GB2286515A - Method and apparatus for flavouring a food product - Google Patents

Abstract

A method and apparatus (20) for flavouring a food product comprises passing the food products into a region (37) of electric charge containing fluent, e.g. powdered, flavouring compound, such that the food product provides a conductive path for current, breaking the conductive path and then re-establishing it. The breaking of the conductive path may be achieved by having two conveyors (26a, 26b) at different heights so that the food product falls from one to the other, by blowing a gas through a conveyor so as to hit the food product or by having an insulated portion of a conveyor. <IMAGE>

Description

Method and ApParatus for Flavouring a Food Product This invention relates to a method and apparatus for flavouring a food product. Many food products require the addition of flavouring compounds after their production.

One known method of applying the flavouring to food products after production is an electrostatic process in which food products are subjected to an electrostatic charge whilst in the presence of a powdered flavouring compound. The charging of the food products tend to cause adherence of powdered flavouring compound thereto.

A known apparatus for the electrostatic flavouring of food products is shown partly in schematic form in Figure 1. In Figure 1, there is shown a flanged, rotatable drum 10 that is mounted in a machine chassis (not shown). Drum 10 may be driven to rotate by means of a drive wheel 11 having a periphery adapted drivingly to engage the outer periphery of the drum 10. Drive wheel 11 is secured in a bearing 12 and is drivingly connected to a suitable motor (not shown).

The cylindrical inner wall of drum 10 carries longitudinally extending vanes 13. The vanes 13 protrude generally perpendicular to the cylindrical inner wall of the drum 10.

A transverse carrier bar 14 is secured adjacent the forward end of the drum 10 and supports a hopper assembly 15 that feeds a flavouring nozzle 16. An electrostatic gun 17 is also supported on bar 14.

In use of the apparatus, food products are fed in at the forward end of the drum which is rotated by means of the drive wheel 11 to tumble the food products once they are inside the drum 10. Flavouring powder is fed from the hopper assembly 15 via the nozzle 16 to the interior of the drum 10, and simultaneously an electrostatic field is generated within the drum by virtue of charging of the electrostatic gun 17. This process causes some of the flavouring powder to become adhered to the food products within the drum 10.

The above described prior art process is suitable for coating food products such as baked or fried products (e.g. potato crisps, potato snacks, wheat snacks and tortilla chips); but the prior art method and apparatus suffer numerous disadvantages.

The primary disadvantage of apparatus such as that shown in Figure 1 is that much of the flavouring powder is wasted since it does not become adhered to food products. Therefore, excessive amounts of flavouring powder have to be applied from the hopper system 15 thereby causing clouds of powder to generate in the vicinity of the machine. Powder settles on various parts of the apparatus, thereby making it difficult to keep the apparatus clean; in addition, workers in the vicinity of the apparatus are in danger of inhaling large quantities of flavouring powder.

Moreover, it is necessary to employ the vanes 13 and the rotating action of the drum 10 in order to turn over the food products during treatment, to try and ensure an even distribution of flavouring powder onto the food products. This action tends to damage delicate food products, and in any event is not particularly successful since the process relies on the slow fall of powder under gravity onto the food products. If a food product is turned twice within a short space of time, one side of the food product will not receive an adequate coating of flavouring, while the other side receives an excessive coating. Moreover, where food products lie one on top of another, it is impossible for the flavouring powder to penetrate evenly to coat all the food products.

According to a first aspect of the invention, there is provided a method of flavouring a food product comprising the steps of: (i) subjecting the food product to an electric field in the presence of a fluent flavouring medium, the food product serving to provide a conductive path for current resulting from the electric field; (ii) disjoining the conductive path in respect of at least a portion of the food product; and (iii) re-establishing the conductive path.

It has been found by the inventors that the at least partial disjoining of the conductive path constituted at least in part by the food product, whilst maintaining the food product in the vicinity of e.g. a powdered flavouring compound and an electric field, causes the food product to become highly agitated and also intimately surrounded on all sides by a uniform quantity of flavouring powder. When the conductive path is re-established, the flavouring powder surrounding the product is immediately strongly attracted to the food product, thereby causing the adherence of an even coating of flavouring to the food product.

Preferably, the fluent flavouring medium is a powdered flavouring.

Conveniently, the electric field is established and the flavouring applied by means of an electrostatic flavouring gun.

The use of an electrostatic flavouring gun (ie. a combined electrostatic gun and discharge device for fluent flavouring media) conveniently obviates the need for separate supplies of flavouring medium and electric charge; and also ensures that the electric field generally coincides with the region of flavouring medium dispensed towards the food product.

In preferred embodiments, the electric field is established by means of one or more sources of electrostatic charge. However, it is possible to devise embodiments of the invention in which a single source of electrostatic charge is used. Moreover, it is possible to use either a single source or multiple sources of fluent flavouring medium.

Preferably, the conductive path is provided by contact of the food product with a conductive member at a different electrical potential from that of the field. Moreover, the disjoining of the conductive path may conveniently be caused by the further step of insulating the food product or a part thereof from the conductive member. This may advantageously be achieved by moving the food product out of conducting contact with the conductive member.

In particularly preferred embodiments of the invention, the food product is moved normal to a surface of the conductive member during the step of insulating. Thus, for example, the food product may readily be allowed to fall away from the conductive member under gravity or be blown clear of the conductive member, thereby leading to advantageously simple embodiments of the invention.

Alternatively, the food product may be moved onto an insulated or insulating member adjacent the conductive member during the step of insulating. This method of insulating the food product may be advantageous in the case of food products that are particularly delicate and prone to damage if subjected to physical impulses and perturbations.

Conveniently, the method additionally includes the step of causing a gas to flow through the region of an electric field during the steps (i) to (iii) identified above.

This additional, optional method step assists in ensuring an even distribution of fluent flavouring medium throughout the region of the electric field, whilst simultaneously minimising wastage of the flavouring medium.

In preferred embodiments, the method steps are carried out in a substantially closed chamber.

According to a second aspect of the invention, there is provided apparatus for flavouring a food product comprising: means for creating an electric field; means for supporting a food product in an electric field created by said means such that the food product provides a conductive path for current resulting from the electric field; means for supplying a fluent flavouring medium to the vicinity of the food product; and means whereby the conductive path may be disjoined and subsequently re-established, at least in respect of part of the food product.

Apparatus according to the invention may be manufactured as an advantageously simple, reliable and robust product. Moreover, such apparatus is highly effective in ensuring the uniform and economical coating of flavouring media onto food products and minimises the risk of damage to the food products themselves.

Conveniently, the apparatus includes a plurality of means for creating an electric field. Alternatively, a single such means may be employed.

It is further preferable that the electric field is created and the flavouring medium supplied by one or more electrostatic flavouring guns.

The advantages of electrostatic flavouring guns mentioned above in relation to the method of the invention apply equally to their use in the apparatus defined herein.

Preferably, the means for supporting the food product comprises a conveyor for moving the food product and formed of a conducting material, whereby when the food product contacts the conveyor the conductive path is established. The use of a conveyor to constitute a means for supporting the food product and establishing the conductive path means that the food product can advantageously be transported through the apparatus whilst simultaneously being flavoured.

In preferred embodiments, the conveyor is discontinuous and the apparatus includes means whereby the food product is moveable from one portion of the conveyor to another, the conductive path being disjoined when the food product is between the conveyor portions. In a particularly preferred embodiment, the apparatus comprises a first conveyor portion spaced vertically from a second conveyor portion, whereby the food product may travel along the first conveyor portion and fall onto the second conveyor portion, the conductive path being disjoined at least partially while the food product falls between the conveyor portions.

The advantage of this arrangement is that the travel of the food product between the first and second conveyor portions is automatic, since the food product falls under gravity. Judicious spacing of the first and second conveyor portions ensure that the food products are guaranteed to be out of contact with the conveyor for at least a portion of the travel, whilst remaining in the electric field and in the vicinity of the flavouring medium.

In such an embodiment, it is preferable that there is at least one electrostatic flavouring gun disposed in the vicinity of the second, lower conveyor portion. Conveniently, at least one electrostatic flavouring gun may also or alternatively be disposed in the vicinity of the first, upper conveyor portion. Various adjustments to the performance of the apparatus may conveniently be made by altering the number and positions of flavouring guns.

Conveniently, the conveyor may include an insulated or insulating portion, the arrangement being such that a food product may be moved along the conveyor via the insulated or insulating portion, the conductive path being disjoined while the food product is on said insulated or insulating portion.

This arrangement permits the conductive path to be disjoined whilst permitting only the minimum perturbation of food products. Thus, this embodiment is advantageous when it is desired to treat particularly delicate food products.

Conveniently, the conveyor may include two portions separated one from the other by the insulated or insulating portion. This arrangement ensures that all the food products travelling along the conveyor are obliged to pass into the region of the insulated or insulating portion, thereby ensuring disjoining of the conductive path in respect of each food product conveyed.

A further possibility is to provide a gas blower, e.g. an air blower, to blow the food product temporarily out of contact with the conveyor. This arrangement may be of utility when it is desired for the apparatus to have a low profile, thus preventing the use of two conveyor portions at different levels as specified hereinabove.

Conveniently, the conveyor or at least one portion of the conveyor is a vibratory distribution conveyor. Such a conveyor has been found to be particularly useful for the conveying of delicate food products.

Conveniently, the apparatus includes means whereby a gas (e.g. air) flow may be induced in the vicinity of the electric field. This feature has been advantageously found to reduce wastage of fluent flavouring medium and to maintain the cleanliness of the apparatus.

The apparatus may preferably include a substantially closed chamber generally enclosing the components thereof. This arrangement ensures that a satisfactory gas flow can be achieved, and that the escape of e.g.

flavouring powder into a factory environment is minimised.

When the apparatus includes a substantially closed chamber, it may preferably include inlet means for an unflavoured food product, and outlet means for a flavoured food product.

It is also preferable that the apparatus includes duct means communicating with the interior of the chamber and a gas (e.g. air) pumping means operatively connected thereto, whereby a gas flow may be induced in the vicinity of the electric field.

Whilst the example of air has been given in relation to the flow of gas, it will be appreciated that other gases may possibly be used. For instance, it is common in the food industry for gas flushing to be achieved using inert gases so as to avoid tainting the food product. The use of an inert gas may also be advantageous in that it is less likely to become charged by the electric field and therefore the risk of discharge elsewhere in the apparatus as the gas is flushed away is reduced.

The apparatus of the invention may be employed to apply flavouring to a wide variety of food products. Examples include potato crisps, potato chips, other potato snacks, wheat snacks, tortilla chips, biscuits and breakfast cereals. However, this list is not exhaustive and numerous other food products may successfully be treated.

There now follows a description of preferred embodiments of the invention, by way of example, with reference being made to the drawings in which: Figure 1 is a perspective, partially schematic view of a prior art flavouring apparatus; Figure 2 is a side elevational, schematic view of apparatus according to the invention; Figure 3 is a perspective view showing food products passing between two conveyor portions of the apparatus of Figure 2; Figure 4a shows the relative positions of food products and fluent flavouring medium while the conductive path is disjoined; Figure 4b shows food products after re-establishment of the conductive path, and having flavouring medium adhered thereto; Figure 5 shows an alternative embodiment of conveyor for use in apparatus of the invention; and Figure 6 shows a further possible conveyor embodiment.

Referring to Figures 2 to 6, there is shown an apparatus 20 in accordance with the invention. The apparatus 20 comprises a substantially closed chamber 21 having a hingeable lid portion 22. Chamber 21 has an inlet for food products indicated generally by the numeral 23 and an outlet for flavoured food products indicated generally by the numeral 24.

Inlet portion 23 is constituted in part by vibratory conveyor 26 supported generally horizontally. Conveyor 26 is constituted by two separate parts, 26a and 26b, supported at opposite ends of the apparatus 20 and disposed one below the other. Part of conveyor portion 26a lies within chamber 21, and part thereof protrudes from chamber 21 via an aperture in the side wall thereof.

Conveyor portion 26a is supported relative to chamber 21 by means (not shown) and by virtue of a vibratory drive 27 in turn mounted via an isolating block 28 on a stand 29 separate from the chamber 21. It will thus be apparent that food products inserted into conveyor portion 26a in the direction and location indicated by arrow A will, on operation of the vibratory drive 27, be conveyed from the exterior of the chamber 21 towards the middle thereof.

Further conveyor portion 26b is similar to conveyor 26a and is supported generally horizontally on the opposite side of chamber 21 to that of conveyor portion 26a. Conveyor portion 26b is so positioned that its free end inside chamber 21 is vertically below the free end of conveyor portion 26a. Thus, as is visible in Figure 3, any food products reaching the end of conveyor portion 26a fall off the free end thereof into the free end of conveyor portion 26b. Conveyor portion 26a lacks a vertical end wall, to facilitate passage of food products therefrom; conveyor 26b includes an end wall 31 to assist in the catching of falling food products.

Conveyor portion 26b is supported relative to the chamber 21 by means (not shown), and by virtue of a further vibratory drive 32 secured thereto and to a support frame 33.

Vibratory drive 32 is mounted to act on the upper edge of conveyor portion 26b thereby to draw food products away from the free end of conveyor portion 26b towards the exterior of chamber 21.

In the embodiment shown, there is an electrostatic flavouring gun 34 supported in the vicinity of the free end of conveyor portion 26a, and a further electrostatic flavouring gun 35 supported in the vicinity of the free end of conveyor portion 26b.

Electrostatic flavouring guns presently available are such as to supply a fluent flavouring medium such as a powdered flavouring compound at the same time as generating an electric field in the vicinity of the powder supplied. In the embodiment shown in Figure 2, the two electrostatic flavouring guns 34 and 35 between them create a region of powder and an electric field bounded approximately by the chain lines 37.

Thus, the region of powder and electric field overlaps the free ends of each of the conveyor portions 26a and 26b, and the space therebetween.

A further feature of the apparatus of Figure 2 is a duct 38 secured via a sealing flange 39 in the hingeable cover 22 of the apparatus. Duct 38 as connected to a pump for, e.g. air, whereby a flow of air through the apparatus may be established. Air is drawn in either through a specific inlet formed in chamber 21, or via the apertures formed in the side walls of chamber 21 to accommodate the conveyor portions 26a and 26b.

In operation of the apparatus of the invention, in accordance with the method of the invention, unflavoured food products are fed into conveyor portion 26a as previously indicated. The unflavoured food products may be fed from a further conveyor (not shown) or from a hopper (not shown) or from any like mechanism.

In general, the vibratory drives 27 and 32 operate continuously to convey all food products through the apparatus. The food products fed to conveyor portion 26a are driven towards the interior of chamber 21. As the food products approach the free end of conveyor 26a, they enter the vicinity of the electric field and the region of flavouring powder provided by flavouring gun 34.

The conveyor portion 26a is at a different (e.g. lower) electrical potential from that of the electric field indicated by chain lines 37.

As each food product enters the vicinity of the electric field, it becomes charged and since the food product is in contact with the conveyor portion 26a there exists a conductive path whereby charge migrates from the food product to the charge sink provided the conveyor portion 26a and any apparatus connected thereto. Thus, in the manner of conventional electrostatic flavouring systems, some flavouring product will adhere to the food products that are in contact with the conveyor portion 26a to the left of the chain line B in figure 3.

When the food products reach the free end of conveyor 26a, they fall off the free end of conveyor portion 26a into the space between the portions 26a and 26b, ie. between the chain lines B and C of Figure 3.

Once the food products fall off the end of conveyor portion 26a, the conductive path previously referred to is disjoined. As best shown in Figure 4a, when this happens the food products become highly charged (there being no sink for charge induced in the food products) and therefore somewhat energised. As the food products fall towards conveyor portion 26b, as best shown in Figure 4a, they become intimately surrounded by large quantities of flavouring powder partly as a result of their capacitance, and partly because their energised state means that they tend to rotate as they fall, thereby ensuring a uniform density of flavouring powder in their vicinity.

As soon as the food products contact the conveyor 26b (ie. when they are to the right of the chain line C of Figure 3) a conductive path is reestablished and the electric potential induced in the food products is instantaneously discharged. The resulting flow of current is believed to alter the polarity of the food products, thereby instantaneously causing all the flavouring powder in the vicinity of the food products to adhere strongly thereto. This situation is shown in Figure 4b. Since in the instant prior to their discharge, the food products are intimately surrounded by an even density of flavouring powder, it follows that on discharging of the food products an even coating of flavouring powder adheres over the entire surface of each food product. Thus, the method and apparatus of the invention are highly efficient in ensuring even flavouring of food products without wastage of flavouring powder.

Once the food products have been electrically discharged by contact with conveyor portion 26b, they are conveyed under the influence of vibratory drive 32 towards the exterior of chamber 21. After emerging from chamber 21, the food products may be conveyed away by a further mechanism (not shown).

In addition to the foregoing method, it is possible to arrange the conveyor portions 26a and 26b such that a food product is never completely out of contact with the charge sink constituted by the conveyor 26. This can be achieved e.g. by raising conveyor portion 26b relative to conveyor portion 26a, so that a food product tending to fall off the free end of the conveyor portion 26a makes conductive contact with conveyor portion 26b before the conductive contact with conveyor portion 26a is broken.

The effect of this arrangement is to disjoin the conductive path only in respect of part of the food product (e.g. its centre portion) with the conductive path being maintained by another part thereof (e.g. the edges). Thus, the effects shown in Figures 4a and 4b would only arise fully in respect of part of each food product. This modified form of the apparatus and method may be helpful in flavouring particular kinds of food product.

Figure 5 shows an alternative embodiment of conveyor that may be employed in the apparatus of the invention.

In Figure 5, there is shown a first conveyor portion 126a connected to a second, downstream conveyor portion 126b by means of an intermediate conveyor portion 126c. Conveyor portion 126c includes a plurality of nozzle-like apertures 41 that act as outlets for a gas (e.g. air) supplied to the underside of conveyor 126 by means of a suitable duct 42 and air box 43. Air box 43 is sealed onto the underside of conveyor 126 so that ai supplied via duct 42 passes through the nozzles 41.

Thus, a plurality of jets of air (indicated by the vertical arrows in Figure 5) act upwardly from the surface of portion 126c of the conveyor 126. An electrostatic flavouring gun 44 is supported in the vicinity of conveyor portion 126c to permit the establishment of an electric field and the supply of e.g. powdered flavouring compounds to the conveyor 126. The electric field extends to either side of central portion 126c, so that the ends of the respective portions 126a and 126b are also subject to the electric field.

It will be appreciated that food products moving in the direction of the horizontal arrows along the conveyor 126 will initially encounter a region of flavouring powder and an electric field whilst still in contact with conveyor portion 126a. At this time, each food product constitutes a conductive path by virtue of such contact. As the food products pass onto intermediate conveyor portion 126c, the air jets blow the food products clear of the conveyor 126 thereby disjoining the conductive path previously established by virtue of contact of the food products with conveyor portion 126a. While the food products are supported by the air jets over portion 126c, the flavouring powder distributes itself about the food products in the manner shown in Figure 4a. Since the food products have a component of motion in the direction of the horizontal arrows in Figure 5, they tend to progress beyond the intermediate conveyor portion 126c to land on the conveyor portion 126b.

When this occurs, the food products immediately discharge in the manner of the food products landing on conveyor portion 26b in Figure 3 and the flavouring compound adheres strongly and evenly to the food products.

Yet a further embodiment of the invention is shown in Figure 6, in which the intermediate portion 126c of the conveyor, the air box 43 and the duct 42 are replaced by a single, intermediate (electrically) insulated or insulating conveyor portion 150. It will be appreciated that the conductive path is automatically disjoined as the food products move onto the insulated or insulating portion 150 and lose contact with the conveyor portion 126a. A conductive path is re-established when the food products move onto the conveyor portion 126b. Thus, the apparatus of Figure 6 operates in the same general manner as that of the previously described embodiments. However, in Figure 6 the food products are not subjected to such violent perturbation. Thus, the embodiment of Figure 6 is likely to be of particular use in flavouring delicate food products.

The partial disjoining of the conductive path referred to in relation to the Figure 2/3 embodiment may readily be achieved in the embodiments of Figures 5 and 6, e.g. by choice of the strength and direction of the air jets in Figure 5, or by adjustment of the size and position of the insulating member 150 in Figure 6.

It will be appreciated that numerous variants of the invention are possible. In particular, the number and positioning of electrostatic flavouring guns may be chosen to provide the most effective flavouring environment for the configuration of the apparatus and the food product and flavouring compound being used. Thus, for example, it may be desirable to provide one or more such guns at the right hand end of the apparatus as shown in Figure 2, and no gun at the left hand end, above conveyor portion 26a. Numerous other arrangements are possible.

Moreover, it is not necessary for the electric field to be established and the flavouring compound to be provided by a common apparatus such as an electrostatic flavouring gun. Electrodes separate from a flavouring compound nozzle may equally be employed.

Claims (30)

1. A method of flavouring a food product comprising the steps of: (i) subjecting the food product to an electric field in the presence of a fluent flavouring medium, the food product serving to provide a conductive path for current resulting from the electric field; (ii) disjoining the conductive path in respect of at least a portion of the food product; and (iii) re-establishing the conductive path.

2. A method according to Claim 1 wherein the fluent flavouring medium S a powdered flavouring.

3. A method according to Claim 2 wherein the electric field is established and the flavouring applied by means of an electrostatic flavouring gun.

4. A method according to any preceding claim wherein the electric field is established by means of one or more sources of electrostatic charge.

5. A method according to any preceding claim wherein the conductive path is provided by contact of the food product with a conductive member at a different electrical potential from that of the field.

6. A method according to Claim 5 wherein disjoining of the conductive path is caused by the further step of insulating the food product from the conductive member.

7. A method according to Claim 6 wherein the step of insulating the food product takes place by movement of the food product out of conducting contact with the conductive member.

8. A method according to Claim 7 wherein the food product is moved normal to a surface of the conductive member during said step of insulating.

9. A method according to Claim 7 wherein the food product is moved onto an insulated or insulating member adjacent the conductive member during said step of insulating.

10. A method according to any preceding claim further including the step of: (iv) causing a gas to flow through the region of the electric field during said steps (i) to (iii).

11. A method according to any preceding claim when carried out in a substantially closed chamber.

12. Apparatus for flavouring a food product comprising: means for creating an electric field; means for supporting a food product in an electric field created by said means such that the food product provides a conductive path for current resulting from the electric field; means for supplying a fluent flavouring medium to the vicinity of the food product; and means whereby the conductive path may be disjoined and subsequently re-established, at least in respect of part of the food product.

13. Apparatus according to Claim 12 comprising a plurality of means for creating an electric field.

14. Apparatus according to Claim 12 or Claim 13 wherein the electric field is created and the flavouring medium supplied by one or more electrostatic flavouring guns.

15. Apparatus according to any of Claims 12 to 14 wherein the means for supporting the food product comprises a conveyor for moving the food product and formed of a conducting material, whereby when the food product contacts the conveyor the conductive path is established.

16. Apparatus according to Claim 15 wherein the conveyor is discontinuous, and wherein the apparatus includes means whereby the food product is moveable from one portion of the conveyor to another, the conductive path being disjoined at least partially when the food product is between the conveyor portions.

17. Apparatus according to Claim 16 comprising a first conveyor portion spaced vertically from a second conveyor portion, wherein the food product may travel along the first conveyor portion and fall onto the second conveyor portion, the conductive path being disjoined while the food product falls between the conveyor portions.

18. Apparatus according to Claim 17 including at least one electrostatic flavouring gun disposed in the vicinity of the second, lower conveyor portion.

19. Apparatus according to Claim 17 or Claim 18 including at least one electrostatic flavouring gun disposed in the vicinity of the first, upper conveyor portion.

20. Apparatus according to Claim 15 wherein the conveyor includes an insulated or insulating portion, the arrangement being such that a food product may be moved along the conveyor via the insulated or insulating portion, the conductive path being disjoined while the food product is on said insulated or insulating portion.

21. Apparatus according to Claim 20 wherein the conveyor includes two portions separated one from the other by said insulated or insulating portion.

22. Apparatus according to Claim 15 including means whereby the food product may be moved temporarily out of contact with the conveyor, thereby to disjoin the conductive path.

23. Apparatus according to Claim 22 wherein the means for moving the food product temporarily out of contact with the conveyor comprises a gas blower, e.g an air blower.

24. Apparatus according to any of Claims 16 to 23 at least one portion of the conveyor is a vibratory distribution conveyor.

25. Apparatus according to any of Claims 12 to 24 further including means whereby a gas (e.g. air) flow may be induced in the vicinity of the electric field.

26. Apparatus according to any of Claims 12 to 25 further including a substantially closed chamber generally enclosing the components thereof.

27. Apparatus according to Claim 26 including inlet means for an unflavoured food product, and outlet means for a flavoured food product.

28. Apparatus according to Claim 26 or Claim 27 including duct means communicating with the interior of the chamber and gas (e.g. air) pumping means operatively connected thereto, whereby a gas flow may be induced in the vicinity of the electric field.

29. A method generally as herein described, with reference to or as illustrated in Figures 2 to 6 of the accompanying drawings.

30. Apparatus generally as herein described, with reference to or as illustrated in Figures 2 to 6 of the accompanying drawings.