WO2015177707A1

WO2015177707A1 - Humidifier for a fuel cell system, fuel cell system and vehicle with a fuel cell system

Info

Publication number: WO2015177707A1
Application number: PCT/IB2015/053649
Authority: WO
Inventors: Leif-Patrik BARTHEL; Simon Hollnaicher; Alfred Kolbe
Original assignee: Nissan Motor Co., Ltd.
Priority date: 2014-05-20
Filing date: 2015-05-18
Publication date: 2015-11-26
Also published as: DE102015004953A1

Abstract

The invention relates to a humidifier for a fuel cell system, which is configured for humidifying a medium capable of being introduced into a fuel cell stack of the fuel cell system. The humidifier includes a plurality of hollow fiber membranes, which circumferentially surround an inflow area (24). A supporting structure (40) with at least one passage opening (44) is disposed in the inflow area (24). The hollow fiber membranes can be supplied with a humidifying medium via the at least one passage opening (44). The at least one passage opening (44) has a length in a longitudinal direction (36) of the inflow area (24), which is greater than half a length of a partial area of the hollow fiber membranes, in which the hollow fiber membranes abut on the supporting structure (40). Furthermore, the invention relates to a fuel cell system with such a humidifier and to a vehicle with a fuel cell system.

Description

Humidifier for a fuel cell system, fuel cell system and vehicle with a fuel cell system

The invention relates to a humidifier for a fuel cell system, which is configured for humidifying a medium capable of being introduced into a fuel cell stack of the fuel cell system. The humidifier includes a plurality of hollow fiber membranes, which

circumferentially surround an inflow area. A supporting structure is disposed in the inflow area, which has at least one passage opening. Via the at least one passage opening, the hollow fiber membranes can be supplied with a humidifying medium, which is introduced into the inflow area. Furthermore, the invention relates to a fuel cell system with such a humidifier and to a vehicle with a fuel cell system.

DE 103 32 493 A1 describes a humidifier for a fuel cell system, in which individual hollow fiber membranes are connected to each other by a mesh-like matrix material. Herein, the hollow fiber membranes form a mat-like compound, which is wound up on a hollow body in the humidifier. Herein, the hollow body is a pipe with a plurality of passage openings. A humidifying medium can come into contact with the hollow fiber membranes via these passage openings, through which the gas flow to be humidified flows.

Furthermore, US 6 755 399 B2 describes a humidifier, in which a humidifying medium is passed through hollow fiber membranes of a fiber bundle, which serves for humidifying supply air supplied to a fuel cell stack in a fuel cell system. Herein, the dry supply air to be humidified enters the humidifier at a first end of the fiber bundle and then flows in counterflow to the humidifying medium flowing through the hollow fibers to the other end of the humidifier. However, a part of the dry supply air to be humidified flows into a bypass pipe already at the first end, which is centrally disposed in the fiber bundle. On the path to the second end, dry supply air exits the bypass pipe via openings disposed in the bypass pipe and then flows around the hollow fiber membranes. Thus, the dry supply air is to be uniformly distributed in the fiber bundle.

However, such a bypass pipe is unbeneficial with regard to the incident flow to the fiber bundle.

Therefore, it is the object of the present invention to provide a humidifier of the initially mentioned kind, a fuel cell system with such a humidifier as well as a vehicle with such a fuel cell system, by means of which particularly good humidification of the medium to be humidified is achievable. This object is solved by a humidifier having the features of claim 1 , a fuel cell system having the features of claim 9 and by a vehicle having the features of claim 10.

Advantageous configurations with convenient developments of the invention are specified in the dependent claims.

In the humidifier according to the invention, the at least one passage opening has a length viewed in a longitudinal direction of the inflow area, which is greater than half a length of a partial area of the hollow fiber membranes, in which the hollow fiber membranes abut on the supporting structure. By this passage opening or these passage openings extending over a comparatively great length of the inflow area, a flow of the humidifying medium particularly well distributed over the length of the humidifier can be realized. In addition, a supporting structure with at least one passage opening of great length can be particularly simply and inexpensively produced since components available as standard can be used. This is associated with improved manufacturability, decreased production time and reduced production cost.

With such a humidifier, which has at least one elongated passage opening, a particularly effective transition of the humidifying medium into the area of the humidifier can be achieved, in which the hollow fiber membranes are disposed and surround the inflow area. The humidifying medium then flows around the hollow fibers constituted by the membranes, through which the medium to be humidified flows. In this manner, particularly good and uniform humidification of the medium to be humidified can be achieved.

Preferably, the length of the at least one passage opening corresponds to the length of the partial area or it is at least 70 percent to 95 percent of the length of the partial area. Thus, a particularly unimpeded transition of the humidifying medium from the inflow area into the space of the humidifier surrounding the inflow area, occupied by the hollow fiber membranes can be ensured.

The supporting structure can be formed as a pipe, which has a plurality of slots constituting the at least one passage opening. Such a pipe with elongated slots provides a particularly stable supporting structure and thus ensures high dimensional stability of the inflow area. In particular, the pipe can be circular-cylindrically formed and have end regions for increasing the stability, in which a wall of the pipe is continuously formed, thus does not have slots. The supporting structure and pipe, respectively, may have a rectangular cross-section, particularly in cases in which the housing of the humidifier has a rectangular cross-section, too. Moreover, not only one, but two or more supporting structures and pipes, respectively, may be provided.

The stability of the pipe can be further increased if the webs bounding the respective slots have at least one stiffening element. By thus reinforced webs, a good transition of the humidifying medium into the space around the supporting structure can be achieved with high robustness of the pipe, in which the hollow fiber membranes are located.

The stiffening element of the respective web can be formed as a rib, which extends from the respective web in radial direction towards the center of the pipe to a certain extent. A wall area of the pipe including the respective web and the rib can have a T-shaped cross- section, whereby a particularly high stability is imparted to the pipe.

In an alternative configuration, the supporting structure can be formed as a profile part, by which at least two chambers are formed in the inflow area, which can be passed by the humidifying medium in the longitudinal direction of the inflow area. Herein, the at least one passage opening is provided by an open side of the respective chamber. Such a profile part is particularly simple and inexpensive in the production, and it can in particular be formed by extrusion.

The profile part can have a plurality of walls bounding the chambers, which extend from a center of the profile part in radial direction up to the hollow fiber membranes abutting on the profile part. Herein, the walls can form an X or a Y in cross-section, or the cross- section can be formed in the manner of a six-beam or six-pointed star with beams of preferably constant thickness. With such a star-shaped profile part with six beams, six chambers capable of being passed are correspondingly formed, which have the open side in radial direction. By such a particularly stable profile part, a particularly great length of the passage openings can be particularly simply provided.

By means of the profile part, chambers each identical in size can also very easily be provided, which is advantageous for a uniform distribution of the humidifying medium.

It has proven further advantageous if the supporting structure is formed as a coil spring, the coils of which abut on the hollow fiber membranes. Herein, the inflow area is formed in the manner of a channel, the walls of which are constituted by the hollow fiber

membranes, wherein these walls are supported by the coils of the coil spring. With such a configuration of the supporting structure, instead of hollow fiber membranes connected to each other, in particular woven with each other, hollow fiber membranes disposed loosely next to each other can also be employed. Namely, the supporting structure formed in the manner of a coil spring prevents individual hollow fibers from entering the inflow area through the passage openings, for instance in that they sag.

Such an advantageous support of the hollow fiber membranes can also be achieved if the supporting structure is provided by a plurality of rings. The rings can also be connected to each other by rods and form an inherently stiff grid together with the rods, which imparts to the inflow area its dimensional stability. Alternatively, a plurality of rods can be provided, which extend in the longitudinal direction of the inflow area and which are connected to each other by means of an inherently stiff grid. Such a grid or mesh then has the passage openings with the great length.

Preferably, the hollow fiber membranes constitute a bundle, which is disposed in a housing of the humidifier. Herein, the housing preferably has a housing wall, which abuts on an outside of the bundle in a downstream partial area viewed in an inflow direction of the humidifying medium into the inflow area. In contrast, in an upstream (viewed in inflow direction) partial area, the housing wall is spaced from the outside of the bundle. By such a configuration of the housing wall, it can be achieved that the humidifying medium first enters the downstream partial area of the inflow area and from there radially enters the space, in which the hollow fiber membranes constituting the bundle are located. From this end region of the bundle, the humidifying medium then flows in counterflow, thus along the hollow fiber membranes, to the upstream partial area, in which the housing wall is spaced from the outside of the bundle. Such a guidance of the humidifying medium in the counterflow results in particularly good humidification of the medium to be humidified.

For a uniform flow of the humidifying medium, it is advantageous if the bundle constituted by the hollow fiber membranes is substantially round formed, thus has a circular- cylindrical shape with the inflow area as a - preferably central - channel.

The fuel cell system according to the invention, which in particular can be employed in a vehicle, includes a humidifier according to the invention. Herein, the exhaust gas of a cathode of a fuel cell stack of the fuel cell system can preferably be introduced into the inflow area of the humidifier. Herein, the exhaust gas of the cathode is preferably usable for humidifying an oxidant capable of being supplied to the cathode of the fuel cell stack as the medium to be humidified. Namely, the oxidant to be humidified, thus for example air or oxygen, then flows through the hollow fiber membranes. This is more favorable than supplying the hollow fiber membranes with the exhaust gas of the cathode, which contains liquid water. Namely, the liquid water could otherwise clog the - usually rather fine - hollow fiber membranes, in particular if the water freezes. The latter could also result in a damage of the hollow fiber membranes, which presently is reliably avoided.

Such a fuel cell system can include a plurality of further components usual in particular for fuel cell systems of vehicles, which presently do not have to be explained in detail.

The vehicle according to the invention includes a fuel cell system according to the invention.

The advantages and preferred embodiments described for the humidifier according to the invention also apply to the fuel cell system according to the invention and to the vehicle according to the invention.

The features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the description of figures and/or shown in the figures alone are usable not only in the respectively specified combination, but also in other combinations or alone, without departing from the scope of the invention. Thus, implementations are also to be considered as encompassed and disclosed by the invention, which are not explicitly shown in the figures or explained, but arise from and can be generated by separated feature combinations from the explained implementations.

Further advantages, features and details of the invention are apparent from the claims, the following description of preferred embodiments as well as based on the drawings. Therein show:

Fig. 1 in sections a fuel cell system of a vehicle, wherein a humidifier for

humidifying supply air for a cathode of a fuel cell stack of the fuel cell system is shown in perspective, which has a coil spring as a supporting structure for a channel-shaped inflow area formed in the humidifier;

Fig. 2 an alternative supporting structure in perspective, which is formed as a pipe with elongated slots; Fig. 3 in a sectional view a further pipe suitable as a supporting structure, in which stiffening ribs are provided on webs of the pipe;

Fig. 4 a further alternative supporting structure in perspective, which is formed as a star-shaped extrusion profile; and

Fig. 5 schematized the flow paths of supply air to be humidified through a variant of the humidifier.

Of a fuel cell system 10 of a vehicle, a humidifier 12 is shown in Fig. 1 , which serves for humidifying an oxidant to be provided for the fuel cell reaction. This oxidant can for example be oxygen or air. The air humidified in the humidifier 12 is supplied to a cathode 16 of a fuel cell stack 18 of the fuel cell system 10 via a line 14. Hydrogen can be supplied to an anode 20 of the fuel cell stack 18 as the fuel for the fuel cell reaction occurring in the fuel cell stack 18. Presently, the exhaust gas of the cathode 16, which contains the product water formed in the fuel cell reaction, is supplied to the humidifier 12 as the humectant. An exhaust gas line 22 provided to this is schematically shown in Fig. 1.

The wet exhaust gas of the cathode 16, which is supplied to the humidifier 12 via the exhaust gas line 22 flows into a channel-shaped inflow area 24 of the humidifier 12. The inflow area 24 is surrounded by hollow fiber membranes 26 (not shown in Fig. 1 ; compare Fig. 5). The supply air to be humidified flows through these hollow fiber membranes 26 and is supplied to the cathode 16 via the line 14. The hollow fiber membranes 26 constitute a circular-cylindrical bundle, in the center of which the channel-shaped inflow area 24 is located. The hollow fiber membranes 26 constituting the bundle are thus disposed in a space 28 annularly enclosing the inflow area 24.

The hollow fiber membranes 26 are passed through closure elements 30, 32 at their ends, which are formed of a casting compound. In the inlet-side closure element 30, a central inlet 34 is provided, via which the exhaust gas serving as the humectant enters the inflow area 24, which is formed as a channel centrally disposed in the space 28. An inflow direction of the exhaust gas into the inflow area 24 is illustrated by an arrow 36 in Fig. 1. By this arrow 36, a longitudinal direction of the inflow area 24 is additionally indicated, which coincides with a longitudinal axis of the humidifier 12. The second, end-side closure element 32 does not have any outlet for the exhaust gas flowing into the humidifier 12 through the inflow area 24, but it is formed closed also in a central area 38 closing the inflow area 24 on the end side. As a result, the exhaust gas first flowing into the inflow area 24 in axial direction of the humidifier 12, thus in the direction of the arrow 36, flows radially out of the inflow area 24. Herein, it flows around the membranes at the outside, which form the hollow fibers, and the humidity transfer from the wet exhaust gas to the dry supply air flowing through the hollow fiber membranes 26 occurs.

In the variant of the humidifier 12 shown in fig. 1 , a coil spring 42 is provided in the inflow area 24 as a supporting structure 40. Partial areas of the hollow fiber membranes 26 abut on the coils of the coil spring 42, which are disposed in the space 28, which is bounded by the closure elements 30, 32 in axial direction. Herein, the spiral coils of the coil spring 42 prevent the partial areas of the hollow fiber membranes 26 from being able to enter the inflow area 24 for instance in that the partial areas sag. Namely, an orientation of the hollow fiber membranes 26 corresponds to the longitudinal direction of the inflow area 24 indicated by the arrow 36.

By the sections free of material of the coil spring 42 provided between the coils of the coil spring 42, a single passage opening is formed, which has a length viewed in the longitudinal direction of the inflow area 24, which corresponds to the distance between the closure elements 30, 32 and thus the partial area of the hollow fiber membranes 26, in which they abut on the supporting structure 40. The exhaust gas can particularly well enter the space 28 containing the hollow fiber membranes 26 through this passage opening of particularly great length.

In Fig. 2, an alternative supporting structure 40 provided for arrangement in the inflow area 24 is shown. The supporting structure 40 shown in Fig. 2 is formed as a pipe, in which a plurality of passage openings in the form of elongated slots 44 is provided in the material constituting the pipe. These slots 44 extend nearly over the entire length of the pipe, which substantially corresponds to the length of the humidifier 12. In respective end regions 46, however, the pipe is formed circumferentially closed.

The material of the pipe present between the slots 44 forms webs 48, which laterally bound the slots 44. With such a pipe as the supporting structure 40, the length of the slots 44 in the longitudinal direction of the humidifier 12 indicated by the arrow 36 substantially corresponds to the length of the hollow fiber membranes 26. However, according to the formation of the circumferentially closed end regions 46, it can occur that the length of the slots 44 corresponds to only between 70 percent and 95 percent of the length of the partial area of the hollow fiber membranes 26, in which the hollow fiber membranes 26 are in contact with the pipe.

The supporting structure 40 shown in Fig. 3 is also formed as a pipe, but here the webs 48 laterally bounding the slots 44 are reinforced by ribs 50. These ribs 50 serve as stiffening elements for the webs 48 and thus for the supporting structure 40 formed as a pipe as a whole. Presently, the ribs 50 extend starting from the webs 48 to a certain extent to a center 52 of the inflow area 24. The areas formed by the webs 48 and the ribs 50 of the supporting structure 40 formed as a pipe are T-shaped in cross-section in the variant shown in Fig. 3, wherein a height of the rib 50, thus its extension in radial direction of the inflow area 24, can be larger than a width of the web 48, thus the extension thereof in circumferential direction of the pipe.

The supporting structure 40 shown in Fig. 4 is an extrusion profile, thus a profile part formed by extrusion. The profile part shown in Fig. 4 has three walls 54 crossing each other each at identical angles, which form a six-beam star with beams of constant thickness in the cross-section. A center 56 of the profile part thus forms the crossing point of the three walls 54. By such a profile part, the inflow area 24 is divided in - presently six - chambers 58, the open sides, thus not bounded by the walls 54, of which form the passage openings for the exhaust gas. Then, in the operation of the humidifier 12, the exhaust gas enters the space 28 with the hollow fiber membranes 26 via these passage openings extending also over the substantially entire length of the humidifier 12.

Such a profile part formed by extrusion, which can have less or more walls 54 and correspondingly less or more chambers 58 in alternative embodiments, can be particularly simply provided with regard to the manufacturing cost and the process management.

In the variant of the humidifier 12 shown in Fig. 5, the exhaust gas flows in the direction of the arrow 36 into the inflow area 24. However, it is closed by the central area 38 of the closure element 32 on the end side. Correspondingly, the exhaust gas flows in particular near the closure element 32 in radial direction out of the inflow area 24. However, in this downstream partial area viewed in the inflow direction of the exhaust gas, a housing wall 60 of a housing of the humidifier 12 abuts on an outside of the bundle, which constitutes the hollow fiber membranes 26. The corresponding partial area 62 of the housing wall 60 is shown abutting on the hollow fiber membranes 26 in Fig. 5. In contrast, in an upstream partial area 64, the housing wall 60 is spaced from an outside of the bundle of the hollow fiber membranes 26. Correspondingly, in this partial area 64, the exhaust gas can also pass directly from the inflow area 24 in radial direction through the bundle of the hollow fiber membranes 26. The part of the exhaust gas, however, which is deflected at the downstream end of the inflow area 24, flows in counterflow to the supply air flowing through the hollow fiber membranes 26 towards the partial area 64 of the housing wall 60, which is spaced from the bundle of the hollow fiber membranes 26.

Corresponding flow arrows 66 indicating this counterflow are presented for illustration in Fig. 5. The flow guidance of the exhaust gas through the humidifier 12 at least partially in counterflow can result in a particularly good transfer of humidity from the exhaust gas to the supply air to be humidified.

In particular in a variant of the humidifier 12, in which the hollow fiber membranes 26 are woven or otherwise connected to each other, the inflow area 24 can be formed merely by winding up the hollow fiber membranes 26 around a center of the bundle formed as a cavity. Then, an inner pipe can be completely omitted as the supporting structure, and the hollow fiber membranes 26 do not have to be supported in the inflow area 24.

Alternatively, a support of the bundle of the hollow fiber membranes 26 from inside, thus in the inflow area 24, can be effected via rings or an inherently stiff mesh or grid or via individual rods, which are connected to each other via a - preferably inherently stiff - mesh.

List of reference characters

10 Fuel cell system

12 Humidifier

14 Line

16 Cathode

18 Fuel cell stack

20 Anode

22 Exhaust gas line

24 Inflow area

26 Hollow fiber membrane

28 Space

30 Closure element

32 Closure element

34 Inlet

36 Arrow

38 Central area

40 Supporting structure

42 Coil spring

44 Slot

46 End region

48 Web

50 Rib

52 Center

54 Wall

56 Center

58 Chamber

60 Housing wall

62 Partial area

64 Partial area

66 Flow arrow

Claims

1. Humidifier for a fuel cell system (10), which is configured for humidifying a medium capable of being introduced into a fuel cell stack (18) of the fuel cell system (10), including a plurality of hollow fiber membranes (26), which circumferentially surround an inflow area (24), wherein a supporting structure (40) with at least one passage opening (44) is disposed in the inflow area (24), wherein the hollow fiber membranes (26) can be supplied with a humidifying medium via the at least one passage opening (44),

characterized in that

the at least one passage opening (44) has a length in a longitudinal direction (36) of the inflow area (24), which is greater than half a length of a partial area of the hollow fiber membranes (26), in which the hollow fiber membranes (26) abut on the supporting structure (40).

2. Humidifier according to claim 1 ,

characterized in that

the length of the at least one passage opening (44) corresponds to the length of the partial area or is 70 % to 95 % of the length of the partial area.

3. Humidifier according to claim 1 or 2,

characterized in that

the supporting structure (40) is formed as a pipe, which has a plurality of slots constituting the at least one passage opening (44).

4. Humidifier according to claim 3,

characterized in that

webs (48) bounding the respective slots have a at least one stiffening element, in particular formed as a rib (50) extending from the respective web (48) in radial direction towards the center (52) of the pipe. Humidifier according to claim 1 or 2,

characterized in that

the supporting structure (40) is formed as a profile part in particular formed by extrusion, by which at least two chambers (58) being able to be passed by the humidifying medium in the longitudinal direction (36) of the inflow area (24) are formed in the inflow area (24), wherein the at least one passage opening is provided by an open side of the respective chamber (58).

Humidifier according to claim 5,

characterized in that

the profile part has a plurality of walls (54) bounding the chambers (58), which extend from a center (56) of the profile part in radial direction up to the hollow fiber membranes (26) abutting on the profile part.

Humidifier according to claim 1 or 2,

characterized in that

the supporting structure (40)

is formed as a coil spring (42), or

is provided by a plurality of rings, or

is formed by an inherently stiff grid, or

is formed by a plurality of rods, which are connected to each other by means of an inherently stiff grid.

Humidifier according to any one of claims 1 to 7,

characterized in that

the hollow fiber membranes (26) in particular connected to each other form an in particular substantially round bundle, which is disposed in a housing of the humidifier (12), wherein the housing has a housing wall (60), which abuts on an outside of the bundle in a downstream partial area (62) viewed in an inflow direction (36) of the humidifying medium into the inflow area (24) and is spaced from the outside in an upstream partial area (64).

Fuel cell system, in particular for a vehicle, including a humidifier (12) according to any one of claims 1 to 8, wherein the exhaust gas of a cathode (16) of a fuel cell stack (18) of the fuel cell system (10) can be introduced into the inflow area (24) of the humidifier (12) and is usable for humidifying an oxidant capable of being supplied to the cathode (16) of the fuel cell stack (18) as the medium to be humidified.

Vehicle with a fuel cell system (10) according to claim 9.