WO2013086542A1 - Salt water spray systems for cloud brightening droplets and nano-particle generation - Google Patents

Abstract

A system and a method for producing solid nano-particles of a material by dispersing very small droplets of liquid in which the material is dissolved. The nano-particles being particularly useful for geoengineering for increasing cloud reflectivity. The system includes: a. pump for supplying the liquid; and b a plurality of orifices included in at least one sprayer. The liquid upon being supplied to said sprayer forming droplets after flowing through the sprayer's orifices. The sprayer is selected from a group consisting of: a. domed sprayers; b. cusped cone sprayers; and c. Taylor cone sprayers (132). The method includes the steps of: a. both pressurizing and heating the liquid so the liquid is in a supercritical state wherein the liquid becomes like a dense gas and the surface tension approaches zero; and b dispersing the pressurized and heated liquid in the supercritical state through an orifice.

Description

SALT WATER SPRAY SYSTEMS FOR

CLOUD BRIGHTENING DROPLETS AMD KANO-PARTICLE GEMERATIO^

Technical Field

The present disclosure relates generally to the technical field of geoengineering to abate global warming and, more particularly, increasing the reflectivity of clouds, i.e. cloud brightening , B¾ckgmund..ikrt

The Latham-Salter (L-S) scheme for increasing cloud brightness proposes increasing cloud density by seeding the air with very small, um sized, droplets of sea ater , The following papers describe the L-S scheme in greater detail.

Latham, J. (2002), "Amelioration of global warming by controlled enhancement of the albedo and longevity of low-level maritime clouds" {PDF}. Atmos . Sci .

Lett. 3: 52-58.

Salter, S, G. Sor ino & J. Latham {2008} , "Sea-going hardware for the cloud albedo method of reversing global warming". Phil. Trans. R. Soc. A 366 (1882):

3989-4006.

The L-S scheme envisions m sized droplets of seawater rising from sea level and increasing the marine boundary cloud reflectivity enough to compensate for radiative forcing caused by the greenhouse effec .

In the original implementation of the L-S scheme, the sprayers under consideration need to spray on the order of 10 L/sec (for 10 ^? droplets/sec) with spray droplets 0.8 μκι in diameter. For cloud brightening, it is the number of salt nuclei, not the volume of water sprayed that is important. Salt crystals on the order of 5-7 x l€r^:':i! kg or larger are needed for successful conversion into droplets in pre-existing maritime boundary layer clouds at 0.5% supersaturatio . Very large sprayers generate cumulative effects that are very difficult to deal with and produce a significant amount of droplet coalescence. Such coalescence is not observed when only a few jets are used, but here very large arrays {tens of millions) of collinear jets need to be used. This large number of parallel jets tends to entrain air, and the net result is that there is lateral air pumping which tends to collapse the jets into each other and produce coalescence of the droplets. disclosure

The present disclosure describes different systems for producing pm sized droplets of a liquid such as seawater.

An object of the present disclosure is providing a system that produces μηι sized droplets of a liquid.

Another object of the present disclosure is providing sprayers adapted for producing pm sized liquid droplets.

Disclosed is a system for producing solid nano- articles of a material by dispersing very small droplets of liquid in which the material is dissolved. The system is particularly useful for geoengineering for increasing cloud reflectivity. The system includes ;

a. pump for supplying the liquid; and

b a plurality of orifices included in at least one sprayer .

The liquid upon being supplied to said sprayer forming droplets after flowing through the sprayer's orifices. The sprayer is selected from a group consisting of:

a , domed sprayers

b , cusped cone sprayers ; and

c, Taylor cone sprayers (132) .

Also disclosed is a method for producing solid nano · particles of a material by dispersing very small droplets of liquid in which the material is dissolved. The method being useful in geoengineering for increasing cloud reflectivity. The method includes the steps of :

a, both pressurizing and heating the liquid so the liquid is in a supercri ical state wherein the liquid becomes like a dense gas and the surface tension approaches zero; and

b dispersing the pressurized and heated liquid in the supercri ical state through an orifice.

These and other features, objects and advantages will be understood or apparent to those of ordinary skill in the art from the following detailed description of the preferred embodiment as illustrated in the various drawing figures.

Brief_...Descript on

FIG. 1 is a cross-sec ional view illustrating a domed sprayer for suitable for Rayleigh spraying.

FIG. 2 is a perspective drawing illustrating a sprayer body adapted for receiving a very large number of the sprayer depicted in FIG. 1.

FIG. 3 is an elevational view illustrating an alternative sprayer body configura ion adapted for receiving the sprayers depicted in FIG. 1.

FIG. 4A is a cross-sectional elevational view illustrating a portion of a charging/screening structure layered upon the domed sprayer of FIG . 1 when mounted in a sprayer body such as that depicted in FIG. 3.

FIG. 4B is a plan view llustrating a portion of charging/screening structure taken along the line 4B-4B in the cross-sectional view of FIG. 4A.

FIG. 5 is a perspective view illustrating a cusped cone sprayer suitable for droplet production that lends itself to very effective charging.

FIG. 6 is a schematic cross -sectional view illustrating the cusped cone sprayer taken along the line 6-6 in FIG. 5 illustrating in detail operation of the cusped sprayer.

FIG. 7 is a semi-transparent perspective view illustrating an alternative embodiment cusped cone sprayer augmented by additional electrodes for inducing Taylor cones on spray droplets .

FIG, 8 is a perspective view illustrating a sprayer wherein liquid emanating from orifices breakup in a electric field generated between parallel plates, the electric field producing 'Taylor cones on the liquid.

PIG. 9 is a cross-sectional view illustrating a classical arrangemen for producing a single Taylor cone.

FIGs. 10A, 10B and IOC are graphs illustrating the relationships of the electric breakdown field and the Taylor cone field as a function of radius under various operating conditions ,

FIG, 11 is a perspective view depicting assemblies of pyramidally-shaped frustrums formed by machining a plate, each frustrum being adapted for forming a Taylor cone.

FIG , 12A is a cros -sectional elevational view illustrating an orifice plate used for forming Taylor cones, the plate being combined with a polymeric fiber filter or other porous material .

FIG. 12B is a cross-sectional elevational view illustrating shows a orifice plate the same as or similar to that depicted in FIG. 12A being combined with a sheet filter formed by groups of small holes formed through the sheet.

FIG, 13 is a cross-sectional elevational view illustrating a laminated construction of significant flow resistance for use in producing Taylor cones.

FIG, 14A and 14B are cross-sectional elevational -views illustrating alternative constructions of Taylor cone sprayers using polyimide or other dielectric membranes supported by a porous substrate to provide a suitable flow resistance.

FIG. 15A is a plan view illustrating a composite array sprayer using very thin membranes.

FIG. 15B is a cross-sectional view taken along the line 15B-15B in FIG. ISA thereby providing as elevational view inside the composite array sprayer.

FIG. 16 shows a schematic scheme to retrieve the kinetic energy f om droplets generated by Taylor cone .

FIG. 1?A is a graph depicting the surface tension of water as a function of temperature.

FIG, 17B is a graph depicting the viscosity of water as a function of temperature. FIG. 18 is a block diagram depicting a one nozzle system for spraying seawater (or salt solutions in general} in supercritical or near supercritical conditions.

FIG. .19 is an isoba ic phase diagram chart for saltwater at various concentrations and various pressures ranging from 240 to 400 bar in 20 bar intervals,

FIG. 20 is a graph that permits selecting operating conditions for the system depicted in FIG. 18 for water having either a 3,2%, a 1,0% or a 0.5%^· salt concentration for two (2) different iso-enthalpy curves respectively for 2676 kj/kg and for 2750 k/kg.

FIG, 21A is a graph depicting operating conditions for the system depicted in FIG. 18 for water having a 0.25% salt concentratio .

FIG. 21B depicts a SEM picture of salt particles produced by the system depicted in FIG. 18 from water having a 0.25% salt concentration, and a particle size histogram for salt particles produced under such operating conditions.

FIG. 22 is a block diagram showing an enhancement of the system depicted in FIG. 18 that permi s removing part or all of the liquid salty phase from the system, and only the vapor phase is sprayed.

FIG. 23 is a block diagram showing a conf guration of the system depicted in FIG. 18 in which a separate exit ove is used to establis the desired operating characteristics for the fluid.

FIG. 24 is a block d agram showing art implementation of the configuration depicted in FIG. 23 for multiple orifices.

FIG. 25 is a cross-sectional elevational view illustrating how a ceramic nozzle may be attached to a tube using a gold wire seal,

FIGs . 26A and 2€B are cross -sectional elevational views illustrating how multiple orifices may be fabricated simultaneously using micromachining ..

FIG. 27 is a graphic cross-sectional illustration of a f1ow~b1.urring no z z1e ,

FIG. 28 shows a block diagram depicting a process for seawater treatment prior to spraying. ·· β ^■■

Best... o&e.. fο ...^

FIG. 1 depicts a domed sprayer 32 that includes thin, dome-shaped membrane 34 of metal , typically less than 25 μκι thick, that is perforated by many spray orifices 36 arranged in a specified pattern. The membrane 34 may be made out of a various metals such as stainless steel, nickel (Ni) or titanium (Ti) with titanium being preferred because of its excellent corrosion -resistance to marine environments, good etching characteristics and commercial availability in the form of a half mil (0.0005 in.) foil.

To form a spray when operating at low pressure, spray orifice 36 need to be made in very thin material. It is found that thin sheets of stainless steel, Ni or Ti are ideal for such purposes , providing both inertness and strength. For example, a sheet of Ti, 12 μκι thick may be etched with deep reactive ion etching (RIE) , using the Bosch etch process. Titanium dry-etches well in a fluorine atmosphere. For this purpose as is well known in the art the membrane 34 is first coated with photoresist, and then etched using fluorine compounds using the Bosch deep RIS process , Optimum spray orifices 36 have a pronounced conical shape such that the apex of the cone is on an exit end of the spray orifices 36. Ideally a hole of conical shape is desired, as this produces a contractio of a liquid jet exiting each spray orifice 36, and for a given jet size minimises the amount of pressure needed to produce a jet of sufficient speed, while maximizing the hole size to avoid clogging. This preferred shape for the spray orifices 36 may be achieved by multiple masking steps with increasing hole diameters, or by changing RIE processing parameters so the etch wall is less vertical .

Alternatively, the spray orifices 36 may be formed by wet etching the 36 using a TiNi film as an etch mask. The isotropic we etching process tends to make an enlarged hole as it progresses which is exactly what is desired for reducing jet flow impedance. The spray orifices 36 preferably have a diameter of approximately 0.5 pm to produce approximately 0.9 pm diameter droplets using the Rayleigh criterion, i.e. breakup wavelength equal to nine times the jet radius. After etching, the membrane 34 is first attached to ring- shaped holder 38, and then hot drawn on a mandrel to produced the preferred spherical shape. A membrane filter 42 closes the side of the holder 38 furthest from the membrane 34 to provide additional filtration for any particles that may be unintentionally present in filtered liquid. The membrane filter 42 is suf iciently porous to supply all the spray orifices 36 with an adequate amount of liquid, A silicon (Si) substrate with many subm cron-sized holes may be used for the membrane filter 42.

As an example, the membrane 34 of the sprayer 32 may have 170,000 spray orifice 36, 0,5 μητ. in diameter arranged in a hexagonal pattern. The sprayer 32 preferably has a radius of curvature of approximately 50 mm and a diameter of approximately 50 mm. A domed shape for the membrane 34 provides a substantial advantage because jets of liquid emitted from the spray orifices 36 are all angularly separated and diverge from each other which decreases the likelihood that droplets will coalesce .

While the membrane 34 depicted in FIG. 1 preferably is dome-shaped, a planar membrane may also be used. The pressure of liquid within a sprayer 32 will deform such a planar membrane into a shape approaching a section of sphere with many of the same advantages that accrue to the dome-shaped membrane 34 ,

The holders 38 of sprayers 32 are then attached to a sprayer body 44, preferable formed with a stepped, cone-shape as depicted in FIG. 2, either by a screw thread or clamping with an O-ring in front of each sprayer 32. The sprayer body 44 is pierced adjacent to each of the sprayers 32 with slots 46 that permits introducing an airflow oriented subs ant ially perpend cular to a plurality of liquid jets spraying from each of the sprayers 32. Ducting for providing an airflow past the sprayers 32 does not appear in the illustration of FIG. 2. The sprayers 32 are staggered to increase access to airflow and at the same time remove space charge at a very high rate,

A conduit 47 included in the sprayer body 44 permits supplying highly filtered seawater or any other liquid under pressure to each of the sprayers 32 and fo ced through the spray orifices 36 thereby producing jets ha break up into droplets. A transducer 48, mounted atop the sprayer body 44 in the illustration of FIG. 2, applies suitable acoustic energy so jets emerging from the spray orifices 36 are all simultaneously exited in the Raleigh mode thereby producing substantially equally-sized droplets {the optimum Rayleigh excitation wavelength is nine times the jet radius) , A total of three- hundred fifty (350) sprayers 32 provides a total liquid flow of 10 L/sec from an assembled sprayer body 44.

Airflow velocity past the sprayers 32 is substantially equal to the velocity of jets spraying from the sprayers 32. An airflow of this velocity separates wakes of droplets emitted from each of the spray orifices 36. Drip channels, not illustrated in FIG. 2, provide for runoff of liquid that raight emerge from non- functional spray orifices 36. The vertical arrangement of the sprayer body 44 is advantageous for this purpose . The arrangement of staggered airflows provides for the equal distribution of space charge {created by the jets as they leave the spray orifices 36} which the airflow carries away .

To obtain maximum resistance to corrosion, the sprayer body 44 may be plated with rhodium (Rh" after fabricating holes that respectively receive the sprayers 32 and provide the slots 46. Rh forms no oxides at low temperature, is very hard and corrosion resistant. A few microns of Rh are sufficient to produce a corrosion resistant layer. Plating the sprayer body 44 with gold (Au) is an acceptable alternative to Rh.

Experiments have demonstrated that very fine seawater jets emitted from small holes in thin conductive sheets (stainless steel, Ti, Ni, Si etc.) acquire electrical charge due to a phenomenon called tribo-charging . Acquiring this electrical charge is highly advantageous because the electrical charge tends to keep the droplets separate and thereby opposes droplet -pair coalescence. It also has been found experimentally that emitted seawater droplets become negatively charged upon leaving the spray orifices 36. This is exactly the desired polarity for the droplets if they are to drift up in the atmosphere. The tribo-charging is proportional to jet velocity and has been measured experimentally for a 10-15 m/sec jet velocity with the charging typically being SO picoa ps per jet for a 5.0 μτη orifice, and 200-300 p coamps per jet for 50 pm orifice,

FIG, 3 depicts an alternative configuration for a sprayer body 52 that also uses the sprayers 32. The sprayer body 52 also employs staggered slanted sections 54 ends of which receive sprayers 32, Again the jets emitted from sprayers 32 are intercepted by airflow emerging from slots 46 piercing ends of each of the slanted sections 54. Space charge density now increases as the droplets travel up the sprayer body 52, but more sprayers 32 can be situated i the assembly.

In some instances, it has been found advantageous to include a charging/screening structure. The charged cloud in front of spray orifices 36 may affect the charge on the droplets as they come out and screening will dramatically lower the emerging space charge effect on the droplet charging. Or alternatively, additional droplet charging may be provided by applying a voltage to such a charging/screening structure.

FIGs. 4A and 4B illustrate a charging/screening structure 60 that is juxtaposed with the sprayer body 52. The charging/screening structure 60 includes a thin layer 62 of insulating material such as polyimide or other suitable material overcoated onto the membrane 34 of the sprayer 32. The charging/screening structure 60 includes a thin metallic electrically conductive electrode layer 64, typically made from copper, that is separated f om the membrane 34 by the insulating layer- 62. Tapered, conical holes 66 are laser drilled or chemically etched through both of the layers 62, 64 to match the spray orifices 36 formed through the membrane 34. Another insulating layer 68, again preferably polyimide, is sprayed onto the metallic layer 64 to provide an insulator that prevents accidental short circuits when the charging/screening structure 60 is exposed to conductive liquids. As is well known in the art for polyimide, an outer surface 72 of the charging/screening structure 60, par icularly surfaces of holes 66, may be treated to become super-hydrophobic, i.e. reaching contact angles of 160 degrees fox" water. Hence, when the sprayer 32 carrying the layer 62 is oriented vertically as in the sprayer body 52, no liquid droplets will stay on walls of the holes 66 thereby preventing water accumulation.

At a distance d toward the membrane 3 below a hole opening of diameter d the metallic layer 64 screens effects of outside electric fields such as that generated by tribo- charging thereby reducing the electric field's effect by almost two orders of magnitude. Electrically interconnecting the layer 64 with the membrane 34, e.g.. grounding both the layer 64 and the membrane 34, eliminates any influence by the outside electric field produced by tribo-charging that results from emitting liquid jets from the spray orifices 36.

PIG. 5 illustrates a cusped cone sprayer 80 adapted for producing small, narrow size-range droplets, and that is also very adaptable for electric dro breakup. The cusped cone sprayer 80 included a curved cone 82 having an apex that extends into and penetrates an orifice 84 formed into a body 86 of the cusped cone sprayer SO, A diameter of the orifice 84 is preferably approximately 200 urn, and the cone 82 preferably has an outer surface with a radius of curvature of approximately 5.0 ram. n the illustration of FIG. 5, the cone 82 is attached to and supported from the body 86 by three (3) legs 88. An end of the body 86 furthest from the cone 82 includes a threaded attachment 92. The cone 82 may be made out of tungsten (W) that has a thin overcoating of tungsten carbide ( C) . The cone 82 may be machined using diamond turning which permits producing suitable indentations on a surface of the cone 82 for inducing desired break-up of a liquid sheet as described in greater detail below.

FIG, 6 depicts operation of the cusped cone sprayer 80 wherein an axi-symmetric jet 94 of liquid emerges from the orifice 84. The apex of the cone 82 pene ates into the orifice 84 sufficiently to guide the jet 94 emitted from the orifice 84, The jet 94 then diverges over the surface of the cone 82, thinning in the process, but maintaining nearly constant speed. Coming from a 2000-psi pressure reservoir, the velocity of the jet 94 may be very high, e.g. 140 m/s. A freestanding liquid sheet 96 formed f om the jet 94 is flattened on the surface of the cone 82 by centrifugal force which may reach , 000, 000 g for a curvature radius of 5.0 ram. Hence the liquid sheet 96 exits the cone 82 radially subsequently breaking up into droplets. As mentioned above, an appropriate roughness may be added to the surface of the cone 82 where the sheet 96 departs from t e cone 82 to initiate breakup. In addition, the cusped cone sprayer 80 may include an ultrasonic transducer 98 to excite the fluid thereby assisting the breakup. If needed, charging electrodes 102 (circular or otherwise) can be located adjacent to where the sheet 96 leaves the cone 82 for electrically charging the liquid thereby further inducing additional atomization. Rayleigh breakup of spayed droplets may occur after leaving the cusped cone sprayer 80 as such droplets evaporate.

FIG. ? depicts an alternative conf guration sprayer 110 that includes the cusped cone sprayer 80. The sprayer 110 has an air inlet 112 for introducing an airflow, typically at 10 m/sec, into a annular passage located between a centrally- located rod electrode 114 and a surrounding cylindrically~ shaped ground electrode 116. Confined to this annular passage the airflow intercepts droplets emerging from the centrally located cusped cone sprayer 80. High pressure liquid is supplied to the cusped cone sprayer 80 via a passage 118 in the threaded attachment 92 of the body 86 to be forced through the orifice 84 past the cone 82. As the radial sheet 36 exits the cone 82 it may be aided in breakingup by the ultrasonic transducer 98. Ring-shaped charging electrodes 102 surrounding the base of the cone 82 may be used to charge the sheet 96 in the breakup process. A voltage applied between the electrode 114 and the ground electrode 116 can also induce Ray- leigh/Taylor instabilities in droplets emitted from the cusped cone sprayer 80, which then finally emerge as a mist from an exit 122 of the sprayer 110.

FIG. 8 illustrates such a method in which liquid forms droplets via Taylor cones. A Taylor cone sprayer 132 include several rows 134 each containing many orifices 136 though which jets of liquid emerge (usually broken up in the Rayleigh mode) . As the jets emerge from each of the orifices 136 they travel between parallel plates 142a, 142b to which a large voltage has been applied to obtain su ficient electric field strength to breakup into droplets the jets emanating from each of the orifices 136, An airflow, indicated by an arrow 144, may be present to help the droplets move between the plates 142a, 142b away from the Taylor cone sprayer 132 and to ultimately carry droplets out of the space between the plates 142a, 142b, The plates 142a, 142b must have sufficient length perpendicular to the rows 134 of orifices 13 to break up the j ts in the electric field, but not so long that the resultant droplets reach the plates 142a, 142b themselves . Orifices emitting air ma be interleaved among orifices 136 emitting liquid. Because emerging droplets can be made to be very mono-disperse, the field required for Taylor breakup for' a given radius will be roughly the same for' most of the droplets, which is an advantageous arrangement for control of the resul ing satellite droplet distribution. The jets emerging from the orifices 136 and the droplets obtained from such jets may become charged electrically either through tribo-charging or through the use of a charging structure similar to that described previously. Cylindrical configurations may also be used. A surfactant may be added to the liquid in orde r to reduce the surface tension and hence the instability threshold,

FIG, 9 illustrates a classical arrangement for a single Taylor cone electrospray . Liquid 152 forced through capillary 154 is drawn outward from the capillary 154 into a Taylor cone 156 under the influence of an applied electric field between capillary 154 and an extraction electrode 158, The field is established b applying a voltage between the capillary 154 and the extraction electrode 158, which may include an opening 162 through which sprayed liquid 152 emerges. Such structures are well known in the literature for almost 40 years and, are sometimes referred to as cone- jet combinations, representing the cone as described by Taylor, and a jet emanating from the cone tip, as described i many publications.

The conductivity of the liquid 152 sprayed may vary by many orders of magnitude, but as the conductivity increases it is found that in order to form a stable tip on the Taylor cone 156 the flow rate must be decreased, and the jet derived from the cone decreases in radius. In fact, for liquid metals in a vacuum, the tip of the Taylor cone becomes small enough to emit ions .

As the jet decreases in radius with increasing conductivity, the surrounding field becomes larger and can exceed the breakdown field in air, which is usually given as 30 kV/cm for parallel plates. However for the field surrounding very thin wires, much larger breakdown voltages are obtained. This is particularly critical for fluids, such as water, that have a high surface tension, as the starting voltage for forming a Taylor cone is proportional to the square root of the liquid's surface tension.

It has been stated by several authors that water, particularly if made conductive, cannot be sprayed in a stable Taylor cone. A recent publication by Lopes-Herrer et al . , JASMS 2004, p 253 describes some intermittent success with water doped up to 1 S/m, but states that higher conductivities are excluded from stable spraying and produce corona. The conductivity of seawater at 4 S/m exceeds that threshold . The presence of corona prevents generating droplets having uniform size using a Taylor cone.

We have found that adding appropriate surfactants in very low concentration lowers the surface tension sufficiently such that, long te m stable Taylor cones can be established, if specific ratios are used. Using anywhere from 0.01 to 0.05% Triton X100, a well-known surfactant, we have found it possible to spray stably without the presence of corona. Other useful surfactants, less toxic and more suitable are, for example, Tween 20, Lutensol^® XP 80, PolyaIdo^¾ 10-1 -KGF or 10-1-CC KGF (polysorbates) . Salt particles produced using surfactant treated seawater increase in size as the surfactant concentration increases, i.e. from 10-20 rim to 60-80 nm. Surfactant concentration is deliberately kept low so that dried salt particles lack a surfac nt monolayer, and hence the salt particles will be activated in a marine cloud. This occurs because of the enormous increase in surface area upon spraying the liquid. Experimentally it lias been found that 40-50-ητ» salt droplets produced this way were activated when put in a chamber with a 0.5% supersaturation, the same as would be expected when no surfactant is present.

An alternative way to enable forming Taylor cones using seawater is to reduce the size of the orifice 136. As can be seen in FIG. 10A, when the radius is smaller than 7 μπι, the breakdown field in air {along a thin conductive cylinder} , indicated by curve 172, is actually larger than the electric field that exists along the Taylor cone, indicated by curve 17 there is no air breakdown and no corona as occurs at l rger diairseters ,

FIG. 10B shows what happens if an appropriate surfactant is added to the water, dropping the surface tension by a factor of 2; the breakdown field limit, indicated by curve 176, is always large that the Taylor field of the cone, indicated by curve 178, and there is no breakdown for any radius.

Lack of corona breakdown can also be achieved by heating the fluid to be sprayed to near its boiling point, thereby reducing the surface tension while at the same time increasing the ambient spraying pressure. Increasing the ambient pressure increases the air breakdown. The increase in ambient only needs to be small, typically a 20% increase above atmospheric pressure is enough to reduce the breakdown. All of this is illustrated in FIG, IOC, which shows that the limit for air breakdown, indicated by curve 182, is everywhere above the field for the Taylor cone, indicated by curve 184. The increased pressure and the resulting airflow also helps to guide the resulting droplets through the scree in front of the cone and dilutes the resulting space-charge.

Hence_., the best mode for spraying without surfactant is to use orifices 136 less than 15 μτ» in diameter and an overpressure of 0.2 bar or more; if surfactant is used larger holes may be used. Best results, i.e. avoiding corona, are obtained with positive polarity on the extraction electrode 158. This gene-rates negatively charged nuclei, which should rise in the earth's electric field Instead of using a constant DC field, an AC component may be applied to control the splitting behavior of droplets. For example, the field may be brought close to break-up, and then the AC field ma be applied (either sinusoidal or pulsed) at an appropriate frequency such as to control the behavior of the drop spitting pattern. This ma control the spitting that occurs in these regions . Alternatively, the droplets may be excited at several of the resonance modes to control the break up and satellite spitting.

In many applications, the droplets may be let go freely into the air, e.g. , cloud whitening or fog making. However, when used for spraying of nano-particles , the product must be collected. This may be conveniently done with electrostatic precipitators, as is well known in the art. Corona discharge is used to diffusion-charge the dried particles, and the electric field then drives them to the collection plates where the product collects.

A very large number of orifices 136 and Taylor cones 156 are needed to produce 10 ' nuclei/sec per ship, since each Taylor cone 156 when spraying seawater, provides 10^!i to 10⁹ nuclei/sec. Traditionally, orifices 136 used for producing Taylor cones 156 have been made by micromachining as described in several theses from MIT (Lozano, etc.) , This is because they are mainly used as small rocket thrusters for spacecraft, where space is at a premium. Such micromachined structures as made by Krpoun (EPL, Doctoral thesis) and Deng et al . {Deng, W., Waits, C. . , Morgan, B. & Gomez, A. 200.9 Compact multiplexing of raonodisperse electrosprays . J. Aerosol Sex . 40 907-918) may be advantageously applied to spraying seawater for the Latham-Salter albedo modification scheme. They have the required sprayer density and produce extremely uniform droplets as described in these publications .

Instead of using deep orifices which are hard to fabricate we have found that excellent results are obtained using porous or fibrous, non-conductive emitters such as the tips of felt pens etc. Large arrays can be made by assembling these tips into arrays or" by milling a plate of porous material in two orthogonal directions, leaving an array of pyramidally-shaped tips as illustrated in FIG. 11. Pyramidally-shaped f ust ums 192 are obtained by intersecting two suc perpendicuiar milling operations. Porous carbon may also foe used for this application. Alternatively, these structures can be made by casting a porous plastic in a mold, Silicon micromachined V-groove and other structures may be used to get fine molds and produce very fine pyramids as is well known in the art. These structures ma also be formed thermally, by using hot forms pressed in 2 perpendicular di ec ions , This tends to seal the pores on the sides and the top, but by machining off tops of the frustrums 192, the ends are freely exposed and water can get out at the top. However, such arrays tend to be fairly large—on the order of 10 m* using 300 μτη separation between adjacent f ustrums 192.

A plate of frustrums 192 is connected to a reservoir to which a suitable pressure is applied so liquid flows from all tips, and Taylor" cones 156 form at the top of all frustrums 1.92. An extraction electrode 153 for each frustrum 192, similar to that depicted in FIG. 9, and a second electrode are used to produce droplets as is well known in the art.

Instead of arrays of frustrums 192 made of porous non- conductive materials, it is also possible to use whole arrays in non-wetting insulators . Orifices mechanically drilled in plastics have been shown to produce stable Taylor cones, with each orifice producing a separate Taylor cone (Lozano et al . , J Coil Sci, 276, 2004, 392).

It is advantageous for this application that the dielectric constant of the plastic be as low as possible, preferably close to unity. This enables the field to penetrate into the plastic and the field lines will terminate more intensely on the fluid itself which is very conductive, behaving as if the dielectric constant is infinite. With this arrangement it becomes possible to have lower starting voltages . By reducing the orifice size it is found that one can spray water without corona, A similar observation has been made by Li et al., (IJMS 272, 2008, 1995 when using a very thin dielectric needle? or by Lopea-Herrera using a very fine silica capillary {JAMS, 15 , 2004, 253} . Such orifices are vastly easier to fabricate in very large numbers than capillaries. Suitable materials are Teflon^® { - 2) , polyethylene (a = 2.3), polycarbonate (a = 3.17}, Peek {a - 3.3} and polyimide (a =3.6} . The latter is a particularly inert material and is well-suited for drilling. With an expansion coefficient matching that of copper, it is extensively used in the electronics industry and therefore is ideal for making electrodes. We have found that UV- laser drilling is ideal for this application. With systems such as the DPSS 1 UV laser, 150 , 000 orifices per second may be drilled in thin plastic sections {up to 1 mil) and 10, 000-20, 000 orifices ma be drilled in thicker plates using several sequential drilling passes. Very smooth clean orifices are obtained in a very large number of materials . These lasers are capable of producing 3.5 watts at 355 nm wavelength at repetition rates of 30 KHz , and 1 watt at 150 KHz .

In order to be suitable, it is imperative that droplets from individual orifices do not coalesce. Each jet and Taylor cone must be anchored on the rim of the orifice's exit or this method for creating nario-part icles fails. This can be accomplished by using an inherent very hydrophobic plastic, or by creating a surface at the exit of the orifices that is extremely hydrophobic. This prevents spreading of the fluid on the surf ce . Such a super-hydrophobic surface may be created in a variet of ways on various plastics, by creating appropriate surface topology or roughness as is well known in the art . Suitable super-hydrophobic coatings can be made by etching the surface of polyimide film with an oxygen plasma to create surface roughness followed by the deposition of a fl orocarbon film a few hundred nanometers thick. Coatings used must preferably be non-conductive, such that the electric field penetration that improves the threshold is maintained. The extraction electrode 158 is made of the same material, which provides temperature matching, but must be metal -coated to act as the extraction electrode 158,

For Taylor- cones best results are obtained with orifices 25-80 pm in diameter if a surfactant is added to seawater . The lower limit for orifice size is effectively determined by a filtration system used to avoid orifice clogging, but both larger and smaller orifices may be used. As stated before, with sufficiently small orifices, not exceeding 15 μπ\, corona disappears even if no surfactant is added to the seawater.

It is necessary to equalize the pressure across all orifices otherwise one Taylor cones in the whole array will overtake all the others. This has traditionally been done by drilling very deep orifices thereby providing each orifice w th its own flow controlling -resistance. We have found it much simpler than drilling very deep orifices to provide a standard polymer ox: any porous filter covering the entrance to all orifices at the same time, and which may be attached to the orifice plate by laser tacking,

PIG. 12A depicts an orifice plate 202 having a plurality of orifices 136 formed therethrough from which Taylor cones 156 extend. In FIG. 12A, a polymeric fiber filter layer 204 is attached to one surface of the orifice plate 202 opposite to the surface from which the Taylor cones 156 extend. For example, using a polymer fiber filter with rated filter size of 0.5 ]xm, it is found that interposing the polymeric fiber filter layer 204 between a source of liquid and the orifices 136 is approximately equivalent to 2 Psi pressure reduction, or about 1/7 a mosphere. Such fiber filters are extremely uniform, and therefore each orifice 136 now experiences a constant and uniform flow resistance. Note that if so desired, as illustrated in FIG. 12B the polymeric fiber filter layer 204 may ^'be replaced by a sheet 206 that is pieced by numerous groups of holes 208, perhaps of 5.0 μητ. diameter, located to match the locations of orifices 136 in the orifice plate 202. In FIG. 12B, the orifice plate 202 having larger diameter orifices 136 is laminated to the sheet 206 so several smaller holes 208 supply liquid to one orifice 136. The juxtaposition of groups of holes 208 formed through the sheet 206 with each orifice 136 in the orifice plate 202 established a controlled flow resistance that is much higher than that provided by each orifice 136 itself since liquid flow depends upon the fourth power of hole radius. ^■ I ? ···

For very small holes, the absolute filters created by alpha particles radiation tracks known as Nucieopore™ or similar filters may be used, 'These filters have very uniform randomly located holes of very uniform dimensions and almost constant diameter ranging from tenths of a μττι to several μτη, Only small sections of the film can be used because they can only support relatively small pressures and ^'hence multiple sections must foe used to create enough throughput. Such films must be supported by a suitable metal or plastic frame.

Alternatively, as illustrated in FIG. 13 a planar plate 212 can be fabricated that provides significant flow resistance, A surface of the planar plate 212 that is juxtaposed with the orifice plate 202 has canals 214 laser-scribed therein. A first end of each canal 214 mates with one of the orifices 136 in the orif ce plate 202 while second end terminates in a through-hole 216. A third plate 222 is pierced by feeding holes 224 respectively located to mate with one of the through-hole8 216. By laminating and bonding the plates 202, 212 and 222 together it is possible to connect each orifice 136 in the orifice plate 202 via a canal 214 that exhibits significant flow resistance to a corresponding feeding hole 224 in the third plate 222.

FIG. 14A illustrates yet another way fox- fabricating a structure for producing Taylor cones 156. In the illustration of FIG. 14A, a substrate 232 of porous polymeric material or any porous material underlies an attached polyimide orifice sheet 234 having the desired orifices 136. The porous substrate 232 provides the required flow resistance and orifice isolation. The orifice sheet 234, which has a thickness of 3 to 4 times the diameter of the orifices 136, can be laser drilled or processed lithographically for forming the orifices 136 therein. This aspect ratio for the orifices 136 is sufficient to provide the desired field augmentation with a low dielectric constant material. The porous substrate 232 (carbon, plastic, metal) also acts as a final filter to keep the orifices 136 from clogging. An extraction electrode 158, similar to that described previously, permits drawing Taylor cones 156 from the orifices 136 of the orifice sheet 234. FIG. 14B illustrates an enhanced version of the structure depicted in FIG. 14A. In the illustration of FIG. 14B, a surface of the orifice sheet 234, made from polyimide or other suitable polymeric material, furthest from the attached substrate 232, is etched to provide projecting cylinders 238, The cylinders 238 are subsequently laser drilled or pierced in any other suitable way to create the orifices 136. An appropriate voltage appiied between the extraction electrode 158 and the adjacent orifice sheet 234 and/or substrate 232 forms the Taylor cones 156. If the Taylor cones 156 are not- contained at the edge of the cylinders 238 by surface tension, liquid flows into the trough between the cylinders 238 without affecting adjacent the Taylor cones 156. The structure depicted in PIG. 14B possesses the advantages associated with long orifices 136 while avoiding deep drilling. In addition to polymeric materials, the orifice sheet 234 may be also made out of plated metals such as Ni, or made with micro injection molding. The extraction electrode 158 may be made of metal by etching or using advanced printed circuit board fabricating techniques . The space between the extrac ion electrode 158 and the orifice sheet 234 is pressurized at a minimum of 0.2 bar to produce airflow through the openings 162 thereby assisting jet formation, sweeping out droplets and diluting any space charge. For example, the orifice sheet 234 may be 5 mils thick, the cylinders 238 may be 3 mils high with a 1 mil diameter orifice 136 drilled therein, and with the extractor plate 5 having openings 162 that are 2.5 mil in diameter.

In polymer membranes 12 to 25 pm thick, smaller holes can be readily drilled using large NA lenses. In fact, holes as small as 1.0 ].im and 0,5 μτη may be drilled in such material. Hence it becomes possible to use such membranes in Rayleigh jet spi-ayei-s . While the yield strength of polyimide is lowe than that of equal thickness foils of Ti or stainless steel, as depicted in FIGs. ISA and 1SB this difficulty can be circumvented by making a composite membrane that supports the foil. For example, a sprayer 240 may be fabricated using a thin foil membrane 242 in a section about one quarter inch in diameter that is bonded to a honeycomb-shaped support substrate 244. The foil membrane 242 may include a hexagonal array of spray orifices 36, Because of the ease of fabrication, such sprayers 240 become an almost disposable item. Such a thinness for the foil membrane 242 also allows for easy backflow, and polyimide membranes 242 may be brought to high temperature for cleaning or autoclaving {sterilization} . As described above, 0.5 μπ* diameter spray orifices 36 would produce droplets approximately 0.9 um as desired in the original L-S cloud albedo scheme. Here typicai spacing between spray orifices 36 may range from 20-100 μτη. Elastic deformation of the foil membrane 242 allows the sprayer 240 to become spherically domed similar to the sprayer 32 described previously. As described above, a spherically domed foil membrane 242 is highly desirable in Rayleigh mode spraying to avoid coalescence. In addition to being useful for spraying liquid, the sprayer 240 is also useful a a filter.

While adding a flowing gas through an annulus concentric with jets produced by the Taylor cone sprayer 132 is probably necessary, much power is used in the process. To enhance salt crystal precipitation from a droplet, the air may be heated to enhance droplet evaporation at the cost of increased energy. In principle a significant portion of flowing gas energy can be recovered through a turbine, which adds to system cost and could interfere with droplet and/or salt crystals movement.

Most of the energy needed to generate the Taylor cone jet appears in the droplets kinetic energy, rather than their surface energy. Droplet ejection velocity may be on the order of hundreds of meters per second, and is by and large wasted. This can probably be overcome by using a dual extraction anode structure such as that illustrated in FIG. 16, The ex rac ion anode structure depicted in FIG 16^' is reminiscent of, but a different from, a Kelvin generator. The extraction anode structure includes an insulating planar substrate 252 that carries an upper left extraction electrode 254a and an upper right extraction electrode 254b that respectively face Taylor cone jets 256a, 256b, As depicted in FIG. 16, the extraction anode structure also includes a lower left extraction electrode 258a and a lower right extraction electrode 258b that in the illustration of FIG. 16 are cross- connected within, the substrate 252 to the upper extraction electrodes 254a, 254b 'The upper extraction electrodes 254a, 254b carry opposite polarities and hence produce oppositely charged droplets.

To produce negatively charged droplets 262a from the left taylor cone jet 256a, the upper left extraction electrode 254a must be positively charged with respect to the taylor cone jet 256a, and the lower left extraction electrode 258a negatively charged. The right taylor cone jet 256b produces positively charged droplets 262b when the upper right extraction electrode 254b is negatively charged and the lower right extraction electrode 258b is positively charged. The droplets 262a, 262b are formed and accelerated by the upper" extraction electrodes 254a, 254b and slowed down by the lower extraction electrodes 258a, 258b, where energy is given up by induction to the source providing the acceleration potential to the droplets 262a, 262b of opposite polarity. Save for frictional losses, in principle kinetic energy in the droplets 262a, 262b could all be recovered since air blown through openings 162a, 162b flushes the droplets 262a, 262b a collection manifold {not depicted in FIG, 16) , where they are swept by the common air low. Voltage sources can be superimposed on the connections between the electrodes such that some velocity on the droplets 262a, 262b is main ained .

This scheme also neutralizes the space charge cloud due to spraying equal amounts of positive and negative charges. To improve field efficiency and reduce coalescence of droplets, banks of rows rather than a single row of apertures would be connected. Since most of the droplets 262a, 262b are immediately dry, coalescence is not a well defined term here, at least not i the usual sense. Coalescence of a positive and negative crystal would not necessarily be a bad thing as it would only double the mass. Hence, using this scheme, it would seem that the electrical power needed for each sprayer (on the order of 100 KM) might in principle be reduced substantially. The main power drain is actually pneumatic, and air low needed to maintai adequate flushing is probably best determined experime tall . Thus three devices and methods have been described that can be used to produce suitable particles for the Latham-Salter application. All three devices require making a very large number of holes. It would be much simpler if conventional spraying nozzles might be used. However there are no commercial nozzles that ca produce droplets small enough for this particular applica ion ,

To reduce the mea diameter of spray droplets, reducing the surface tension of the sprayed liquid which, unfortunately, is fixed at room temperature would be very advantageous. By heating the liquid to a supercritical state the liquid's characteristics become similar to those of a dense gas and the liquid's surface tension approaches aero, FIG. 17A depicts the surface tension of water as a function of temperature, and PIG. 17B depicts the viscosity of water as a function of temperature. As indicated by the graphs of FIGs. 17A and 17B, both the surface tension and viscosity of water approach zero as temperature increases, a condition favorable to very fine liquid dispersion. The decrease in surface tension and viscosity of water as temperature increases is accompanied by a reduction, to some degree , i its density.

Hence by heating seawater (or saltwater) to its critical temperature under pressure it becomes possible to disperse it almost like a gas into extremely fine droplets. FIG . 18 illustrates a prototype, single nozzle system 270 for accomplishing this. Here saltwater or pure water, draw respectively from a saltwater reservoir 272 or from a pure water reservoir 274, flows through a 2 way valve 276 to a high pressure pump 278, A suitable experimental pump is for example a Haskell pneumatic-driven fluid pimp such as one dispensing roughly 10 cc of fluid with each stroke. The system 270 permits monitoring the water's pressure using a pressure gauge transducer 282 such as an Asheroft digital pressure gauge. The system 270 may also include a accumulator 284 for reducing any negative pressure excursions that occur during the intake stroke of high pressure pump 278, The high pressure water then enters a serpentine tube 286, typically made of titanium having a typical diameter in a range from, one-half inch (0.5 in) to one-sixteenth inch (0.0625 in) .

An oven 292, formed by two (2) mating aluminum slabs that have been machined to make intimate contact with the serpentine tube 286, encloses the serpentine tube 286, Each aluminum slab is heated by a cartridge heater (not shown) inserted there into. A tempex'atux'e control system 294 regulates oven temperature -responsive to a signal received from a thermocouple inserted into one of the slabs. Before heated, pressurized water leaves a nozzle 296 its temperature is measured by a thermocouple 298 immersed in the water . The serpentine tube 286 within the oven 292, which is thick, may use a liner of a material such as titanium and its alloys or zirconium and its alloys with a majority of the serpentine tube 286 being made from a less expensive material such as stainless steel. Thin layers of plated gold or rhodium may also be used to form a non-corrosive liner the inside of the serpentine tube 286 the heater tubing. Preferably, the gold is applied by coating the inside of the serpentine tube 236 with an organic gold solution, which is then fired at high temperature, e.g. 600 ÷C leaving a thin layer of strongly attached gold \«

When the fluid emerges from the nozzle 296 (usually at supersonic speed) , due to the sudden reduction in pressure, it expands explosively and this, coupled with the lack of surface tension and viscosity, produces an extremely small -sized droplet spray.

It should be noted that adding a gas such as air or nitrogen, dissolved into to the liquid will further enhance the supercritical fluid's dispersion as is noted in the operation of effervescent spray nozzles, as such gas desolvat.es and expands upon exiting from the nozzle.

The nozzle 296 typically comprises a cylind ically-shaped orifice formed in metal or ceramic that is typically 20 to 150 μϊϊΐ in diameter, with aspect ratio (length to diameter} preferably in the range of 1 to 10 {without limitation) . The nozzle 296 preferably includes a conically-shaped entrance to the cylindrical orifice to improve flow characteristics . Supercritical seawater is extremely corrosive and since the nozzle 296 needs to withstand both high pressure and high temperature, material selection is extremely important in order to avoid stress corrosion. Few materials are suitable for the nozzle 296, and many ordinary high pressure nozzle materials such as sapphire fail under- the operating conditions of the system 270, Many of the standard corrosion-resistant materials such as stainless steels, or nickel alloys such as Inconel^® and Monel^t¾ exhibit only limited lifetimes. Several ceramics have been found to exhibit resistance to supercritical seawater, particularly for the nozzle 296. Ceramics of choice are high- purity silicon carbide, diamond, diamond-like carbon, aluminum oxide and the like. Thin coatings of such ceramics, or graphite or vitreous carbon might be applied to the metals suggested below. However, it may be possible to use other materials for the nozzle 296 such as silicon carbide and titanium, the latter preferably over coated with nitride or carbide. To make a nozzle 296 from titanium, the orifice may first be drilled in titanium (preferably grade 2) and then the orifice's surface modified by nitriding or carburizing, as is well known in the industry, using reactive gases at high temperature. Zirconium and its alloys might also be a useful material for the nozzle 296. Nozzles may fabxucated entirely from these materials, or simple orifice plates containing the spray hole may be mad , The best material identified thus far for the nozzle 296 is diamond.

Operation of the system 270 may be best understood with isobaric diagrams as illustrated for various isobars appearing in FIG. 19, The liquid is under almost constant pressure during heating save for flow losses along the serpentine tube 286. We select for example 360 bar as the operating pressure, and a salt concentration of 1% (i.e., 0 on a log scale) . On heating, the liquid state follows the arrow, there being no phase separation un il the temperature reaches 428 °C. However the properties of the liquid substantially change during the heating, the liquid becoming much less dense, vapor-like, losing surface tension and becoming much less viscous. At the intersection of the vertical line and the 360 bar isobar, there is only a low-density fluid, or ^wvapor" , of 1% salt concentration. On further heating, phase separation starts occurring. A very salty (16.5% salt, i.e., log 1.2) higher density liquid will split off. When such a mixture is sprayed through the nozzle 296, the vapor phase sprays very well giving reasonably narrow particle size distributions of the desired- size dry salt particles, while the liquid phase gives rise to much larger particles and broader distributions, often produced as irregular nozzle "spitting" . If the temperature is further increased at 360 bar, e.g. to 445 °C (point B) , the vapor phase becomes less concentrated in salt as can be seen (producing thereby smaller" salt crystals when sprayed) , while the liquid phase becomes even more salty (almost 30%^·) . The amount of liquid that is formed also increases very rapidly with rising temperature .

For a given pressure, the best operating point is the temperature T at the intersection of the isobar with the line of concentration (i.e., point A, 423 °C at 360 bar) . Only vapor with the full salt concentration of the original liquid is sprayed, and no salty liquid is formed at the entrance to the nozzle 296 (the vapor can of course go throug phase separation within the nozzle 296) . This is one preferred embodiment for spraying. Point A provides the highest enthalpy for the fluid, without the formation of salty liquid. Hence, in principle , the temperature is set such tha the liquid reaches point A at the end of the serpentine tube 286 just as the liquid enters the noszle 296. Liquid of 1% salt concentration may also be sprayed a a temperature below point A, but results tend to be less favorable, and larger droplets occur.

The points in FIG. 19 at the intersections of the constant salt line with the various isobars define a curve in P-T space fox- a particular salt concentration, which is called the two- phase line for that concentration. That is where brine is being split off, for various pressures, a various associated temperatures .

There is another additional condition that ca advantageously be matched. The expansion through the nozzle 296 is an isenthalpic process (i.e., enthalpy is conserved) . The fluid expands to one atmosphere , and in order for it to expand to dry steam and avoid the formation of large liquid droplets the enthalpy of the fluid must at least, be equal to the specific enthalpy of dry steam i.e., 2676 kJ/kg.

Experimentally, it is observed that when, pure water is sprayed in the system 270, and satisfying this enthalpy criterion, the spray exiting from the nozzle 296 is nearly invisible, which indicates complete vaporization and the absence of any large liquid droplets.

Hence the operating point for the system 270 can be judiciously selected, satisfying both conditions, i.e., two- phase boundary and suitable enthalpy. For a number of salt concentrations, the two-phase line is plotted in FIG. 20, As indicated above, this defines a locus of points in P~T space. At the sarae time, the requirement for a specific enthalpy value of 2676 kJ/fcg defines a separate curve in P-T space. Where both curves meet, both conditions are satisfied. Curves 302, 304, and 306 represent the two-phase boundary lines for salt concentrations of 3.2%, 1,0%, and 0.5%, respectively. Curves 312 and 314 represent constant specific enthalpy curves in P-T space for 2676 and 2750 kJ/kg, respectively. Selecting 2676 as sufficient, suitable operating points are then found for these three salt concentrations at points A, B and C, i.e. the respective intersections between curves l, 2, and 3 with curve 4 (for higher desired specific enthalpy e.g., 2750 kJ/kg, the intersections are defined by A', B' and C ) . Thus, if a .3.2% salt solution is being sprayed, then at point A, i.e. approximately 505 °C and 540 bar, all salt will be present in a vapor- phase, and there will be enough enthalpy to evaporate all liquid.

As the enthalpy of salt is negligible, this then provides a means for setting u the system 270 when a certain salt concentration is to be sprayed. For example, if a 3.2% salt concentration is to be sprayed, the system 270 first sprays pure water with the liquid temperature set at 505 °C and the pressure is then adjusted to approximately 540 bar until the light scattering from the spray plume disappears or becomes very faint (alternatively, the roles of P and T may be changed for adjustment purposes) . This technique permits fine tuning operating conditions of the system 270.

PIG. 21A presents operating condition graphs for the system 270 when spraying water with a 0.25% salt concentration. Note that the enthalpy curve in FIG, 21A intersects the P~T curve at both high and low P-T values. The -region about the lower of the two intersections, i.e. at 330 °C and 130 bar, may be used advantageously for spraying, although strictly speaking operating the system 270 under such conditions would not be supercritical spraying. PIG. 218 shows results for salt- particles produced with the system 270 when spraying water with the 0,25% salt concent ation. The left half of FIG, 21B is a SE3 image of salt particles produced in this way, and the right half of PIG. 21B is a log-normal salt particle size histogram. This distribution of salt particle sizes, and others obtained at different salt concentrations, indicates that the salt particles are suitable for use in cloud brightening.

It should be noted that the small size of the emerging particles allows for easily monitoring operation of the system 270. Illuminating the nozzle 296 with a high intensity white light while the system 270 produces micron sized particles permits observing a very white plume emanating from the nozzle 296. When operating correctly in the submicron regime, due to the strong wavelength dependence of Rayleigh scattering, the scattered light intensity will decrease rapidly in intensity and become blue. Simple observation of the plume emanating from the nozzle 296 by a trained operator using a flashlight provides for a very good measure of the system's operating condition, and can be used for monitoring the system's performance .

As mentioned above, spraying very salty liquid degrades salt particle size and the particles' size distribution yielding very large {> 100 nm) particles, and very broad particle size distributions, both of which are undesirable. It has been noted that the liquid, in spite of being typically very salty, can emerge through extremely small openings (e.g., cracks or leaks at connections) , The liquid within the system 270, having very low viscosity and surface tension, if given time to coagulate from what is imagined to initially be a fine "mist," clings to tube wails and can easily be collected at the lowest point of the system and drained off. This will remove part of the input salt, but upon spraying the removal operation vastly imp-roves the resulting particle size distribution, A modification of the system 270 to facilitate the removal operation appears in FIG. 22. in that FIG. the serpentine tube 286 is heated by the oven 292. A reservoir 322, located below the serpentine tube 286 and ahead of nozzle 296, collects liquid at the lowest point in the system 270 through an orifice 324.

As illustrated in FIG. 23, for optimum operation the oven 292 may be advantageously split into two separate ovens 292a and 292b. Ideally, as indicated in the FIG. 19 isobaric phase diagram chart for saltwater the temperature of the liquid should reach point A at the end of the serpentine tube 286 (assuming 360 bar pressure} . However, this combina ion of temperature and pressure is experimentally difficult to obtain or assert. The heat transfer coefficient of supercritical water is difficult to determine, and is known to vary sharply in the critical region in ways that are difficult to predict. The temperature profile across the cross -section of the serpentine tube 286 may also fluctuate. The highest temperature occurs at the wall of the serpentine tube 286, and liquid may condense there well before doing so in the middle of the serpentine tube 286. In addition, the operation of the high pressure pump 278, such as the aforementioned Haskell pump, may produce rapid periodic decreases in pressure during the pump's intake stroke . Such lo pressure transients may temporary nucleate liqrid drops within the serpentine tube 286 from the hot, pressurized saltwater. The accumulator 284 included in the system 270 illustrated in FIG. IS advantageously attenuates such pressure excursions.

While liquid formation in the serpentine tube 286 by itself may not be disadvantageous if the drops are sufficiently small, formation of very large drops causes drastic temporary interruptions in the spray which results in producing very large salt particles. To avoid such events i is advantageous to continuously remove all salty liquid from the serpentine tube 286 immediately upon its formation thereby minimising the formation of liquid drops. To alleviate this situation, a pair of ovens 292a, 292b advantageously replace the single oven 292 depicted in FIG, 18,

FIG, 23 illustrates this configuration for heating liquid within the serpentine tube 286 using the two ovens 292a, 292b. A first oven 292a heats a larger cross -section segment of the serpen ine tube 286, i.e. serpentine tube segment. 286a, to a temperature well below the desired operating point A in FIG. 19. Keeping the temperature of the oven 292a 5 to 20 °C below operating point A is sufficient for preven ing liquid formation inside serpentine tube segment 286a. Preferably, a thermocouple 332, located at the end of the larger cross-section serpentine tube segment 286a, monitors the temperature in the ove 292a, The second oven 292b surrounds and heats a smaller cross-section segment of the serpentine tube 286, i.e. serpentine tube segment 236b, which connects to the nozzle 296. As described previously for FIG. 22 the system 270 may also advantageously include the reservoir 322 and orifice 32 . Decreasing the diameter of the serpentine tube 286 in the serpentine tube segment 286b increases the liquid's velocity and enhances turbulence thereby tending to sweep away any incipient liquid drops forming at the wall of the serpentine tube segment 286b, The interior of the serpentine tube segment 286b is preferentially polished very smooth, and may also be coated with substances such as diamond film to reduce friction and adhesion. Moreover, acoustic energy may be applied to the serpentine tube 286 so nascent drops shake loose and to be swept along the serpentine tube 286 toward the nozzle 296. The temperature of the serpentine tube segment 286b is ad usted to heat the liquid sufficiently that it sprays at the final desired temperature. Changing the temperature of the serpentine tube segment 286b usually causes a redistribution along the entire length of the serpentine tube 286 which makes interpretation difficult. The configuration depicted in FIG. 23 allows for independent control of the liquid's temperature, velocity and dwell time. A system such as that depicted in a combination of FIGs.

18 and 23 is particularly desirable if many nozzles 296 are used, which would be the preferred way of operating. In PIG. 24, a manifold 342 delivers liquid to several serpentine tubes 286 each of which is separately heated by an oven 292b and terminates at a nozzle 296. The heat supplied respectively to each of the serpentine tubes 286 by the oven 292 through which the serpentine tube 286 passes may be controlled by a thermocouple as described previously. Because of differing flows and velocities in each of the serpentine tubes 286, it would be extremely difficult to get the same spray conditions from each nozzle 296.

An orifice 352 in each of the nozzles 296 may be sealed in place as illustrated in FIG. 25 using a gold wire seal 354. As depicted in FIG. 25, the orifice 352 is sealed against the serpentine tube 286 with the gold wire seal 354 and cap 356 that attaches to the serpentine tube 286 to thereby retain all the components of the nozzle 296. Gold has been found to be unreactive at the temperatures processing conditions of the system 270, and sufficiently malleable to make a very tight seal .

Using micro-fabrication techniques , several orifices can be fabricated simultaneously, FIGs. 26A and 26B illustrates the fabrication of an orifice plate 360 which begins with micromaching a silicon mandrel 362 to form pyramids 364. Each pyramid 364 has a well defined top 366 (SO μτη square} and well defined crystailographic planes to a specified depth, e.g. 300 microns, so the height of the pyramids 364 equals the desired thickness of the orifice plate 360. Such techniques are well known in the art. The m udre1 362 is then overcoated with a layer 372 of silicon carbide, diamo d, TiN, Tic etc, or any of the othe suitable material. After depositing the layer 372, the top surface 374 is then polished to remove protruding ridges 376 down to the tops 366 of t e pyramids 364. Then the mandrel 362 is completely etched away using standard etching techniques, thereby leaving f ee standing the diamond or silicon carbide layer 372 that is pierced by orifices 382 of the proper size. At the same time, by the same process the ridges 376 may be etched, thereby subdividing the diamond or silicon carbide layer 372 into long strips. This method yields a strip 386 depicted in FIG. 26B having the orifices 382. Such a strip 386 of orifices 382 may then be clamped to the face of a tube and sealed thereto with a soft gold wire to provide multiple orifices for spraying. The strips 386 ma be fabricated using any size silicon wafer, and may have orifices 382 that are 25 to 150 μιτι square, separated 2 to 10 mm.

It should be noted that the materials which are found suitable to serve as support for spray orifices in this supercritical water application are under extremely high corrosive and tensile stress. These materials are therefore also suitable as linings for" the tubes or vessels anywhere where supercritical water is used such as in the destruction of PCB ' s , the extractio of oil and other fuels from celluiosic material. A coating of a few micron of silicon carbide, diamond or diamond like carbon, TiM, TiC, etc. applied or deposited is therefore very advantageous to increase the lifetime of such vessels.

Thus far only single orifice nozzles or multi -orif ce nozzle assemblies have been described. Αχ-rays of these assemblies may be used and arranged to create the desired μπι sized droplets of seawater rising from a ship for increasing the marine boundary. This will typically require from one to several thousand small nozzles of the various types described herein .

The number of nozzles may be reduced by using larger, flow-blurring nozzles, as described by Alfonso Ga an-Calvo. With the nozzles described thus far, heating the droplets may assist particle formation without affecting the spray distribution. However, in the flow-blurring nozzle, another fluid is added before forming droplets. This enables meeting the desired enthalpy criteria by adding the enthalpy of the second fluid before spraying the liquid,

FIG. 27 depicts the operation of a flow blurring nozzle 400. A liquid 402 that is to be dispersed enters the flow blurring nozzle 400 via a tube 404. Dispersion of the liquid 402 can be assisted by introducing gas 408 or a liquid which, under the proper conditions, backflows into the flow of liquid 402, mixes turbulently, and enhances dispersion of the liquid 402 during expansion. For making salt particles, the liquid 402 would be supercritical saltwater, approximately at operating condition A in FIG. 19. By heating the gas 408 (e.g., using the exhaust of a ship's engine), it becomes possible to increase the enthalpy of the mixture, as a large part, of the gas 408 becomes entrained in the liquid 402 before dispersal . Hence the mixture may be made to satisf the conditio of matching the enthalpy of dry steam, whereas the supercritical fluid by itself does not have to match that enthalpy. Hence, in principle any condition for dispersing the liquid 402 may be chosen, and the condition may be matched by adjusting the flow and temperature of the added gas 408. However, operation of the flow blurring no zle 400 requires additional energy.

Another nozzle type and pump that may be used, and which is read ly available for commercial use, is that used for commercial water jet cutting. Here water is pumped at room temperature to pressures from 60,000 to 100, 000 psi . The resultant extreme turbulence creates -very fine drops. Hence seawater may be sprayed this way which gives rise to micron sized droplets having fairly broad distribution. Such machines have nozzles ranging fro 50 to 200 microns. Water jet cutting nozzles include a secondary chamber surrounding the jet for adding abrasive particles thereto. The added abrasive particles provide most of the cutting action. For dispensing small salt particles the abrasive particles may be replaced with a solution of suitable surfactant. Hence the surfactant is therefore immediately attached to the surface of the jet, which is where its action is desired and further enhances the jet's breakup.

Seawater is a combination of various salts besides NaCl (including calcium, magnesium and potassium salts) and some of these salts are prone to deposition during heating. Hence the water may be preheated in a separate vessel, where the offending salts are precipitated and eventually removed. Methods for removing the precipitating salts are well known in the underwater oil exploration industry, where such treated seawater is used for injection, to avoid plugging cracking pores. Various manuf c urers such as Dow, Osmonics, and Hydronautics provide membranes for this purpose. The preparation method is schematically illustrated in FIG. 28. Here incoming seawater is first filtered i block 412 to remove particulates. Then the filtered seawater undergoes desaliniza- tion in block 414 to obtain the desired concentration of sodium chloride. Either simultaneously or sequentially, in block block 416 heat -precipitating ions are removed using the same process as used i the oil exploration industry. The process depicted in FIG. 28 may be added on to the desalination process available on most seafaring vessels.

With the methods described here {Taylor cones and supercritical saltwater) there is virtually no concern about resultant salt particles' buoyancy. These methods do not rely on the need for substantial atmospheric evaporation of sprayed droplets, as in most cases almost enough energy is supplied to produce near complete evaporation of droplets . ith supercritical saltwater, it has been determined experimentally under laboratory conditions that the plume lifts readily even without wind assist and evaporation is nearly instantaneous , thereby optimizing the efficiency of nucleus formation.

The original Latham-Salter method envisions creating special sailing ships solely for nuclei dispensing purposes. Using seafaring ships, it is envisioned that salt particles created by the sprayers could be mixed with the ship's exhaust gases to ensure that launching upward and reaching the desired target marine boundary layer clouds. If mixing with ship exhaust proves undesirable because of coagulation, then alternative heat exchangers, utilizing the waste heat from ship engines may be used such that the salt particles created by the sprayers is mixed with only clean warm air to reach its target. Heat exchangers using the waste energy from ship engines may, of course, also be used in assisting the heating of the seawater, or if converted to mechanical energy for use in its pressuriza ion.

For all of these reasons, deployment of regular ships is highly desirable. While the ships may not always be in the desired location because they follow the usual shipping routes, a signal may be sent from a central satellite command when the ship reaches the region that is suitable for cloud seeding. In this way no special ships need to be built and the operation can be piggy backed with the existing fleet of cargo ships. The cloud whitening could be combined with micro bubbles in the trail of the ship, thereby increasing the albedo of the ocean itself ,

Although the present invention has been described in terms of the presently preferred embodiment, it is to be understood that such disclosux-e is purely illustrative and is not to be interpx-eted as limiting. Consequently, without departing from the spirit and scope of the disclosure, various alterations, modifications, and/or alternative applications of the disclosure will, no doubt, be suggested to those skilled in the art after having read the preceding disclosure. Accordingly, it is intended that the following claims be interpreted as encompassing all alterations, modifications, or alternative applications as fall within the true spirit and scope of the disclosure.

Claims

2h ..S:ia.ims What is claimed is :

1. A system for producing solid nano-particles of a material by dispersing very small droplets of liquid in which the material is dissolved, the system being adaptable for use in geoengineering for increasing cloud reflectivity, the system comprising :

a, pump for supplying the liquid; and

b a plurality of orifices included in at least one sprayer, the liquid upon being supplied to said sprayer forming droplets after flowing through the orifices, the sprayer being selected from a group consisting of:

i. domed sprayers (32, 240);

ii . cusped cone sprayers (82); and

iii. Taylor cone sprayers (132).

2 , A method for producing solid nano-particles of a material by dispersing very small droplets of liquid in which the material is dissolved, the method being adaptable for use in geoengineering for increasing cloud reflectivity, the method comprising the steps of:

a. both pressurizing and heating the liquid so the liquid is in a supercritical state wherein the liquid becomes like a dense gas and the surface tension approaches zero ; and

b dispersing the pressurized and heated liquid in the supercritical state through an orifice.