Humidifier for fuel cell

The present invention provides a humidifier for a fuel cell, in which a plurality of hollow fiber membranes having different diameters are appropriately arranged to control the flow direction of dry air introduced into the humidifier, thus uniformly humidifying the dry air.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims under 35 U.S.C. §119(a) the benefit of Korean Patent Application No. 10-2009-0116517 filed Nov. 30, 2009, the entire contents of which are incorporated herein by reference.

BACKGROUND

(a) Technical Field

The present disclosure relates, generally, to a humidifier for a fuel cell. More particularly, it relates to a humidifier for a fuel cell, in which a plurality of hollow fiber membranes having different diameters are appropriately arranged to control the flow direction of dry air introduced into the humidifier, thus suitably uniformly humidifying the dry air.

(b) Background Art

An electrolyte membrane in a fuel cell is preferably humidified for the operation of the fuel cell, and, accordingly, a humidifier which performs humidification by water exchange between exhaust gas (humid air) discharged from the fuel cell and dry air supplied form the outside is used.

In particular, a compact humidifier which consumes less power and requires a small installation space is required in a fuel cell. Although there are various types of humidifiers such as an ultrasonic humidifier, a steam humidifier, an evaporative humidifier, etc, a humidifier using hollow fiber membranes is suitably used in the fuel cell.

As shown inFIG. 1, a typical air supply system in a fuel cell system includes a membrane humidifier100, in which dry air is supplied from the outside by an air blower202and, exhaust gas discharged from a fuel cell stack200passes through the membrane humidifier100such that the dry air is humidified by water contained in the exhaust gas while passing through hollow fiber membranes provided in the membrane humidifier100.

FIG. 2is a cross-sectional view showing the configuration of an exemplary hollow fiber membrane humidifier.

As shown inFIG. 2, the humidifier100preferably includes a housing101. The housing101preferably includes a first inlet102through which dry air is suitably introduced and a first outlet103through which humidified air is suitably discharged. In particular, a hollow fiber membrane module107is suitably disposed in the inside of the housing101, and a plurality of hollow fiber membranes106are accommodated in the hollow fiber membrane module107.

In the humidifier100using the hollow fiber membranes106with the above-described configuration, when exhaust gas (humid air) discharged from the fuel cell stack is supplied to the inside of the housing101through a second inlet104, the water in the exhaust gas is separated by capillary action of the hollow fiber membranes106, and the separated water is condensed while passing through capillary tubes of the hollow fiber membranes106and collected in the hollow fiber membranes106.

Then, the exhaust gas, from which water is separated, moves to the outside of the hollow fiber membranes106and is discharged to the outside through a second outlet105of the housing101.

Further, outside air (dry air) is supplied through the first inlet102of the housing101by the operation of the air blower and passes through the hollow fiber membranes106. Accordingly, since the water separated from the humid air is collected in the hollow fiber membranes106, the dry air is suitably humidified by the water and then supplied to the fuel cell stack through the first outlet103.

As shown inFIG. 2, since the plurality of hollow fiber membranes106are suitably concentrated in the hollow fiber membrane module107, it is difficult for the humid air introduced through the second inlet104to permeate through the hollow fiber membrane module107. In particular, the rate at which the humid air is diffused into the hollow fiber membrane module107is very low, which makes it more difficult for the humid air to permeate through the hollow fiber membrane module107.

Accordingly, the humid air passing through the outside of the hollow fiber membrane module107accommodated in the housing101does not penetrate into the center of the hollow fiber membrane module107as shown in the dotted line box ofFIG. 2but mainly flows along the periphery of the hollow fiber membrane module107as shown by the arrows ofFIG. 2. As a result, the rate at which the humid air is diffused into the hollow fiber membrane module107is suitably reduced, which decreases the humidification efficiency.

Accordingly, the hollow fiber membranes106located in the center of the hollow fiber membrane module107cannot be suitably supplied with sufficient water, and thereby the overall efficiency of the membrane humidifier is reduced.

Further, in the conventional membrane humidifier, the dry air introduced through the first inlet102mainly flows through the center (as shown in the dotted line box ofFIG. 2) of the hollow fiber membrane module107, and as a result the efficiency of the membrane humidifier is further reduced.

This is illustrated in the simulation test results ofFIG. 3.

It can be clearly seen fromFIG. 3that most of the dry air flows only through the center of the hollow fiber membrane module107.

Accordingly, since the dry air introduced through the first inlet102mainly flows through the center of the hollow fiber membrane module107(as shown in the dotted line box ofFIG. 2) and the humid air introduced through the second inlet104flows along the periphery of the hollow fiber membrane module107, the overall humidification efficiency of the humidifier may be suitably reduced.

Such a problem becomes more serious when the amount of dry air is large, i.e., when the fuel cell stack provides high power output.

Another problem of the conventional humidifier is caused by the hollow fiber membranes and the arrangement thereof.

Despite the advantage that the membrane humidifier is applicable for use with a vehicle, available hollow fiber membrane materials are very expensive, and thus it is the manufacturing cost is high.

In most cases, sufficient humidification is required in a low current region of the fuel cell system, and much water is produced in high power and high current regions to the extent that a cathode does not require humidification. Nevertheless, most of the conventional humidifiers are operated without varying the amount of humidification in both the low and high current regions. In particular, in the case where the hollow fiber membranes are made of only Nafion, a high humidity of more than 80% RH is provided even in the high current region.

Further, a bundle of hollow fiber membranes having the same diameter is disposed in the conventional membrane humidifier, and the hollow fiber membranes are made of expensive Nafion, which is disadvantageous in terms of manufacturing cost.

Since a large amount of water is produced and a high humidity is provided in the high current region of the fuel cell system, an increase in resistance of cathode material transfer and a flooding phenomenon may occur, which results in air starvation of the cathode. As a result, the deterioration of the fuel cell catalyst is accelerated and thus the durability of the fuel cell is suitably reduced.

Accordingly, there is a need in the art for humidifiers for a fuel cell.

SUMMARY OF THE DISCLOSURE

The present invention provides a humidifier for a fuel cell, in which a plurality of hollow fiber membranes having a small diameter are suitably disposed in the center of a hollow fiber membrane module and a plurality of hollow fiber membranes having a large diameter are suitably disposed around the periphery of the hollow fiber membrane module so as to ensure uniform humidification for dry air and prevent the occurrence of flooding and an increase in load of an air blower.

In one preferred embodiment, the present invention provides a humidifier for a fuel cell, the humidifier preferably including a hollow fiber membrane module and a plurality of hollow fiber membranes suitably arranged in the hollow fiber membrane module, wherein the hollow fiber membranes may have different diameters and may be appropriately arranged in the hollow fiber membrane module.

In another preferred embodiment, a plurality of hollow fiber membranes having a small diameter may be suitably arranged in the center of the hollow fiber membrane module, through which dry air supplied from the outside by an air blower mainly flows, and a plurality of hollow fiber membranes having a large diameter may be suitably arranged in the periphery of the hollow fiber membrane module, through which humid air discharged from a fuel cell stack mainly flows.

In another preferred embodiment, a plurality of first hollow fiber membranes having the smallest diameter may be suitably arranged in the center of the hollow fiber membrane module, a plurality of third hollow fiber membranes having the largest diameter may be suitably arranged in the periphery of the hollow fiber membrane module, and a plurality of second hollow fiber membranes having an intermediate diameter may be suitably arranged between the first and third hollow fiber membranes.

The above features and advantages of the present invention will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated in and form a part of this specification, and the following Detailed Description, which together serve to explain by way of example the principles of the present invention.

DETAILED DESCRIPTION

As described herein, the present invention includes a humidifier for a fuel cell, the humidifier comprising a hollow fiber membrane module and a plurality of hollow fiber membranes arranged in the hollow fiber membrane module.

In one embodiment, the hollow fiber membranes have different diameters and are arranged in the hollow fiber membrane module.

In another embodiment, the hollow fiber membranes have different diameters and are arranged in the hollow fiber membrane module.

In another related embodiment, a plurality of hollow fiber membranes having a small diameter are arranged in the center of the hollow fiber membrane module, through which dry air supplied form the outside by an air blower mainly flows.

In another related embodiment, a plurality of hollow fiber membranes having a large diameter are arranged in the periphery of the hollow fiber membrane module, through which humid air discharged from a fuel cell stack mainly flows.

FIG. 4is a schematic diagram comparing the arrangement of hollow fiber membranes of a humidifier in accordance with an exemplary embodiment of the present invention and that of a conventional humidifier.

As described herein, the fuel cell humidifier has a structure in which a hollow fiber membrane module is suitably disposed in the inside of a housing, and a plurality of hollow fiber membranes are accommodated in the hollow fiber membrane module in the form of a bundle. It is known that dry air supplied from the outside by an air blower mainly flows through the center of the hollow fiber membrane module and humid air discharged from a fuel cell stack flows along the periphery of the hollow fiber membrane module.

Accordingly, the present invention provides a humidifier for a fuel cell, in which a plurality of hollow fiber membranes having different diameters are appropriately arranged to suitably improve the humidification performance for dry air introduced into the humidifier and solve the problems associated with the conventional humidifiers.

Preferably, a plurality of hollow fiber membranes having different diameters are appropriately arranged in the humidifier of the present invention, in which hollow fiber membranes having a larger diameter are suitably arranged from the center to the periphery.

Preferably, hollow fiber membranes having a smaller diameter are suitably arranged from the periphery to the center of the humidifier.

Referring toFIG. 4, a bundle of hollow fiber membranes having the same diameter is suitably arranged in a hollow fiber membrane module10of the conventional membrane humidifier to humidify air by water exchange in the hollow fiber membrane module10.

Accordingly, as described herein, the dry air introduced into the conventional humidifier flows into the hollow fiber membranes arranged in the center of the hollow fiber membrane module, and the humid air is suitably supplied to the outside of the hollow fiber membranes arranged along the periphery of the hollow fiber membrane module. Accordingly, the humidification efficiency of the humidifier, in which the humid air humidifies the dry air, is suitably reduced.

According to certain preferred embodiments of the present invention, a plurality of hollow fiber membranes having different diameters are appropriately arranged in such a manner that hollow fiber membranes having a larger diameter are suitably arranged from the center of the hollow fiber membrane module to the periphery thereof.

For example, as shown inFIG. 4, a plurality of first hollow fiber membranes11having the smallest diameter are suitably arranged in the center of the hollow fiber membrane module10, a plurality of third hollow fiber membranes13having the largest diameter are suitably arranged in the periphery of the hollow fiber membrane module10, and a plurality of second hollow fiber membranes12having an intermediate diameter are suitably arranged between the first and third hollow fiber membranes11and13.

Accordingly, although the dry air introduced into the humidifier by the air blower mainly flows through the first hollow fiber membranes11arranged in the center of the hollow fiber membrane module10, the amount of dry air flowing into the first hollow fiber membranes11is suitably reduced since the diameter of the first hollow fiber membranes11is small. Preferably, the dry air which does not flow into the first hollow fiber membranes11is suitably diffused to the periphery of the first hollow fiber membranes11by the flow pressure and thus flows into the second and third hollow fiber membranes12and13having larger diameters.

Accordingly, while the dry air flows through the first hollow fiber membranes11arranged in the center of the hollow fiber membrane module10, it does not intensively flow into the first hollow fiber membranes11but is smoothly diffused into the second and third hollow fiber membranes12and13. As a result, the dry air can be uniformly distributed over the entire hollow fiber membrane module10.

Therefore, according to further preferred embodiments of the present invention, a large amount of exhaust gas (humid air) introduced from the fuel cell stack to the inside of the hollow fiber membrane module10of the humidifier flows along the periphery of the hollow fiber membrane module10. Preferably, the humid air supplied from the outermost of the hollow fiber membrane module10is smoothly diffused into the third and second hollow fiber membranes13and12and, at the same time, provides sufficient water to the dry air flowing into the third and second hollow fiber membranes13and12as well as the first hollow fiber membranes11, thus suitably improving the humidification efficiency for the dry air supplied to the fuel cell stack.

Preferably, since the third hollow fiber membranes13arranged along the periphery of the hollow fiber membrane module10have the largest diameter, a gap between the third hollow fiber membranes13is suitably increased such that the humid air smoothly flows into the gaps and is easily diffused into the hollow fiber membranes. As a result, the humidification efficiency for the dry air flowing into the third and second hollow fiber membranes13and12as well as the first hollow fiber membranes11is suitably improved.

In other exemplary embodiments, for example in the case of the hollow fiber membranes adopted in the membrane humidifier, the amount of humid air diffused into the hollow fiber membranes having a larger diameter should be suitably increased, and thus the humidification performance may be somewhat reduced. However, since the humid air introduced from the fuel cell stack to the humidifier mainly flows along the periphery of the hollow fiber membrane module10and is first in contact with the third hollow fiber membranes13arranged along the periphery of the hollow fiber membrane module10to provide sufficient water, it is possible to suitably prevent the humidification performance from being reduced due to a reduction in the amount of humidification, even when the third hollow fiber membranes13having the largest diameter are arranged along the periphery of the hollow fiber membrane module10. Accordingly, in further preferred embodiments of the present invention as described herein, it is possible to provide uniform humidification to the dry air in the entire hollow fiber membranes.

Further, as described herein, in the case of a high power region where a large amount of water is suitably produced in the fuel cell stack due to the same humidification conditions, catalyst deterioration occurs due to a flooding phenomenon occurring in the fuel cell stack, and thereby the durability of the fuel cell stack is suitably reduced. However, according to the arrangement of the hollow fiber membranes of the present invention, the dry air flowing into the third and second hollow fiber membranes13and12as well as the first hollow fiber membranes11is uniformly humidified, and thus the air humidified enough to produce water is not suitably supplied to the fuel cell stack. Accordingly, it is possible to prevent the occurrence of flooding phenomenon in a high power region where a large amount of water is produced in the fuel cell stack itself.

As described herein, the present invention provides, but is not limited only to, the following effects.

In the arrangement of the hollow fiber membrane module for the fuel cell humidifier, the first hollow fiber membranes, which have a higher humidification performance and expand by absorbing water, are suitably arranged in the center of the hollow fiber membrane module and the second hollow fiber membranes, which have a lower humidification performance and do not expand by water, are suitably arranged in the periphery of the hollow fiber membrane module so as to provide the same humidification performance as the conventional membrane humidifier and prevent the increase in the pressure drop in the membrane humidifier and the increase in the load of the air blower.

Further, it is possible to suitably prevent the occurrence of flooding phenomenon in a high power region where a large amount of water is produced in the fuel cell stack itself.

Furthermore, in the arrangement of the hollow fiber membrane module, since the first hollow fiber membranes are suitably formed of expensive Nafion and the second hollow fiber membranes are suitably formed of cheap polyetherimide or polyphenylsulfone, it is possible to manufacture a membrane humidifier which is advantageous in terms of manufacturing cost.