EP0646407A1

EP0646407A1 - Vortex mixer

Info

Publication number: EP0646407A1
Application number: EP94306975A
Authority: EP
Inventors: Michael Joseph Bowe
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1993-10-05
Filing date: 1994-09-23
Publication date: 1995-04-05
Also published as: GB9419225D0; GB2282546A; GB9320455D0; AU7434894A

Abstract

A method of operating a vortex mixer in such a manner as to minimise back-streaming in the discharge from the vortex mixer.

Description

The present invention relates to vortex mixers.
Vortex mixers are devices which include a cylindrical mixing chamber having an axial outlet and a plurality of inlets so arranged that a vortex is set up in the mixing chamber when fluid is admitted to the mixing chamber via the inlets. The arrangement may be such that two or more liquid reagents can be admitted to the chamber, or a single reagent or additive can be added to a main liquid flowing through the mixer.
The liquid leaving the vortex mixer does so in the form of a vortex. As a result, there is a degree of reverse flow along the inside of the vortex. This reverse flow can extend for a distance equal to several tens of the diameter of the exit pipe from the mixing chamber.
When it is considered advantageous to operate vortex mixers under plug flow conditions, such as when it is desired to control competing chemical reactions, this phenomenon has an undesirable effect.
According to the present invention there is provided a method of mixing fluids by means of a vortex mixer as hereinbefore defined, wherein there is included the operation of minimising reverse flow in the mixed fluid issuing from the vortex mixer.
Also according to the invention there is provided an apparatus for mixing fluids, comprising a vortex mixer as hereinbefore defined, wherein there is included means for minimising reverse flow in mixed fluids issuing from the vortex mixer.
The outlet from the mixing chamber preferably has an axially extending portion the diameter of which is greater than a third of that of the mixing chamber of the vortex mixer.
There may also be provided a radial diffuser such as to induce a radial component in the flow of the fluid issuing from the mixing chamber of the vortex mixer. The radial diffuser may comprise a baffle at right angles to the flow of the mixed fluid issuing from the mixing chamber of the vortex.
Another form of radial diffuser which can be used is a plate having an axial inlet and at least one radially extending channel formed in it.
Alternatively the axially extending portion of the outlet from the mixing chamber of the vortex mixer can have a form such that the diameter of the axially extending portion of the outlet from the mixing chamber of the vortex mixer increases in the direction of flow of the mixed fluid issuing from the mixing chamber of the vortex mixer.
The invention will now be described, by way of example, with reference to the accompanying drawings, in which,

Figure 1 is a cross-section of an embodiment of the invention,
Figure 2 is a cross-section of a second embodiment of the invention, and
Figure 3 shows various forms of radial diffuser that can be utilised in carrying out the present invention.

Referring to Figure 1, an apparatus for mixing two reagents consists of a vortex mixer 1 consisting of a cylindrical mixing chamber 2 which has inlets 3 and 4 for two liquids to be mixed and an axial outlet 5. The inlets 3 and 4 are so arranged that fluids entering the mixing chamber 1 through them do so with a tangential component of velocity so that a vortex is set up in the chamber 2 which leads to the mixing of the fluids. The outlet 5 from the chamber 2 is so shaped and dimensioned in relation to the velocity of flow of the mixed fluids through the chamber 2 that the mixed fluids issue from the chamber 2 in the form of a spray 6, which discharges into a gas filled collecting vessel 7, only a part of which is shown. In Figure 1 the outlet 5 is cylindrical in form and has an internal diameter approximately equal to half that of the mixing chamber 1. The gas in the vessel 7 may be air, an inert gas, or a reactive gas as the circumstances require. Even though the mixed fluids issuing from the chamber 2 do so as a vortex, any central reverse flow is made up of the gas in the vessel 7 and does not include the mixed fluids issuing from the chamber 2.
Figure 2 shows a cross-section of a second embodiment of the invention including a number of vortex mixers 21 and 22 in series, only two of which are shown. As before, the vortex mixers 21 and 22 each have a mixing chamber 2 with two inlets 3 and 4 and an axial outlet 5. However, between the vortex mixers 21 and 22 there is a radial diffuser section 23 which is arranged to break the vortex in the mixed fluid leaving the vortex mixer 21 before supplying it to the inlets 3 and 4 of the vortex mixer 22. In addition fluid pressure is recovered so reducing the pumping forces required. The radial diffuser 23 is shown in more detail in Figure 3. Similar radial diffusers are included between each vortex mixer in the series, and at the outlet from the final vortex mixer.
Referring to Figure 3, in the arrangement shown in Figure 3(a) the outlet 5 from the mixing chamber 2 has a frusto conical form so as to impart a radial component into the flow of fluid passing along it. Other forms of outlet 5 which are divergent can be used. Figure 3(b) shows a vortex-breaking radial diffuser for use with the embodiment of Figure 1, which consists of a circular baffle plate 31 which is positioned at right angles to the mixed fluid issuing from the outlet 5 from the mixing chamber 2. The baffle plate 31 is held in position by means of struts 32. Figure 3(c) shows another vortex-breaking radial diffuser which consists of a plate 33 which has a large inlet hole 34 which communicates with the outlet 5 from the mixing chamber 2 and a plurality of radially disposed outlets 35. The plate 33 may be integral with the base of the mixing chamber 2 as shown in Figure 3(c).
Figure 3(d) shows in more detail the radial diffuser which is incorporated as item 23 in the embodiment of the invention described with reference to Figure 2. The radial diffuser 23 consists of a cylindrical block 36 in which there is formed an axial cylindrical recess 37. The recess 37 has a diameter equal to the separation between the outer edges of the inlets 3 and 4 to the vortex mixer 22 which follows the vortex mixer 21. The central region of the recess 37 is filled with a boss 38 which has a diameter equal to the separation between the inner edges of the inlets 3 and 4 of the vortex mixer 22. In the centre of the recess 37 is a hole 39 which communicates with the outlet 5 from the vortex mixer 21. Thus fluid issuing from the vortex mixer 21 is diverted to flow radially through the channel 40 formed between the block 36 and the boss 38 before entering the vortex mixer 22.
In practice, it is convenient to form the boss 38 as part of the mating surface between the vortex mixer 22 and the radial diffuser 23. Alternatively, the boss 38 can be held in position by webs which may be so disposed as to assist in destroying vortex flow in the fluid issuing from the vortex mixer 21.

Claims

A method of mixing fluids by means of a vortex mixer (2, 3, 4, 5) as hereinbefore defined, wherein there is included the operation of minimising reverse flow in the mixed fluid issuing from the vortex mixer (2, 3, 4, 5).
A method according to Claim 1 wherein there is included the operation of inducing a radial component into the flow of the mixed fluid issuing from the vortex mixer (2, 3, 4, 5).
A method according to Claim 1 or Claim 2 wherein there is included the operation of disrupting vortex flow in the mixed fluid issuing from the vortex mixer (2, 3, 4, 5)..
An apparatus for mixing fluids, comprising a vortex mixer (2, 3, 4, 5) as hereinbefore defined, wherein there is included means (5) for minimising reverse flow in mixed fluids issuing from the vortex mixer (2, 3, 4, 5).
An apparatus according to Claim 4 wherein there is included an axially extending outlet (5) from the mixing chamber (2) of the vortex mixer (2, 3, 4, 5) having a diameter greater than a third of the diameter of the mixing chamber (2) of the vortex mixer (2, 3, 4, 5).
An apparatus according to Claim 5 wherein the diameter of the outlet (5) from the mixing chamber (2) of the vortex mixer (2, 3, 4, 5) is approximately half that of the said mixing chamber (2).
An apparatus according to any of Claims 4 to 6 including means (5; 23; 31, 32; 33, 34, 35) for inducing a radial component into the flow of mixed fluid issuing from the vortex mixer (2, 3, 4, 5).
Apparatus according to Claim 7 wherein the means for inducing a radial component into the flow of mixed fluid issuing from the vortex mixer (2, 3, 4, 5) comprises an axially extending outlet (5) of divergent cross-section.
Apparatus according to any of Claims 4 to 8 wherein there is included means (22; 31, 32; 33, 34, 35) for disrupting vortex flow of the mixed fluid issuing from the vortex mixer (2, 3, 4, 5).
Apparatus according to Claim 9 wherein the means for disrupting vortex flow of the mixed fluid issuing from the vortex mixer comprises a radial diffuser (22; 31, 32; 33, 34, 35) adapted to convert the flow of the mixed fluid issuing from the vortex mixer (2, 3, 4, 5) into radially directed flow.
Apparatus according to Claim 10 wherein the means for converting the flow of the fluid issuing from the vortex mixer (2, 3, 4, 5) into radially directed flow includes a surface (31, 35) positioned substantially at right angles to the axis of the outlet (5) from the mixing chamber (2) of the vortex mixer (2, 3, 4, 5).
An apparatus according to any preceding claim wherein there is included a plurality of vortex mixers (2, 3, 4, 5) in series the outlet (5) from one vortex mixer (2, 3, 4, 5) being connected to the inlets (3, 4) of a succeeding vortex mixer (2, 3, 4, 5).
Apparatus according to Claim 12 wherein there is included means for disrupting vortex flow in the fluid issuing from the final vortex mixer (2, 3, 4, 5).