An assembly comprising a central fluid distributor and a multi-fiber spinneret

Abstract

The present disclosure relates to a center fluid distributor for a multi-fiber spinneret for producing hollow fiber membranes in a phase inversion process.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a central fluid distributor for a multi-fiber spinneret for producing hollow fiber membranes in a phase inversion process. BACKGROUND

[0002] Semi-permeable hollow fiber membranes applied to medical devices such as capillary dialyzers and capillary filters are mostly manufactured using a phase inversion process. A spinneret having a nozzle with two concentric orifices, an outer ring slit and a central hole is commonly used. A polymer solution is extruded through the outer ring slit of the nozzle into a precipitation bath, while a central fluid is extruded through the inner hole of the nozzle. The central fluid is provided to the spinneret at a predetermined pressure to generate a constant flow of the central fluid through the central fluid of the nozzle. Precise volume flow of the central fluid is important in order to produce hollow fibers having a desired size.

[0003] A spinning unit for producing hollow fiber membranes usually comprises a large number of individual spinnerets and produces several hundreds of hollow fiber membranes at the same time. In order to reduce the installation space required for the spinnerets, multi-fiber spinnerets, i.e. spinnerets comprising multiple nozzles in a single spinneret housing, have been proposed. A double spinneret has been disclosed in co-pending European patent application No. 19219557.6.

[0004] Each nozzle in a multi-fiber spinneret has to be connected to a central fluid supply providing a constant flow. Thus, for a double spinneret comprising two nozzles, two central fluid connectors are required; for a spinneret comprising three nozzles, three central fluid connectors are required, and so on. This is difficult to achieve due to the limited space within the spinning machine.

[0005] On the other hand, when all nozzles of a multi-fiber spinneret are supplied with central fluid from a single connector, the central fluid flow varies between the individual nozzles. This is due to manufacturing tolerances of the hole diameters in the nozzles, resulting in an uneven distribution of the central fluid flow between the nozzles. Thus, the hollow fiber membranes produced by the individual nozzles of a multi-fiber spinneret do not have the same inner diameter.

[0006] It is an object of the present disclosure to provide a central fluid distributor for a multi-fiber spinneret which allows a precise control of the volume flow of the central fluid through the nozzles of the multi-fiber spinneret and which has a compact design.

[0007] EP 3581373 A1 discloses a spinneret, apparatus and method for manufacturing filaments for use in fibrous nonwoven fabric. The spinneret has a spinneret body having a ratio of overall length to hydraulic diameter and defining an orifice extending through the spinneret body, wherein the orifice comprises capillaries opening at a surface of the spinneret body for extruding polymeric filaments therefrom, wherein the capillaries are arranged in a plurality of different rows at the surface of the spinneret body, and wherein the plurality of different rows are arranged in a plurality of different zones at the surface of the spinneret body. The spinneret body of the spinneret can have a ratio of overall length to hydraulic of at least 3% and / or an inter-zonal length to hydraulic ratio of at least 2% and / or a hydraulic diameter, length, and for at least three different capillary zones, the length to hydraulic diameter ratio can gradually increase or decrease from zone to zone, which can apply to cross-flow quenching or quenching from a single side. The spinneret body is designed to better accommodate different operational proximities of the various different zones to quench air sources or sources at commercially useful throughputs and fiber uniformity.

[0008] WO 2020 / 097183 A1 discloses a spunbond fibrous nonwoven web and method of making the same. A spinneret having a length, a width and a thickness and further having a plurality of channels extending through the thickness of the spinneret, the channels having inlet openings in an upper surface of the spinneret and outlet orifices in a lower surface of the spinneret, and further having capillaries in fluid communication with the inlet openings and outlet orifices is used.

[0009] US 2002 / 195737 A1 discloses an apparatus and method for spinning hollow bicomponent filaments. The apparatus includes a distributor, a spinneret having a hole, and a shim having openings secured between the distributor plate and the spinneret. The distributor supplies a first polymer having an MV to a first portion of the spinneret hole and a second polymer having a lower MV to a recessed portion of the spinneret. The shim openings are positioned over the spinneret hole and extend away from the first portion of the hole to allow the second polymer to flow from the recessed portion through the shim openings to a second portion of the spinneret hole. The two polymers travel along the opposite first and second portions of the hole until exiting the spinneret through respective asymmetric C-shaped orifices. The dimensions of the orifices are such that hydraulic splitting between the polymers does not occur and thus potential filament kinking is avoided. Upon exiting the orifices, the polymers self-join to form hollow filaments and are quenched. Due to the different MV characteristics of the polymers, the filaments self-curl into a helical configuration.

[0010] DE 3022313 A1 discloses hollow fibers having a plurality of separate hollow portions extending through the entire length of the fiber, so that there is a through channel, constituting a semipermeable, multiple hollow fiber. A spinneret for producing semipermeable hollow fibers has a number of separate openings for injecting a first fluid and a corresponding number of annular grooves around each opening. The annular grooves are interconnected to form a continuous groove for extruding the fiber-forming material. SUMMARY

[0011] A central fluid distributor for a multi-fiber spinneret is provided that allows for precise control of the volumetric flow of central fluid through individual nozzles of the multi-fiber spinneret. The central fluid distributor saves installation space that would otherwise be required for multiple central fluid flow control units. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 Side, top and bottom views of a double spinneret with embodiments of the central fluid distributor of the present disclosure are shown;

[0013] Figure 2 is Figure 1 a cross-sectional view of the assembly shown along the line A-A. DETAILED DESCRIPTION

[0014] The present disclosure provides a central fluid distributor that allows for precise control of the volumetric flow of central fluid through nozzles of a multi-fiber spinneret. The central fluid distributor can be installed on a multi-fiber spinneret, saving installation space that would otherwise be required for multiple central fluid flow control units.

[0015] The present disclosure also provides an assembly for producing hollow fiber membranes that includes a central fluid distributor and a multi-fiber spinneret.

[0016] In the context of the present disclosure, the term "multi-fiber spinneret" is used for a spinneret that includes multiple nozzles in a single spinneret housing, each nozzle having two concentric orifices, enabling the simultaneous production of multiple hollow fiber membranes. In one embodiment, the multi-fiber spinneret is a double spinneret that includes two nozzles. In other embodiments, the multi-fiber spinneret includes more than two nozzles, such as three to twelve nozzles.

[0017] The central fluid distributor of the present disclosure includes a single inlet end for central fluid and at least two capillary tubes in fluid communication with the inlet end. The orifices of the at least two capillary tubes define outlet ends for the central fluid and are configured to distribute the flow of central fluid provided at the inlet end between the outlet ends in a manner that the flow rates through all of the central fluid needles of the multi-fiber spinneret are the same when the outlet ends are connected to central fluid needles of the nozzles of a multi-fiber spinneret that includes at least two nozzles that provide central orifices.

[0018] The central fluid distributor of the present disclosure solves the problem of uneven distribution of central fluid flow between the individual nozzles of a multi-fiber spinneret due to manufacturing tolerances of the bore diameter (inner diameter of the central orifice) in the nozzles. The central fluid flow through all the nozzles of the multi-fiber spinneret is equalized. This is achieved by placing a capillary tube upstream of each nozzle of the multi-fiber spinneret. The length of these tubes is adjusted to achieve the same central fluid flow through each nozzle, e.g., by cutting the capillary tubes to a certain length. In the context of the present disclosure, the central fluid flow through all the nozzles is considered to be the same if the ratio of the central fluid flow through any two nozzles is in the range of 0.95 to 1.05. The capillary tubes are arranged within a housing that is configured to be connected to the central fluid inlets of the nozzles of a multi-fiber spinneret comprising at least two nozzles. The central fluid distributor ensures a constant central fluid flow, thereby ensuring a constant inner diameter of the hollow fiber membranes produced. The hydraulic characteristics of the central fluid distributor are fixed, and therefore, heat, vibrations, or long-term use are unlikely to change the hydraulic characteristics, and therefore, the inner diameter of the hollow fibers produced by the multi-fiber spinneret.

[0019] The central fluid distributor of the present disclosure requires only a single connection to a constant flow source of central fluid to supply all the nozzles of a multi-fiber spinneret. Therefore, it has only a single inlet end for the central fluid and multiple outlet ends for the central fluid, each outlet end defined by an orifice of a capillary tube in fluid communication with the inlet end. The central fluid distributor comprises at least two outlet ends. In one embodiment, the central fluid distributor comprises two outlet ends. In other embodiments, the central fluid distributor comprises three to twelve outlet ends. The capillary tubes in the central fluid distributor control the fluid flow through the central fluid distributor. The capillary tubes are configured to distribute the flow of the central fluid provided at the inlet end of the central fluid distributor among the outlet ends of the central fluid distributor in a manner that the flow rate through all the central fluid needles of a multi-fiber spinneret is the same when the outlet ends are connected to the central fluid needles of the nozzles of the multi-fiber spinneret comprising at least two nozzles that provide a central orifice. In the context of the present disclosure, the flow rate through all the central fluid needles is considered to be the same if the ratio of the flow rate through any two central fluid needles is in the range of 0.95 to 1.05. The length of each capillary tube is adjustable to offset the differences in flow capacity between the individual central fluid needles caused by differences in the dimensions of the individual central fluid needles. In one embodiment, the dimensions of the individual capillary tubes are adjusted to equally distribute the fluid flow between the central fluid needles of a multi-fiber spinneret connected to the central fluid distributor, e.g., by cutting the individual capillary tubes to a certain length, or replacing the individual capillary tubes with longer or shorter capillary tubes as needed.

[0020] In one embodiment, each capillary tube is arranged within a housing that is configured to be connected to the central fluid inlets of the nozzles of a multi-fiber spinneret comprising at least two nozzles.

[0021] In one embodiment, each housing is connected to a spinneret insert of the multi-fiber spinneret. The spinneret insert comprises a chamber for the center fluid and a hollow needle connected to the bottom of the chamber and provides a central orifice of the multi-fiber spinneret nozzle.

[0022] In one embodiment, the housing comprises a first housing part arranged in a hole of the bottom face of the center fluid distributor and a second housing part connected to the first housing part and at least partially protruding from the hole. In other embodiments, a sealing element, such as a ferrule, is arranged around the capillary tube between the first housing part and the second housing part and provides a fluid seal.

[0023] The present disclosure also provides an assembly comprising the center fluid distributor of the present disclosure mounted on a multi-fiber spinneret comprising at least two nozzles.

[0024] The center fluid distributor comprises a plurality of capillary tubes corresponding to the number of nozzles in the multi-fiber spinneret. The capillary tubes are in fluid connection with a single feed end of the center fluid distributor for the center fluid. Each capillary tube is in fluid communication with the central orifice of one of the nozzles of the multi-fiber spinneret, so that the central orifice of each nozzle can be supplied with center fluid via the corresponding capillary tube in the center fluid distributor. The central orifice is provided by a center fluid needle. The capillary tubes in the center fluid distributor are configured to evenly distribute the center fluid flow between the center fluid needles of the multi-fiber spinneret (i.e. the central orifice of the nozzles).

[0025] In one embodiment, an adapter is located between the center fluid distributor and the multi-fiber spinneret, joining the center fluid distributor to the multi-fiber spinneret. The adapter provides additional mechanical stability to the assembly. In one embodiment of the assembly of the present disclosure, each capillary tube of the center fluid distributor is arranged within a housing and a portion of each housing protrudes from the bottom face of the center fluid distributor. The protruding portion of each housing is inserted into a center fluid inlet of the multi-fiber spinneret. The adapter provides a sleeve for receiving the protruding portion of each housing and a recess for receiving the center fluid inlet of the multi-fiber spinneret.

[0026] In one embodiment, the multi-fiber spinneret is composed of two different building blocks, a spinneret body and a multi-spinneret insert, which are assembled to form the multi-fiber spinneret. The spinneret body has orifices on its upper side. The orifices lead to a cavity of the spinneret body and a spinneret insert has been introduced into the cavity through each orifice. The multi-fiber spinneret thus comprises a spinneret body and at least two spinneret inserts arranged within the cavity of the spinneret body. In one embodiment, the multi-fiber spinneret is a double spinneret, i.e. the spinneret body has two orifices for spinneret inserts.

[0027] A first building block, a spinneret body, defines the outer wall of a compartment for a polymer solution and the outer wall of an annular slit of a nozzle of a multi-fiber spinneret located at the bottom face of the spinneret body. The spinneret body has a feed end for the polymer solution which is connected to the compartment for the polymer solution in the multi-fiber spinneret which is defined by the inner surface of the cavity of the spinneret body and the outer surface of the spinneret insert. The compartment comprises a plurality of rotationally symmetric shells around the spinneret insert which are interconnected by tubular conduits in the spinneret body.

[0028] The nozzle of the multi-fiber spinneret has two concentric orifices, an outer annular slit and a central orifice. The outer annular slit of each nozzle is connected to the compartment for the polymer solution in the multi-fiber spinneret and the central orifice of each nozzle is formed by a hollow needle located in the spinneret insert.

[0029] A second building block, a spinneret insert, defines a portion of the inner wall of the compartment for the polymer solution and comprises a chamber for a central fluid connected to a hollow needle which extends into one of the nozzles of the multi-fiber spinneret when the multi-fiber spinneret is assembled. The hollow needle further defines the inner wall of the central orifice and the annular slit of the corresponding nozzle of the multi-fiber spinneret.

[0030] The present disclosure also provides a method of calibrating an assembly of the present disclosure. The feed end for the central fluid of an assembly comprising a central fluid distributor of the present disclosure mounted on a multi-fiber spinneret is connected to a source of a constant flow of a liquid. In one embodiment, the liquid is the central fluid. In another embodiment, the fluid is water.

[0031] The flow rates through each needle of the multi-fiber spinneret (i.e. through each nozzle) are measured and the measured flow rates are compared to each other. If the ratio of the measured flow rates is in the range of 0.95 to 1.05, the flow rates are considered to be consistent. If the flow rates are not consistent, the length of the capillary tubes in the central fluid distributor is adjusted to eliminate the discrepancy and achieve consistent flow rates through all needles. This adjustment can be made by reducing the length of the individual capillary tubes, for example, by cutting, or by replacing the individual capillary tubes with longer or shorter capillary tubes, as needed for each situation.

[0032] The flow rates through all needles are then measured again to verify that the flow rates are consistent. If the flow rates are still not consistent, the process is repeated until the flow rates through all needles of the multi-fiber spinneret are consistent.

[0033] The calibration procedure is performed before the assembly is used for the first time in the production of hollow fiber membranes. It only needs to be performed once unless a component of the assembly has to be replaced at a later point in time, for example, due to maintenance. For example, if one of the spinneret inserts or one of the central fluid needles is replaced, a re-calibration of the assembly is necessary to ensure that the inner diameter of the produced hollow fiber membranes is constant.

[0034] The present disclosure also provides a method for producing a hollow fiber membrane, comprising feeding a polymer solution to the feed end for polymer solution of the multi-fiber spinneret of the present disclosure, while feeding a center solution to the feed end for center fluid of the center fluid distributor of the assembly, extruding the polymer solution through the outer annular slit of the multi-fiber spinneret nozzle, while extruding the center solution through the center fluid needle of the multi-fiber spinneret.

[0035] Suitable polymer solutions and suitable center fluids for producing semi-permeable hollow fiber membranes are well known in the art. For example, a solution comprising 1) at least one polysulfone, polyethersulfone, or polyarylethersulfone, and 2) at least one polyvinylpyrrolidone can be used as the polymer solution. In one embodiment, the at least one polysulfone, polyethersulfone, or polyarylethersulfone and the at least one polyvinylpyrrolidone are dissolved in 3) a mixture of N-methyl-2-pyrrolidone (NMP) and water. In one embodiment, the center fluid comprises water and N-methyl-2-pyrrolidone. In other embodiments, a mixture of water and NMP is used as the center fluid.

[0036] The center fluid distributor and assembly of the present disclosure will now be further explained with reference to the accompanying drawings.

[0037] Figure 1 A side view (top), top view (middle), and bottom view (bottom) of an embodiment of the center fluid distributor 10 of the present disclosure mounted on a double spinneret 30 comprising two nozzles 35, 36 is shown. The center fluid distributor 10 is joined to the double spinneret 30 by an adapter 20. The center fluid distributor 10 has a single inlet end 11 for connecting to a source of constant flow of center fluid (not shown). The center fluid distributor 10 is mounted on the spinneret 30 by screws 50.

[0038] Figure 2 is Figure 1 A cross-sectional view of the assembly shown along the line A-A. The center fluid of constant flow enters the center fluid distributor 10 at the inlet end 11 (connector). The center fluid is then distributed in the center fluid distributor 10 through the holes 12. The center fluid then flows through the capillary tubes 15, 16 (the nominal inner diameter of the capillary tubes is about 200 pm and the length is approximately 40 mm) into the center fluid chambers 42, 47 and then through the center fluid needles 41, 46 (the inner diameter of the needles is about 170 pm and the length is approximately 4 mm) of the spinneret inserts 40, 45.

[0039] The capillary tubes 15, 16 are held within a capillary tube housing formed by a first housing portion 13, a second housing portion 21, and a ferrule 14 disposed between the first housing portion 13 and the second housing portion 21 as a seal to prevent fluid bypass. The second housing portion 21 is inserted into the center fluid inlets 43, 48 of the spinneret inserts 40, 45.

[0040] The adapter 20 joins the central fluid distributor 10 to the multi-fiber spinneret 30. The adapter 20 provides a sleeve 25 for receiving the portion of the second housing portion 21 that protrudes from the bottom face of the central fluid distributor 10. The adapter also provides a recess 26 for receiving the portion of the spinneret insert 40, 45 that protrudes from the spinneret body 31. The protruding portion includes the central fluid inlets 43, 48 of the spinneret insert 40, 45. The adapter 20 protects the protruding portion from damage and provides additional mechanical stability to the assembly.

[0041] O-rings 22 provide a seal between the central fluid distributor 10, the second housing portion 21, and the adapter 20. O-rings 23 provide a seal between the adapter 20, the second housing portion 21, and the spinneret insert 40, 45. O-rings 24 provide a seal between the second housing portion 21, the central fluid inlets 43, 48 of the spinneret insert 40, 45, and the central fluid chambers 42, 47 of the spinneret insert 40, 45.

[0042] The diameter of the bore 12 in the central fluid distributor 10 is so large that the hydraulic resistance of the bore 12 is negligible compared to the hydraulic resistance of the capillaries 15, 16 and the needles 41, 46. The nominal central fluid flow through each spinneret insert 40, 45 is approximately 2.0 milliliters per minute, and the flow is laminar.

[0043] The flow ratio of the central fluid through the spinneret inserts 40, 45 can be described as follows:

[0044]

[0045] where, is the volumetric flow; l is the length of the capillary 15, 16 (DK) or needle 41, 46 (D); r is the inner radius of the capillary 15, 16 or needle 41, 46. Designations A refer to the first spinneret insert 40, first needle 41, and first capillary 15, respectively. Designations B refer to the second spinneret insert 45, second needle 46, and second capillary 16, respectively.

[0046] The dual spinneret 30, together with the central fluid distributor 10 mounted thereon, is tested on a test bench. The flow rate through each needle 41, 46 of the spinneret 30 is then measured with a constant flow of distilled water. The lengths l of the capillaries 15 and 16 are then adjusted respectively according to the deviation between the measured flow rates DK，A , l DK，B . The flow rates are then measured again to check the improvement. If necessary, the process is repeated until the flow rates through both needles 41, 46 are identical, i.e. C A = 1 (± 0.05).

[0047] Spinneret inserts 40, 45 are disposed within a cavity 33 of a body 31 of a dual spinneret 30. The spinneret body 31 has an inlet 32 for a polymer solution and two nozzles 35, 36 at its bottom. Each nozzle 35, 36 comprises a circular orifice at the bottom of the cavity 33. The needles 41, 46 of the spinneret inserts 40, 45 each extend into the nozzles 35, 36, defining the central orifice of the nozzles 35, 36 and the inner boundary of the outer annular slit of the nozzles 35, 36. The cavity 33 comprises a conduit 34. The cavity 33 and the outer surface of the spinneret inserts 40, 45 together define a chamber for the polymer solution. During operation of the spinneret 30, the polymer solution is extruded through the outer annular slit of the nozzles 35, 36, while the central fluid is extruded through the central orifice of the nozzles 35, 36 formed by the needles 41, 46, to form a hollow fiber membrane.

[0048] List of reference signs

[0049] 10 central fluid distributor

[0050] 11 central fluid feed end

[0051] 12 bore

[0052] 13 first capillary housing part

[0053] 14 collar

[0054] 15 first capillary

[0055] 16 second capillary

[0056] 17 gasket

[0057] 20 adapter

[0058] 21 second capillary housing part

[0059] 22 O-ring

[0060] 23 O-ring

[0061] 24 O-ring

[0062] 25 sleeve

[0063] 26 notch

[0064] 30 spinneret

[0065] 31 spinneret body

[0066] 32 polymer solution end

[0067] 33 cavity

[0068] 34 polymer solution conduit

[0069] 35 first nozzle

[0070] 36 second nozzle

[0071] 40 first spinneret insert

[0072] 41 first spinneret insert needle

[0073] 42 first central fluid chamber

[0074] 43 first spinneret insert central fluid inlet

[0075] 45 second spinneret insert

[0076] 46 second spinneret insert needle

[0077] 47 second central fluid chamber

[0078] 48 second spinneret insert central fluid inlet

[0079] 50 screw

Claims

1. An assembly comprising a multi-fiber spinneret (30) and a central fluid distributor (10), the multi-fiber spinneret (30) comprising at least two nozzles (35, 36), the central fluid distributor (10) comprising a single feed end (11) for a central fluid and at least two capillaries (15, 16) in fluid communication with the feed end (11); the orifices of the at least two capillaries (15, 16) defining outlet ends for the central fluid, the outlet ends being connected to central fluid needles (41, 46), each of the central fluid needles (41, 46) providing a central orifice of a nozzle (35, 36) of the multi-fiber spinneret (30), the at least two capillaries (15, 16) being configured to distribute the flow of central fluid provided at the feed end (11) between the outlet ends in a manner that the flow rates through all of the central fluid needles (41, 46) of the multi-fiber spinneret (30) are identical, wherein, The length of each capillary (15, 16) is adjustable to offset flow differences between the respective central fluid needles (41, 46) caused by size differences of the respective central fluid needles (41, 46).

2. The assembly of claim 1, wherein, The central fluid distributor (10) comprises two capillaries (15, 16).

3. The assembly of claim 1, wherein, Each capillary (15, 16) is arranged within a housing (13, 14, 21) configured to be connected to a central fluid inlet (43, 48) of a nozzle (35, 36) of the multi-fiber spinneret (30).

4. The assembly of claim 2, wherein, Each capillary (15, 16) is arranged within a housing (13, 14, 21) configured to be connected to a central fluid inlet (43, 48) of a nozzle (35, 36) of the multi-fiber spinneret (30).

5. The assembly of claim 3, wherein, Each housing (13, 14, 21) is configured to be connected to a spinneret insert (40, 45) of the multi-fiber spinneret (30).

6. The assembly of claim 3, wherein, The housing (13, 14, 21) comprises a first housing portion (13) arranged in a hole of a bottom face of the central fluid distributor (10) and a second housing portion (21) connected to the first housing portion (13) and at least partially protruding from the hole.

7. The assembly of claim 5, wherein, The housing (13, 14, 21) comprises a first housing portion (13) arranged in a hole of a bottom face of the central fluid distributor (10) and a second housing portion (21) connected to the first housing portion (13) and at least partially protruding from the hole.

8. The assembly of claim 6, wherein, A sealing element (14) is arranged between the first housing portion (13) and the second housing portion (21) around the capillaries (15, 16) and provides a fluid tight seal.

9. The assembly of any one of claims 1-8, wherein, An adapter (20) is located between the central fluid distributor (10) and the multi-fiber spinneret (30) joining the central fluid distributor (10) to the multi-fiber spinneret (30).

10. The assembly of claim 9, wherein, Each capillary (15, 16) of the central fluid distributor (10) is arranged within a housing (13, 14, 21), a portion (21) of each housing (13, 14, 21) protruding from a bottom face of the central fluid distributor (10), and wherein the protruding portion (21) of each housing (13, 14, 21) is inserted into a central fluid inlet (43, 48) of the multi-fiber spinneret (30), the adapter (20) providing a sleeve (25) for receiving the protruding portion (21) of each housing (13, 14, 21) and a recess (26) for receiving the central fluid inlet (43, 48) of the multi-fiber spinneret (30).

11. A method of calibrating an assembly according to any one of claims 1 to 10, comprising the steps of: connecting a feed end (11) of the assembly for a center fluid to a source of a constant flow of liquid; measuring the flow rate of the liquid through each needle (41, 46) of the multi-fiber spinneret (30); comparing the measured flow rates; and, in the event that the flow rates are not uniform, adjusting the length of the capillary tubes (15, 16) in the center fluid distributor (10) to achieve uniform flow rates through all needles (41, 46); again measuring the flow rates through all needles (41, 46) to verify that the flow rates are uniform; and, in the event that the flow rates are still not uniform, repeating the above process until the flow rates through all needles (41, 46) of the multi-fiber spinneret (30) are uniform.

12. The method of claim 11, wherein, The liquid is water.

13. A method for producing a hollow fiber membrane, comprising: simultaneously supplying a polymer solution to a feed end (32) of a multi-fiber spinneret (30) for the polymer solution and supplying a center fluid to a feed end (11) of the center fluid distributor (10) of the assembly of any one of claims 1 to 8 for the center fluid; extruding the polymer solution through the outer annular slit of the nozzle (35, 35) of the multi-fiber spinneret (30) and simultaneously extruding the center fluid through the center fluid needles (41, 46) of the multi-fiber spinneret (30).

14. The method of claim 13, wherein, The polymer solution comprises: 1) a polysulfone, polyether sulfone, or polyarylether sulfone; and 2) at least one polyvinylpyrrolidone.

15. The method of claim 13 or 14, wherein, The center fluid comprises water and N-methyl-2-pyrrolidone. The center fluid comprises water and N-methyl-2-pyrrolidone.

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