portion 40AP and 40AN can include a fan 413 arranged in the chamber 41 and coupled to the control module for controllable enhancing the element flow stream 43. The apparatus 40A receives electrical power from an electrical power source 100 coupled to the chamber 41, charger 42, seeder 45 and their components for providing electrical power for operation of the apparatus. Fig. 5A and 5B illustrate a schematic view of exemplary configurations of electrodes that can be used with the charger 42 for charging the elements 44. The charger 42 includes one or more unipolar electrodes 151 capable to produce an electric field, when the electrode(s) is/are charged either positively or negatively. The particular seeding elements 44 can be electrically charged when they are passed through the electric field or brought into contact with the electrodes 151. Likewise, the particular seeding elements 44 can be electrically charged owing to an electric discharge (e.g. corona discharge) between the elements and the electrodes. The unipolar electrode 151 can be configured either in the form of one or more two-dimensional grids (shown in Fig. 5A) or a three-dimensional grid (shown in Fig. 5B) with a controllable size of its cells 152. The elements 44 can pass either through the grid cells without a contact or with a contact to the grid's frame. A control of the charging of the elements 44 can, for example, be provided by means of altering a magnitude of electric potential applied to the grid electrode and/or by changing the dimension of the grid cells. Turning back to Fig. 4A, when required, each of the portions of the apparatus 40A can also include a suction device 414, such as a pump, arranged in the inlet 411 for the facilitation of the receiving of the input air flow stream 48. When required, each of the portions of the apparatus 40A can also include a feeder 415 coupled to or associated with the chamber 41 for allowing the introduction of raw material thereto. Examples of the raw material include, but are not limited to various commercially produced flares such as French flare, Newai flare, D383 flare, Sanormal flare, etc. The air flow stream 43 is mixed with a particulate material derived from the raw material and fed to the charger 42 via the outlet 412. In this case, a combined element flow stream that includes both particles and water droplets, can be fed to the charger 42, and further to the seeder 45. In turn, the charged seeding elements 47 will contain the charged particles together with the charged atmospheric water droplets. When required, each of the portions of the apparatus 40A can also include a burner 416 coupled to the chamber 41 for burning the raw material so as to form the particulate material as a combustion product. In order to control the operation of the apparatus, the control module 200 of the apparatus 40A is equipped with various known devices for indicating and regulating certain parameters such as the amount and kind of the raw material to be used, the strain of the air in the air flow stream 48, the strain of the element flow stream 43, the strain of the charged element flow stream 46, the size, charge and concentration of the charged seeding elements 47 in the charged element flow stream 46, etc. Accordingly, the control module 200 of the apparatus can include a first strain regulator 418 arranged in the chamber 41 for producing a first sensor signal representative of the strain of the air in the air flow stream 48. The control module 200 is responsive to the first sensor signal for controlling the strain. The control module 200 can also include a second strain regulator 419 arranged in the outlet 412 for producing a second sensor signal representative of the strain of the element flow stream. The control module 200 is responsive to the second sensor signal for controlling the strain. Further, the module can also include a third strain regulator 420 arranged in the seeder 45 for producing a third sensor signal representative of the strain of the charged element flow stream 46. The control module 200 is responsive to the third sensor signal for controlling the strain. The control module 200 can include a charge regulator 421 coupled to the charger 42. The regulator is responsive to a signal produced thereby for controlling the charge magnitude and/or polarity of the charged seeding elements. According to the invention, the desired values of the charge of the seeding elements depends on the size distribution of the droplets in the atmosphere, and are calculated by using the collision model (as described above) that describes the collisions between the charged seeding elements and the atmospheric water droplets. It should be noted that the values of the charge of the seeding elements generated by the portions 40AP and 40AN can be either equal or different, as required from the calculation based on the collision model. When the apparatus 40A includes the burner 416, the control module 200 can include a temperature regulator 417 coupled to the burner 416. The temperature regulator 417 is responsive to a temperature signal produced thereby for controlling the temperature in the burner 416. Referring now to Fig. 4B, there is illustrated a schematic block diagram of an apparatus for controlling atmospheric conditions in the portion of the atmosphere, according to another embodiment of the present invention. This apparatus is indicated by a reference numeral 40B is similar to the apparatus (4 A in Fig. 4A) in the fact that it also includes two substantially identical apparatus portions 40BP and 40BN for controllable producing positively and negatively charged seeding elements, a power source 100, and a control module 200 for controlling the operation of the apparatus. The controllable producing also implies providing required concentration of charged elements of each polarity. The optimal values of the concentration and the charge of the seeding elements depend on the size distribution of the droplets in the atmosphere, and are calculated by using the collision model, as described above. Each of the apparatus portions 40BP and 40BN includes a chamber 611, a charger 612, and a seeder 615. The apparatus 40B distinguishes from the apparatus 40A in the fact that the apparatus portions 40BP and 40BN further include a feeder 720 of uncharged water droplets coupled to the chamber 611. According to one embodiment of the invention, the feeder 720 includes a tank containing water 721 (used as a raw material), and a droplet maker 722. The droplet maker 722 can, for example, be an ultrasonic mist generator capable of producing discreet droplets of desired size. As described above, the droplet size effects the collision efficiency. Thus, the controllable producing of charged elements further implies providing the charged water droplets of desired size. The control of the droplet size can be achieved by varying operating ultrasonic frequency. The droplet maker 722 is coupled to the control module 200. The droplet maker 722 is responsive to a droplet size signal produced by the control module 200. The chamber 611 of each of the apparatus portions 40BP and 40BN includes a fan 616 enabled and positioned for providing an element flow stream 618, driving the uncharged water droplets (i.e., elements 625) produced by the droplet maker 722 in the charger 612 configured for controllably charging the droplets, as described above. After charging, a charged element stream 619 is controllably released in the atmosphere by the seeder 615. It should be appreciated that when required, the chamber 611 may include an inlet 623 for receiving an input air flow stream 624 and providing the element flow stream 618 instead of or together with the fan 616. According to embodiment of the invention, the chamber 611 can further include a water collection section 656 for collecting and precipitating atmospheric droplets from the input air flow stream 624, and thereby compensating for the water 721 taken from the tank of the feeder 720. The collection section 656 is in communication with the feeder 720 via a manifold 657. The collection section 656 can, for example, include a rotor 658 arranged for displacing the atmospheric water droplets to walls of the collection section 656. According to this embodiment, the displaced droplets can be absorbed on the walls of the collection section 656, and thereafter the collected water can be discharged from the walls into the feeder 720 through the manifold 657. It should be noted that each of the apparatus portions 40BP and 40BN can include a strain regulator 620 electrically coupled to the fan 616 and controlled by control module 200 for regulating the stream 618 of the uncharged elements 625, as described above in connection with the embodiment shown in Fig. 4A. Likewise, each of the apparatus portions 40BP and 40BN includes a strain regulator 621 arranged in the seeder 615 for producing a sensor signal representative of the strain of the stream 618. The control module 200 is responsive to this sensor signal for controlling the strain of the stream 618, and consequently, regulating also the streams 619 of the charged elements 626. Referring now to Fig. 4C, there is illustrated a schematic block diagram of the apparatus of the present invention for controlling atmospheric conditions in the portion of the atmosphere, according to yet another embodiment of the present invention. The apparatus (indicated by a reference numeral 40C) includes two substantially identical apparatus portions 40CP and 40CN for controllable producing positively and negatively charged seeding elements, a power source 100, and the control module 200 for controlling the operation of the apparatus. Each of the apparatus portions 40CP and 40CN includes a seeder 628 and a chamber 670 associated with a charger, thereby it combines the functions of the chamber and charger of the apparatus shown in Fig. 4A and 4B. The chamber 670 includes a feeder 730 that comprises a tank containing water 721, and the droplet maker 722. According to this embodiment of the invention, the power source 100 is coupled directly to the water 721 for providing an electric potential thereto, for example, via an electrode 723. In such a case, the droplet maker 722 arranged in each of the apparatus portions 40CP and 40CN is capable of producing discreet droplets 732 and 733 charged positively and negatively, respectively. Each of the apparatus portions 40CP and 40CN can include a fan 671 enabled and positioned for driving the charged water droplets 732 and 733 produced by the droplet makers 722 in the atmosphere. It should be appreciated that when required, the chamber 670 may include an inlet 633 for receiving an input air flow stream 634 and providing the element flow stream 618 instead of or together with the fan 671. Likewise, the chamber 670 can further include a water collection section (not shown in Fig. 4C) arranged for collecting and precipitating atmospheric droplets, and thereby compensating for water 721, as described above with reference to Fig. 4B. The control module 200 is configured to be responsive to signals produced by the power source 100, the droplet maker 722, the fan 671 and the strain regulators 620 and 621 for control of the working parameters of the apparatus, as described above with reference to Fig. 4A and 4B. Referring now to Fig. 4D, there is illustrated a schematic block diagram of the apparatus of the present invention for controlling atmospheric conditions in the portion of the atmosphere, according to yet another embodiment of the present invention. The apparatus (indicated by a reference numeral 40D) includes two substantially identical apparatus portions 40DP and 40DN for controllable producing positively and negatively charged seeding elements 649, a power source 100, and the control module 200 for controlling the operation of the apparatus. Each of the apparatus portions 40DP and 40DN represents a spraying device including a chamber 639 and a seeder 638. The chamber 639 includes a feeder 641 containing water, a manifold 642 configured for providing the water to a spray nozzle 643 of the seeder 638. The chamber can include a fan 644 providing an air stream 645 sufficient for spraying the water from the nozzle 643 in the form of water droplets 649. The manifold 642 includes an electrode 646 coupled to the power source 100 for charging the water passing therethrough with the desired electric potential. The nozzle 643 includes an orifice regulator 647 arranged at the nozzle orifice for producing an orifice dimension signal representative of the orifice dimension. The control module 200 is responsive to this signal for varying the orifice dimension. This feature enables controlling the droplet size which depends on the orifice dimension. Each of the apparatus portions 40DP and 40DN further includes a strain regulator 648 electrically coupled to the fan 644 and controlled by control module 200 for regulating velocity of the air stream 645. The operation of the strain regulator 648 is similar to the equivalent device described above with reference to Figs. 4A-4C. It should be appreciated that when required, the chamber 639 may include an inlet 650 for receiving an input air flow stream 651 and providing the air flow stream 645 instead of or together with the fan 644. According to the invention, the desired values of the sizes of the water droplets, the charges and polarity of the droplet as well as the concentration of the droplets in the atmosphere are calculated by using the collision model, as described above. This model enables to find optimal values for these parameters, depending on the size distribution of the atmospheric droplets. According to one embodiment of the invention, controlling the atmospheric conditions for the purpose of rain regulation by seeding electrically charged particles in clouds can be carried out by the apparatus that is mounted on a flying object, e.g., an airplane, helicopter or dirigible. For the controllable dispersal of fog or ground mist, the apparatus can be carried on a motorized vehicle. Likewise, the water droplets of fog can be treated by a low flying airplane controllably dispersing the electrically charged particles in accordance with the invention. According to another embodiment of the invention, the control of the atmospheric conditions can be effected from a ground located source, e.g. from a chimney-stack. In this case, the charger, of the kind described above, can be mounted within the chimney-stack in order to charge the smoke particles ejected into the atmosphere when clouds or fog are in the vicinity of the chimney-stack. The controllable scattering of the charged smoke particles not only affects the atmospheric conditions, but can also scavenge the atmosphere from the ejected materials. As such, those skilled in the art to which the present invention pertains, can appreciate that while the present invention has been described in terms of preferred embodiments, the concept upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, systems and processes for carrying out the several purposes of the present invention. It is apparent that although the examples based on the numerical experiments were shown for interaction between the neutral drop and electrically charged droplets (particles), the technique of the present invention can be applied for controlling the collision rate between the charged drops and neutral droplets (particles), or charged drops and charged droplets (particles). Moreover, any reference to a specific implementation in terms of usage of the chamber, the charger, the control module, or any other components are shown by way of a non-limiting example. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. Finally, it should be noted that the word "comprising" as used throughout the appended claims is to be interpreted to mean "including but not limited to". It is important, therefore, that the scope of the invention is not construed as being limited by the illustrative embodiments set forth herein. Other variations are possible within the scope of the present invention as defined in the appended claims and their equivalents.

Claims

CLAIMS:

1. An apparatus for controlling atmospheric conditions in a portion of the atmosphere containing microscopic water droplets dispersed therein, the apparatus comprising: (a) two apparatus portions for controllable producing negatively and positively charged seeding elements, respectively, where each apparatus portion includes: (i) a chamber for providing an element flow stream of a seeding material containing uncharged seeding elements having a predetermined size; (ii) a charger downstream of or associated with the chamber and in communication therewith for charging said uncharged seeding elements in said element flow stream so as to produce charged seeding elements having a predetermined polarity and charge magnitude; and (iii) a seeder for controllable scattering said charged seeding elements in said portion of the atmosphere; (b) an electrical power source for providing electrical power required for operation of the apparatus; and (c) a control module for controlling operation of the apparatus on the basis of a collision model describing collisions between said charged seeding elements and said microscopic water droplets.

2. The apparatus of claim 1 wherein said seeding material includes atmospheric water droplets.

3. The apparatus of claim 2 wherein said chamber includes an inlet for receiving an input air flow stream from atmosphere and transferring the input air flow stream comprising the atmospheric water droplets to the chamber, thereby providing an element flow stream.

4. The apparatus of claim 3 further including a suction device arranged in said inlet.

5. The apparatus of claim 1 wherein said seeding material includes particles of a particulate material 5

6. The apparatus of claim 5 wherein the chamber comprises a feeder for providing a predetermined amount of the particulate material derived from a required kind of a raw material.

7. The apparatus of claim 6 wherein said chamber includes a fan for providing an air flow stream for mixing with said particulate material, thereby ιo producing an element flow stream.

8. The apparatus of claim 6 further comprising a burner coupled to the chamber for burning said raw material so as to form the particulate material as a combustion product.

9. The apparatus of claim 8 wherein said combustion product is soot particles. 15

10. The apparatus of claim 1 wherein the chamber includes a feeder containing water and a manifold configured for providing the water to a spray nozzle for creating water droplets.

11. The apparatus of claim 10 wherein said manifold includes an electrode coupled to the power source for charging the water passing therethrough with the

20 desired electric potential, thereby creating charged water droplets.

12. The apparatus of claim 1 wherein the chamber further comprises a feeder containing water as a raw material.

13. The apparatus of claim 12 wherein said feeder includes droplet maker configured for making water droplets of desired size.

25 14. The apparatus of claim 13 wherein the droplet maker is an ultrasonic mist generator.

15. The apparatus of claim 12 wherein the chamber further comprises a water collection section for collecting and precipitating atmospheric droplets from said input air flow stream, where said collection section includes a rotor arranged for

30 displacing the atmospheric water droplets to the walls of the collecting section.

16. The apparatus of claim 12 wherein said water is coupled to said electrical power source via an electrode for providing an electric potential thereto.

17. The apparatus of claim 1 wherein said portion of the atmosphere is a portion of cloud. 5

18. The apparatus of claim 1 wherein said portion of the atmosphere is a portion of fog.

19. The apparatus of claim 1 wherein said microscopic water droplets are substantially electrically neutral.

20. The apparatus of claim 1 wherein the seeding elements have a spread of 10 sizes ranging from sub-micron to several micron sizes.

21. The apparatus of claim 1 wherein the value of the charge of the seeding elements ranging from about ±10^" Coulomb to about ±10^" Coulomb.

22. The apparatus of claim 1 wherein the charger comprises at least one electrode for producing an electric field.

15 23. The apparatus of claim 22 wherein said at least one electrode is configured in a form of at least one grid.

24. The apparatus of claim 23 wherein the grid is selected from two- dimensional and three-dimensional grids.

25. The apparatus of claim 1 wherein the charger comprises at least one 20 electrode configured for producing an electric discharge.

26. The apparatus of claim 3 wherein said control module includes a first strain regulator arranged in the inlet for producing a first sensor signal representative of a strain of the air in the air flow stream, the control module being responsive to said first sensor signal for controlling the strain.

25 27. The apparatus of claim 1 wherein said control module includes a second strain regulator arranged in the outlet for producing a second sensor signal representative of a strain of the element flow stream, the control module being responsive to said second sensor signal for controlling the strain.

28. The apparatus of claim 1 wherein said control module includes a third

30 strain regulator arranged in the seeder for producing a third sensor signal representative of a strain of the charged element flow stream, the control module being responsive to said third sensor signal for controlling the strain.

29. The apparatus of claim 8 wherein said control module includes a temperature regulator arranged in the chamber and is responsive to a signal produced thereby for controlling temperature in the burner.

30. The apparatus of claim 1 wherein said control module includes a charge regulator arranged in the charger and is responsive to a signal produced thereby for controlling the charge magnitude and/or polarity of the charged particles.

31. The apparatus of claim 13 wherein said control module is coupled to said droplet maker responsive to a droplet size signal produced by the control module for controlling the size of said water droplets.

32. The apparatus of claim 1 for use with a flying object.

33. The apparatus of claim 1 for use with a ground located source.

34. The apparatus of claim 33 wherein said ground located source is a chimney-stalk.