WO2007022556A1

WO2007022556A1 - Improvements to solar heat engines and industrial chimneys

Info

Publication number: WO2007022556A1
Application number: PCT/AU2005/001239
Authority: WO
Inventors: Norman Philibert Louat
Original assignee: Louat, Heather
Priority date: 2005-08-22
Filing date: 2005-08-22
Publication date: 2007-03-01

Abstract

The present invention relates generally to the fields of industrial chimneys and solar heat power generators. More particularly, this invention relates to collecting and guiding air heated from the burning of fuel or through the action of sunlight. The heat engine of this invention uses the greenhouse effect to heat air between a dark coloured base and a transparent surface. Vanes located between the base and the transparent surface cause the moving heated air to rotate about the centre of the structure, such that air escaping through a centrally located aperture in the transparent surface has a vortex-like flow which alleviates the need for a physical chimney to prevent ambient air from mixing with the escaping air.

Description

IMPROVEMENTS TO SOLAR HEAT ENGINES AND INDUSTRIAL CHIMNEYS BACKGROUND OF THE INVENTION

Field of Invention

The tide of this invention is "Improvements to Solar Heat Engines and Industrial Chimneys". The present invention relates generally to the field of industrial chimneys and of solar energy power generators. More specifically, the present invention is related to collecting and guiding air heated by the burning of fuel or through the action of sunlight. In the case of solar heating this can result in a flow suitable to drive a power-generating turbine, hi this connection this invention has particular application in providing a power source in sunny areas and as a large-scale air exchange system to provide community-wide cooling and cleaning. In reference to industrial chimneys it allows the creation of the draught normally achieved through the use of tall towers without the use of a tower as such.

Discussion of Prior Art

Using solar heated air to induce an updraft is known in the art in various configurations as illustrated by US patents: 4,118,636; 4,224,528; 4,275,309; 5,096,467; 4,388,533; 4,414,477; 5,734,202.

Typically a surface, capable of absorbing heat, collects energy from impinging sunlight. A clear glass or plastic material usually encloses the heat-collecting surface to help trap the heat. The transparent material additionally may have an opening which allows heated air to escape from the greenhouse structure and other openings to allow ambient air to be drawn into the greenhouse structure. More particularly, as air is heated within the greenhouse structure, it becomes less dense than the surrounding air and rises through any outlet in the transparent material. Air in the surrounding environment is drawn into the greenhouse structure to replace the air which escapes.

One notable observation is that the height to which the rising air climbs controls how much air escapes and enters the greenhouse structure.

Finally, some type of wind-driven turbine is introduced in the flowing air to drive an electric generator.

Such devices, as described in the prior art, have at least two shortcomings: (1) they typically involve only linear air movement within the greenhouse and (2) they require a physical, chimney-like structure to contain any resulting updraft.

A few prior devices mention thermally inducing vortex-like, or rotational, air flow rather than simple linear flow, but appear to do so only within an attached physical chimney. Vortex-like Pa airflow simply means a column of flowing air which has tangential components of velocity of magnitude comparable with those of the upward motion. The importance of achieving a vortex-like flow relates to the effect such flow has on the height of the generated updraft. The purpose of a chimney or smokestack is to prevent the inward flow of ambient air into the column of hot air rising from the chimney, thus allowing the updraft to flow unimpeded. To achieve a higher up-draft, a higher chimney is required. However, manufacturing costs and engineering complexity increase as the height of a physical chimney increases. Due to the centrifugal forces associated with rotation, a vortex-like flow obviates the need for a chimney because it inhibits the mixing of the rising air with ambient air. The patents of Lucier, 4,275,309, and Valentin, 4,452,046, contemplate rotational air flow but still envisage a tall, physical chimney-like structure. They differ from the present invention which uses a specific vortex flow instead of a physical chimney to isolate the resulting rising ah^*. The absence of a physical chimney decreases both the engineering complexity and manufacturing costs associated with solar-powered wind generators. Whatever the precise merits, feature* and advantages of the above cited references, none of them achieve or fulfills the purposes of the present invention. Accordingly, an object of this aspect of the present invention is to provide a solar-powered air flow generator which is simple to build and inexpensive to manufacture.

Another object of the present invention is to provide means of deflection of air flow within the structure so as to result in a rotational component. Still another object of the present invention is to provide an appropriately shaped and positioned aperture within a solar powered air-flow generator which will allow escaping, heated air to flow upwards in a vortex-like manner and, optionally, drive a turbine.

Still another object of the present invention is to provide a solar- powered air-flow generator which removes local, heated air in a spiral ing updraft and replace it through a flow of downward moving cooler, cleaner air.

A further object of the present invention is to provide a solar powered air-flow generator which inhibits the mixing of ambient air with the produced up-draft by imparting a vortex-like flow on the escaping air rather than using a physical chimney. The virtual chimney created by the vortex-like flow supports updrafts which exceed those supported by feasible physical chimneys. A further object of this invention is to provide essentially the same air-flow pattern when the source of heat is the burning of some fuel rather than from solar radiation These and other objects are achieved following the lines indicated in the detailed description that follows.

SUMMARY O F THE INVENTION Problems and disadvantages associated with the prior art are addressed and overcome by the present invention. Deflections within the present solar-powered air-flow generator cause the solar-heated air within the entire structure to move in a rotational manner. Consequent on the principle of the conservation of angular momentum, air which escapes the structure with rotation as component of its velocity, retains that rotation at all levels. This movement allows it . to rise in the atmosphere without mixing with the environment; without a physical chimney. This result is true independent of the source of heat which raises the temperature of the air and so reduces its density, hi the case of solar heating it would seem from the ensuing discussion that cheap power can be obtained by the use of a process which encapsulates the essentials of the world's weather cycle. The weather cycle represents one of the largest engines operating on this planet m the weather cycle, as in any heat engine, there is both a source and a sink for heat. Mechanical work is done when the heat is transported between source and sink, hi the weather cycle, heat is supplied, mainly at the earth's surface, by radiation from the sun. This heat is converted into mechanical work through convective air currents which transport the heat to the upper levels of the atmosphere, where it is radiated to the heat sink provided by outer space.

The primary task of the following discus is an examination of the properties of a model system. This system involves three essential elements: a heat collector, a central orifice in the heat collector containing a turbine which drives an electric generator and finally, an air column which forms an extension of the central tower, hi turn, the conclusions of this examination are detailed below.

The heat collector will take the form of a large, rather flat truncated cone, circular in plan, highest near its center and consist of light transparent sheets fixed in position through the action of a sufficiently rigid skeleton. It should be realized at the outset that commercially significant power is measured in hundreds of megawatts and that, since the sun provides about 1 kilowatt per square meter, we should envisage collectors whose radii, are conveniently measured in kilometers. (A circular collector of 1 kilometre radius would provide an energy input of ~ 3 X 10' watts ). Air entering at the periphery, in particular, with a component of tangential velocity imposed by the presence of vanes, will absorb heat from the sun and flow inwards toward a central orifice. Conservation of angular momentum will result hi an increase in tangential velocity with decreasing radial distance.

The next item is the central orifice. This will have circular cross-section and enclose an axially disposed turbine which will be caused to rotate by the ascending air. The material circumscribing the orifice has only to support itself and the turbine and to be capable of preventing radial air flow. The final item is the air column. Calculation shows that if the efficiency of the engine is to be such as to allow the off-take of significant power, the height of the column must be such as to be conveniently measured in kilometers. In principle, as in the familiar smoke- stack, such a column can be provided by a solid structure. In practice, the cost associated with such an approach would be prohibitive. To recognize how this difficulty can be surmounted it is helpful to understand the role of a smoke-stack. hi a smoke-stack or industrial chimney, the pressure, at the same height, of the air moving inside is lower than that of the still air outside bv an amount which increases steadily with distance from the top of the stack. Thus, the wall of the stack acts as a barrier, that is to say, it provides a force which aets to prevent the inward flow of air. Were the wall not there, inward flow and the resultant mixing would continue until the pressure differential and the attendant upward motion of the air were essentially extinguished. Crucial to the operation of the engine is the fact that the barrier to this inward flow need not be material but can be provided through the centripetal forces associated with rotation Indeed, calculation shows that inward motion can be suppressed by imparting tangential components of air velocity whose maximum is comparable in magnitude to the speed of the upward motion in the column. An interesting outcome of these calculations is the prediction of the existence of a central region in which there is no motion. This is gratifying in view of the observation of well known "eye" in a hurricane and the recent observation using Doppler radar of similar phenomena in tornadoes. It should be remembered that these natural phenomena depend on the same properties of the rotational air column as those invoked in respect of the proposed heat engine.

The phenomena identified above differ from those of conventional heat engine only in the "fuels" involved. In the two cases cited above, as well as in the sea spout, energy is stored in the heat of vaporization of water and liberated when the vapour condenses, resulting in a rise in the temperature of the air. In the case of the engine, as in that of the so-called dust-devil, this temperature is raised by the direct action of the sun. In all three cases, energy is transported from ground level to the upper reaches of the atmosphere.

Since air is transported upwards there must be a compensating flow in the reverse direction.

Characteristically, this air is cleaner and cooler than that which it replaces. The reduction in temperature can be significant Its magnitude should approach the temperature increase engendered by local (atmospherically unstable) heating at ground level. Its impact is familiar to all who have experienced the cool breezes which often precede thunderstorms.

It is apparent that the operation of this engine would be environmentally friendly. Again, since fuel employed is free the only apparent ongoing costs are those associated with maintenance. This would suggest that this approach would lead to the production of power at significantly smaller costs than those of more conventional methods.

The essentials of the engine considered here are of course independent of the source of heat

Claims

Claim 1

Heat engines in which the need for tall physical chimneys, which provide a barrier to the pressure induced flow of air to the inside the said chimneys, is obviated by a vertically unbounded vortex in the air itself.

Claim 2

As in claim 1 in which solar energy is collected and used to heat air in, what is when viewed in plan, a normally circular structure, bounded at its lower surface by the normally flat and dark coloured ground and at most of its upper surface by a strengthened and continuous sheet of translucent material such as glass or plastic, highest at its centre, height H above ground level and open only to the outside along the length of its periphery and near its centre where the sheet changes form and becomes an open-ended cylindrical tower of height H and radius K, said tower being of strength sufficient to support a device such as a wind turbine.

Claim 3

As in claims 1 and 2, in whichas an attractive option, the geometry of the structure is such that the product hr, of the height, h, of the upper surface above ground level at a radius, r, is a constant.

Claim 4

As in claims 1, 2 and 3 in which the upper surface is strengthened and its motion constrained above and below by such devices as steel wire netting, the resulting triple-layer sandwich being fixed in position, at suitable intervals, by attachment to the tops of posts set in the ground.

Claim 5

As in claims 1, 2, 3 and 4 in which the inward flow of air from the opening at the periphery is modified at some unspecified radius from the centre, by the presence of circumferentially overlapping and essentially stationary vanes mat span the whole distance between upper and lower surfaces and which vanes are oriented so as to impose a steadily increasing tangential component on the flow of air between the periphery and the tower at the centre of the structure, thereby satisfying a necessary condition for the appearance of a vortex.

Claim 6

As in claims 1 , 2, 3, 4 and 5 in which the pitch of the vanes specified in claim 5 is regulated using electronic feed- back in such a way as to maximize the flow of air through the engine, Claim 7

As in claims 1, 2 ,3 ,4 ,5 and 6 in which the pitch of a second set of vanes located within the tower at a radius r_s and height h. is adjusted in such a way that the flow of air within the tower is, for radii r less than r^ uniform and directed purely upwards

Claim 8

As in claims 1, 2, 3, 4, 5, 6 and 7 in which, the radius of the central tower is greater than a certain value now calculated at 63 metres, at which radius the loss of energy through processes involving the viscosity and or the thermal conductivity of air is equal to ten percent of the input energy to the engine-

Claim 9

As in claims 1, 5, 6, 7 and 8 in which the source of heat is a fire located below the bottom of the central tower, in which case all the vanes mentioned in the foregoing are located within the central tower.