US3844926A

US3844926A - Separation apparatus

Info

Publication number: US3844926A
Application number: US00393950A
Authority: US
Inventors: M Smyth; R Murdoch; J Gibson
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1972-09-06
Filing date: 1973-09-04
Publication date: 1974-10-29
Anticipated expiration: 1991-10-29
Also published as: SE7704843L; SE408967B; DE2344671C2; SE423155B; DE2344671A1; GB1431887A

Abstract

A separation apparatus suitable for electropheretic separation of enzyme mixtures has been devised having an inlet means comprising a substantially uninterrupted annular chamber bounded by substantially co-axial outer and inner walls, inlet means by which migrant material and a migrant-supporting fluid can be introduced into the annular chamber at a first region thereof, means for generating a force field by which the migrant material in the annular chamber can be subjected to a force field to produce a differential response, as regards movement in a direction radially of the chamber, between the migrant and the supporting fluid and/or between fractions of the migrant, outlet means for selectively removing from the annular chamber, at further regions remote from the first region, the supporting fluid with or without separated fractions of the migrant, and means adapted to permit a relative rotation between the inner and outer walls about the common axis thereof thereby to stabilise flow conditions in the flow chamber, at least said outer wall being rotatable about said axis, wherein the inlet means comprises a plurality of orifices which communicate with an annular opening for introducing migrant material into the annular chamber, a migrant material supply means, a porous material positioned between the migrant material supply means and the orifices, and means constraining the migrant material to pass through the porous material, the arrangement being such that migrant material from the supply means passes through the porous material into the orifices, and thence into the annular opening and into the annular chamber; and wherein the outlet means comprises a plurality of collecting chambers, each collecting chamber having a collecting chamber inlet distributed around the collecting chamber and having interconnected channels for conducting a separated fraction from the collecting chamber inlet and along a plurality of non-linear paths to converge at chamber outlet means disposed within the chamber, the arrangement being such that the minimum path length for the separated fraction from the collecting chamber inlet to the chamber outlet means is the same from all points on the collecting chamber inlet.

Description

United States Patent [1 1 Smyth et a1.

[ SEPARATION APPARATUS [75] Inventors: Michael James Smyth, Newbury; Robert Murdoch, Reading; John Anderson Gibson, Abingdon, all of England [73] Assignee: United Kingdom Atomic Energy Authority, London, England [22] Filed: Sept. 4, 1973 [21] Appl. No: 393,950

[30] Foreign Application Priority Data Sept. 6, 1972 Great Britain 41435/72 [52] US. CL"; 204/299, 204/180 R, 204/300 [51] Int. Cl B01d 13/02, B0lk 5/00 [58] Field of Search 204/299, 300, 180 R [56] References Cited UNITED STATES PATENTS 670,351 3/1901 Schwerin 204/301 1,034,668 8/1912 Wright 204/304 1,558,382 10/1925 Marx 204/180 R 2,500,878 3/1950 Sieling 204/180 R 2,739,938 3/1956 Wiechers 204/301 3,197,394 7/1965 McEven 204/180 R 3,616,453 10/1971 Philpot 204/299 Primary Examiner-John H. Mack Assistant Examiner-A. C. Prescott Attorney, Agent, or FirmLarson, Taylor & Hinds [451 Get. 29, 1974 grant material and a migrant-supporting fluid can be introduced into the annular chamber at a first region thereof, meansfor generating a force field by which the migrant material in the annular chamber can be subjected to a force field to produce a differential response, as regards movement in a direction radially of the chambenbetween the migrant and the supporting fluid and/or between fractions of the migrant, outlet means for selectively removing from the annular chamber, at further regions remote from the first region, the supporting fluid with or without separated fractions of the migrant, and means adapted to permit a relative rotation between the inner and outer walls about the common axis thereof thereby to stabilise flow conditions in the flow chamber, at least said outer wall being rotatable about said axis, wherein the inlet means comprises a plurality of orifices which communicate with an annular opening for introducing migrant material into the annular chamber, a migrant material supply means,-a porous material positioned between the migrant material supply means and the orifices, and means constraining the migrant material to pass through the porous material, the arrangement being such that migrant material from the supply means passes through the porous material into the orifices, and thence into the annular opening and into the annular chamber; and wherein the outlet means comprises a plurality of collecting chambers, each collecting chamber having a collecting chamber inlet distrib uted around the collecting chamber and having interconnected channels for conducting a separated fraction from the collecting chamber inlet and along a plurality of non-linear paths to converge at chamber outlet means disposed within the chamber, the arrangement being such that the minimum path length for the separated fraction from the collecting chamber inlet to the chamber outlet means is the same from all points on the collecting chamber inlet.

7 Ciaims, 5 Drawing Figures PATENTEU BUT 29 1974 3,844,926

SHEET 10F 3 I 001291914 3.844.926 PAYNE sum 2 or 3 1 SEPARATION APPARATUS This invention relates to a separation apparatus.

In the specification ofU.K. Pat. NO. 1,186,184, there is described and claimed separation apparatus comprising a substantially uninterrupted annular chamber bounded by substantially co-axial outer and inner walls, inlet means by which migrant material and a migrantsupporting fluid can be introduced into the annular chamber at a first region thereof, means for generating a force field by which the migrant material in the annular chamber can be subjected to a force field to produce a differential response, as regards movement in a direction radially of the chamber, between the migrant and the supporting fluid and/or between fractions of the migrant, outlet means for selectively removing from the annular chamber, at further regions remote from the first region, the supporting fluid with or without separated fractions of the migrant, and means adapted to permit a relative rotation between the inner and outer walls about the common axis thereof thereby to stabilise flow conditions in the flow chamber, at least said outer wall being rotatable about said axis.

Such a separation apparatus will be referred to hereinafter as separation apparatus of the kind defined. The separation apparatus is classified as electrophoretic, magnetic, centrifugal, or chemical (which latter may be diffusive, dialytic, partitive or absorptive) according to the force field mainly employed, which is chosen to suit the properties of the migrant.

The inlet means is of considerable importance in establishing effective working of the separation apparatus, in that it is an important factor in determining the flow characteristics of the migrant material and a migrant-supporting fluid introduced into the annular chamber. The inlet means specifically described in the specification of UK. Pat. No. 1,186,184 includes an inlet for the migrant material comprising a set of seven small horizontal holes, arranged in two staggered vertical rows, through which liquid migrant is discharged into the separation chamber, and in a variation the horizontal holes are arranged in circumferential lines. In both these specific cases, the abovementioned specification states that these seven holes together act like a slit. but are easier to form than a slit. With such a slitlike arrangement, the migrant is caused to flow as a substantially uniform flat helical ribbon The outlet means for selectively removing from the annular chamber, at further regions remote from the first region, the supporting fluid with or without separated fractions of the migrant is also of importance in that many separated fractions may have to be removed. The outlet means specifically described in the specification of UK. Pat. No. l,l86,l84 comprises 24 sets of holes, each set being for drawing off a different component which will flow through associated passages to different collecting vessels.

We have now provided an inlet means which gives rise to improved flow characteristics ofthe migrant material in the annular chamber and also an improved outlet means.

Thus, according to this invention, there is provided a separation apparatus of the kind defined wherein the inlet means comprises a plurality of orifices which communicate with an annular opening for introducing migrant material into the annular chamber, a migrant material supply means, a porous material positioned between the migrant material supply means and the orifices, and means constraining the migrant material to pass through the porous material, the arrangement being such that migrant material from the supply means passes through the porous material into the orifices, and thence into the annular opening and into the annular chamber; and the outlet means comprises a plurality of collecting chambers, each collecting chamber hav' ing a collecting chamber inlet distributed around the collecting chamber and having inter-connected channels for conducting a separated fraction from the collecting chamber inlet and along a plurality of nonlinear paths to converge at chamber outlet means disposed within the chamber, the arrangement being such that the minimum path length for the separated fraction from the collecting chamber inlet to the chamber outlet means is the same from all points on the collecting chamber inlet. The inlet means of the apparatus of this invention may, if required, be used to supply migrant supporting fluid to the annular chamber.

We have found that the inlet means of the present apparatus gives rise to considerably improved flow characteristics in the annularchamber and thereby improves the efficiency of the separation apparatus. We believe that this may be due, at least partly, to the porous material acting as a diffuser to the migrant material passing through it thereby creating a slight back pressure. This gives rise to a smooth, even, substantially pulseless flow of migrant material to the annular opening and thence into the annular chamber, thereby en-' hancing the effecient operation of the apparatus.

Preferably, in the inlet means, the plurality of orifices is constituted by a single continuous annular orifice which is divided into the plurality of slits by means of one or more spacers. Also, we prefer that the porous material is in the form of a porous plastics material such as porous polythene.

We have found that the outlet means of the present apparatus enables selective removal of separated fractions to be effected in a ready and efficient manner. This arises from the fact that all of the separated frac tion entering a particular chamber inlet has substantially equal chance of reaching the chamber outlet means because of the above-mentioned minimum path length provision. We prefer that the plurality of chambers is constituted by a stacked plurality of plates which are axially spaced from each other, by for example, a plurality of washers. This has the advantage that the outlet means may be readily and simply assembled from from plates and washers. We also prefer that each plate has the channels formed therein and constituted by a plurality of circular, concentrically arranged channels and a plurality of radially extending channels which interconnect adjacent, circular channels, the outermost circular channel comprising the collecting chamber inlet.

The separation apparatus of the invention has wide application in separation processes. However, we have found it to be particularly useful in the electrophoretic separation of enzyme mixtures, where the production of a particular enzyme may be of the order of several kilograms per day.

The invention also includes a separation apparatus of the kind defined wherein the inlet means comprises a plurality of orifices which communicate with an annular opening for introducing migrant material into the annular chamber, a migrant material supply means, a

porous material positioned between the migrant material supply means and the orifices, and means constraining the migrant material to pass through the porous material, the arrangement being such that migrant material from the supply means passes through the porous material into the orifices, and thence into the annular opening and into the annular chamber.

The invention further includes a separation apparatus of the kind defined wherein the outlet means comprises a plurality of collecting chambers, each collecting chamber having a collecting chamber inlet distributed around the collecting chamber and having interconnected channels for conducting a separated fraction from the collecting chamber inlet and along a plurality of non-linear paths to converge at chamber outlet means disposed within the chamber, the arrangement being such that the minimum path length for the separated fraction from the collecting chamber inlet to the chamber outlet means is the same from all points on the collecting chamber inlet.

The invention still further includes a plate for the outlet means of the separation apparatus of this invention wherein the plate has a chanelled surface comprising an inlet channel adjacent the edge of the plate and interconnected channels for conducting fluid from the inlet channel and along a plurality of non-linear paths to converge at a chamber outlet means, the arrangement being such that the minimum path length for fluid from the inlet channel to chamber outlet means is the same from all points on the inlet channel.

The invention will now be specifically described, by way of example only, with reference to the accompanying drawings, wherein FIG. 1 is a sectional side elevation of an electrophoretic separation apparatus;

FIG. 2 is a sectional side elevation showing the inlet means in detail;

FIG. 3 is a section on the line AA of FIG. 2;

FIG. 4 is a sectional side elevation showing one outlet of the outlet means; and

FIG. 5 is a plan view of a plate used to constitute the outlet means.

Referring to FIG. I, a rigidly mounted cylindrical stator l comprises two parts: an upper part 2 and a lower part 3. Defined within the stator l is a supply channel 4, which terminates at its lower end in a tubular portion 8 of the lower part 3 of the stator l. The upper end of the supply channel 4 extends through an outlet means 9 for separated components and through an end-piece 10 mounted on the outlet means 9.

A cylindrical rotor 5 is rotatably mounted to embrace the stator I and to define an annular separation chamber 6 between itself and the stator l. The separation chamber 6 has an inlet orifice 31 at its lower end. The rotor 5 has a drive shaft 7, by means of which the rotor 5 may be rotatably driven.

The rotor 5 has an inwardly directed lip 10a at its upper end for securing the end-piece l0 and the outlet means 9 in position. Bearing seals and 39 are recessed within the rotor 5 to facilitate its rotation.

Recessed within the stator l is a cathode system III which comprises an electrolyte compartment 12 bonded on its inner side by a stainless steel electrode 13 and on its outer side by a porous resin bonded matrix tube 14, which supports a cellulose membrane 15, which ispermeable to ions. The electrolyte compartment I2 is provided with an inlet tube 17 and an outlet tube 18 each of which extend upwardly through the supply channel 4. Recessed within the rotor is an anode system 16 which comprises an electrolyte compartment 19 bounded on its outer side by a stainless steel electrode 20 and on its innerside by a porous resin bonded matrix tube 21, which supports a cellulose membrane 15a, which is permeable to ions. The electrolyte compartment 19 has eight inlet tubes, of which two only, 19:: and 1912, are shown, and eight outlet tubes, 3 of which two only, 23 and 23:! are shown. The inlet tubes e.g., 19a and 19b communicate with an inlet pipe 22 which extends upwardly through the supply channel 4.

Referring now to FIGS. 2 and 3 in conjunction with FIG. 1, the upper part 2 and the lower part 3 of the stator l are separated by a star-shaped spacer 25, the fingers of which define eight orifices, eg 2511, between the upper part 2 and the lower part 3. The spacer 25 is of such size that a gap is provided between the extremities of the fingers of the spacer 25 and the circumference of the stator l to define a continuous annular opening 26 which communicates with the eight orifices, e.g., 25a. The annular opening 26 is arranged for introducing migrant material into the separation chamber 6. An annular trough 27 housing porous plastics material 28 in the form of polythene of fifty micron mean pore diameter'is recessed in the lower part 3 of the stator l. The trough 27 which has an inlet tube 29,

communicates with the orifices, e.g. 25a.

Referring to FIGS. 4 and 5 in conjunction with FIG. 1, theoutlet means 9 comprises a plurality of stacked circular plates, of which one only, 36 is shown. The plates, e.g., 36, each have large central orifice 37 and each is spaced from the next adjacent plate by a washer, of which one only. 32, is shown, to provide a plurality of annular collecting inlets of which one only, 33 is shown. Each plate, e.g., 36, has formed therein a maze-like system of channels 38 communicating with the collecting inlet 33. The system of channels 38 comprises a plurality of circular, concentrically arranged channels and a plurality of radially extending channels which interconnect adjacent, circular channels. The system of channels 38 converges at outlet 34, which communicates with a tube 35 which passes upwardly through the stacked plates. The arrangement of the channels is such that the minimum path length from the collecting inlet, e.g., 33, to the outlet, e.g., 34, is the same from all points on the collecting inlet, e.g., 33. Each plate, e.g., 36, has its own tube, e.g., 35, passing upwardly through the stacked plates.

In operation of the apparatus depicted in FIGS. 1, 2, 3, 4 and 5, a carrier buffer is supplied to the inlet orifice 31 from a tube (not shown) extending through the supply channel 4. The buffer is thence fed to the annular separation chamber 6 and passes upwardly therethrough. Migrant fluid is supplied to the inlet tube 29 from a tube (not shown) extending through the supply channel 4. The migrant fluid thence passes through the porous plastics material 28 in the trough 27, into the orifices, e.g., 25a, then into the annular opening 26 and into the separation chamber 6. An electrolyte is supplied to the electrolyte compartment 12 via the inlet tube 17 and leaves the compartment 12 via the outlet tube 18. Also, an electrolyte is fed into the electrolyte compartment l9 via the inlet pipe 22 and the inlet tubes ll9a and 19b and leaves the compartment 19 via the outlet tubes 23 and 23a. At the same time, the electrode 13 is connected as the cathode to a source of e.m.f. and the electrode is connected as the anode to the source ofe.m.f. Also, the rotor 5 is rotated in the direction indicated by the arrow a by a drive (not shown) driving the drive shaft 7.

The migrant flows upwardly in the separation chamber 6 from the annular opening 26, being assisted by the flow of carrier buffer in the same direction. The flow pattern of the migrant is helical. In the region of the separation chamber 6 between the cathode system 11 and the anode system 16, the migrant is electrophoretically separated into its components. This is shown in FIG. 1 for two components only, which follow the paths indicated by the arrows b and c respectively. The separated components pass upwardly beyond the region of the separation chamber between the cathode system 11 and the anode system 16. A separated component enters a collecting inlet, e.g., 33 in the outlet means 9 and follows its own independent path along the system of channels 38 to the outlet, e.g., 34. Thence, the component passes up the associated tube 35 and out of the apparatus to be collected.

The following example illustrates the use of the apparatus depicted in FIGS. 1 to 5.

EXAMPLE l A carrier buffer constituted by a 0.05 Molar solution of tris (hydroxymethyl) aminomethane citrate of conductivity 1,000 millimho/cm was passed upwardly through the chamber 6 at a rate of 1,500 cc/min. Migrant fluid constituted by a bovine blood serum dialysed against the buffer solution was passed into the chamber 6 at a rate of 20 cc/min. A catholyte constituted by an ammonium acetate solution of conductivity 35 millimho/cm was fed into the electrolyte compartment 12 at a rate of 50 cc/min. An anolyte constituted by an ammonium phosphate solution of conductivity 35 millimho/cm was fed into the electrolyte compartment 19 at a rate of 50 cc/min. At the same time, the electrodes 13 and 20 were connected to a 35 volt source and a current of amps passed. Also, the rotor 5 was rotated at a rate of 120 rpm.

After a run of 2 /2hours, 70 percent of the available albumin in the serum was recovered in an exceptionally pure state at two of the collecting inlets 33 in the outlet means 9.

We claim:

1. In a separation apparatus comprising a substantially uninterruped annular chamber bounded by substantially co-axial outer and inner walls, inlet means by which migrant material and a migrant-supporting fluid can be introduced into the annular chamber at a first region thereof. means for generating a force field by which the migrant material in the annular chamber can be subjected to a force field to produce a differential response. as regards movement in a direction radially of the chamber, between the migrant and the supporting fluid and/or between fractions of the migrant, outlet means for selectively removing from the annular chamber, at further regions remote from the first region, the supporting fluid with or without separated fractions of the migrant. and means adapted to permit a relative rotation between the inner and outer walls about the common axis thereof thereby to stabilise flow conditions in the flow chamber, at least said outer wall being rotatable about said axis the improvement wherein the inlet means comprises a plurality of orifices which com- 6 municate with an annular opening for introducing migrant material into the annular chamber, a migrant material supply means, a porous material positioned between the migrant material supply means and the orifices, and means constraining the migrant material to pass through the porous material, the arrangement being such that migrant material from the supply means passes through the porous material into the orifices, and thence into the annular opening and into the annular chamber; and the outlet means comprises a plurality of collecting chambers, each collecting chamber having a collecting chamber inlet distributed around the collecting chamber and having interconnected channels for conducting a separated fraction from the collecting chamber inlet and alonga plurality of nonlinear paths to converge at chamber outlet means disposed within the chamber, the arrangement being such that the minimum path length for the separated fraction from the collecting chamber inlet to the chamber' outlet means is the same from all points on the collecting chamber inlet.

2. in a separation apparatus comprising a substantially uninterrupted annular chamber bounded by substantially co-axial outer and inner walls, inlet means by which migrant material and a migrant-supporting fluid can be introduced into the annular chamber at a first region thereof, means for generating a force field by which the migrant material in the annular chamber can be subjected to a force field to produce a differential response, as regards movement in a direction radially of the chamber, between the migrant and the supporting fluid and/or between fractions ofthe migrant, outlet means for selectively removing from the annular chamber, at further regions remote from the first region, the supporting fluid with or without separated fractions of the migrant, and means adapted to permit a relative rotation between the inner and outer walls about the common axis thereof thereby to stabilise flow conditions in the flow chamber, at least said outer wall being rotatable about said axis the improvement wherein'the inlet means comprises a plurality of orifices which communicate with an annular opening for introducing migrant material into the annular chamber, a migrant material supply means, a porous material positioned between the migrant material supply means and the orifices, and means constraining the migrant material to pass through the porous material, the arrangement being such that migrant material from the supply means passes through the porous material into the orifices, and thence into the annular opening and into the annular chamber.

3.. in a separation apparatus comprising a substantially uninterrupted annular chamber bounded by substantially co-axial outer and inner walls, inlet means by which migrant material and a migrant-supporting fluid can be introduced into the annular chamber at a first region thereof, means for generating a force field by which the migrant material in the annular chamber can be subjected to a force field to produce a differential response, as regards movement in a direction radially of the chamber, between the migrant and the supporting fluid and/or between fractions of the migrant, outlet means for selectively removing from the annular chamber, at further regions remote from the first region, the supporting fluid with or without separated fractions of the migrant, and means adapted to permit a relative rotation between the inner and outer walls about the common axis thereof thereby to stabilise flow conditions in the flow chamber, at least said outer wall being rotatable about said axis the improvement wherein the outlet means comprises a plurality of collecting chambers, each collecting chamber having a collecting chamber inlet distributed around the collecting chamber and having interconnected channels for conducting a separated fraction from the collecting chamber inlet and along a plurality of non-linear paths to converge at chamber outlet means disposed within the chamber, the arrangement being such that the minimum path length for the separated fraction from the collecting chamber inlet to the chamber outlet means is the same from all points on the collecting chamber inlet.

4. A separation apparatus according to claim 3 wherein the plurality of chambers is constituted by a stacked plurality of plates which are axially spaced from each other.

5. A separation apparatus according to claim 4 wherein each plate has channels formed therein the constituted by a plurality of circular, concentrically archamber outlet means is the same from all points on the inlet channel.

7. A plate according to claim 6 wherein the channelled surface comprises a pluralityof circular, concentrically arranged channels and a plurality of radially extending channels which interconnect adjacent, circular channels. I

Claims

1. In a separation apparatus comprising a substantially uninterruped annular chamber bounded by substantially co-axial outer and inner walls, inlet means by which migrant material and a migrant-supporting fluid can be introduced into the annular chamber at a first region thereof, means for generating a force field by which the migrant material in the annular chamber can be subjected to a force field to produce a differential response, as regards movement in a direction radially of the chamber, between the migrant and the supporting fluid and/or between fractions of the migrant, outlet means for selectively removing from the annular chamber, at further regions remote from the first region, the supportinG fluid with or without separated fractions of the migrant, and means adapted to permit a relative rotation between the inner and outer walls about the common axis thereof thereby to stabilise flow conditions in the flow chamber, at least said outer wall being rotatable about said axis the improvement wherein the inlet means comprises a plurality of orifices which communicate with an annular opening for introducing migrant material into the annular chamber, a migrant material supply means, a porous material positioned between the migrant material supply means and the orifices, and means constraining the migrant material to pass through the porous material, the arrangement being such that migrant material from the supply means passes through the porous material into the orifices, and thence into the annular opening and into the annular chamber; and the outlet means comprises a plurality of collecting chambers, each collecting chamber having a collecting chamber inlet distributed around the collecting chamber and having interconnected channels for conducting a separated fraction from the collecting chamber inlet and along a plurality of non-linear paths to converge at chamber outlet means disposed within the chamber, the arrangement being such that the minimum path length for the separated fraction from the collecting chamber inlet to the chamber outlet means is the same from all points on the collecting chamber inlet.

2. In a separation apparatus comprising a substantially uninterrupted annular chamber bounded by substantially co-axial outer and inner walls, inlet means by which migrant material and a migrant-supporting fluid can be introduced into the annular chamber at a first region thereof, means for generating a force field by which the migrant material in the annular chamber can be subjected to a force field to produce a differential response, as regards movement in a direction radially of the chamber, between the migrant and the supporting fluid and/or between fractions of the migrant, outlet means for selectively removing from the annular chamber, at further regions remote from the first region, the supporting fluid with or without separated fractions of the migrant, and means adapted to permit a relative rotation between the inner and outer walls about the common axis thereof thereby to stabilise flow conditions in the flow chamber, at least said outer wall being rotatable about said axis the improvement wherein the inlet means comprises a plurality of orifices which communicate with an annular opening for introducing migrant material into the annular chamber, a migrant material supply means, a porous material positioned between the migrant material supply means and the orifices, and means constraining the migrant material to pass through the porous material, the arrangement being such that migrant material from the supply means passes through the porous material into the orifices, and thence into the annular opening and into the annular chamber.

3. In a separation apparatus comprising a substantially uninterrupted annular chamber bounded by substantially co-axial outer and inner walls, inlet means by which migrant material and a migrant-supporting fluid can be introduced into the annular chamber at a first region thereof, means for generating a force field by which the migrant material in the annular chamber can be subjected to a force field to produce a differential response, as regards movement in a direction radially of the chamber, between the migrant and the supporting fluid and/or between fractions of the migrant, outlet means for selectively removing from the annular chamber, at further regions remote from the first region, the supporting fluid with or without separated fractions of the migrant, and means adapted to permit a relative rotation between the inner and outer walls about the common axis thereof thereby to stabilise flow conditions in the flow chamber, at least said outer wall being rotatable about said axis the improvement wherein the outlet means Pg,17 comprises a plurality of collecting chambers, each collecting chamber having a collecting chamber inlet distributed around the collecting chamber and having interconnected channels for conducting a separated fraction from the collecting chamber inlet and along a plurality of non-linear paths to converge at chamber outlet means disposed within the chamber, the arrangement being such that the minimum path length for the separated fraction from the collecting chamber inlet to the chamber outlet means is the same from all points on the collecting chamber inlet.

5. A separation apparatus according to claim 4 wherein each plate has channels formed therein the constituted by a plurality of circular, concentrically arranged channels and a plurality of radially extending channels which interconnect adjacent, circular channels.

6. A plate for the outlet means of the separation apparatus according to claim 4 wherein the plate has a channelled surface comprising an inlet channel adjacent the edge of the plate and interconnected channels for conducting fluid from the inlet channel and along a plurality of non-linear paths to converge at a chamber outlet means, the arrangement being such that the minimum path length for fluid from the inlet channel to chamber outlet means is the same from all points on the inlet channel.

7. A plate according to claim 6 wherein the channelled surface comprises a plurality of circular, concentrically arranged channels and a plurality of radially extending channels which interconnect adjacent, circular channels.