GB2461575A

GB2461575A - Spray nozzle

Info

Publication number: GB2461575A
Application number: GB0812330A
Authority: GB
Inventors: Peter David Wilson
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-07-05
Filing date: 2008-07-05
Publication date: 2010-01-06
Anticipated expiration: 2028-07-05
Also published as: GB0812330D0; GB2461575B

Abstract

A spray nozzle for spraying a coating liquid on to food products includes a reservoir chamber 2 having a substantially cylindrical wall 4 and a discharge port 8 that is formed in a base of the reservoir chamber and through which the coating liquid is discharged in the form of a stream of droplets. A gas inlet 10 is adapted to supply pressurised gas (e.g. compressed air) to the reservoir chamber 2 in a substantially tangential direction such that the gas flows in a substantially circular direction within the reservoir chamber. A liquid inlet 12 is similarly adapted to supply the coating liquid at pressure to the reservoir chamber 2 in a substantially tangential direction such that the coating liquid flows in the same substantially circular direction within the reservoir chamber. A liquid vortex is created within the reservoir chamber to shear the coating liquid into droplets at the discharge port 8. A plunger means can be moved relative to the discharge port 8 in a direction substantially parallel with the longitudinal axis of the reservoir chamber 2 and is used to control the spray cone angle.

Description

TITLE

Spray nozzles

DESCRIPTION

Technical Field

The present invention relates to spray nozzles, and in particular to spray nozzles for applying a coating liquid such as a flavouring slurry or batter to food products.

Background Art

Food products like dried pasta and snack food products such as potato chips, tortilla chips, corn chips, extruded snacks and the like can be flavoured by coating them with a wet flavouring mixture or slurry that consists of flavouring particles suspended in an edible oil such as vegetable oil. The flavouring slurry is usually applied to the food products by a delivery means as they pass through a rotating flavouring drum. The delivery means typically includes one or more spray nozzles for applying the flavouring slurry to the food products in droplet form.

Summary of the Invention

The present invention provides an improved spray nozzle comprising a reservoir chamber having a substantially cylindrical wall and a discharge port, a gas inlet for supplying pressurised gas to the reservoir chamber in a substantially tangential direction such that the gas flows in a substantially circular direction within the reservoir chamber in a predetermined sense (e.g. clockwise or anti-clockwise depending on the orientation of the gas inlet), a liquid inlet for supplying pressurised liquid to the reservoir chamber in a substantially tangential direction such that the liquid flows in a substantially circular direction within the reservoir chamber in the predetermined sense before being discharged through the discharge port, and plunger means positioned within the reservoir chamber that can be moved relative to the discl-1arg joii. in a direeiiori subswntiaiiy paraiiei with the longitudinal axis of the reservoir chamber.

The liquid is preferably discharged through the discharge port in the form of a stream of droplets.

The rate at which the liquid is discharged through the discharge port is preferably substantially constant and can be selected by varying the pressure of the gas (e.g. compressed air) that is supplied to the reservoir chamber through the gas inlet. The gas pressure can also be varied to select the desired droplet size. The gas inlet can be connected to any suitable source of pressured gas including a cylinder, pressurised storage vessel or reservoir etc. by any suitable piping. The gas pressure is preferably kept substantially constant during the steady-state operation of the spray nozzle but can be varied using any suitable control valve that can be adjusted manually or automatically under the direction of a control unit, for example. In other words, once the particular gas pressure that achieves the desired rate for the liquid discharge and/or the droplet size has been detennined then the gas pressure is preferably kept substantially constant until any further adjustment is needed.

The spray pattern of the droplets and/or the spray cone angle can be adjusted by varying the position of the plunger relative to the discharge port. More particularly, moving the plunger towards the discharge port provides a focal point for the droplets and narrows the spray cone angle. The extent of plunger movement towards the discharge port may be such that at least a head part of the plunger can be received within an opening or aperture defining the discharge port. The plunger may be temporarily fixed in a particular position when the desired spray pattern and/or spray cone angle has been achieved for the particular operating conditions of the spray nozzle. The movement of the plunger can be carried out manually or by any suitable mechanical means, for example.

Although the spray nozzle is intended to be used to spray a coating liquid for food products, Ii j icdiiy appreciated that the spray nozzle can also be used to spray other liquids such as industrial coatings, paints, oils, water, chemicals, insecticides and pesticides, detergents, fluidised fuels etc. The coating liquid may be pumped directly to the liquid inlet of the spray nozzle from a mixing vessel that will normally be part of a food processing plant. The mixing vessel produces the coating liquid by mixing together suitable amounts of dry mixture and liquid using an impeller. The dry mixture may be in the form of flavouring particles in which case the coating liquid may be a flavouring slurry that can be used to coat a wide variety of different food products including dried pasta and snack food products such as potato crisps, potato chips, tortilla chips, corn chips, extruded snacks and the like. The flavouring particles may be supplied in the form of granules or powder. The dry mixture may also be a dry batter mix in which case the coating liquid will be a batter that can be used to coat food products such as processed fish and meat products and the like. The liquid supplied to the mixing vessel may be water or an edible oil such as a vegetable, seed or nut oil, for example.

The spray nozzle may be located within a rotating flavouring drum, for example, such that the coating liquid is sprayed onto the food products as they pass through the flavouring drum.

The pump used to transfer the coating liquid from the mixing vessel to the liquid inlet of the spray nozzle is preferably a peristaltic pump operating at variable speed. This is because the moving parts of the peristaltic pump do not come into contact with the coating liquid and there is no risk of contamination. The liquid inlet can be connected to the outlet of the peristaltic pump by any suitable piping. It will be appreciated that the output flow of a peristaltic pump is a pulsating flow and this means that the pressure of the coating liquid that is supplied to the liquid inlet of the spray nozzle will experience short regular drops. Maintaining a substantially constant rate for the discharge of the coating liquid is important because of the need to ensure that an even coating is applied to the food products over the course a batch run. However, any changes in the pressure at which the coating liquid is supplied to the liquid inlet arising from the pulsating flow of the peristaltic pump are effectively smoothed by the use of the reservoir chamber that contains a certain volume of the coating liquid during operation of the spray nozzle. Keeping a certain volume of the coating liquid in the reservoir chamber therefore ensures that the coating liquid is discharged through the discharge port at a substantially constant rate and with a regular spray pattern. The same effect can also be used to smooth other changes in the pressure at which the coating liquid (or other liquid, if applicable) is supplied to the liquid inlet.

The reservoir chamber may typically contain about 0.2 litres of liquid during steady-state operation of the spray nozzle which.will circulate within the reservoir chamber in the form of a liquid vortex or whirlpool as described in more detail below.

In general terms, the liquid inlet can be connected to any suitable source of pressured liquid including the outlet of any suitable pump type (including, but not limited to, a positive displacement pump), a cylinder, pressurised storage vessel -or reservoir etc. by any suitable piping.

If no gas is supplied to the gas inlet then the liquid will flow in a substantially circular direction within the reservoir chamber as a result of being supplied in a tangential direction before being discharged out of the discharge port as a steady stream under gravity. It will be readily appreciated that the gas is introduced into the reservoir chamber such that it flows in the same substantially circular direction. The introduction of the pressurised gas therefore has the effect of increasing the speed of the rotation of the liquid within the reservoir chamber. During steady-state operation of the spray nozzle, the introduction of the pressurised gas leads to the creation of a fast moving liquid vortex or whirlpool within the reservoir chamber which acts to shear the liquid so that it is discharged through the discharge port in droplet form. In the case where the liquid is a coating liquid, the rotation of the liquid vortex within the reservoir chamber also serves to keep the particles of the dry mixture suspended in the water or edible oil, for example. This ensures that the food products are evenly coated and prevents problems such as "spotting" where food products are coated with discrete clumps of particles of dry mixture instead of the dry mixture being evenly distributed.

The speed of rotation of the liquid vortex within the reservoir chamber will typically be such that the centre of the liquid vortex defines a passage in communication with the discharge port through which most of the pressurised gas may be discharged. In other words, most of the gas supplied through the gas inlet into the region of the reservoir chamber above the surface of the liquid vortex will eventually flow through the passage at the centre of the liquid vortex and out of the spray nozzle through the discharge port. However, at least part of the gas may actually be entrained within the liquid vortex and this may assist in the formation of droplets at the discharge port.

The liquid inlet is preferably arranged closer to the discharge port than the gas inlet in the axial direction. Since the spray nozzle will normally be positioned with the discharge port facing downwardly, this means that the pressuriséd gas will always be supplied to the delivery chamber above the surface of the liquid vortex and will therefore actively force the liquid out through the discharge port.

The opening or aperture in the reservoir chamber defining the discharge port may have any suitable size and shape (e.g. circular or ellipse-shaped) depending on the desired spray pattern. The size of the opening or aperture may depend at least in part on the viscosity of the liquid that is supplied through the liquid inlet. For example, in the case where the spray nozzle is used to spray a coating liquid having a viscosity of about 50 mPa.sec then the opening may be circular and have a diameter of about 0.8 cm. The discharge port will be located in a base of the reservoir chamber when the spray nozzle is mounted for use.

The reservoir chamber may further include a frusto-conical wall between the cylindrical wall and the discharge port to assist in the creation of the liquid vortex and the discharge of the liquid through the discharge port.

The present invention further provides an apparatus for applying a coating liquid to food products, comprising a coating region, a mixing vessel for mixing together a * liquid and a dry mixture to form a coating liquid, and a pump for pumping the coating ijuid tu x dciivcry means for appiying the coating liquid to the food products as they pass through the coating region, wherein the delivery means includes a spray nozzle as described above where the liquid inlet of the spray nozzle is connected to the pump.

Drawings Figure 1 is a plan view of a spray nozzle according to the present invention; Figure 2 is a first side view of the spray nozzle of Figure 1 along line A; Figure 3 is a second side view of the spray nozzle of Figure 1 along line B; Figure 4 is a cross section view of the spray nozzle of Figure 1 along line C-C showing the plunger in a first position; and Figure 5 is a cross section view of the spray nozzle of Figure 1 along line C-C showing the plunger in a second position.

A spray nozzle for applying a flavouring slurry to food products will now be described with reference to Figures 1 to 5. The spray nozzle is suitably mounted within a rotating flavouring drum (not shown) to spray the food products with flavouring slurry as they move through the flavouring drum under gravity.

The spray nozzle includes a reservoir chamber 2 that is defined by a cylindrical wall 4 and a chamfered (frusto-conical) wall 6 at the base. The chamfered wall 6 defines a circular opening 8 through which the flavouring slurry is discharged as a stream of droplets.

As shown in Figures 1 to 3, the spray nozzle includes an air inlet 10 that has a vertical part 1 Oa and a horizontal part 1 Ob that is arranged to supply compressed air into the reservoir chamber 2 in a tangential direction relative to the cylindrical wall 4.

Similarly, a liquid inlet 12 has a vertical part l2a and a horizontal part 12b that is also arranged to supply flavouring slurry at pressure into the reservoir chamber 2 in a tangential direction relative to the cylindrical wall 4. It will be readily appreciated that both the compressed air and the flavouring slurry will flow in the same circular direction within the reservoir chamber 2 (i.e. clockwise as shown in Figure 1).

Thr,ugIoiit the Figures, ihe flow of the compressed air is indicated schematically by the non-filled block arrows and the flow of flavouring slurry is indicated schematically by the filled block arrows. The opening of the liquid inlet 12 is located axially below the opening of the air inlet 10 (i.e. closer to the opening 8) such that the compressed air that is supplied through the air inlet forces the volume of flavouring slurry that is contained within the reservoir chamber 2 out of the opening 8 at a constant rate.

The droplet size will normally be selected to ensure an even coating of the food products and may depend on the composition of the flavouring slurry as well as the operating parameters of the spray nozzle described below.

A mixing vessel (not shown) produces the flavouring slurry by mixing together dry flavouring particles and vegetable oil. The flavouring slurry is pumped from the mixing vessel (not shown) to the liquid inlet 12 of the spray nozzle by a peristaltic pump (not shown). The liquid inlet 12 may be connected to the outlet of the peristaltic pump (not shown) using any suitable coupling or piping. A typical average supply pressure for the flavouring slurry is about 2 bar (2x 1 O Pa) but the supply pressure may suffer short and regular drops as a result of the pulsating flow of the peristaltic pump. These changes in supply pressure do not result in corresponding changes in the rate at which the flavouring slurry is discharged through the opening 8 or the spray pattern of the droplets for the reasons mentioned above.

The rate at which the flavouring slurry is discharged through the opening 8 remains substantially constant during steady-state operation of the spray nozzle and is determined by the supply pressure of the compressed air. The supply pressure of the compressed air will also determine the droplet size of the flavouring slurry. The air inlet 10 may be connected to a compressed air source (e.g. a cylinder, pressurised storage vessel or reservoir, or a common feedline installed in the food processing plant) using any suitable coupling and piping. A typical range of supply pressures for the compressed air is between about 0.25 bar (2.5x104 Pa) and about 2 bar (2xl05 Pa).

A control valve (not shown) may be located between the compressed air source and thc ai iiiCt I C iü uiiLroi he supply pressure. Ihe supply pressure can be changed manually or under the direction of a control unit.

During steady-state operation of the spray nozzle, flavouring slurry and compressed air are supplied to the reservoir chamber 2 through the liquid inlet 12 and the air inlet 10, respectively, in a tangential direction. The swirling compressed air above the volume of flavouring slurry creates a fast moving liquid vortex or whirlpool of flavouring slurry FS within the reservoir chamber 2 that shears the flavouring slurry into droplets at the opening 8. The surface 14 of the liquid vortex during steady-state operation of the spray nozzle is shown in Figures 4 and 5 and it can be seen that the centre of the liquid vortex will typically be in communication with the opening 8.

This means that most of the swirling compressed air in the region above the surface 14 of the liquid vortex can flow directly through the centre of the liquid vortex and out through the opening 8. However, at least some of the compressed air will be entrained within the flavouring slurry and may assist in the formation of droplets at the opening 8.

With reference to Figures 4 and 5, a plunger 16 includes a rounded head part 18 and a stem part 20 that is mounted to an upper part 22 of the spray nozzle. The stem part 20 has an external screw threaded part that, cooperates with a corresponding internal screw thread on a bore 24 provided in the upper part 22 or mounting block of the spray nozzle such that rotation of the plunger 16 relative to the reservoir chamber 2 causes the head part 18 of the plunger to move towards or away from the opening 8 in a direction that is parallel to the longitudinal axis of the reservoir chamber. The plunger 16 may be temporarily retained in a suitable position by a locking nut 26.

Although the movement of the plunger 16 is described here as being manual, it will be readily appreciated that the movement may be carried out using any suitable mechanical means, optionally under the direction of a control unit. The extent of axial movement of the plunger 16 may be restricted or limited by any suitable means.

At its maximum lowest extent, the head part 18 of the plunger may be received in the opening 8 as shown in Figure 4. The movement of the plunger 16 is used to adjust the spray pattern andlor the spray cone angle of the droplets of flavouring slurry discharged through the opening 8. Moving the plunger 16 towards the opening 8 narrows the spray cone angle and moving the plunger away from the opening widens the spray cone angle. This is shown in Figures 4 and 5. More particularly, in Figure 4 where the plunger 16 is at its maximum lowest extent the spray cone angle represented schematically by the droplets of flavouring slurry being discharged through the opening 8 is narrower than that shown in Figure 5 where the plunger 16 is at is maximum highest extent (i.e. the head 18 of the plunger is furthest away from the opening 8).

A spray cone angle of about 400 is typical but this may depend on the composition of the flavouring slurry and the food products that are to be coated.

Claims

CLAIMS1. A spray nozzle comprising: a reservoir chamber having a substantially cylindrical wall and a discharge port; a gas inlet for supplying pressurised gas to the reservoir chamber in a substantially tangential direction such that the gas flows in a substantially circular direction within the reservoir chamber in a predetermined sense; a liquid inlet for supplying pressurised liquid to the reservoir chamber in a substantially tangential direction such that the liquid flows in a substantially circular direction within the reservoir chamber in the predetermined sense before being discharged through the discharge port; and plunger means positioned within the reservoir chamber that can be moved relative to the discharge port in a direction substantially parallel with the longitudinal axis of the reservoir chamber.
2. A spray nozzle according to claim 1, wherein the liquid inlet is arranged closer to the discharge port than the gas inlet in the axial direction.
3. A spray nozzle according to claim I or claim 2, further comprising a frusto-conical wall between the cylindrical wall and discharge port.
4. An apparatus for applying a coating liquid to food products comprising: a coating region; a mixing vessel for mixing together a liquid and a dry mixture to form a coating liquid; and a pump for pumping the coating liquid to a delivery means for applying the coating liquid to the food products as they pass through the coating region; wherein the delivery means includes a spray nozzle according to any preceding claim where the liquid inlet of the spray nozzle is connected to the pump.
5. An apparatus according to claim 4, wherein the pump is a peristaltic pump.
6. A spray nozzle substantially as herein described and with reference to the drawings.