The present invention relates to a fluid mixer device and a method of mixing fluids, and is concerned particularly, although not exclusively, with a mixer device for mixing a gaseous component and a liquid component in a pressurized tank, and with a method therefor.

In pressurized fluid systems used for extinguishing fires, typically a liquid such as water will be stored under super-atmospheric pressure in a container with a pressurized gas, which may be air, carbon dioxide or nitrogen, for examples.

In systems that seek to deliver a fine mist of liquid, a mixing device is used in which gas and liquid are mixed, so that the latter is made to form minute droplets. The gas and liquid can be stored in separate tanks, sometimes one within the other, or else the gas can simply fill the void in the container above the volume of liquid.

With previously considered mixing devices, a problem arises as the container begins to discharge. As the pressure inside the tank reduces the pressure with which the mixture is expelled also reduces. Furthermore, the characteristics of the mist begin to change, as it is difficult to maintain a consistent droplet size.

The liquid and gas components of the mix enter the mixer device through separate ports. During use, as the liquid level in the tank diminishes/ in certain orientations of the tank the mixer may not be supplied with liquid, leading to inconsistencies in the mist. This problem becomes particularly noticeable when the container is worn as a backpack, when the wearer may adopt different positions during its use.

Embodiments of the present invention aim to provide a mixing device and a method of mixing, in which the above- mentioned drawbacks with prior devices are addressed.

The present invention is defined in the attached independent claims, to which reference should now be made. Further, preferred features may be found in the sub-claims appended thereto.

According to one aspect of the present invention, there is provided a mixer-regulator device for mixing a first fluid and a second fluid, the device comprising a mixer body defining a mixer chamber, first and second fluid inlets and a fluid outlet, a rotor arranged in use to rotate to mix the first and second fluids at a first pressure to form a mixture, and a baffle arranged in use to deflect the flowing mixture, wherein the baffle extends substantially across the mixing chamber, and wherein the mixture exits the outlet at a second pressure, lower than the first pressure .

The baffle is preferably arranged in use to extend across substantially the entire mixing chamber, The baffle is preferably arranged downstream of the rotor and upstream of the outlet.

In a preferred arrangement the baffle is generally platelike or laminar.

The baffle preferably has one or more apertures. In a preferred arrangement one or more of the apertures has a surface that is non-parallel with the axis of rotation of the rotor.

In a preferred arrangement the device is arranged to mix first and second fluids of which one is a liquid and the other is a gas.

The mixture may comprise droplets of liquid suspended in a gas .

The droplets of liquid may be arranged in use to strike the baffle and fragment or explode.

Preferably the body is generally cylindrical. Preferably the body has a convergent portion, which may comprise a frusto-conical portion, towards the outlet. The rotor may comprise a spindle and may include one or more vanes.

There may be a plurality of vanes which may be spaced substantially equally around the spindle. In a preferred arrangement there are four substantially equally spaced vanes .

The rotor may be arranged in use such that the vanes block the first and second inlets substantially simultaneously. The rotor may be arranged in use such that the vanes unblock the first and second inlets substantially simultaneously.

The or each vane may comprise a surface which is arranged in use to be driven by pressurized fluid to cause the rotor to rotate.

The baffle may be generally disc-shaped.

According to another aspect of the present invention, there is provided a mixer-regulator device for mixing a first fluid and a second fluid, the device comprising a mixer body defining a mixer chamber, first and second fluid inlets and a fluid outlet, wherein the first and second fluids enter the device at a first pressure, and the mixture exits the outlet at a second pressure, lower than the first pressure, wherein the first and second inlets are located on or towards a first side of the body and the outlet is located on or towards a second side of the body.

The first and second sides of the body may be substantially opposed sides. The fluid inlets preferably comprise inlet feed pipes, which may be pi otally connected to the mixer device and/or which may be flexible. One or both of the inlet feed pipes may be weighted at or towards its end. The device may be according to any statement herein.

The invention also includes a container comprising a mixer- regulator device according to any statement herein.

According to a further aspect of the present invention, there is provided method of mixing a first fluid and a second fluid, the method comprising mixing the first and second fluids in a mixer body defining a mixer chamber, and having first and second fluid inlets and a fluid outlet, a rotor arranged in use to rotate to mix the first and second fluids at a first pressure to form a mixture, and a baffle arranged in use to deflect the flowing mixture, wherein the baffle extends substantially across the mixing chamber, and wherein the mixture exits the outlet at a second pressure, lower than the first pressure.

In a preferred arrangement the method comprises a method of mixing a liquid and a gas.

The mixture may comprise droplets of liquid suspended in a gas .

The droplets of liquid may be arranged in use to strike the baffle and fragment or explode.

According to further aspect of the present invention, there is provided a method for mixing a first fluid and a second fluid, the method comprising mixing the first and second fluids in a device comprising a mixer body defining a mixer chamber, first and second fluid inlets and a fluid outlet, wherein the first and second fluids enter the device at a first pressure, and the mixture exits the outlet at a second pressure, lower than the first pressure, wherein the first and second inlets are located on or towards a first side of the body and the outlet is located on or towards a second side of the body.

The invention may include any combination of the features or limitations referred to herein, except such a combination of features as are mutually exclusive, or mutually inconsistent.

A preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which:

Figure 1 shows schematically a pressurized container including a mixing according to an embodiment of the present invention;

Figure 2 is a schematic sectional view of the mixing device of Figure 1;

Figure 3 is a schematic exploded view of the mixing device of Figure 2;

Figure 4 is a schematic view of the mixing device of Figures 2 and 3 in assembled form; Figure 5 is a schematic view of a first embodiment of mixer device in use; Figure 6 is a schematic view of a second embodiment of mixer device in use;

Figures 7-10 show comparisons of the embodiment of Figure 5 with a previously considered mixing device; and

Figures 11a and lib show schematically the flow of a gas and water mixture through a mixing device in accordance with an embodiment of the present invention. Turning to Figure 1, this shows generally at 100 a pressurised container, or tank, of fluid, for use in fighting fires.

The tank 100 comprises a wall 120 and an outlet nozzle 130. Inside the tank is a mixer/regulator 140 having a gas inlet pipe 150 and a liquid inlet pipe 160. The lower half of the tank as shown has water W at a level L, while in the space above the water is nitrogen dioxide ND. The liquid inlet pipe 160 has a single opening at a distal end 160a. The gas inlet pipe has a plurality of openings 150a along its length. The lower, or distal ends of the pipes are weighted by weights 170.

Figure 2 shows the mixer/regulator 140 in schematic sectional view. The device, which is preferably of plastics material, but could be of metal, comprises a substantially cylindrical, hollow body 180, comprising an upper part 180a and a base 180b with water inlet port 190 and gas inlet port 200 at a base portion 180a of the body. In use, the inlet ports 190 and 200 are connected respectively to the water inlet pipe 160 and the gas inlet pipe 150 shown in Figure 1.

Inside the body 180 is a rotor 210, comprising four symmetrically mounted vanes 212 and an integrally formed spindle 214 arranged for rotation axially within the body 180. Vertically above the rotor 210 and axially spaced therefrom is a disc-like baffle 220. Above the baffle 220 is an outlet port 230 which, in use, is fluidically connected to the outlet nozzle 130. An upper portion of the spindle 214 is received into a bearing/socket in the baffle 220, whereas the spindle is mounted at its opposite end in a bearing/socket of the base portion 180b.

Arrows Al and A2 indicate respectively the inflowing water and gas. Arrow A3 shows a path of the water/gas mixture.

Figure 3 shows the device in schematic exploded view. The vanes 212 are shaped so that water and gas entering under pressure through the ports 190 and 200 cause the rotor to rotate axially. As the rotor turns, the vanes alternately open and close the inlet and outlet ports 190 and 200 together. This means that the ports are alternately both open, and then both closed, four times during each complete rotation of the rotor, to mix the water and gas. The water and gas mixture, consisting of fine droplets of water suspended in the pressurised gas, is thrown radially outwards by the rotor and then hits the baffle 220. The baffle has two sloping apertures 222 located 180 degrees apart around its circumferential edge. As the water/gas mixture strikes the sloping sides of the apertures 222 the droplets break up, causing an even finer mist.

Figure 4 is a "transparent effect" schematic view of the device in assembled form.

Figure 5 shows the device schematically as it is configured in a tank (not shown) . The water level is indicated at L. It can be seen that at least one of the inlet holes 150a on the gas inlet pipe 150 is above the water level. Gas and water enter the mixer device at the ports 200 and 190 as described previously, the water and gas become mixed in the rotor 210, and the water droplets collide with the baffle 220 to reduce the droplet size further. The fine mist then exits the outlet port 230.

Figure 6 shows schematically an alternative embodiment of device, in which there is no gas inlet pipe 150, but the gas inlet port 200 is above the water level, allowing the gas to enter the device 140 directly.

Figures 7-10 show schematically a comparison of the embodiment of Figure 5 with a previously considered apparatus. The previously considered apparatus (prior art) is represented at 1000 and comprises a tank 1120, a mixer 1140, a gas inlet port 1200 fed by a gas inlet pipe 1150 and a water inlet port 1190. An outlet pipe 1130 carries the water/gas mixture out of the device 1140. In the previously considered apparatus 1000, the water enters the water inlet 1190 directly, and from below the device 1140 in the orientation shown in the drawing. However the gas inlet port is on the opposite side of the device 1140, ie an upper side in the orientation shown.

The reason for the gas and water inlet ports being on opposed sides of the device, lies in the internal geometry of the device 1140. Specifically, the device 1140 uses a rotor to alternately open the gas and water inlet channels.

However, this arrangement can lead to operational problems, dependent upon the orientation of the device with respect to the liquid in the tank. This can become evident particularly when the tank is worn as a backpack, for example by a user fighting a fire.

In the orientation represented in Figure 7, both sets of apparatus work without problem as in each case the water and gas ports are supplied properly.

However, in Figure 8 the tanks are tilted at approximately 45 degrees to the vertical. The prior art apparatus 1000 ceases to function correctly as, even though gas is still able to reach the gas inlet port 1200, the water level has fallen below the water inlet port 1190. In contrast, with the apparatus 100, according to an embodiment of the invention, the water and gas inlet pipes, 160 and 150, are able to convey water and gas to the ports 190 and 200 respectively. This is because the pipes are both located below the device 140 and the weights 170 keep the ends of the flexible pipes at a lowest region of the tank. Figure 9 shows schematically the situation in which the tanks are substantially horizontal. Again, with the prior art example, the water is unable to reach the water inlet port 1190. In contrast, the apparatus according to the embodiment of the present invention is able to continue to function normally with both the water inlet port 190 and the gas inlet port 200 being properly served. The situation depicted schematically in Figure 10 is somewhat similar to that of Figure 9, in that the apparatus is horizontal, but with a higher level L.

In this situation, the cylinder is horizontal and the gas tube is below the water level. This causes an inconsistency in the mixture. The prior art apparatus will discharge more gas and less water in this configuration, or possibly no water at all. However, thanks to the flexible pipes 150 and 160, and the fact that these pipes are on the same side of the mixer, the apparatus shown on the right, in accordance with the embodiment of the present invention, will continue to function normally until all the water in the tank has been used. Figures 11a and lib show, schematically, the effect on the flow of the rotor and baffle. Because of the compressibility of gas, small packets of gas, upon experiencing the reduction of pressure upon exiting the rotor, explode at the exits of the rotor spaces causing water to disperse. The rotor is intentionally made to have low drag to make the sudden pressure change distance as short as possible. The rotor is made in a swirl-form shape so as to make it spin around its axle under pressure of water and gas, so that gas and water ports feed same channels on an intermittent basis. Upon leaving the rotor the mixed-phase flow impacts upon a static baffle or chicane.

The baffle' s openings 222 are orientated to cancel the component of the linear momentum that is non-coaxial with the alignment of the channels in between the vanes, which the oncoming flow has upon exiting the spinning rotor. Due to conservation of momentum, should there be no decompression, the velocities of the fluid entering the rotor and exiting the baffle apertures would be almost the same. However, the flow is very much compressible; and the rotations of the rotor add a planar component to the velocity Vp. This internal flow must accelerate before the resultant velocity Vr of the flow reaches the exit velocity. The velocity vectors not only have different orientation, but also different magnitude and the difference increases with the angular velocity of the rotor. A pressure drop makes up for the difference in the magnitude between the velocities of the fluid exiting the rotor, Vr, and that of the fluid exiting the baffle apertures. The difference is related to the velocity Vp, which depends on the rate of the axial flow through the rotor. Therefore a self-regulating mechanism of pressure drop limitation, activated when the rotations of the rotor become excessive, is created.

The baffle promotes, if not controls, water atomization by way of splashing the miniscule water droplets against the sides of its apertures. This is possible because this is a mixed-phase flow, originating in the rotor channels. This additional mechanism is possible, because the difference of specific weights of gas and water makes droplets travel along different trajectories than the air particles in the areas of pronounced changes in the flow velocity field. Upon being literally ejected from the rotor channels by the bubbles of air expanding due to the pressure decrease near channel exit, droplets break up further and travel with initial velocity Vr, toward the fixed baffle having walls non-parallel to their trajectories. At such distances friction effects are negligible, so that the initial velocity component remains largely unchanged, but upon decomposing Vp, a destruction of droplets is observed as they collide with the fixed wall with velocity Vw and a reverse movement of droplets due to the presence of the Vc component of velocity. This mechanism is very important also for regulating the pressure drop on the mixed-phase flow, because the droplet stream carries most of the linear momentum and a large part of its kinetic energy. There will be a further breakup of water droplets when they negotiate the trailing edge of the baffle.

The purpose of the baffle plate is to further divide the liquid molecules after the mixing chamber. The two orifices on the baffle are equally spaced. This plate does not block (close) the fluid flow through the rotor.

The baffle plate does not separate the fluids (liquid and gas) inlet port from the mixing chamber as this comes after mixing stage.

When the tank is fully charged, the contents are at their greatest pressure, and when the discharge valve is opened the difference in pressure causes gas and water to flow through the mixer, turning the rotor. The angular velocity of the rotor is at its maximum, as is the component Vp. However the pressure drop across the rotor is at its maximum, leading to the formation of larger droplets. The kinetic energy with which these droplets impact the apertures of the baffle ensures that they become broken up.

In contrast, when the tank is partly discharged, the pressure in the tank will be less, and so will the angular velocity of the rotor, and hence the component Vp. However, the pressure drop across the rotor will be less, and so smaller droplets are formed. These have less kinetic energy, because Vp is smaller, but they require less energy to break them.

Accordingly, the droplet size remains broadly consistent throughout the discharge of the tank, unlike with prior art systems . The above example is of mixing water with nitrogen dioxide. However, other liquids and/or other gases could be used, and foam may be added to the mixture in certain applications. In cases of high pressure-drop and for heavy- duty applications, the baffle may have to be made of a metal, such as stainless steel for example.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance, it should be understood that the applicant claims protection in respect of any patentable feature or combination of features referred to herein, and/or shown in the drawings, whether or not particular emphasis has been placed thereon.