This invention concerns static mixers to be inserted into pipes in order to mix fluids flowing along them. Such mixers take the form of one or more obstructions in the pipe which create a loss of pressure, and the energy so released into the flowing fluid promotes mixing . They are widely used in the chemical processing industries for mixing liquids and solids, but they are also used for mixing two or more different liquids together, or for mixing complex combinations of several liquids and solids.

Existing static mixers generally operate along the following lines. A first device within the pipe deflects the flowing fluid so that it rotates around the pipe axis in a particular sense: then a second device dcwnstream of the first device deflects the flowing fluid so that the sense of rotation is abruptly reversed. If necessary additional devices may be inserted at intervals further downstream to impose further abrupt changes in the sense of rotation of the fluid. The energy dispersal caused by these sudden reversals of rotational sense supplies the energy to the fluid that is required for mixing.

In the proposed new type of static mixer, the energy dispersal and mixing is created by imposing a system of twin-cell or multi-cell rotation upon the contents of the pipe.

Thus according to this invention there is provided a static mixer for one or mere fluids flowing in a pipe comprising means ro divide Th flowing fluid(s) into az leas- TWO streams within the oi e

and to deflect the resulting streams so that each stream rotates in a sense opposite to the sense of at least one adjacent stream.

Mixers according to the invention may be employed either to homogenise two or more different materials (e.g a liquid and a gas or solid particles and a gas , as already mentioned) or to mix warmer and cooler regions of the same flowing material (e.g. to increase heat transfer at the pipe wall) or simply to increase turbulence (e.g. for use upstream of a vortex-shedding flowmeter: such meters are reputed to be more efficient if preceded by a turbulence - generating device) .

Thus, according to a further aspect of the - invention, a method of mixing a non-homogeneous fluid, ^' or of increasing the turbulence of a fluid, flowing in a pipe comprises dividing the flowing fluid into at least two streams within the pipe and deflecting the resulting streams so that each stream rotates about an axis parallel to its direction of flow and in a sense opposite to that of at least one other stream.

Where the flow is,divided into only two streams, as is preferred, a system of twin-cell rotation is established within the flowing fluid. However, the flow may be divided into a greater number of streams to establish multi-cell rotation: four streams will give rise to four-cell rotation, and so on.

The mixer may be formed from a thin plate having a planar circumferential portion which can therefore be inserted between two pipe sections bolted rogether, the plate having, orifices through which

separate divided streams can flow and deflectors to impart the rotation to them. The orifices and deflectors may be formed inexpensively by cutting and bending the plate, or in more elaborate geometries by fabrication.

The deflectors may comprise flat flaps partially cut out from the plate and bent relative to the plane of the plate. They may be bent from the plane of the plates so that in use they face either upstream or downstream, or both. In other embodiments the deflectors may be curved.

Alternatively, instead of being ntegral with the plate and formed simply by cutting and bending the material of the plate, each flap may be hingedly attached to the plate, at the edge of the associated orifice, so that it extends downstream in use, and is spring-urged towards the closed position, so that an increase in pressure of the flowing fluid will cause the flaps to open further against the spring action.

The mixer device may additionally be provided with one or more pressure-relieving by-pass apertures not intended to impart rotation to the portion of fluid flowing through them. Such apertures may also be provided with hinged spring-loaded flaps.

In one preferred embodiment, the means to divide the flowing fluid into two streams comprises a mixer according to claim 2, wherein said means comprises a plate having end portions shaped to fit against

axially spaced and opposite wall portions of the pipe respectively, and a deflector portion between the end portion, such that when the mixer is fitted inside the pipe, the deflector portion is not parallel to the pip ₃ axis and substantially equal gaps are left on each side of the deflector portion through which fluid can pass.

An advantage of a mixer according to the invention is that it can be compact so that the energy release is concentrated within a short length of pipe. This is clearly of great value when it is required to homogenize temporarily a mixture of liquid and gas, or gas and solid particles and/or liquid droplets.

_V arious mixers embodying the invention will now be described by way of example and with reference to the accompanying drawings in which each of figures 1 to 8 shows a different mixer.

Figure 1 shows a particularly simple design, in which the mixer consists of a flat plate I, with straight sides and curved end portions 2 bent in opposite directions relative to the plate 1. The curvature of the end portions 2 is the same, as that of the wall of the pipe 4 into which the mixer is fitted, so that the end portions 2 fit closely against axially space _d and opposite portions of the inside of the pipe wall with the plate 1 extending diagonally across the pipe, with the result that the flowing fluid can pass it only by accelerating through the substantially equeal-sized gaps 3 on either side of the plate 1, between the plate and pipe wall.

The plate 1 is installed symmetrically within the pipe so that the passages 3 carry equal streams 5 and because these streams have both axial and transverse components in their velocity, they necessarily create the desired twin-celled rotation. The pressure loss across the plate 1, and hence the intensity of mixing, will depend upon both the size of the passages 3 and the velocity of flow in the pipe.

From the point of view of simplicity of construction and easy insertion in an existing pipeline, there is considerable advantage in a device which by virtue of its compactness can be inserted by being sandwiched between an adjacent pair of pipe flanges. Examples of such devices are shown in Figures 2 to 5.

The device shown in Figure 2 has a plate 6 blocking the lower portion of the cross-section of the pipe, with a pair of curved vanes 7 dividing the flow into two equal and symmetrically-disposed streams 5 each of which has a component in the forward direction, a component in the downward direction, and a component towards the wall of the pipe. This arrangement will create the required twin-celled rotation as the two streams rotate about an axis parallel to the flow direction and in opposite senses.

An alternative device is shown .in Figure 3, which consists of a circular plate 3, having two aligned transverse cuts 10 extending towards one another from opposite sides . The lower portion 9 of the plate is flat and completely blocks the corresponding part of the pipe 4, whilst the two

upper quadrants 11 are bent forward in a symmetrical fashion to provide a pair of partially opened vertically-hinged flaps opening into the pipe. When the angle of opening is suitably regulated (angles between 20 degrees and 30 degrees have been found to be particularly effective) this arrangement creates twin-celled rotation with great efficiency.

The device may be simply constructed from a single piece of circular plate, with the two flaps bent to a fixed position; this permits extremely inexpensive construction. However, in many applications variable geometry may be required, and this can easily be provided by hinging the two flaps 11 at 13 and biassing them by means of springs 12, as shown in Figure 4. By this means the pressure loss at high flow ⁷ rates can be substantially reduced.

It should be observed ^* that although the devise shown in Figs.2 to 4 are shown with the openings towards the top of the pipe and with the lower portion of the pipe blocked they do not have to be installed in that orientation but may have the openings elsewhere, for example, at the bottom or the side. Likewise, they need not be installed in horizontal sections of pipe.

A further variant of the device shown in Fig.3 is that shown in Fig.5. In this, there are two pairsof bent flaps 11 and 11a pointing downstream (like flaps 11 in Fig.3) and upstream respectively. In this way the twin-celled rotation effect may be enhanced

whilst creating a lower pressure loss than with the device shown in Fig.3. If variable geometry is required, then the pair of flaps 22 pointing downstream may be spring-loaded.

The device shown in Fig.6 comprises two part-circular plates 14, formed by cutting a whole circle along a chord, spaced apart in the direction of flow and rotated through 180° relative to one another about the pipe axis. Ea'ch plate blocks about two-thirds of the pipe cross-sectional area, and the two plates are

spaced apart by about half a- pipe diameter by means of a spacer 15 which includes a pair of deflector vanes 16, each of which directs one ^* half of the flowing fluid downwards and towards the wall of the pipe, thus creating the necessary twin-cell rotation. ■ These deflector plates may be of fixed angle as shown, but this design is intended especially to facilitate variable geometry, since it ^' is particularly easy to provide spring loading of the vanes 16. One possible disadvantage of the device of Figure 6 is that the rotation may be to some extent be suppressed by the position of the device itself. This

disadvantage is overcome 'in the modified arrangement of Figure 7, where a similar device is constructed with the plates 14 and the associated vanes 16 tilted in the direction of flow as shown, so that the rotation has a forward component as well as downward and radial components.

For certain applications comparatively gentle agitation of the flowing fluid may be all that is required to promote suitable mixing. In such cases, it is possible to limit the pressure drop by supplying, as well as the necessary pair of apertures to create the required twin-celled rotation, one or more additional apertures to allow a portion of the flow to pass straight through and without having any rotation imparted to it. In this arrangement the flow passing straight through the pressure-relieving aperture should be mixed sufficiently by the twin-celled rotation created by the remainder of the device. An example is shown in Figure 8, which is similar to the device of Figure ^' 3 but with the addition of an aperture. This aperture may be a. simple hole in the plate, but as shown the hole 17 is provided with a flap 18, so arranged to deflect the by-pass flow downwards into the region where the twin-celled rotation is at its most powerful. An additional refinement is to provide the pressure-relieving aperture 17 with, a hinged, spring-loaded flap instead of the fixed flap 18 shown in Figure 8. In this case, the hinge is preferably near the wall of the pipe, so that the flap deflects the by-pass flow towards the centre of the pipe, bxzz. in some applications it may be preferable to in•:■•£- . ^' iz flap aicr.g - chord, thu.. αirectinσ the c—αss flov; ow the wail of c c

pipe instead of ⁷ the contrc