Vortex station

Abstract

This invention relates to a vortex station and method for producing a vortex similar to one of a group consisting of dust-devils and waterspouts. The apparatus comprises a ground platform forming a base for the vortex station, a plurality of vanes to direct an air flow into a vortex station and about the vortex station in a substantially swirling manner, at least one wind turbine disposed near the centre of said vortex station, in a path of a concentrated air flow, wherein the movement of the air in the vortex station is such that an atmospheric buoyancy vortex is created in the centre of the vortex station, a supply of a working fluid (e.g. water) to the vortex station at or near the centre of the vortex station such that the air is of a saturated condition or an at least partially saturated condition with the working fluid (e.g. water), the working fluid (e.g. water) supplied at a sufficient quantity or amount so as to assist with maintaining buoyancy and stability of a vortex created.

Claims

1. A vortex station for producing a vortex in an outdoor environment, comprising: a ground platform forming a base for the vortex station; a plurality of swirl vanes to direct an air flow into the vortex station and about the vortex station from an ambient environment; at least one wind turbine centrally located or disposed at or near the base of the ground platform, and defining a center about which the turbine rotates in a path of a concentrated air flow, the swirl vanes rising in height above the wind turbine and arranged in a substantially circular manner about the periphery of the vortex station, and wherein the turbine is located within an inflow of air from the vanes, in proximity to ground platform and whence into the vortex, wherein the ground platform being free of a tower or cylindrical wall that encloses the vortex; and a supply of heated vaporizable liquid or working fluid to the vortex station via a plurality of nozzles mounted on the ground platform that surround the center, the supply of heated vaporizable liquid or working fluid causing saturation or near saturation of the ambient temperature air flow, free of external heating of the air outside the swirl vanes.

2. The vortex station of claim 1, wherein the movement of the air in the vortex station is such that an atmospheric buoyancy vortex having a maximum height of approximately the tropopause is created in the center.

3. The vortex station of claim 2, wherein the swirl vanes are inclined at an angle to the radial relative to the center, so that an angle at which the air enters the turbine in the inflow is set by the angle of the swirl vanes.

4. The vortex station of claim 3, wherein the swirl vanes are curved in the shape of a yacht sail.

5. The vortex station of claim 4, wherein the swirl vanes are adjustable in angle relative to the radial.

6. The vortex station of claim 5, wherein the turbine defines a plurality of vertical blades rotating about the center.

7. The vortex station of claim 1, wherein the turbine defines a plurality of vertical blades rotating about the center.

8. The vortex station of claim 1, wherein the vaporizable liquid or working fluid is water or a heated water stream.

9. The vortex station of claim 1, wherein the air flowing into the vortex station is conditioned so as to allow release of a sufficient amount of latent heat through condensation in the created vortex core so as to maintain buoyancy and stability of the created vortex.

10. The vortex station of claim 1, wherein the plurality of nozzles are configured to produce a fine spray of the vaporizable liquid or working fluid.

11. The vortex station of claim 4, wherein the swirl vanes are constructed of fabric.

12. The vortex station of claim 7, wherein said vortex station further comprises an annular roof above the nozzles and the turbine about at the center.

13. The vortex station of claim 1, wherein the turbine comprises a plurality of concentric turbines with a plurality of concentric blade sets.

14. The vortex station of claim 1, wherein, said nozzles direct the vaporizable liquid or working fluid into and against the inflow of air into the vortex.

15. The vortex station of claim 1, wherein the ground platform defines a concave shape.

16. The vortex station of claim 15, wherein ground platform includes a drain for collection of the vaporizable liquid or working fluid.

17. The vortex station of claim 16, wherein the drain is fluidly connected to a reservoir or storage facility for directing fluid to the nozzles.

Description

DRAWING DESCRIPTION

(1) A number of embodiments of the invention will now be described by way of example with reference to the drawings as briefly described below.

(2) FIG. 1 (prior art) is an illustration of Meridional in flows induced by viscosity and shear near the ground (Barcilon 1967).

(3) FIG. 2 (prior art) is an illustration of a streamline in plan of air entering the vortex near the ground (Barcilon 1967).

(4) FIG. 3 (prior art) is a waterspout off the Florida Keys (Renno 2008).

(5) FIG. 4 is a diagram showing concentration of vorticity (Mullen, Maxworthy 1977).

(6) FIG. 5 is an illustration showing vortex circulation (Renno 2008).

(7) FIG. 6 is an illustration of modified turbulence (Lewellen, Lewellen et al. 2000) pressure perturbation shown in solid lines and vertical velocity in greyscale.

(8) FIG. 7 is an illustration of a vortex-generator in plan that was the subject of laboratory experiments (Mullen, Maxworthy 1977).

(9) FIG. 8 is graph showing scaled temperature excess vs radius, 60° vane angle, 778W (Mullen, Maxworthy 1977).

(10) FIG. 9 is a graph showing scaled temperature excess vs height (Mullen, Maxworthy 1977).

(11) FIG. 10 is a graph showing modelled and measured tangential velocity in the Mullen and Maxworthy experiment using a modification of Renno's heat-engine theory to explain the tangential velocity in the experimental vortices.

(12) FIG. 11 (prior art) is plot showing heights of dust devils under strong convention (Hess, Spillane 1990).

(13) FIG. 12 (prior art) is a plot showing vertical velocity variance under convection (Spillane, HESS 1988).

(14) FIG. 13 is a bare tephigram of variation in dust-devil height as a fraction of the convective height, demonstrating the importance of the height of the super adiabatic layer, rather than the height of the convective layer, in predicting dust devil wind speeds.

(15) FIG. 14 is an illustration of radiosonde taken at Whenuapai, NZ at 13:00 NZDT on 17th December 2015 (metvuw.com) annotated.

(16) FIG. 15 is a diagram of the vortex station of the present invention.

(17) FIG. 16 is a diagram showing core advection and meridonial flows in the vortex station of the present invention.

(18) FIG. 17 is an illustration showing core advection with sufficient vertical gradient of vertical velocity from condensation for the vortex created in the present invention.

(19) FIG. 18 shows part of the vortex station of the present invention.

(20) FIG. 19 shows airflow through vanes in the vortex station of the present invention.

(21) FIG. 20 illustrates water flows in the vortex station of the present invention.

(22) FIG. 21 is a cross-sectional view of the vortex station and vortex of the present invention.

(23) FIG. 21A is a perspective view of the vortex station and vortex of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(24) Throughout the description like reference numerals will be used to refer to like features in different embodiments.

(25) The inventors have developed an improvement to conventional heat-engine theory to allow an improved prediction of vortex height and consequent thermodynamic efficiency and wind-speeds in atmospheric buoyancy vortices, through a reconsideration of the nature of the cold reservoir of the heat engine. Preliminary modelling suggests an economic and carbon-neutral method of converting waste heat into electricity with an overall efficiency of approximately 5%. Embodiments of a VCV or vortex station are provided and detailed below that are capable of converting waste heat to electricity.

(26) The costs of tall structures and large turbines of the prior art are avoided, since a VCV concentrates the buoyancy power as high wind-speeds at or near ground level. The VCV itself may be very large and may be established at a very low or significantly relatively lower cost than prior art type vortex generating systems. The swirling flows in these rising hot-air columns resist radial motion through hydrodynamic stability and thereby suppress normal turbulent mixing and make energy from buoyancy available to do work at the ground. This action may be exploited or utilised by placing a small wind turbine near ground level in the area of or near to the maximum wind-concentration in the core of the VCV. This is typically at the base of the VCV. Reference to a small wind turbine is made as being smaller relative to an ordinary wind turbine of equivalent power. Suitable wind turbines may comprises of vertical blade type turbines, etc.

(27) Atmospheric buoyancy vortices require a source of buoyancy and a source of concentrated horizontal circulation (hereafter referred to as “swirl”). The dominant source of swirl is concentration of environmental circulation by the end wall effect, which takes place in the boundary layer near the ground as a result of friction at the interface and wind shear above it. Swirl is advected in the core updraft, helping sustain the vortex as it rises.

(28) In temperate conditions condensation is dominant in driving convection but in dry deserts absolutely unstable boundary layers may develop above the desert floor as a result of advection from colder zones and heating (e.g. radiant heating) from the ground, allowing dust devils to be driven by dry adiabatic convection.

(29) A buoyancy vortex can be considered as containing four zones: 1. Core: a cylindrical volume on a vertical axis with constrained strong cyclostrophic flows and positive buoyancy. 2. Potential vortex: a much larger cylinder on the same axis as the core, containing weaker cyclostrophic flows that can be considered as inviscid, irrotational and neutrally buoyant—diffusion, vorticity and buoyancy can be ignored. 3. End wall disc: the area where the potential flows meet the ground and are subject to the end-wall effect. Significant wind concentration occurs at the centre of the disc. 4. Plume above: the turbulent plume formed down-wind of (above) the core when core restraint breaks down.

(30) Three processes are fundamental in a buoyancy vortex: I. End Wall Effect II. Heat Engine III. Hydrodynamic Stability

(31) These processes are treated separately in the literature but operate together so their interrelationships are important. Particularly, the persistence of the vortex to higher altitudes depends upon the hydrodynamic stability of the core wall suppressing turbulent mixing. There is still diffusion of vorticity and heat outwards to the potential vortex around it as the core advects so it ‘winds down’ with increasing height until the wall can no longer suppress turbulence—at which point the core breaks down to a turbulent plume—unless some other process can overcome the diffusion. Positive axial acceleration in the core acts to resist diffusion of vorticity and heat, since air-parcels are thereby stretched and so reduced in diameter. Conservation of angular momentum and a reduction in diameter act to concentrate vorticity against radial diffusion.

(32) The height to which a buoyancy vortex persists before breakdown to a turbulent plume affects the airflows at the ground since the plume does not contribute to those flows. Energy is instead expended in the plume in lifting and warming of entrained air through turbulent mixing. It is therefore suggested that the plume should be considered as the cold reservoir of the heat-engine driving the vortex flows.

(33) The core may have a one-cell (updraft only) or two-cell structure (a ring of updraft with a central down-draft) depending on swirl strength relative to buoyancy strength and sometimes a breakdown from one-cell to two-cell structure at intermediate height. This is a different phenomenon to the breakdown to a plume. Plume breakdown occurs within the vortex below the plume but appears to be insignificant and hence apparently does not need to be considered to model the heat engine.

(34) The End Wall Effect

(35) The end wall effect biases the cyclostrophic balance (wherein radial pressure gradient is balanced by centrifugal force) in the vortex flows near the ground. The pressure gradient arises from the buoyancy of the core. Friction at the interface and wind shear above it reduce tangential velocity and centrifugal force, allowing air to be drawn in by the radial pressure gradient. Swirl is thus concentrated into the base of the vortex. Many papers have been published examining this effect over a long period. Barcilon 1967 made an analysis of a pre-existing potential vortex under a suddenly imposed kinematic viscosity, using the Napier Stokes equations under a non-dimensionalised analysis to show a meridional recycling of swirl and predict that flows from the potential vortex sink into the end wall disc due to viscosity and acquire inward radial motion as they approach the ground as seen in FIG. 1.

(36) The predicted stream-lines shown in plan (from Barcilon 1967) in FIG. 2 are similar to those seen in FIG. 3, a waterspout off the Florida Keys (from Renno 2008) where the in flow is made visible by ripples on the sea.

(37) Another way to model the end wall effect is suggested in (Mullen, Maxworthy 1977) by considering advection of vorticity, see FIG. 4, where concentration of vorticity is shown.

(38) More recently numerical analysis using computer models has been possible. For instance (Lewellen, Lewellen et al. 2000, Lewellen, Lewellen 2007) have used LES (Large Eddy Simulation) models to show that turbulence in the end wall disc reinforces the end wall effect and produces wind intensification in the corner flows at the base of the core. This subject has been intensely studied over a long time because of the safety implications of such corner flows in tornados.

(39) For the VCV the inventor believes the implications are the following: the core should not be put in an enclosure that does not also contain the potential vortex and the ground plane without interrupting the recycling of swirl. flow intensification in the core is maximised when a 2-cell structure is established just above the ground—referred to as a drowned vortex jump (DVJ). In a DVJ the corner flows at the base of the vortex can have twice the speed of the cyclostrophic flows in the core wall.

(40) The Heat Engine

(41) In (Renno, Burkett et al. 1998) the authors model the thermodynamics of the convective processes in dust-devils that are responsible for maintaining the pressure differential in the core. They assume any convective phenomenon can be viewed as a heat-engine and consider a dust-devil in quasi-steady state, implying work done by the heat engine balances mechanical friction, in order to model the maximum bulk-thermodynamic intensity of a vortex in cyclostrophic balance. They assume flows are incompressible, heat input is sensible heat flux at the surface and heat output is radiation from subsiding air-flows (at the average temperature of the convective slab). They assume the convective flows are adiabatic, that the engine is reversible and that energy loss through mixing of high entropy updraft air with lower entropy ambient air is implicitly included through the definition of the cold temperature with respect to CAPE. By following an air parcel through a path as shown in FIG. 5, showing vortex circulation, they derive relationships for pressure differentials and cyclostrophic flow velocities.

(42) In (Renno, Bluestein 2001) the analysis is extended to waterspouts. An expression is derived for the pressure differential arising from core buoyancy:

(43) $\begin{array}{cc}\Delta p\approx p_{\infty }\left\{1-\exp \left\{\left(\frac{\mathrm{\gamma \eta }}{\mathrm{\gamma \eta }-1}\right)\left[\left(\frac{C_p}{R}\right)\left(\frac{T_0-T_{\infty }}{\stackrel{\_}{T_s}}\right)+\left(\frac{L_v}{R}\right)\left(\frac{r_0-r_{\infty }}{\stackrel{\_}{T_s}}\right)\right]\right\}\right\}& \left(1\right)\end{array}$

(44) Cyclostrophic balance is assumed and an expression is derived for tangential velocity at the radius of the core wall using the ideal gas law:

(45) $\begin{array}{cc}{V}_a=\sqrt{{\mathrm{RT}}_{\infty }\left\{1-\exp \left\{\left(\frac{\mathrm{\gamma \eta }}{\mathrm{\gamma \eta }-1}\right)\left[\left(\frac{C_p}{R}\right)\left(\frac{T_0-T_{\infty }}{\stackrel{\_}{T_s}}\right)+\left(\frac{L_v}{R}\right)\left(\frac{r_0-r_{\infty }}{\stackrel{\_}{T_s}}\right)\right]\right\}\right\}}& \left(2\right)\end{array}$ where: Δp is the pressure differential and p.sub.∞ is the pressure at infinite radius and ground level γ is the fraction of the total frictional energy dissipated at the surface.

(46) $\eta =\left(\frac{T_h-T_c}{T_h}\right)$ is the reversible efficiency of the heat engine C.sub.p is h|eat capacity of air at constant pressure R is the gas constant for air T is absolute temperature L.sub.v is latent heat of vaporisation of water per unit mass r is the water vapour mixing ratio T.sub.s is the entropy averaged temperature of heating a is the radius of the core

(47) The papers give estimates of tangential wind speeds in the core wall that are well supported with cited observations for dust devils and more generally supported for water-spouts.

(48) In (Renno 2008) the authors address irreversibility explicitly. They show γ˜1 and that pressure drop is greatest in the area of highest velocities just inside the wall. Thermodynamic efficiencies are shown to approach the Carnot efficiency, suggesting irreversibilities are small. The dominant irreversibilities are suggested to be those involved in change of phase. This seems reasonable if the irreversibilities of mixing within the turbulent plume are excluded.

(49) Hydrodynamic Stability and Modified Turbulence

(50) The core of the vortex must be constrained in some way to suppress mixing and make energy available to do work at the ground. This constraint comes from radial hydrodynamic stability in the core wall arising from two factors: cyclostrophic balance and stable stratification of density.

(51) Air parcels in cyclostrophic flow are like satellites in orbit, except that the force providing centripetal acceleration comes from the radial pressure gradient rather than gravity and the air parcels are exerting pressure on each other rather than being in free fall. Under a constant pressure gradient, there is an equilibrium radius for a parcel of constant tangential velocity and radial disturbance away from equilibrium is resisted. Buoyant displacement under centripetal acceleration also acts to encourage a stable stratification of density, with the less dense fluid towards the centre. These effects can combine to produce hydrodynamic stability sufficient to interrupt turbulent mixing at the core wall.

(52) Under normal flow conditions the high Reynolds number at the core wall of a concentrated vortex would produce rapid turbulent mixing of all quantities, including temperature and vorticity, as seen in a turbulent plume (Rouse, Yih et al. 1952, Morton, Taylor et al. 1956). The normal process of turbulent diffusion involves a cascade of scale, whereby all quantities under diffusion are passed from the main flow (the vortex in our case) to smaller eddies and still smaller eddies, with each step of the cascade producing smaller-scale structures with larger surface area to volume ratios, until at the bottom of the cascade the gradient in the properties can be passed on by molecular diffusion. This greatly accelerates diffusion.

(53) This cascade is interrupted by sufficient hydrodynamic stability in the core wall. Turbulence is not completely suppressed but is much modified. While diffusion outside the core wall is close to the laminar condition diffusion inwards towards the centre can simultaneously be turbulent, as shown in FIG. 6, a cross section of a high-swirl 2-cell vortex LES simulation.

(54) Different criteria for stability have been offered: (Howard, Gupta 1962) gave a criterion based on angular momentum. (Leibovich, Stewartson 1983) derived a different criterion from separate considerations of three-dimensional perturbations under radial shears in azimuthal and axial velocity. (Emanuel 1984) demonstrated that the criteria of (Howard, Gupta 1962) and (Leibovich, Stewartson 1983) are equivalent for a concentrated vortex and that the instability must therefore be inertial in character. (Lewellen 1993) suggested the Richardson number criterion of stratified turbulence can be modified for axisymmetric swirling flows to give a criterion for stability that also includes the gradient of potential temperature.

(55) $\begin{array}{cc}\frac{{\theta }^{\prime }}{{\theta }_0}<\frac{2{\Gamma }^{\prime }}{\Gamma }-\frac{w^{\mathrm{\prime 2}}{r}^3}{4{\Gamma }^2}& \left(3\right)\end{array}$ where θ is potential temperature Γ is circulation w is axial velocity r is radius the prime denotes differentiation with respect to radius

(56) Wall stability is increased with increasing vorticity and temperature gradient, since the temperature gradient at the wall of a buoyancy vortex is negative. In consequence, turbulent energy in the core wall is transformed into inertial waves running in the wall, analogous to Kelvin-Helmholtz instability. As long as the hydrodynamic stability is sufficient to sustain the inertial waves produced (Maxworthy, Hopfinger et al. 1985) the cascade of scale is interrupted and the diffusion of properties in the wall is much reduced (Stewartson, Leibovich 1987).

(57) The question that then arises is how to predict the height to which hydrodynamic stability will allow the vortex to persist before diffusion of vorticity and temperature lead to the breakdown to a plume. (Dergarabedian, Fendell 1967) offers an analysis of vortex intensification and decay based on an asymptotic expansion of the Napier Stokes equations non-dimensionalised with respect to an Ekman number. It is a laminar analysis of a 1-cell vortex but may be useful in modelling the processes of vorticity concentration and diffusion outside the core wall under conditions of modified turbulence. The Ekman number is given by:
E=v/Γ.sub.∞  (4)
where v is kinematic viscosity and Γ.sub.∞ is the environmental circulation.

(58) The analysis suggests that for a vortex to concentrate the Ekman number must be much less than one and the product of the area of the updraft and the gradient of average vertical velocity within it must be significantly greater than the kinematic viscosity.

(59) Therefore a large vortex in atmosphere requires only a small vertical acceleration for the core to be sustained and concentrated, but smaller vortices require greater vertical acceleration.

(60) Necessarily Divergent Lapse Rates

(61) A theory of necessarily divergent lapse rates is suggested to explain vortex height in atmosphere for large vortices, which assumes the core persists and advects upwards while CAPE is positive and the core lapse rate is less than the environmental lapse rate. Positive vertical acceleration arises from the divergent lapse rates as the rate of release of CAPE increases with height. Concentration of vorticity overcomes diffusion of vorticity, so the core advects upwards. This is consistent with the theory of potential vorticity (Ertel, Rossby 1949). So a dry buoyancy vortex with an adiabatic core lapse rate is concentrated in rising through a super adiabatic environmental lapse rate and a saturated buoyancy vortex with a pseudo adiabatic core lapse rate is concentrated by the increase of potential temperature in most atmospheres except under temperature inversion. In both cases the vorticity is concentrated as a result of the divergence between the environmental and core lapse rates. Once there is no divergence and no vertical acceleration, the vortex decays to a turbulent plume rapidly, in a height of the order of the diameter from which swirl was concentrated. The turbulent plume, rather than the convective slab, is taken to form the cold reservoir of the heat engine driving the vortex flows.

(62) Evidence from the Literature

(63) Laboratory Experiments

(64) FIG. 7 shows a vortex-generator with adjustable peripheral vanes to generate swirl and a heated plate to induce buoyancy as used by (Mullen, Maxworthy 1977). The generator was mounted in a draft-proof cabinet, lightly extracted from above to produce a neutral stratification. Their analysis is based on functional parameters well established in the analysis of turbulent plumes (Morton, Taylor et al. 1956) scaled to power input.

(65) Measurements of velocity were made using neutrally buoyant bubbles and strobe photography. Temperature was measured using sweeping tungsten-wire resistance thermometers.

(66) Temperature profiles were derived for a range of vane angles and power inputs, as seen for example in FIG. 8, showing a 2-cell structure.

(67) FIG. 8 shows Scaled Temperature excess vs Radius, 60° vane angle, 778W (Mullen, Maxworthy 1977).

(68) FIG. 9 shows the rate of decay of maximum temperature differential (scaled to input power) with height for two vortices. The vortices have different power inputs. One is a 1-cell vortex and the other a 2-cell vortex. They show a common inflection point in their scaled temperature profiles. Above the inflection the profiles show a z.sup.−5/3 dependence, which is characteristic of a turbulent plume. The height of the inflection is approximately equal to the diameter of the swirl vanes in both vortices.

(69) Table 1 shows results from (Mullen, Maxworthy 1977) annotated to show vortices for which the temperature profile is given or can be extrapolated from the paper.

(70) TABLE-US-00001 TABLE 1 Circulation Strengths (Mullen, Maxworthy 1977) annotated Vortex circulation strength and core diameter 346 778 1058 1382 Vane angle (°) J sec.sup.−1 J sec.sup.−1 J sec.sup.−1 J sec.sup.−1 30 Γ = 968 Γ = 1181 Γ = 1452 d = 9.6 d = 11.5 d = 12.7 45 Γ = 1323 Γ = 1542 Γ = 2142 Γ = 1910 d = 17.2 d = 18.4 d = 17.8 d = 19.7 60 Γ = 1865 Γ = 2600 Γ = 2994 Γ = 2916 d = 19.9 d = 20.6 d = 20.8 d = 21.6 75 Γ = 3671 Γ = 4342 Γ = 5445 d = 21.8 d = 26.6 d = 25.6 d = 26.2 Γ in cm.sup.2 sec.sup.−1 and d in cm.

(71) Tangential velocity is estimated at the core wall, which is taken for this purpose to have the outer diameter of the area of steep radial temperature gradient at the base of the vortex. For instance, FIG. 8 shows profiles for vortex 5 in Table 1, dt=16 cm. In Table 1 d is given as the maximum extent of the bubble-tracks within the core and dt<d. The tangential velocity is then calculated as:
v.sub.ot=Γ/πd.sub.t  (5) Equation (2) is then used to calculate V.sub.a The friction efficiency is assumed to be γ=95% The thermodynamic efficiency is assumed to be

(72) $\eta =\frac{T_h-T_c}{T_h}$ T.sub.h=T.sub.∞+ΔT.sub.h and T.sub.c=T.sub.∞+ΔT.sub.c T.sub.h is taken from the given profiles or extrapolations between adjacent vortices ΔT.sub.c is estimated from FIG. 9 as being ΔT.sub.c=30.Math.Q.sup.2/3° C. (scaling to power a used by (Mullen, Maxworthy 197)). This gives the cold reservoir temperature at the point where the core degrades into the plume above.

(73) Using ΔT.sub.c=0 (equivalent to the temperature at the top of the convective layer for a vortex in atmosphere) would overestimate the velocities seen in the experiment, although ΔT.sub.c=ΔT.sub.h/2 (equivalent to the average temperature of the convective slab) is a closer approximation. Since the atmosphere in the cabinet is neutrally stratified the vortices breakdown rapidly.

(74) FIG. 10 shows the correlation obtained between modelled and measured tangential velocities.

(75) Field Data for Dust Devils

(76) (Ryan, Carroll 1970) made a field study in the Mojave Desert collecting data on atmospheric temperature profiles to 1500 m; environmental wind direction, velocity and vorticity; dust-devil diameter, location, direction of rotation, structure and internal wind velocities. Wind velocity is presented as being proportional to the square root of the height of the super adiabatic layer but there is much scatter. This is consistent with the proposed theory.

(77) (Hess, Spillane 1990) made a study of dust-devils occurring in Australia and noted a correspondence in the statistics for dustdevil height (shown in FIG. 11) and vertical velocity variance normalised by the convection velocity w*(Deardorff 1970) (Spillane, HESS 1988) (shown in FIG. 12)—both shown against h, the height of the convective layer This is consistent with the proposed theory.

(78) FIG. 11 shows two populations. The upper population shows a mean height of 0.51 h, which is consistent with the proposed theory if velocity profiles follow FIG. 12. The lower population can perhaps be explained as occurring in a super adiabatic layer formed by radiant heating from the ground.

(79) The theory also explains the variation in dust-devil height seen in the upper population of FIG. 11, as shown in FIG. 13 (in which variation in dust devil height as a fraction of the convective height is shown).

(80) FIG. 13 is a bare tephigram (with the structure omitted for clarity) showing two different atmospheric conditions sharing the same convective height (h). The air is dry so the core air ascends following the adiabatic lapse rate shown in red. T.sub.s is the surface temperature. T.sub.conv is the temperature at the top of the convective layer.

(81) Two different super adiabatic atmospheres are shown sharing a common height of the convective layer. The first atmosphere is shown in blue. The environmental lapse rate is less than the adiabatic rate until height H.sub.c1. Assuming the vortex breaks down to a plume at that point, the cold reservoir temperature is then T.sub.c1.

(82) The second atmosphere is shown in purple. The environmental lapse rate is less than the adiabatic rate until height H.sub.c2.

(83) Assuming the vortex breaks down to a plume at that point, the cold reservoir temperature is then Tc2. Linear environmental lapse rates are shown for clarity. In reality they would presumably vary monotonically but the argument still holds. So H.sub.c2>H.sub.c1 and T.sub.c2<T.sub.c1 since temperature falls with height. As a result the vortex efficiency is greater under the second atmosphere than under the first and the wind speeds produced are higher, which is consistent with the scatter in the results of the upper population of FIG. 11 and (Ryan, Carroll 1970).

(84) Given the geometry of the tephigram, for dry vortices the mean vortex height will tend to half the convective height, as shown in FIG. 11 and the cold reservoir temperature will tend to the average temperature of the convective slab, as assumed in (Renno, Burkett et al. 1998) but variation around the mean can be expected.

(85) The cold reservoir temperature will thus be higher than the environmental temperature at the height of the plume, since the process lapse rate within the core is less than the environmental lapse rate up to this altitude, so it is inappropriate to assume the cold reservoir temperature is equal to the environmental temperature at the height to which the vortex persists.

(86) The proposed theory suggests that a positive gradient of vertical velocity is necessary to the formation of a concentrated buoyancy vortex, as well as sources of buoyancy and swirl. The inventor believes this explains why such vortices are rare, even where CAPE and swirl are readily available.

(87) Implications for a VCV

(88) Drowned Vortex Jumps (DVJ) and Wind Concentration

(89) The DVJ structure can produce wind intensification of approximately two in a VCV of suitable swirl. The wind speeds produced in the DVJ are high for a vortex of moderate thermal efficiency. The inventors believe the use of a turbine within the area of maximum wind concentration may be more effective than attempting to enclose the vortex and place turbines in an encircling wall. Accordingly, a VCV can be provided with turbines located within the areas of maximum wind concentration.

(90) Pseudo Adiabatic Lapse Rates and Vertical Acceleration

(91) The inventors also believe that, outside of the super adiabatic atmospheres which occur occasionally in dry deserts, concentrated buoyancy vortices can be made to advect high into the atmosphere using a source of saturated air, or saturating at least some of the air being introduced to the vortex or VCV, as the or a source of core buoyancy.

(92) Accordingly, according to an embodiment of the present invention, there can be provided or supplied a source for the saturation (whether as a partial or total saturation, e.g. increasing the relative humidity of at least some of the air being introduced to the vortex or VCV, such as for example from greater than about 0% RH (relative humidity) to about 100% RH) may be utilised to improve or increase core buoyancy. It will be appreciated that the relative humidity may be any value greater than zero, and up to 100% RH, including but not limited to for example: greater than about 0% RH to about 100% RH, greater than about 1% to about 100% RH, greater than about 5% RH to about 100% RH, greater than about 10% RH to about 100% RH, greater than about 15% RH to about 100% RH, greater than about 20% RH to about 100% RH, greater than about 30% RH to about 100% RH, greater than about 35% RH to about 100% RH, greater than about 40% RH to about 100% RH, greater than about 45% RH to about 100% RH, greater than about 50% RH to about 100% RH, greater than about 55% RH to about 100% RH, greater than about 60% RH to about 100% RH, greater than about 65% RH to about 100% RH, greater than about 70% RH to about 100% RH, greater than about 75% RH to about 100% RH, greater than about 80% RH to about 100% RH, greater than about 85% RH to about 100% RH, greater than about 90% RH to about 100% RH, greater than about 95% RH to about 100% RH, More preferably, a 100% RH flow of air to the vortex station is advantageously provided for, which may be achieved by conditioning of the in flow of air being directed into the vortex station, or may be achieved by conditioning of the air once inside of the vortex.

(93) The provision or source of the saturation (whether as a partial or total saturation, e.g. increasing the relative humidity of at least some of the air being introduced to the vortex or VCV), may be achieved by directing a source or supply of relatively warm or heater liquid (e.g. water) to an arrangement which dispenses the warm or heated liquid into the air flow being introduced to the vortex or VCV. The warmed or heated liquid may be optionally actively heated to elevate the temperate to encourage vaporisation of the liquid once introduced to the air flow, or may be indirectly or passively heated, for example using a waste heat stream from a product plant or process, thereby further maximising energy efficiency usage from the production plant or process.

(94) The supply or source of saturation may be temperature controlled, or may have its temperature measured so as to provide an input to a controller to control the quantity or flow rate of the supply or source of saturation to the air flow being introduced to the vortex or VCV. In this way, the supply or source can be actively monitored and controlled based on other measured parameters of the vortex or VCV.

(95) Dry vortices in temperate atmospheres will only advect to a height of the same order as the diameter of the source of circulation that formed them, so will have low thermal efficiencies. Saturated air cools more slowly in ascending as condensation releases latent heat. As condensate will be centrifuged out of the vortex core, the core should closely follow the pseudo adiabatic lapse rate. The pseudo adiabatic lapse rate for a saturated hot reservoir of sufficient temperature is divergent from the environmental lapse rate up to the tropopause, except under conditions of thermal inversion. Additionally, according to (Renno 2008), pressure drop is greatest in the area of highest velocities just inside the wall. On this basis, the inventor believes that any condensation will act to preferentially contribute heat in those areas (by way of releasing heat of condensation when the vapour condenses to a liquid), thereby contributing to further intensifying and stabilising or increasing the stability of the vortex.

(96) The inventor believes that large saturated vortices will therefore advect high into the atmosphere, until they encounter the tropopause or another significant temperature inversion, as shown in FIG. 14.

(97) Here a vortex is fed with saturated air at T.sub.h=40° C. According to the disclosure herein, the vortex should persist to the tropopause with the core following the pseudo adiabatic lapse rate to T.sub.c1=2° C., assuming the vortex can ride through the inversion at A-B. Note that the environmental temperature at the tropopause is shown at point C as negative 50° C.

(98) Other models of buoyancy vortices for power generation (Michaud 2009, Michaud, Monrad 2013) analyse the vortex as a heat-engine running to the tropopause and assume that the cold reservoir temperature is the environmental temperature at that height. This yields estimates of cold reservoir temperature around negative 80° C. and consequently high estimates of Carnot efficiency and conversion efficiency may be achieved. The assumption that a dry vortex will run to the tropopause does not seem to be supported.

(99) (Nizetic 2011) presents a somewhat different analysis based on CAPE and the total enthalpy supplied to the vortex and assumptions on heat-to-work efficiency based on consideration of Carnot and modified Brayton thermodynamic cycles. Again, the cold reservoir is modelled as having the environmental temperature at the tropopause and estimates of efficiency on that basis would be higher than the proposed theory would suggest.

(100) The vortex generation and stability defined by the inventor is at odds with these assumptions and suggests that: buoyancy vortices only advect upwards while there is available CAPE and the core lapse rate is less than the environmental lapse rate. other than in conditions with super adiabatic environmental lapse rates, as may occur occasionally in dry deserts, this will only produce a vortex to a significant height and moderate efficiency if the core is saturated and thus subject to a pseudo adiabatic lapse rate. even if such a vortex persists to the tropopause the cold reservoir temperature is significantly above the environmental temperature at the height at which the vortex degrades to a turbulent plume, since the core lapse rate is less than the environmental lapse rate, by definition.

(101) Preliminary Analysis of a VCV Using equation (2) and assuming: environmental conditions shown in FIG. 14 input air to the vortex is raised to 40° C. and fully saturated, so T.sub.h=T.sub.0=40° C. and r.sub.0=50 g/kg a DVJ structure results with a wind concentration of 2 with a wind turbine mounted in the area of maximum flow concentration input airflow follows the streamline in plan of FIG. 2. the turbine can extract 50% of the mechanical power of the flows through it from the sounding T.sub.1=T.sub.∞=18° C. and r.sub.∞=6.5 g/kg friction efficiency γ=95% temperature of heating is T.sub.s=40° C. thermodynamic efficiency

(102) $\eta =\frac{T_h-T_c}{T_h}=12\%$ V.sub.a=119 m/s, so this is a very powerful v|ortex even if compared to an F5 tornado, but not as powerful as if the cold junction was at −50° C. 49.2 MW of available waste heat can be converted to an electrical output of 1.9 MW—an overall efficiency of 3.9%—in a VCV of 1.3 m core radius, derived from a swirl-vanes of 13 m radius. Assuming the water is input at 60° C. and cooled to 40° C., 49.2 MW requires a flow of F=P.sub.tot/(C.sub.wΔT)=600 l/s.

(103) The required pumping power is then P.sub.p=p{dot over (V)}=345 kPa.Math.600 l/s=207 kW, based on curves for commercially available dust-suppression nozzles.

(104) A counter-intuitive result of this model is that the thermodynamic efficiency of the VCV increases if the temperature of the saturated input airflow is reduced. The temperature of the cold reservoir falls by more than the reduction of temperature at the hot reservoir (assuming the lapse rate divergence is still sufficient for the vortex to advect to the tropopause) since the pseudo adiabatic lapse rate more closely approaches the adiabatic for lower mixing ratios, as for example seen in FIG. 14: For T.sub.h=25° C., r.sub.0=20 g/kg, T.sub.c=−25° C., so

(105) $\eta =\frac{T_h-T_c}{T_h}=17\%,$  V.sub.a=81 m/s and overall efficiency is 5.4% For T.sub.h=20° C., r.sub.0=14.8 g/kg, T.sub.c=−40° C., so

(106) $\eta =\frac{T_h-T_c}{T_h}=21\%,$  V.sub.a=68 m/s and overall efficiency is 66%

(107) This suggests a trade-off exists for the VCV between conversion efficiency and vortex stability under temperature inversion, depending on the temperature of the saturated input airflow.

(108) Conclusions

(109) A theory of necessarily divergent lapse rates is developed to allow the heat engine theory of (Renno, Burkett et al. 1998, Renno, Bluestein 2001) to be used to explain wind velocities occurring in laboratory vortices and dust devils and statistics of the height of dust devils, by a modification of the assumptions with respect to the cold reservoir. This theory is then used to scale a virtual chimney vortex (VCV) for the purposes of generating electricity from the waste heat available in cooling water streams at existing power stations or from other waste heat streams from product plants or processes (or indeed any heat stream may be used). This suggests that an overall conversion efficiency of approximately 5% is achievable in a VCV. On the assumption that existing power station efficiency is approximately 33%, so the waste heat is twice the electrical output, this implies power station efficiency can be increased by 10% through using such a device. A 1 MW electrical output would be available from a VCV of approximately 2 m core diameter, involving swirl vanes of 20 m diameter.

Vortex Station or VCV Embodiments

(110) FIGS. 15 to 21 show an atmospheric buoyancy vortex, turbines and equipment (vortex station) that enables the buoyancy vortex to be created and for power to be extracted from it.

(111) The figures show one embodiment of a vortex station or VCV that is capable of converting waste heat into electricity.

(112) According to the disclosure herein, at least one, or optionally a plurality of, wind turbines are preferably placed at or near ground level in the area of maximum wind-concentration in the core of the VCV that is preferably at the base of the VCV.

(113) In some embodiments a plurality of concentric turbines may be used, or simply one turbine with many concentric blade sets.

(114) Hereinafter, reference to “turbine” may refer to one or more turbines.

(115) In the prior art, often vortex engines typically require a costly vertical cylindrical wall surrounding an arena to create the vortex and they make no use of condensation to produce a gradient of vertical velocity to stabilise and concentrate the vortex.

(116) According to the disclosure herein, the VCV provides an apparatus and mechanism or process for providing or supplying a source of liquid to either partially or fully saturate an air flow being introduced or fed to a vortex or a VCV so as to use subsequently utilise the released energy of latent heat of condensation of vapour added to the air flow of the vortex, which in turn contributes to the production of a gradient of vertical velocity for stabilising or increasing stability and concentrating the vortex. As a result, a man-made vortex can be generated that achieves relatively high aspect ratios.

(117) Further, the vortex will concentrate if the action of axial strain (or a vertical gradient of vertical velocity as it might otherwise be termed) in concentrating the swirling flows exceeds the action of turbulent mixing of momentum and heat in diffusing them.

(118) The vortex stability arising from sufficient hydrodynamic stability in a concentrated vortex acts to suppress turbulent mixing. Therefore, for a concentrated vortex, lapse rate divergence (wherein the core cools more slowly in rising than the surrounding air) acts to maintain the vortex in rising against the action of diffusion, thereby allowing a vortex with a relatively high aspect ratio to develop.

(119) In the absence of axial strain, a columnar vortex above a ground plane has an expected aspect ratio of about 15:1, the height to the plume being about 15 times the core diameter, due to momentum considerations. Dust devils running in an atmosphere with super adiabatic lapse rate can run to aspect ratios above 400:1, limited only by the depth of the super adiabatic layer that provides lapse-rate divergence in the dry condition.

(120) By using saturated or at least partially saturated core air flows the core cooling can be slowed down to the pseudo adiabatic lapse rate, as condensation releases latent heat. In this way lapse rate divergence and subsequent axial strain can be maintained to a greater height; potentially to the tropopause, which is in the order of 10 km above ground. The ability of air to carry water vapour in solution declines as pressure and temperature reduce. Therefore, it is not necessary to raise the incoming air to saturation or 100% relative humidity at the ground, only to create a mixing ratio high enough that saturation occurs and condensation, lapse-rate divergence and axial strain come into effect before the rising vortex loses the stability created by the end wall effect and heating occurring at the ground. On this basis, the supply or source of the saturating liquid can be controlled so as to provide a sufficient quantity or flow rate to provide for a condensable liquid as a vapour to the air flow, and for that sufficient quantity to provide energy to the vortex, via the latent heat of condensation.

(121) Given the expected aspect ratio for a vortex in the absence of axial strain, thus smaller vortices require air that is near to 100% RH at the ground. While larger vortices will concentrate with a ground level feed of airflow at less than 100% RH, as long as the RH will reach 100% at a height less than the core height that arises without axial strain. So while a cyclone runs with air at a comparatively low RH, while the VCV as disclosed herein may utilise a source or supply of heated water which is subsequently pumped through one or more nozzles or spray devices to achieve a relatively saturated air flow substantially at or near the ground or base of the vortex.

(122) In one embodiment, the temperature for the supply or source of saturation (e.g. water using in the vortex station of the present invention arises from two considerations. 1) As shown in FIG. 14, ordinary atmospheres contain bands or layers of stability such as that shown at A-B. Saturated air starting at the ground at T.sub.h=40° C. will rise along the pseudo-adiabatic curve shown through T.sub.c2 to T.sub.c1, thus maintaining lapse-rate divergence and vortex stability up to the tropopause, which appears at 250 mbar. T.sub.c1 give a Carnot efficiency of

(123) $\frac{T_h-T_{c}1}{T_h}=12\%$ In a similar atmosphere, but lacking the stable layer at A-B, lower temperatures of saturated air could be used. In the extreme, T.sub.h=20° C. would give a core following

(124) the pseudo adiabatic. Now T.sub.c1=−40° C., so

(125) 0$\frac{T_h-T_{c}1}{T_h}=21\%$
since the cold reservoir temperature falls by more than the imposed change in the hot reservoir temperature. So there is a trade-off between the higher efficiency at low core temperature versus the higher core stability at high core temperature, which would require control of the core temperature in use, depending on atmospheric conditions. 2) For a desired core air temperature the volume of water that must be pumped through one or more nozzles or sprayer devices depends on the water temperature. The heat content of the source or supply of saturation (e.g. water flow) under the temperature drop it goes through to equilibrium must equal the heat flux involved in evaporation or vaporisation and warming of the air flows to the equilibrium temperature.

(126) So for a saturated air flow to the vortex at about 40° C., the water flow rate needed for water fed at about 50° C. is twice that for water fed at about 60° C., assuming the water is cooled to about 40° C. in both cases. For a lower temperature differential from water to air, a finer mist is needed to allow for the heat transfer rate required. These effects combine to increase the pumping losses incurred in driving the vortex with cooler water.

(127) For the vortex station of one particularly embodiment, the temperature of the source or supply for partial or complete saturation (e.g. water supply) is about 60° C. with about 50° C. being a practical lower limit for power generation purposes. If net power output is not the primary concern in applications such as transporting polluted ground air to height or raising moisture to height for rain enhancement, a lower water feed temperature is allowable.

(128) Accordingly, for the present invention the working fluid (e.g. water stream which is heated) may be provided at a temperature of greater than about 40° C., or may be greater than about 45° C., or may be greater than about 50° C., or may be 60° C. or more,

(129) A secondary water cooling circuit of many existing thermal power stations often contains large quantities of waste heat in water flows above 60° C., which are typically otherwise sent to evaporating cooling towers. Thus the vortex station of the present invention could utilise the heat from such heated waste water streams.

(130) Nozzles or Sprayers

(131) The nozzles or spray devices may be located in the in flow or air flow being introduced to the vortex, just above the ground or at the base of the vortex, and preferentially while under the roof, to encourage the vortex to start or initiate. Once the vortex has been started or initiated, extra nozzles or spray devices still in the in flow at the ground or at the base of the vortex but radially further out from the centre or core of the vortex may be used for providing or supplying the source of saturation (e.g. water).

(132) The nozzles or spray devices do not need to be angled so that the sprayed liquid is fed into the vortex with angular momentum, but may optionally be configured to do so. Angular momentum of the vortex is primarily generated from the vanes at the periphery of the vortex station.

(133) High Aspect Ratio

(134) The aspect ratio is the ratio of the height of the vortex plume to the diameter of the core.

(135) The core diameter is considered to the diameter of maximum tangential wind speed—measured with an anemometer or a laser (PIV). The height of the vortex used for the aspect ratio (Γ) is from the base to the head of the core, which is where the core starts spreading out (i.e. when the core turns into a turbulent plume).

(136) The efficiency of the heat engine depends upon the Carnot efficiency

(137) $\frac{T_{\mathrm{hot}}-T_{\mathrm{cold}}}{T_{\mathrm{hot}}}.$

(138) T.sub.cold is determined by the height of the vortex and the lapse rate is set by the properties of air. The height depends upon maintaining vortex stability in rising against the effects of turbulent diffusion of heat.

(139) In one embodiment, a vortex 2 is created at the vortex station 1 by pumping water, preferably hot, through a manifold of nozzles 3 situated beneath an annular roof 4, in order to create flows of warm, saturated air 5, which forms the vortex 2. This air 5 is buoyant relative to the surrounding atmosphere because it is hotter and contains more water vapour (water vapour is less dense than air) so it rises up the vortex 2 and air 6 is drawn in at the ground to replace it. Such an arrangement is for example shown by FIGS. 15 and 21.

(140) To help initiate or start the vortex, the nozzles or spray devices are configured to produce a relatively fine droplet of water to produce a suitable heat-transfer area and Nusselt number high enough to approach saturation of the air flow the water is being introduced into. As the vortex builds strength, wind shear then assists to automatically break-down larger water droplets, so coarser nozzles or spray heads or spray devices and lower pumping pressures (with lower pumping loses) are possible in normal running, thereby further helping reduce the energy demands of running or maintaining the vortex.

(141) Swirl is preferably imparted to the in drawn air (or air introduced to the vortex) 6 by drawing it through vanes 7. Preferably the vanes 7 are inclined at an angle to the radial, set in a surrounding circle around the vortex (termed a “swirl-henge”). The angle at which the air enters is set by the angle of the vanes.

(142) The vanes may be formed using yacht-sail technology (i.e. for example may be flexible materials) as these can provide a low cost vane set up. The vanes may be reconfigurable or adjusted as to angle or their shape. In other forms the vanes may be made of composite material(s).

(143) A small section of the swirl henge, is for example shown in FIG. 19, but in use, the swirl-henge completely surrounds the base of the vortex 2, so all input air acquires swirl in being drawn through the swirl-henge.

(144) The annular roof 4 is preferably placed in the null-flow zone of the meridional circulation (that is circulation that is occurring in one vertical half of a cross section including the centreline), which is characteristic of a drowned vortex jump (DVJ) flow-field 20 (see FIG. 16) which occurs spontaneously in vortices of sufficient swirl. By constructing the roof 4 in the null flow zone 21, the roof is made or configured so as to restrict the airflows at the point of maximum wind concentration 22, at the base of the vortex station.

(145) At least one turbine 8 is situated at the centre and at the ground 9 of the vortex station 1.

(146) The turbine(s) is preferably a turbine with vertical blades moving around a vertical axis (similar to a Magnus-type turbine). The vertical blades may be fixed or adjustable.

(147) The roof 4 is configured to restrict airflows into the vortex station and causes them to pass through the turbine(s) 8, without distorting the corner flows of the DVJ, which produce the wind concentration at the point of maximum wind concentration 22. When the turbine(s) is placed in the area of maximum wind concentration 22 (at or near the ground 9 of the vortex station 1) maximum power extraction can be achieved. Also, the use of such a turbine produces a radial pressure drop in the in flow 22, which acts to stabilise the foot 11 of the vortex 2 against being disturbed laterally, for instance by an external wind.

(148) The figures will now be described in further detail.

(149) In FIG. 15 there is shown an embodiment in which air 6 is drawn into the vortex 2 through the end-wall effect. Airflow is concentrated at the base 11 of the vortex 2 and the path of an air parcel rising in the core can be tracked through the vortex (by the arrow indicated as 12). The core wall is shown in FIG. 15 by the dashed line indicated as 13, and the core has a centre indicated as 10. The airflows going around the vortex core (the potential vortex) are indicated by the outer extent of the potential vortex 14. In the core of the vortex the airflows tangential velocity is greater than axial velocity which in turn is greater than radial velocity.

(150) FIG. 16 shows core advection (without vertical acceleration) and meridional flows in a vortex station of the present invention. The area 22 is of maximum wind speeds within a drowned vortex jump (DVJ) structure. The line indicated as 23 is the line of null meridional flow. Line 24 indicates the area of the vortex with a hydro dynamically stable core wall. Here vorticity is diffusing outwards to the potential vortex through molecular diffusion. Flows outside the wall are near laminar. Core diameter is near constant but expanding slowing with height as the vortex is winding down (as vorticity and tangential speeds reduce). At 25 dynamic stability is now insufficient to suppress turbulence, so the core breaks down into a turbulent plume. The height of breakdown (h) is of the same order as the diameter of the swirl henge (D).

(151) FIG. 17 shows core advection with sufficient vertical gradient of vertical velocity from condensation. Diffusion of vorticity is matched at area 30 by concentration of vorticity. As an air-parcel moves from A to B it accelerates. The top accelerates more than the bottom; A.sub.1.fwdarw.B.sub.1.fwdarw.C.sub.1, A.sub.2.fwdarw.B.sub.2.fwdarw.C.sub.2, so it is stretched and becomes thinner and there is reduced diameter and conserved angular momentum which concentrates vorticity. The core diameter is therefore constant or reduced in rising from area 30 to area 31. The vertical scale 32 of the vortex is fore-shortened here. The vortex core may then advect to the tropopause, at approximately 10 km altitude. Advantageously, a sufficient quantity or flow rate of water in the form of evaporated or vaporised moisture (for saturating either completely or partially an air flow being added to the vortex) is added to the vortex, such that the latent-heat being released by condensation of that moisture is sufficient to provide acceleration to overcome diffusion of vorticity, the core advects. At the tropopause, or other significant atmospheric temperature inversion, acceleration is removed and the core ‘winds’ down. The winding down of the vortex is shown as 25 in FIGS. 16 and 17.

(152) In a further embodiment, FIG. 18 shows part of a vortex 2. A single turbine 8 is shown here, but a plurality of turbines could be used in a full system. Preferably the blades of the turbine are mounted vertically and rotate around the vertical axis of the vortex 2. Preferably the pressure drop across the turbine 8 is radial and acts to intensify the vortex by increasing the pressure reduction in the core, which avoids destabilising the vortex and resists lateral displacement of the core base, for instance by wind; thus the core cannot be blown away.

(153) In another embodiment, FIG. 19 shows airflow through the vanes and into a vortex. As described above, the “swirl-henge” 7 vanes are in effect airfoils (preferably using yacht-sail technology). Swirl is imparted to the input airflow as it is drawn in at the vanes 7. In area 40 (along the vertical axis of the vortex 2) swirl is intensified by the end-wall effect. Heat is added to the input airflow by pumping water (preferably hot) through nozzles to produce sufficient surface area for heat-transfer to produce a saturated or partially saturated air-flow to the core, underneath the roof 4 and on the ground plane. Preferably the vertical turbine blades rotate in a circle at the inner diameter of the roof 4.

(154) In another embodiment, FIG. 20 for example shows water flows in a vortex station. A water supply 41 (of preferably hot water) is pumped into the vortex station 1. Nozzles 3 direct the water into and against the in flow of air, to produce a fine mist or spray with a relatively large or great surface area for heat and transfer of the mist or spray into the air flow in the form of vapour or as an evaporation of the water. Most of the water sprayed or otherwise jetted into the vortex falls out of the vortex as condensate and is carried or directed to a central drain at 42 for collection and recycling. The drainage of water is assisted by the vortex airflow and by having a concave floor 9 on the vortex station 1.

(155) Advantageously, the concave floor of the vortex station may also contribute to a stabilisation of the vortex because the air flow goes through a change of greater than 90°—and so higher acceleration of air flows are resultant.

(156) FIG. 21 shows a further embodiment of a vortex station 1 in cross-section. The roof 4 is placed in the null-zone of meridional flows to prevent radial flows circumventing the turbine 8.

(157) Input water 42 is fed through a manifold of nozzles 3 to produce a fine mist or spray with sufficient area for heat-transfer and vaporisation.

(158) Unless the context clearly requires otherwise, throughout the description, the words “comprise”, “comprising”, and the like, are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense, that is to say, in the sense of “including, but not limited to”.

(159) Although this invention has been described by way of example and with reference to possible embodiments thereof, it is to be understood that modifications or improvements may be made thereto without departing from the scope of the invention. The invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, in any or all combinations of two or more of said parts, elements or features. Furthermore, where reference has been made to specific components or integers of the invention having known equivalents, then such equivalents are herein incorporated as if individually set forth.

(160) Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.