Humidity unit for a fuel cell system, fuel cell system and vehicle with a fuel cell system

Abstract

Humidifier for a fuel cell system (10), which is designed for humidifying a medium that can be introduced into a fuel cell stack (18) of the fuel cell system (10), comprising a plurality of hollow fiber membranes (26) which circumferentially surround an inlet region (24), wherein a support structure (40) with at least one through-opening (44) is arranged in the inlet region (24), wherein the hollow fiber membranes (26) can be supplied with a humidifying medium via the at least one through-opening (44), characterized in that the at least one through-opening (44) has a length in a longitudinal direction (36) of the inlet region (24) which is greater than half the length of a partial region of the hollow fiber membranes (26) in which the hollow fiber membranes (26) abut the support structure (40) and are thus in contact with it.

Description

The invention relates to a humidifier for a fuel cell system, which is designed to moisten a medium that can be introduced into a fuel cell stack of the fuel cell system. The humidifier comprises a plurality of hollow fiber membranes, which surround the circumference of an inflow region. In the inflow region a support structure is arranged, which has at least one passage opening. The hollow-fiber membranes can be acted upon via the at least one passage opening with a moistening medium, which is introduced into the inflow region. Furthermore, the invention relates to a fuel cell system having such a humidifier and to a vehicle having 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 one another by a net-like matrix material. The hollow fiber membranes form a mat-like composite which is wound onto a hollow body in the humidifier. The hollow body is a • tube with a plurality of through openings. Via these passage openings, a moistening medium can come into contact with the hollow-fiber membranes, through which the gas stream to be moistened flows.DE 101 06 722 A1 describes hollow fiber membrane modules for use as so-called "immersion modules" in filtration and / or dialysis processes, in particular when, owing to the use of contaminated liquids or liquids leading to deposits, adverse effects due to "fouling" effects are expected, and a process for producing such hollow fiber membrane modules.DE 10 2004 029141 A1 describes a membrane module for a submerged operation comprising a fiber bundle made of a multiplicity of hollow-fiber membranes which are cast with an open end into a head piece and are surrounded in the submerged operation by a liquid to be filtered, a permeate collecting space adjoining the head piece and having at least one permeate outlet for the permeate flowing out of the interior of the hollow-fiber membranes, and a gas feed which has a tube guided through the head piece. The tube ends in the interior of the fiber bundle and has a gas outlet for a gaseous medium which, after the transition from the tube into the liquid to be filtered, substantially rises as bubbles between the hollow fiber membranes of the bundle. According to the invention, the fiber bundle is divided into sections each comprising a group of hollow fiber membranes. Between the sections there remain free spaces which extend from the tube as far as the outer periphery of the head piece and promote an inflow of the liquid to be filtered into a foot region of the fiber bundle adjoining the head piece.DE 10 2004 022 310 A1 describes a moisture exchange module which has a bundle of hollow-fiber membranes through which a first gas stream flows, which are permeable to moisture. The bundle of hollow fiber membranes is arranged in a jacket space with line elements for the supply and discharge of a second gas stream flowing around the hollow fiber membranes. The conduit elements are arranged in the bundle of hollow fiber membranes and have numerous openings in their periphery. This can preferably be used in the field of moistening supply air to fuel cell systems.Furthermore, U.S. Pat. No. 6,755,399 B2 describes a humidifier in which a humidifying medium is conducted through hollow fiber membranes of a fiber bundle which serves for humidifying supply air supplied from a fuel cell stack in a fuel cell system. The dry supply air to be humidified enters the humidifier at a first end of the fiber bundle and then flows in counter-current to the humidifying medium flowing through the hollow fibers toward the other end of the humidifier. However, a portion of the dry supply air to be humidified already flows at the first end into a bypass pipe which is arranged centrally in the fiber bundle. On the way to the second end, dry supply air exits the bypass tube via openings which are arranged in the bypass tube and then flows around the hollow-fiber membranes. Thus, the dry supply air is to be distributed uniformly in the fiber bundle.However, such a bypass pipe is disadvantageous in view of the inflow of the fiber bundle.It is therefore the object of the present invention to provide a humidifier of the type mentioned at the beginning, a fuel cell system with such a humidifier and a vehicle with such a fuel cell system, by means of which particularly good moistening of the medium to be moistened can be achieved.This object is achieved by a humidifier with the features of claim 1, a fuel cell system with the features of claim 9 and by a vehicle with the features of claim 10. Advantageous embodiments with expedient developments of the invention are specified in the dependent patent claims.In the humidifier according to the invention, the at least one passage opening has a length, as seen in a longitudinal direction of the inflow region, which is greater than half a length of a partial region of the hollow-fiber membranes in which the hollow-fiber membranes abut the support structure. Through this passage opening or passage openings extending over a comparatively large length of the inflow region, a flow of the humidifying medium distributed particularly well over the length of the humidifier can be realized. In addition, a support structure with at least one passage opening of great length can be produced particularly easily and cost-effectively, since components available as standard can be used. This is associated with improved mikroability, reduced production time and reduced production costs.With such a humidifier, which has at least one elongated passage opening, a particularly effective transfer of the humidifying medium into the region of the humidifier, in which the hollow fiber membranes are arranged and surround the inflow region, can be achieved. The moistening medium then flows around the hollow fibers formed by the membranes, through which the medium to be moistened flows. In this way, a particularly good and uniform moistening of the medium to be moistened can be achieved.Preferably, the length of the at least one passage opening corresponds to the length of the sub-region or it is at least 70 percent to 95 percent of the length of the sub-region. In this way, a particularly unhindered transfer of the moistening medium from the inflow region into the space of the humidifier occupied by the hollow fiber membranes and surrounding the inflow region can be ensured.The support structure can be designed as a tube, which has a plurality of slots forming the at least one passage opening. Such a tube with elongated slots provides a particularly stable supporting structure and thus ensures a high dimensional stability of the inflow region. The tube can in particular be circular-cylindrical and, in order to increase the stability, have end regions in which a wall of the tube is formed continuously, that is to say has no slots. The supporting structure or the tube can, however, also have an angular cross section, in particular in cases in which the housing of the humidifier likewise has an angular cross section. Furthermore, not only one but two or more supporting structures or tubes can be provided.The stability of the tube can be further increased if the webs which delimit the respective slots have at least one stiffening element. Webs reinforced in this way allow good transfer of the moistening medium into the space around the supporting structure in which the hollow-fiber membranes are located, with high robustness of the tube.The stiffening element of the respective web can be designed as a rib which extends from the respective web in the radial direction a certain distance towards the center of the tube. A wall region of the tube comprising the respective web and the rib can have a T-shaped cross section, as a result of which a particularly high stability is imparted to the tube.In an alternative embodiment, the support structure can be designed as a profile part, by means of which at least two chambers are formed in the inflow region, through which the moistening medium can flow in the longitudinal direction of the inflow region. In this case, the at least one passage opening is provided by an open side of the respective chamber. Such a profile part is particularly simple and cost-effective to produce, and it can be formed in particular by extrusion.The profile part can have a plurality of walls delimiting the chambers, which walls extend from a center of the profile part in the radial direction as far as the hollow fiber membranes adjoining the profile part. 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-tooth star with beams of preferably constant thickness. In such a star-shaped profile part with six jets, six flow-through chambers are formed accordingly, which have the open side in the radial direction. By means of such a particularly stable profile part, a particularly large length of the passage openings can be provided in a particularly simple manner.Also, by means of the profile part, chambers of the same size can be provided in each case very easily, which is advantageous for a uniform distribution of the moistening medium.It has been found to be further advantageous if the supporting structure is designed as a helical spring, the windings of which are in contact with the hollow-fiber membranes. In this case, the inflow region is formed in the manner of a channel, the walls of which are formed by the hollow-fiber membranes, these walls being supported by the windings of the helical spring. In such a configuration of the supporting structure, instead of hollow-fiber membranes connected to one another, in particular interwoven, hollow-fiber membranes can also be used which are arranged loosely next to one another. The supporting structure, which is designed in the manner of a helical spring, prevents individual hollow fibers from passing through the passage openings into the inflow region, for example by sagging.Such an advantageous support of the hollow fiber membranes can also be achieved if the support structure is provided by a plurality of rings. The rings can also be connected to one another by rods and together with the rods form an inherently rigid grid which gives the inflow region its dimensional stability. Alternatively, a plurality of rods can be provided, which extend in the longitudinal direction of the inflow region and which are connected to one another by means of a self-rigid grid. Such a grid or net then has the passage openings with the great length.Preferably, the hollow fiber membranes form a bundle which is arranged in a housing of the humidifier. In this case, the housing preferably has a housing wall which, in a downstream partial region, as seen in an inflow direction of the moistening medium into the inflow region, bears against an outer side of the bundle. In an upstream partial region (as viewed in the inflow direction), on the other hand, the housing wall is spaced apart from the outer side of the bundle. Such a configuration of the housing wall allows the moistening medium to first pass into the downstream partial region of the inflow region and from there to enter radially into the space in which the hollow fiber membranes forming the bundle are located. From this end region of the bundle, the moistening medium then flows in counter-current, i.e. along the hollow fiber membranes, to the upstream partial region in which the housing wall is spaced apart from the outside of the bundle. Such a guiding of the moistening medium in counter-current leads to a particularly good moistening of the medium to be moistened.For a uniform flow of the moistening medium, it is advantageous if the bundle formed by the hollow fiber membranes is substantially round, i.e. has a circular cylindrical shape with the inflow region as a-preferably central-channel.The fuel cell system according to the invention, which can be used in particular in a vehicle, comprises a humidifier according to the invention. In this case, the exhaust gas of a cathode of a fuel cell stack of the fuel cell system can preferably be introduced into the inflow region of the humidifier. The exhaust gas of the cathode can be used here preferably for moistening an oxidizing agent that can be supplied to the cathode of the fuel cell stack as the medium to be moistened. Then, namely, the oxidizing agent to be humidified, i.e., for example, air or oxygen, flows through the hollow fiber membranes. This is more favorable than subjecting the hollow fiber membranes to the exhaust gas of the cathode, which contains liquid water. The liquid water could otherwise clog the hollow fiber membranes, which are usually quite fine, especially if the water freezes. The latter could also lead to damage to the hollow-fiber membranes, which in the present case is reliably avoided.Such a fuel cell system can comprise a large number of further components which are customary in particular for fuel cell systems of vehicles and which need not be explained in detail in the present case.The vehicle according to the invention comprises 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 combinations of features mentioned above in the description and the features and combinations of features mentioned below in the description of the figures and / or shown alone in the figures can be used not only in the respectively specified combination but also in other combinations or alone without departing from the scope of the invention. Therefore, embodiments are also to be considered included and disclosed by the invention, which are not explicitly shown or explained in the figures, but which emerge from the explained embodiments and can be generated by separate combinations of features.Further advantages, features and details of the invention are evident from the claims, the following description of preferred embodiments and on the basis of the drawings. The following are shown: FIG. 1 shows a detail of 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 humidifier has a helical spring as a supporting structure for a channel-shaped inflow region formed in the humidifier; FIG. 2 is a perspective view of an alternative supporting structure which is designed as a tube with elongate slots; FIG. 3 is a sectional view of a further tube suitable as a supporting structure, in which reinforcing ribs are provided on webs of the tube; FIG. 4 shows a perspective view of a further, alternative supporting structure which is designed as a star-shaped extruded profile; and FIG. 5 schematically shows 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 oxidizing agent to be provided for the fuel cell reaction. This oxidizing agent can be, for example, 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 may be supplied to an anode 20 of the fuel cell stack 18 as fuel for the fuel cell reaction occurring in the fuel cell stack 18. Here, the exhaust gas of the cathode 16 containing the product water formed in the fuel cell reaction is supplied to the humidifier 12 as humidifying means. An exhaust gas line 22 provided for this purpose is shown schematically in FIG. 1.The moist exhaust gas of the cathode 16 supplied to the humidifier 12 via the exhaust gas line 22 flows into a channel-shaped inflow region 24 of the humidifier 12. The inflow region 24 is surrounded by hollow-fiber membranes 26 (not shown in FIG. 1 ) (compare FIG. 5 ). Through these hollow fiber membranes 26 the supply air to be humidified flows, which is supplied to the cathode 16 via the line 14. The hollow fiber membranes 26 form a circular cylindrical bundle, in the center of which the channel-shaped inflow region 24 is located. The hollow fiber membranes 26 forming the bundle are thus arranged in a space 28 which annularly surrounds the inflow region 24.At their ends, the hollow fiber membranes 26 are passed through closure elements 30, 32, which are formed from a casting compound. In the inlet-side closure element 30, a central inlet 34 is provided, via which the exhaust gas serving as humidifying means reaches the inflow region 24, which is formed as a channel arranged centrally in the space 28. An inflow direction of the exhaust gas into the inflow region 24 is illustrated in FIG. 1 by an arrow 36. This arrow 36 simultaneously indicates a longitudinal direction of the inflow region 24, which coincides with a longitudinal axis of the humidifier 12.The second, end closure element 32 does not have an outlet for the exhaust gas flowing into the humidifier 12 through the inflow region 24, but is also embodied as closed in a central region 38 closing the inflow region 24 at the end. As a result, the exhaust gas flowing into the inflow region 24 first in the axial direction of the humidifier 12, i.e. in the direction of the arrow 36, flows radially out of the inflow region 24. In this case, it flows around the outside of the membranes which form the hollow fibers, and the moisture transfer takes place from the moist exhaust gas to the dry supply air flowing through the hollow fiber membranes 26.In the variant of humidifier 12 shown in FIG. 1, a helical spring 42 is provided as support structure 40 in inflow region 24. The partial regions of the hollow fiber membranes 26 abut the windings of the helical spring 42 and are arranged in the space 28 which is bounded in the axial direction by the closure elements 30, 32. The spiral windings of the helical spring 42 prevent the partial regions of the hollow fiber membranes 26 from entering the inflow region 24, for example by the partial regions sagging. Namely, an orientation of the hollow fiber membranes 26 corresponds to the longitudinal direction of the inflow region 24 indicated by the arrow 36.The portions provided between the windings of the helical spring 42 and free of material of the helical spring 42 form a single passage opening which, as seen in the longitudinal direction of the inflow region 24, has a length which corresponds to the distance between the closure elements 30, 32 and thus to the partial region of the hollow-fiber membranes 26 in which they bear against the supporting structure 40. Through this passage opening of particularly great length, the exhaust gas can pass particularly well into the space 28 containing the hollow-fiber membranes 26.FIG. 2 shows an alternative supporting structure 40 provided for arrangement in the inflow region 24. The support structure 40 shown in FIG. 2 is formed as a tube in which a plurality of passage openings in the form of elongate slots 44 are provided in the material forming the tube. These slots 44 extend nearly the entire length of the tube, which substantially corresponds to the length of the humidifier 12. In respective end regions 46, however, the tube is formed to be closed on the circumferential side.The material of the tube present between the slots 44 forms webs 48 which laterally delimit the slots 44. In the case of such a tube as a 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, depending on the configuration of the circumferentially closed end regions 46, it may happen that the length of the slots 44 corresponds only to between 70 percent and 95 percent of the length of the portion of the hollow-fiber membranes 26 in which the hollow-fiber membranes 26 are in contact with the tube.The supporting structure 40 shown in FIG. 3 is likewise designed as a tube, but here the webs 48 which laterally delimit the slots 44 are reinforced by ribs 50. These ribs 50 serve as stiffening elements for the webs 48 and thus for the support structure 40 formed as a tube as a whole. In the present case, the ribs 50 extend from the webs 48 for a certain distance towards a center 52 of the inflow region 24. the regions of the supporting structure 40 formed as a tube formed by the webs 48 and the ribs 50 are T-shaped in cross section in the variant shown in FIG. 3, wherein a height of the rib 50, i.e. its extension in the radial direction of the inflow region 24, can be greater than a width of the web 48, i.e. its extension in the circumferential direction of the tube.The support structure 40 shown in FIG. 4 is an extruded profile, i.e. a profile part formed by extrusion. The profiled part shown in FIG. 4 has three walls 54 which cross each other at identical angles and which form a six-armed star with beams of constant thickness in cross section. A center 56 of the profile part thus forms the intersection point of the three walls 54. By means of such a profile part, the inflow region 24 is divided into-in the present case six-chambers 58, the open sides of which, that is to say sides not bounded by the walls 54, form the passage openings for the exhaust gas. Via these passage openings, which likewise extend over the substantially entire length of the humidifier 12, the exhaust gas then reaches the space 28 with the hollow fiber membranes 26 during operation of the humidifier 12.Such a profile part formed by extrusion, which in alternative embodiments can have fewer or more walls 54 and correspondingly fewer or more chambers 58, can be provided particularly easily with regard to production costs and process management.In the variant of the humidifier 12 shown in FIG. 5, the exhaust gas flows into the inflow region 24 in the direction of the arrow 36. However, this is closed at the end by the central region 38 of the closure element 32. Accordingly, the exhaust gas flows out of the inflow region 24 in the radial direction, in particular in the vicinity of the closure element 32. In this downstream portion, as viewed in the inflow direction of the exhaust gas, however, a housing wall 60 of a housing of the humidifier 12 abuts an outer side of the bundle forming the hollow fiber membranes 26. The corresponding partial region 62 of the housing wall 60 is shown in FIG. 5 in contact with the hollow fiber membranes 26.In an upstream partial region 64, on the other hand, the housing wall 60 is spaced apart from an outer side of the bundle of hollow-fiber membranes 26. Accordingly, in this partial region 64, the exhaust gas can also pass directly from the inflow region 24 in the radial direction through the bundle of hollow-fiber membranes 26. The portion of the exhaust gas, which is deflected at the downstream end of the inflow region 24, however, flows counter-current to the supply air flowing through the hollow fiber membranes 26 toward the partial region 64 of the housing wall 60, which is spaced apart from the bundle of the hollow fiber membranes 26.Corresponding flow arrows 66 indicating this counter-flow are shown in FIG. 5 for illustrative purposes. The flow guidance of the exhaust gas through the humidifier 12 at least partially in counter-current can lead to a particularly good transfer of moisture 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 interwoven or otherwise connected to one another, the inflow region 24 can be formed merely by winding the hollow fiber membranes 26 around a center of the bundle formed as a cavity. Then, an inner tube as a supporting structure can be completely omitted, and the hollow fiber membranes 26 do not need to be supported in the inflow region 24.Alternatively, the bundle of hollow fiber membranes 26 can be supported from the inside, i.e. in the inflow region 24, via rings or an inherently rigid network or grid, or via individual rods which are connected to one another via a preferably inherently rigid network.List of reference characters10 Fuel cell system 12 Humidifier 14 Line 16 Cathode 18 Fuel cell stack 20 Anode 22 Exhaust line 24 Inflow region 26 Hollow fiber membrane 28 Space 30 Closure element 32 Closure element 34 Inlet 36 Arrow 38 Central region 40 Supporting structure 42 Helical spring 44 Slot 46 End region 48 Web 50 Rib 52 Center 54 Wall 56 Center 58 Chamber 60 Housing wall 62 Partial region 64 Partial region 66 Flow arrow

Claims

Humidifier for a fuel cell system (10), which is designed for humidifying a medium which can be introduced into a fuel cell stack (18) of the fuel cell system (10), having a plurality of hollow-fibre membranes (26) which surround an inflow region (24) on the circumference, wherein a supporting structure (40) having at least one passage opening (44) is arranged in the inflow region (24), wherein the hollow-fibre membranes (26) can be acted upon 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 region (24) which is greater than half a length of a partial region of the hollow-fibre membranes (26) in which the hollow-fibre membranes (26) bear against the supporting structure (40) and are thus in contact therewith.Humidifier according to claim 1, characterised in that the length of the at least one passage opening (44) corresponds to the length of the sub-region or amounts to 70% to 95% of the length of the sub-region.Humidifier according to claim 1 or 2, characterised in that the support structure (40) is formed as a tube, which has a plurality of slots forming the at least one passage opening (44).Humidifier according to claim 3, characterised in that the webs (48) delimiting the respective slots have at least one stiffening element, in particular designed as a rib (50) extending from the respective web (48) in the radial direction towards the centre (52) of the tube.Humidifier according to claim 1 or 2, characterised in that the support structure (40) is formed as a profile part, by means of which at least two chambers (58) through which the humidifying medium can flow in the longitudinal direction (36) of the inflow region (24) are formed in the inflow region (24), wherein the at least one passage opening is provided by an open side of the respective chamber (58).Humidifier according to claim 5, characterised in that the profile part has a plurality of walls (54) which delimit the chambers (58) and which extend from a centre (56) of the profile part in the radial direction as far as the hollow fibre membranes (26) which bear against the profile part.Humidifier according to claim 1 or 2, characterised in that the support structure (40) - is formed as a helical spring (42) or - is provided by a plurality of rings or - is formed by an inherently rigid grid or - is formed by a plurality of rods which are connected to one another by means of an inherently rigid grid.Humidifier according to one of claims 1 to 7, characterised in that the hollow fibre membranes (26), which are in particular connected to one another, form a bundle which is arranged in a housing of the humidifier (12), wherein the housing has a housing wall (60) which, as seen in an inflow direction (36) of the humidifying medium into the inflow region (24), bears against an outer side of the bundle and is spaced apart from the outer side in an upstream partial region (64).Fuel cell system, in particular for a vehicle, having a humidifier (12) according to 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 region (24) of the humidifier (12) and can be used as the medium to be humidified for humidifying an oxidizing agent which can be supplied to the cathode (16) of the fuel cell stack (18).Vehicle comprising a fuel cell system (10) according to claim 9.

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