Patent Description:
The applicant's earlier patent application, published as <CIT>, described the background state of the art at that time, and also a newly developed portable device in which steam is generated by burning a fuel, and that generated steam is then subsequently mixed with the still-hot combustion gases and with ambient air, in desired proportions, to create a vapour mixture which can be dispersed in a plantation as a protective thermal fog to reduce potential frost damage.

The purpose of that thermal fog is to act as a heat carrier and to transfer combustion heat from the fuel to the plantation, and secondly to act as an insulating blanket or barrier, to reduce radiative heat loss from the plantation, especially at night when temperatures typically fall. In this way more of the solar heat energy previously absorbed during daytime can be usefully retained in the plantation.

It is however still the case that the two most commonly used and popular systems to protect against frost damage are those that use water sprinklers and those that use a distributed system of open fuel burners. Water sprinklers are used with the principal objective of maintaining the presence of liquid water even while ice forms at <NUM>, since frost damage due to freezing plant sap is not normally expected until the temperature has dropped to about -<NUM>. However, the sprinkler approach requires substantial investment in equipment as well as copious water consumption, which ultimately washes away into surface and underground aquifers. Furthermore, because it relies on the continuous formation of new ice on the plants once the temperature has fallen to freezing point (<NUM>), there is a risk of overburdening and damaging the plants with the weight of ice formed.

The open fuel burners are used as local heaters to combat the falling air temperature.

However, this system is very inefficient in its use of fuel and combustion heat, most of which is lost by convection to the upper air. In attempts to overcome this heat loss by blowing the combustion gases directly into the plantation space, there is a serious risk of very high temperature gas scorching the plants.

<CIT> discloses a spraying apparatus in which a liquid to be sprayed is atomized by combustion gases discharged from a combustion chamber in a pulsating stream.

The present invention arose from the inventors work in the use of a thermal fog as a protection against frost damage, and seeks to improve upon the prior art.

The invention is defined by the independent claim.

In accordance with one aspect, there is provided an apparatus according to claim <NUM>.

The apparatus may further comprise a fuel tank configured to hold a fuel therein.

Preferably, the fuel is a liquid fuel. Preferably, the fuel tank is fluidly connected to the burner. Preferably, the apparatus comprises feed means for feeding fuel from the fuel tank to the burner. The feed means may comprise a pump.

Preferably, the apparatus comprises means for feeding the combustion gas along the enclosed conduit.

The means for feeding the combustion gas along the enclosed conduit may comprise a first blower. The first blower may be configured to feed the combustion gas from the burner into the enclosed conduit. The first blower may be disposed upstream of the burner and configured to feed atmospheric air into the burner.

Alternatively, or additionally, the means for feeding the combustion gas along the enclosed conduit may comprise a second blower. The second blower may be configured to feed the gas comprising water vapour from the enclosed conduit to the ejector. Accordingly, second blower may be disposed between the enclosed conduit and the ejector.

It may be appreciated that a blower may be an air pump.

A first, upstream portion of the enclosed conduit may define a combustion chamber.

A first, upstream portion of the enclosed conduit may be disposed substantially adjacent to a second, downstream portion of the enclosed conduit. Preferably, the second, downstream portion of the enclosed conduit is disposed substantially around the first, upstream portion of the enclosed conduit. Accordingly, the first, upstream portion and second, downstream portion of the enclosed conduit may share a dividing wall.

The first, upstream portion of the enclosed conduit may have a cylindrical cross-section. The second, downstream portion of the enclosed conduit may comprise an annulus disposed around and on the same longitudinal axis as first, upstream portion of the enclosed conduit.

The second, downstream portion of the enclosed conduit may comprise a plurality of passages. Each of the plurality of passages may substantially extend between distal and proximal ends of the first upstream portion. Accordingly, the second, downstream portion of the enclosed conduit may comprise at least <NUM>, at least <NUM>, at least <NUM>, at least <NUM>, at least <NUM>, at least <NUM> or at least <NUM> passages. Advantageously, the plurality of passages increases the length of the enclosed conduit.

A first passage may comprise a first end which is fluidly connected to the first upstream portion and a second end which is fluidly connected to a second passage which is downstream thereof. A final passage may comprise a first end which is fluidly connected to a preceding, upstream passage and a second end which is fluidly connected to an outlet conduit. Intermediate passages may each comprise a first end which is fluidly connected to a preceding, upstream passage and a second end which is fluidly connected to a downstream passage.

The apparatus may comprise an insulator. The insulator may be disposed substantially adjacent to the extended conduit. The insulator may be disposed over or substantially around the extended conduit. In embodiments where the second, downstream portion of the enclosed conduit is disposed substantially around the first, upstream portion of the enclosed conduit, the insulator may be disposed substantially adjacent to the second, downstream portion of the enclosed conduit. The insulator may be disposed over or substantially around the second, downstream portion of the enclosed conduit.

The outlet conduit may extend between the enclosed conduit and the ejector. The second blower may be disposed on the outlet conduit.

The outlet conduit may comprise an air inlet configured to allow ambient air to be drawn into the outlet conduit. The outlet conduit may comprise a valve. The valve may be configured to allow a user to control whether or not ambient air is drawn into the outlet conduit.

Preferably, the plurality of injectors are disposed along an external surface of the enclosed conduit. The plurality of injectors may be disposed along the second, downstream portion of the enclosed conduit. Accordingly, the plurality of injectors may be disposed along an external surface of the second, downstream portion of the enclosed conduit. The plurality of injectors may comprise a plurality of spray nozzles.

Preferably, the apparatus comprises a water tank. Preferably, the apparatus comprises one or more conduits which extend between the water tank and the plurality of injectors. Preferably, the apparatus comprises a pump configured to feed water from the water tank to the plurality of injectors.

The apparatus may comprise a water filter. Preferably, the water filter is disposed between the pump and the water tank.

The apparatus may comprise a power source. The power source may comprise a generator or a battery. The power source may be configured to power the first blower. The power source may be configured to power the second blower. The power source may be configured to power the pump.

The apparatus may comprise a plurality of ejectors. The plurality of ejectors may comprise at least two, at least three or at least four ejectors. In embodiments where the apparatus comprises at least two ejectors preferably at least one ejector is configured to release the gas comprising water vapour as a jet on a first side of the apparatus and at least one ejector is configured to release the gas comprising water vapour as a jet on a second side of the apparatus, wherein the second side is substantially opposite to the first side. As explained above, in some embodiments, the jet has a range of <NUM>. Accordingly, with a jet disposed on each side, the apparatus may be used to treat an area which is <NUM> wide.

Preferably, the apparatus comprises at least four ejectors, wherein at least two ejectors are configured to release the gas comprising water vapour as a jet on a first side of the apparatus and at least two ejectors are configured to release the gas comprising water vapour as a jet on a second side of the apparatus, wherein the second side is opposite to the first side. Preferably, an ejector on each side of the apparatus is configured to release the gas comprising water vapour as a jet in a proximal direction. Preferably, an ejector on each side of the apparatus is configured to release the gas comprising water vapour as a jet in a distal direction.

Preferably, the direction of the or each ejector is adjustable. Accordingly, it may be possible to adjust the direction of a jet produced by the ejector. The direction of the jet may be adjustable in a horizontal plane. Alternatively, or additionally, the direction of the jet may be adjustable in a vertical plane. In a preferred embodiment, the direction of the jet is adjustable in both a horizontal plane and a vertical plane.

The apparatus may comprise a valve configured to selectively release a fluid from the enclosed conduit. Advantageously, this allows the release of water from enclosed conduit after the apparatus has been used.

In accordance with another aspect, there is provided a vehicle comprising the apparatus of the invention.

The vehicle may comprise a wheeled vehicle. The vehicle may comprise a trailer or a motorised vehicle. The trailer may comprise a connector configured to attach the trailer to a motorised vehicle.

All of the features described herein (including any accompanying claims, abstract and drawings), may be combined within the scope of the invention limited by the appended claims.

Embodiments of the invention are illustrated by way of example in the accompanying drawings, in which:.

In <FIG> of the drawings, thermal fog generating apparatus <NUM> is shown standing on a platform <NUM> carried on a wheeled vehicle <NUM>. In <FIG>, the wheeled vehicle is a trailer provided with a coupling <NUM> by which it can be drawn behind a tractor <NUM>, as shown in <FIG>.

The apparatus <NUM> includes an evaporator unit <NUM> and a distribution system. As explained in more detail below, the evaporator unit <NUM> is configured to heat, evaporate and cool water. The distribution system is configured to release the fluid from the apparatus from ejection units <NUM>, <NUM>, which are pivotally mounted on support <NUM>, to generate a thermal fog.

The evaporator unit <NUM> is in the shape of a cylinder with a proximal end <NUM> and a distal end <NUM>, and is securely supported over the platform <NUM> by front and rear cradle blocks <NUM>. The cradle blocks <NUM> space the evaporator unit <NUM> apart from the platform <NUM> to prevent overheating. The evaporator unit <NUM> has a tap (not shown) disposed in a lower part thereof to allow evacuation of water after work has been completed.

As shown in <FIG>, the evaporator unit <NUM> comprises a combustion chamber <NUM>, which is located centrally therein, and is surrounded by a eight interconnected passages <NUM>-<NUM> which extend parallel to each other, in an axial direction, substantially between the proximal and distal ends <NUM>, <NUM> of the evaporator unit <NUM>. The combustion chamber <NUM> defines an aperture <NUM> substantially adjacent to the proximal end <NUM> of the evaporator unit <NUM>, which fluidly connects the chamber <NUM> with a first passage <NUM>.

<FIG> shows a simplified view of the passages <NUM>-<NUM>. For clarity, the passages <NUM>-<NUM> have been shown in a planar configuration. However, it will be appreciated that in the apparatus the passages will extend around the cylindrical combustion chamber <NUM>. As shown in <FIG>, the first passage <NUM> is disposed adjacent to a second passage <NUM> and a first wall <NUM> is disposed therebetween. An aperture in the first wall <NUM> is provided substantially adjacent to the distal end <NUM> of the combustion chamber <NUM>, fluidly connecting the first and second passages <NUM>, <NUM>. Similarly, the second passage <NUM> is disposed adjacent to a third passage <NUM> and a second wall <NUM> is disposed therebetween. An aperture in the second wall <NUM> is provided substantially adjacent to the proximal end <NUM> of the combustion chamber <NUM>, fluidly connecting the second and third passages <NUM>, <NUM>. This pattern continues for the remaining passages <NUM>-<NUM>, with the apertures in the separating walls <NUM>-<NUM> alternating between being disposed substantially adjacent to the proximal end <NUM> or the distal end <NUM> of the evaporator unit <NUM>. As shown in <FIG>, the eighth passage <NUM> is disposed adjacent to the first passage <NUM>, with an eighth wall <NUM> disposed therebetween. No aperture is provided in the eighth wall.

An outlet conduit <NUM> is provided on the proximal end <NUM> of the evaporator unit <NUM> and is fluidly connected to the eighth passage <NUM>. The outlet conduit <NUM> comprises a valve (not shown). When the valve is closed, a gas flowing from the passages <NUM>-<NUM> flows to a blower <NUM> with adjustable performance. The blower <NUM> is configured to cause the gas to then travel along a conduit <NUM> to the ejectors <NUM> and <NUM>. Support <NUM> is a radially graduated circular scale fixed to the platform <NUM> with a centre pivot in which the two ejectors <NUM> and <NUM> are rotably fixed, allowing a user to vary how a fog ejected from ejectors <NUM>, <NUM> is distributed.

Alternatively, when the valve is open, atmospheric air may be drawn down conduit <NUM> and become entrained in the warm gas. This allows the gas to be further cooled, if necessary, prior to being ejected.

A water tank <NUM> is suspended under platform <NUM>. A pipe (not shown) extends between the water tank <NUM> to a water filter <NUM>, which is mounted on the rear of platform <NUM>. Water is drawn from the tank <NUM> and through the water filter <NUM> by a water pump <NUM>. A further conduit <NUM> extends between the filter <NUM> and four water distribution pipes 32a-d. The distribution pipes 32a-d extend substantially parallel to the evaporator unit <NUM> with one pipe 32a disposed on a lower left side of the evaporator unit <NUM>, one pipe 32b on a lower right side of the evaporator unit <NUM>, one pipe 32c on an upper left of the evaporator unit and one pipe 32d on an upper right sides of the evaporator unit <NUM>. Five pairs of inlet conduits <NUM> are provided on each distribution pipe 32a-d. The inlet conduits deliver the filtered water to injector nozzles <NUM>, which intern inject it into the passages <NUM>-<NUM>. Accordingly, each distribution pipe 32a-d is configured to supply two of the passages <NUM>-<NUM> with water at five separate points along the length of the passage <NUM>-<NUM>.

Accordingly, each of the passages <NUM> to <NUM> is provided with five nozzles configured to deliver the same quantity of water at the same pressure.

An injector nozzle <NUM> is shown in more detail in <FIG>. As shown in the Figure, a mounting ring <NUM> is welded to an external surface of the combustion chamber <NUM>. The mounting ring <NUM> is disposed around an aperture <NUM> in the external surface of the combustion chamber <NUM>. The injector nozzle <NUM> is reversibly attached to the welded mounting ring <NUM>. The injector nozzle <NUM> comprises a hollow injector shell <NUM>, which is reversibly coupled directly to the mounting ring <NUM>. A mounted injector body <NUM> is disposed, in double threaded engagement, inside the hollow injector shell <NUM>. This arrangement allows the spray only, and not the metal <NUM>, to be in contact with the passing gases. Furthermore, the nozzle <NUM> is readily accessible for maintenance, inspection and service requirements.

A burner <NUM> is disposed on the rear of platform <NUM>. The burner is configured to receive liquefied fuel from fuel tank, which is also mounted on the rear of the platform <NUM>. In the burner <NUM>, the fuel is mixed with an excess of atmospheric air, ignited, and injected into the combustion chamber <NUM>. The excess of air, which is provided by an air blower (not shown) optimises the combustion of the fuel.

The apparatus <NUM> further comprises an electrical power supply <NUM> disposed towards the front of platform <NUM>. The electrical power supply <NUM> produces electrical power to power the pump <NUM> and the blower <NUM>. In an alternative embodiment, the electrical generator <NUM> can be replaced by the electrical power produced by an independent electrical generator powered by the PTO of the tractor. The electrical system should be provided with the adequate security controls.

In use, the evaporator unit <NUM> is covered by a thick insulator filled curtain (not shown), which hangs on frame hooks <NUM> disposed on the upper distribution pipes 32c, 32d. The curtain isolates the evaporator unit, preventing loss of heat and protecting the operator.

When a user wishes to use the apparatus <NUM>, they would activate the electrical generator <NUM> to power the pump <NUM> and the blower <NUM>. The user would then first feed the liquefied fuel and air to the burner <NUM> and ignite the fuel. As explained above, excess air will be provided, and the proportion which could be up to <NUM>% excess of the stoichiometric requirement of the fuel to obtain maximum efficiency.

The ignited fuel and air in the burner <NUM> is injected into the combustion chamber <NUM> where it continues to combust as it travels along the length of the chamber <NUM> to the proximal end <NUM>. The combustion gases then travel from the combustion chamber <NUM>, through the aperture <NUM> and enter the first passage <NUM>. The combustion gases travel along the first passage <NUM> until they reach the distal end <NUM> of the evaporator unit <NUM>. At this point, the combustion gases pass through the aperture in the first wall <NUM> into the second passage <NUM>. The combustion gases continue to travel through the passages <NUM>-<NUM> until they reach the eighth passage <NUM>. The gases then flow along the outlet conduit <NUM>, to the blower <NUM> and along the conduit <NUM> to the ejectors <NUM> and <NUM> where it is released into the atmosphere.

Due to the action of pump <NUM>, water is drawn from the water tank <NUM>, through the filter <NUM>, along the conduit <NUM>, along the distribution pipes 32a-d, along the inlet conduits <NUM>, which will discharge it into the passages <NUM>-<NUM> via the nozzles <NUM>. Due to the delivery of the water, the temperature of the combustion gases in the passages <NUM>-<NUM> is reduced gradually from a starting temperature of about <NUM> to about <NUM>. This is caused by the evaporation of the injected water, forming water vapour in a superheated state. The gas becomes saturated at <NUM>. The volume ratio of liquid water to liquefied fuel used by the apparatus running under steady conditions is normally exactly linked stoichiometrically in such a way that the total water to be evaporated will be supplied with the exact amount of fuel necessary for that evaporation.

The saturated gas then flows along the outlet conduit <NUM>, to the blower <NUM>, along the conduit <NUM> and out of the ejectors <NUM> and <NUM>. Once the gas is ejected it contacts atmospheric air at low temperatures and condenses rapidly onto nearby plants, transferring the condensation heat by conduction to the plant. The gas remaining in the air delivers the condensation heat to the local atmosphere.

<FIG> illustrates the apparatus <NUM> in action for protecting a plantation against frost. The most common type of plantation where the invention will be used may contain deciduous fruit trees, such as apple tree, pear trees or stone fruit trees, or in a vineyard. Accordingly, the apparatus may be used in temperate areas prone to frost in springtime. However, it may be appreciated that frost can also affect subtropical plantations, which may contain citrus trees, and sometimes even tropical plantations, which may contain coffee plants. The apparatus <NUM> may be used in all of these plantations. It will be noted that a general feature of such plantations is that they are commonly arranged in rows at convenient separation or space for agricultural machinery to work comfortably within the rows, as shown in <FIG>.

<FIG> shows the wheeled vehicle <NUM> carrying the apparatus <NUM> is coupled to, a tractor <NUM>. The tractor <NUM> draws the apparatus <NUM> along a track <NUM> through an orchard containing lines of fruit trees <NUM> extending at right angles to the track on both sides thereof. The ejectors <NUM>, <NUM> are producing jets <NUM>, <NUM> as described above which will penetrate not only deeply along the rows but also into the spaces therebetween. Accordingly, the paired jets <NUM>, <NUM> on each side of the apparatus <NUM> will wet significant area of the trees <NUM> as the tractor moves forward. The speed which the tractor moves at will a large effect on the quantity of the thermal fog that contacts each tree <NUM>.

To obtain maximum coverage, if the apparatus is disposed next to a first row of trees <NUM>, then the forward pointing ejectors <NUM> will ideally be positioned to direct the jet <NUM> along a second row of trees <NUM> directly in front of the first row <NUM>. As the tractor <NUM> moves forward the jet <NUM> will contact trees <NUM> that are closer to the track <NUM>, contacting each tree <NUM> in turn. The backwards pointing ejectors <NUM> may be similarly configured.

At the impact area on the tree trunk the thermal fog will produce a mass of vapour and gases which will scatter into the plant canopy in all directions. These scattered waves of warm gases and vapour can be optimized by channelling them with small baffles conveniently attached to the tree trunk at the impact area.

Furthermore, part of the uncondensed jet may ascend by convection to an elevated level in the atmosphere above the plantation and, cooling as it rises, may form a thermal fog barrier which acts as a blanket over the plantation. Thus, the thermal fog can act to both add and retain heat, as both carrier and barrier.

The specific embodiment of the invention that has been described and illustrated in the accompanying drawings can be readily set up and prepared for use by one person in a very short time. It is usually only necessary to fill the water tank <NUM>, to ensure that there is sufficient fuel in the fuel tank for the burner <NUM>, to ensure that the electrical power supply <NUM> is fully charged, and to couple the trailer <NUM> to the tractor <NUM>. In this way, the thermal protection of a plantation can be commenced in a very short time after a frost warning is received.

It may be appreciated that the total surface area to be treated against the threat of frost is essentially a function with the following variables:.

Furthermore, the pump <NUM> should have a power capacity to maintain a working pressure such that it is able to eject the gas from the ejectors <NUM>, <NUM> at an adequate speed. For instance, the gas may be ejected at a pressure of about <NUM> atmosphere.

The correct quantity of water may also be calculated to ensure that the gas which is ejected has a final temperature of about <NUM>. The blower <NUM> should also have a suction capacity capable of maintaining a working pressure equal or slightly lower than the pressure in the evaporator unit <NUM>.

For calculating the thermal fog production regime in m<NUM>/Ha it is necessary, in principle if not in practice, to know the chemical composition of the fuel to be used and the stoichiometric quantity of oxygen to be taken from air for achieving perfect chemical combustion. The stoichiometric mass of air needed to combust the fuel may be calculated, and an excess of air may then be added. Generally an excess of about <NUM>% is used to obtain optimal combustion. The total volume of the air and combustion gases can then be calculated. To this volume, the volume of water vapour which will be produced can be added. The volume of water vapour will be in the order of <NUM> litres of water vapour per litre of water evaporated under atmospheric pressure and at <NUM>. In this way the total volume of gas to be suctioned and ejected by the blower <NUM> can be determined.

The basic components resulting from this combustion will be carbon dioxide and water, with the fog produced resembling a natural fog.

The invention can use liquid fuels for industrial use or heating in accordance with existing regulations for conventional agro-production. However, in a preferred embodiment, but a clean fuel or biofuel, free of heavy metals or acid contaminants, is used. This protects the crop from pollutants and ensures that the process is environmentally friendly. Such fuels are economic to use due to the high thermal efficiency of the system.

The thermal fog delivers heat energy to the plantation is by means of heat transfer mechanisms. In particular, the thermal fog can deliver heat energy by direct heat conduction to a surface with which it comes into contact. For instance, it can transfer heat to the ground vegetation, soil, plant trunks, leaves and fruit. Alternatively, it can transfer heat to the surrounding air. The water vapour component on the thermal fog will condense transferring condensation heat at a rate of about <NUM> kJ/litre of water being deposited. The resulting condensate will form a water film on the impacted surfaces. The liquid water forming the film can lose further energy of about <NUM> kJ/litre due to cooling prior to freezing. Some of this energy will also be transferred to the surface upon which the film is deposited. It should be noted that the vapour which remains in the air will transfer the same amount of energy warming the air. Additionally, the water will release energy amounting to about <NUM> kJ/litre water as it forms ice.

It may be appreciated that the heat will be transferred to air over the plantation. In particular, after being ejected hot gas will initially travel upward. It will contact cold air as it rises, transferring heat thereto and losing buoyancy as it does. Accordingly, the hot gases will heat a substantial area over the plantation and will act as a heat barrier.

Claim 1:
An apparatus (<NUM>) for generating a thermal fog, the apparatus (<NUM>) comprising:
- a burner (<NUM>) configured to be provided with a fuel source and air;
- an enclosed conduit configured to receive a combustion gas from the burner (<NUM>);
- a plurality of injectors (<NUM>) disposed along the enclosed conduit and configured to inject liquid water into the enclosed conduit to thereby provide a gas comprising water vapour; and
- an ejector (<NUM>) configured to release the gas comprising water vapour as a jet (<NUM>) to provide a thermal fog,
wherein a second, downstream portion of the enclosed conduit is disposed substantially around a first, upstream portion of the enclosed conduit, such that the first, upstream portion and second, downstream portion of the enclosed conduit share a dividing wall,
wherein the first, upstream portion of the enclosed conduit has a cylindrical cross-section and the second, downstream portion of the enclosed conduit comprises an annulus disposed around and on the same longitudinal axis as first, upstream portion of the enclosed conduit, and
wherein the plurality of injectors (<NUM>) are disposed along an external surface of the second, downstream portion of the enclosed conduit.