Patent Publication Number: US-2023163329-A1

Title: Membrane humidifier for fuel cells

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC §119 to Korean Patent Application Nos. 10-2021-0160278, filed on Nov. 19, 2021, 10-2021-0160325, filed on Nov. 19, 2021, and 10-2021-0160335, filed on Nov. 19, 2021, in the Korean Intellectual Property Office, the disclosures of which are incorporated by reference herein in their entirety. 
     BACKGROUND 
     1. Field 
     The present disclosure relates to a membrane humidifier for a fuel cell having a built-in hollow fiber membrane cartridge, and more particularly, to a membrane humidifier for a fuel cell, in which a bulkhead is provided to make a hollow fiber membrane cartridge to be easily assembled and dismounted and to increase airtightness of each flow path, and a plurality of hollow fiber membrane cartridges are detachably mounted in a single hollow fiber housing. 
     2. Description of the Related Art 
     Fuel cells are a power generation type cell that produces electricity by combining hydrogen and oxygen. Unlike general chemical cells such as dry cells and storage batteries, fuel cells can produce electricity continuously as long as hydrogen and oxygen are supplied, and the efficiency thereof is about twice that of an internal combustion engine due to no heat loss. In addition, since the chemical energy generated by the combination of hydrogen and oxygen is directly converted into electrical energy, the emission of pollutants is low. Accordingly, fuel cells are environmentally friendly and reduce concerns about resource depletion due to increased energy consumption. According to the type of electrolyte used, fuel cells can be largely classified as polymer electrolyte membrane fuel cells (PEMFC), phosphoric acid fuel cells (PAFC), molten carbonate fuel cells (MCFC), solid oxide fuel cells (SOFC), and alkaline fuel cell (AFC). 
     Each of these fuel cells operates on the same principle, but they differ from each other in terms of the type of fuel used, operating temperature, catalyst, electrolyte, etc. From among these fuel cells, polymer electrolyte fuel cells are known to be the most promising not only for small-scale stationary power generation equipment but also for transportation systems because they operate at a lower temperature than other fuel cells and can be manufactured in small sizes due to high power density. 
     One of the most important factors in improving the performance of polymer electrolyte fuel cells is maintaining of water retention ratio by supplying a certain amount of moisture to a polymer electrolyte membrane or a proton exchange membrane (PEM) of a membrane-electrode assembly (MEA). This is because when the polymer electrolyte membrane dries, the power generation efficiency rapidly decreases. Polymer electrolyte membranes can be humidified by using the following methods: 1) a bubbler humidification method in which water is supplied by allowing a target gas to pass through a diffuser after filling the pressure-resistant container with water; 2) a direct injection method in which the amount of supplied moisture required for fuel cell reaction is calculated and water is supplied directly to a gas flow pipe through a solenoid valve; and 3) a humidification membrane method in which water is supplied to a gas fluidized bed using a polymer separation membrane. 
     Among them, a humidification membrane method that humidifies a polymer electrolyte membrane by providing water vapor to the gas supplied to the polymer electrolyte membrane using a membrane that selectively transmits only the water vapor contained in the exhaust gas, is advantageous in that the humidifier can be reduced in weight and size. As the selective permeable membrane used in the humidification membrane method, it is preferable to use a hollow fiber membrane having a large permeation area per volume when forming a module. That is, when a humidifier is manufactured using a hollow fiber membrane, the hollow fiber membrane with a large contact surface area can be highly integrated so that a fuel cell can be sufficiently humidified even with a small amount, low-cost materials can be used, and moisture and heat contained in the unreacted gas discharged at high temperature from the fuel cell can be recovered and reused through a humidifier. 
     As described above, membrane humidifiers for fuel cells configured to perform humidification using hollow fiber membranes have been proposed in various shapes and structures. However, in the case of membrane humidifiers for fuel cells of the related art, many hollow fiber membranes and a housing of a membrane humidifier are integrally coupled to each other by a resin layer. Accordingly, due to the difficulty in assembling the membrane humidifier, productivity is lowered, and when the hollow fiber membrane deteriorates due to a long service period, the hollow fiber membrane alone cannot be replaced. Therefore, the entire membrane humidifier must be discarded. In addition, in membrane humidifiers for fuel cells of the related art, one hollow fiber membrane bundle is placed in one membrane humidifier housing. Accordingly, even when a defect occurs in only some of the hollow fiber membrane bundle, only defected hollow fiber membranes of the bundle cannot be replaced. Therefore, the entire membrane humidifier must be discarded. 
     A resin layer is made of an expensive material, and when the entire opposite ends of the membrane humidifier housing are filled with the resin layer as in the prior art, the manufacturing costs are very high. The resin layer bonding the hollow fiber membrane to the membrane humidifier housing has a coefficient of thermal expansion that is different from that of the membrane humidifier housing. Accordingly, when the resin layer and the membrane humidifier housing are heated and cooled several times, the resin layer and the membrane humidifier housing may be finely spaced apart from each other. As such, when the resin layer and the membrane humidifier housing are spaced apart from each other, the wet air and the dry air can meet directly so that normal membrane humidification cannot be performed. 
     SUMMARY 
     Provided is a membrane humidifier for a fuel cell, having enhanced airtightness, in which a resin layer is configured to fill only opposite sides of a hollow fiber membrane cartridge, thereby reducing the amount of resin layer used, and a plurality of hollow fiber membrane cartridges are detachably mounted in one membrane humidifier housing, thereby facilitating the assembly and replacing of components, and a bulkhead is provided to increase the airtightness of a wet air flow path and a dry air flow path. 
     Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments of the disclosure. 
     According to an aspect of an embodiment, a membrane humidifier for a fuel cell, includes a hollow fiber membrane cartridge including a cartridge housing which is formed as a hollow having openings facing opposite sides of the cartridge housing in the longitudinal direction thereof and which has a side wall having a plurality of vent holes, a hollow fiber membrane inserted into an interior of the cartridge housing, and a resin layer filling an inner space of opposite sides of the cartridge housing in the longitudinal direction thereof, a membrane humidifier housing in which the hollow fiber membrane cartridge is formed, and a bulkhead formed in an interior of the membrane humidifier housing, wherein the bulkhead has mounting holes into which ends of the cartridge housing in the longitudinal direction thereof are inserted. 
     In an embodiment, the resin layer may be provided to cover opposite ends of the cartridge housing in the longitudinal direction thereof and the outer surface of opposite sides of the cartridge housing in the longitudinal direction. 
     In an embodiment, the cartridge housing further includes a protruding rib surrounding a middle portion of the cartridge housing in the longitudinal direction thereof, and the vent holes are formed in a side wall of the cartridge housing in the longitudinal direction thereof and in another side thereof opposite to the side wall with respect to the protruding rib. 
     In an embodiment, the membrane humidifier housing may include a partition wall having an insertion hole into which the cartridge housing is inserted. 
     In an embodiment, the bulkhead has a protrusion protruding on an outer end of the mounting hole, and the resin layer is in contact with the protrusion. 
     In an embodiment, an O-ring sealing a gap between the protrusion and the resin layer, may be further included. 
     According to an aspect of another embodiment, a membrane humidifier for a fuel cell, includes a hollow fiber membrane cartridge comprising a cartridge housing which is formed as a hollow having openings facing opposite sides of the cartridge housing in the longitudinal direction thereof and which has a side wall having a plurality of vent holes, a locking protrusion protruding opposite sides thereof in the longitudinal direction thereof, and a flange spaced from the locking protrusion, a hollow fiber membrane which is inserted into an interior of the cartridge housing, and a resin layer which fills inner spaces of opposite sides of the cartridge housing in the longitudinal direction thereof, and a membrane humidifier housing in which the hollow fiber membrane cartridge is formed, and a plurality of through-holes filled with the resin layer are formed between a protrusion and the flange. 
     In an embodiment, the resin layer may be provided to cover opposite ends of the cartridge housing in the longitudinal direction thereof and the outer surface of opposite sides of the cartridge housing in the longitudinal direction. 
     In an embodiment, the cartridge housing further includes a protruding rib surrounding a middle portion of the cartridge housing in the longitudinal direction thereof, and the vent holes are formed in a side wall of the cartridge housing in the longitudinal direction thereof and in another side thereof opposite to the side wall with respect to the protruding rib. 
     In an embodiment, the membrane humidifier housing may include a partition wall having an insertion hole into which the cartridge housing is inserted. 
     In an embodiment, the resin layer has an outer edge that is bent to be in the shape of steps, and the locking protrusion is in contact with a bent portion of the resin layer. 
     In an embodiment, a protrusion height of the flange may be greater than a protrusion height of the locking protrusion, and the resin layer covers up to a point where the flange is formed, and is stacked up to the protrusion height of the flange. 
     According to an aspect of an embodiment, a membrane humidifier for a fuel cell, includes a hollow fiber membrane cartridge including a cartridge housing which is formed as a hollow having openings facing opposite sides of the cartridge housing in the longitudinal direction thereof and which has a side wall having a plurality of vent holes, a hollow fiber membrane inserted into an interior of the cartridge housing, and a resin layer filling an inner space of opposite sides of the cartridge housing in the longitudinal direction thereof, a membrane humidifier housing in which the hollow fiber membrane cartridge is formed, and a bulkhead formed in an interior of the membrane humidifier housing, wherein the bulkhead is spaced apart from the cartridge housing. 
     In an embodiment, the cartridge housing may be connected to the bulkhead through the resin layer. 
     In an embodiment, an O-ring may be further included between the protrusion and the resin layer. 
     In an embodiment, the cartridge housing has a locking protrusion protruding on opposite sides thereof in the longitudinal direction thereof and a flange spaced apart from the locking protrusion. 
     In an embodiment, the resin layer may be formed up to a height at which the flange is formed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of certain embodiments of the disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
         FIGS.  1  and  2    are a perspective view and a cross-sectional perspective view of a membrane humidifier for a fuel cell according to an embodiment of the present disclosure; 
         FIG.  3    is a perspective view of a hollow fiber membrane cartridge included in the present disclosure; 
         FIG.  4    is a side view of a cartridge housing; 
         FIG.  5    is a cross-sectional view of a hollow fiber membrane cartridge included in the present disclosure; 
         FIG.  6    is an exploded perspective view showing the coupling structure of a bulkhead and a first housing; 
         FIG.  7    is an exploded perspective view showing the coupling structure of the first housing and a third housing; 
         FIG.  8    is a cross-sectional view of a membrane humidifier for a fuel cell according to the present disclosure; 
         FIGS.  9  and  10    are cross-sectional views showing the sealing structure of a membrane humidifier housing; 
         FIGS.  11  and  12    are a perspective view and a cross-sectional perspective view of a membrane humidifier for a fuel cell according to another embodiment of the present disclosure; 
         FIGS.  13  and  14    are a perspective view and an exploded perspective view showing a structure in which the bulkhead is coupled to opposite ends of a hollow fiber membrane cartridge; 
         FIG.  15    is a partial perspective view of a cartridge housing included in the present disclosure; 
         FIG.  16    is a vertical sectional view showing a structure in which a hollow fiber membrane cartridge and a membrane humidifier housing are coupled through the bulkhead as a coupling medium; 
         FIG.  17    is a perspective view of an O-ring and a head seal included in the present disclosure; 
         FIG.  18    is a perspective view of a pair of bulkheads according to the present disclosure; 
         FIG.  19    is a horizontal cross-sectional perspective view of a first housing included in the present disclosure; 
         FIG.  20    is a perspective view of a membrane humidifier for a fuel cell according to another embodiment of the present disclosure; 
         FIGS.  21  and  22    are an exploded perspective view and a perspective cross-sectional view of a hollow fiber membrane cartridge and a fuel cell membrane humidifier having the same according to the present disclosure; 
         FIG.  23    is a perspective cross-sectional view of a housing included in a membrane humidifier for a fuel cell according to the present disclosure. 
         FIG.  24    is a partial perspective view of a cartridge included in a membrane humidifier for a fuel cell according to the present disclosure; 
         FIGS.  25  and  26    are perspective and cross-sectional views showing a structure in which a hollow fiber membrane and a resin layer are coupled to a cartridge; 
         FIG.  27    is an exploded perspective view showing the coupling structure of a bulkhead and a cap; and 
         FIG.  28    is a vertical cross-sectional view of the membrane humidifier for a fuel cell according to the present disclosure, showing the directions in which the wet air and the dry air flow. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, the present embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. The embodiments are merely described below, by referring to the figures, to explain aspects. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. 
     Hereinafter, a membrane humidifier for a fuel cell according to an embodiment of the present disclosure will be described in detail with reference to  FIGS.  1  to  10   . 
       FIGS.  1  and  2    are a perspective view and a cross-sectional perspective view of a membrane humidifier for a fuel cell according to the present disclosure,  FIG.  3    is a perspective view of a hollow fiber membrane cartridge included in the present disclosure, and  FIG.  4    is a side view of a cartridge housing, and  FIG.  5    is a cross-sectional view of a hollow fiber membrane cartridge included in the present disclosure. 
     The membrane humidifier for fuel cell according to the present disclosure is a type of humidifier configured such that moisture of wet air passing outside a hollow fiber membrane  220  is transferred to dry air passing through the inside of the hollow fiber membrane  220 , and the hollow fiber membrane  220  is not integrally coupled to a membrane humidifier housing  100 , but is placed inside a hollow fiber membrane cartridge  200  that is detachably coupled to the membrane humidifier housing  100 , wherein a bulkhead  500  is mounted on one side of the hollow fiber membrane cartridge  200  in the longitudinal direction thereof, and the one side of the hollow fiber membrane cartridge  200  in the longitudinal direction thereof is inserted into the bulkhead  500 . 
     That is, the membrane humidifier for fuel cell according to the present disclosure includes: the hollow fiber membrane cartridge  200  including a cartridge housing  210  formed in the shape of a hollow tube having openings facing opposite sides in the longitudinal direction and having a plurality of vent holes  212  on the side wall, the hollow fiber membrane  220  inserted into the interior of the cartridge housing  210  such that opposite ends thereof in the longitudinal direction face the openings of the cartridge housing  210 , and a resin layer  230  filling the inner space of the cartridge housing  210  on opposite sides thereof in the longitudinal direction such that opposite ends of the hollow fiber membrane  220  in the longitudinal direction thereof are exposed to the outside; a membrane humidifier housing  100  in which the hollow fiber membrane cartridge  200  is provided and which includes a wet air inlet  131  and a wet air outlet  112  communicating with the vent holes  212 , and a dry air inlet  121  and dry air outlet  132  communicating with the hollow fiber membrane  220 ; and a bulkhead  500  which has an outer edge that is mounted to be in close contact with the inner surface of one side of the membrane humidifier housing  100  in the longitudinal direction thereof, and which has a mounting hole  510  which is formed in the central portion thereof and into which one end of the cartridge housing  210  in the longitudinal direction thereof is inserted. 
     As described above, when the hollow fiber membrane cartridge  200  is mounted on the membrane humidifier housing  100  by using the bulkhead  500  as a coupling medium, the hollow fiber membrane cartridge  200  can be easily assembled or replaced, and in the case where the shape or size of the hollow fiber membrane cartridge  200  is changed, only the bulkhead  500  is replaced and the membrane humidifier housing  100  may be commonly used. 
     In addition, regarding the membrane humidifier for fuel cell according to the present disclosure, instead of completely filling the inner space of opposite sides of the membrane humidifier housing  100  in the longitudinal direction thereof with the resin layer  230 , only the inner space of opposite sides of the cartridge housing  210  in the longitudinal direction thereof is filled with the resin layer  230 . Accordingly, the use of resin layer  230 , which is expensive, can be significantly reduced, and the manufacturing costs of the product can be reduced. 
     Meanwhile, the membrane humidifier housing  100  includes: a first housing  110  which is formed in a hollow tube shape with open opposite sides in the longitudinal direction thereof and into which the hollow fiber membrane cartridge  200  is inserted; a second housing  120  coupled to cover one side (left side in this embodiment) of the first housing  110  in the longitudinal direction thereof; and a third housing  130  coupled to cover the other side in the longitudinal direction (the right side in this embodiment) of the first housing  110 . The dry air inlet  121  and the dry air outlet  132  may be formed in the second housing  120  and the third housing  130 , respectively, and the wet air inlet  131  and the wet air outlet  112  may be formed in the third housing  130  and the first housing  110 , respectively. 
     Therefore, the dry air introduced into the second housing  120  through the dry air inlet  121  passes through the cartridge housing  210  along the flow path inside the hollow fiber membrane  220  and is delivered to the interior of the third housing  130  and then is drawn out through the dry air outlet  132  (see the dotted arrow). In addition, the wet air introduced into the interior of the third housing  130  through the wet air inlet  131  flows into the interior of the hollow fiber membrane cartridge  200  through the vent holes  212  of the hollow fiber membrane cartridge  200  and then flows, while in contact with the outer surface of the hollow fiber membrane  220 , through the wet air outlet  112  of the first housing  110 . 
     On the other hand, a protruding rib  213  may be formed on an outer surface of a middle portion of the cartridge housing  210  in the longitudinal direction thereof and divides the inner space of the membrane humidifier housing  100  into a front portion and a rear portion of the membrane humidifier housing  100 , and the vent holes  212  are formed on one side wall of the cartridge housing  210  in the longitudinal direction thereof and another side wall thereof in the longitudinal direction thereof with respect to the protruding rib  213 . The wet air introduced through the wet air inlet  131  is not directly discharged through the wet air outlet  112 . Instead, the wet air may be introduced into the interior of the cartridge housing  210  through the vent holes  212  formed on the side wall of rear portion of the cartridge housing  210  (right side in this embodiment) and may flow toward the frontward, and then, passing through the vent holes  212  formed on the side wall of the front portion of the cartridge housing  210  (left side in this embodiment), the wet air is discharged through the wet air outlet  112  of the first housing  110 . 
     As such, when the dry air flows while in contact with the inner surface of the hollow fiber membrane  220  and the wet air flows while in contact with the outer surface of the hollow fiber membrane  220 , the moisture in the wet air is transferred to the dry air so that the dry air may be humidified. This humidification principle is the same as of the related art, and thus a detailed description thereof will be omitted. 
     In this regard, in this embodiment, the membrane humidifier housing  100  includes three housings, that is, the first housing  110 , the second housing  120 , and the third housing  130 . However, in one or more embodiments, the membrane humidifier housing  100  may consist of two housings or four or more housings, or a single housing. 
     Meanwhile, to prevent the resin layer  230  coupled to the cartridge housing  210  from being easily removed from the cartridge housing  210 , the cartridge housing  210  includes a locking protrusion  214  and a cartridge flange  215 . The locking protrusion  214  is formed entirely over opposite ends of the cartridge housing  210  in the longitudinal direction and protrudes outward (specifically, toward the direction in which the protrusion is made along the lateral direction of the cartridge housing  210 ), and the cartridge flange  215  is formed at a point spaced a certain distance from the locking protrusion  214 . 
     At this time, the locking protrusion  214  is provided to be completely embedded in the resin layer  230 . Accordingly, even when the resin layer  230  is not fixed on the surface of the cartridge housing  210  and peeled off, as long as the locking protrusion  214  is damaged, the coupling of the resin layer  230  to the cartridge housing  210  may be maintained. 
     Furthermore, of the side wall of the cartridge housing  210 , in a portion between the locking protrusion  214  and the cartridge flange  215 , a plurality of through-holes  216 , which is to be filled with the resin layer  230 , may be formed. The resin layer  230  is initially in a liquid state, and when in contact with the cartridge housing  210 , undergoes a curing process to be integrally coupled to the cartridge housing  210 . As described above, when the through-holes  216  are formed in a portion of the side wall of the cartridge housing  210  surrounded by the resin layer  230 , the resin layer  230 , which is a liquid state, fills the through-holes  216  in the process in which the resin layer  230  is brought into contact with the cartridge housing  210 . As a result, the bonding strength between the resin layer  230  and the cartridge housing  210  is very high. 
     In addition, the cartridge flange  215  is a component for limiting the distance at which the hollow fiber membrane cartridge  200  is inserted into the bulkhead  500 , and the seating structure and function of the cartridge flange  215  will be described in detail with reference to  FIG.  9   . 
       FIG.  6    is an exploded perspective view showing the coupling structure of the bulkhead  500  and the first housing  110 ,  FIG.  7    is an exploded perspective view showing the coupling structure of the first housing  110  and the third housing  130 ,  FIG.  8    is a cross-sectional view of a membrane humidifier for a fuel cell according to the present disclosure, and  FIGS.  9  and  10    are cross-sectional views showing the sealing structure of the membrane humidifier housing  100 . 
     As illustrated in  FIG.  6   , a head flange  520  extending at a right angle is formed on a portion of the outer surface of the bulkhead  500  adjacent to the hollow fiber membrane cartridge  200 , and the head flange  520  is pressed and fixed between the first housing  110  and the second housing  120 . 
     At this time, the cartridge flange  215  of the cartridge housing  210  may be in close contact with the surface (the right surface in this embodiment) of the bulkhead  500  as illustrated in  FIG.  9   , and in this regard, an O-ring  300  may be press-fitted at the contact surface between the cartridge flange  215  and the bulkhead  500  to prevent the leakage of air through the contact surface between the cartridge flange  215  and the bulkhead  500 . 
     On the other hand, the second housing  120  is provided with a seating groove in which the head flange  520  is seated, and the head flange  520  is coupled to the second housing  120  such that the head flange  520  is completely embedded in the seating groove. In addition, the first housing  110  is coupled to cover a surface of the head flange  520  that faces the first housing  110  (a right side in this embodiment) and a surface of the second housing  120  facing the first housing  110  (the right side in this embodiment), and a head seal  400  may be press-fitted at a point where the first housing  110 , the second housing  120 , and the head flange  520  meet each other to prevent the leakage of air. 
     At this time, when the O-ring  300  and the head seal  400  are manufactured and installed as separate components, the O-ring  300  and the head seal  400  need to be installed separately, which results in a long assembling time. Also, during the O-ring  300  is installed, the location of the head seal  400  may be changed, and during the head seal  400  is installed, the location of the O-ring  300  may be changed, which leads to an assembly defect problem. Therefore, the O-ring  300  and the head seal  400  may be integrally connected by a plurality of bridges  410  as shown in this embodiment. 
     The third housing  130  has two air paths, that is, the wet air inlet  131  and the dry air outlet  132 , and to prevent the contact between the wet air passing through the wet air inlet  131  and the dry air passing through the dry air outlet  132 , the third housing  130  includes a wet airflow path  133  and a dry airflow path  134  which are separated from each other by a flow path dividing plate  135 . In this case, the wet airflow path  133  is configured to allow the space between the cartridge housing  210  and the membrane humidifier housing  100  to communicate with the wet air inlet  131 . In addition, the dry airflow path  134  is configured to allow the other end of the hollow fiber membrane cartridge  200  in the longitudinal direction thereof to communicate with the dry air outlet  132 . 
     In addition, to prevent the dry air that has passed through the interior of the hollow fiber membrane  220  from entering the wet airflow path  133 , an extension plate  240  may be formed on the other longitudinal side of the cartridge housing  210 . The extension plate  240  may extend in the radial direction of the hollow fiber membrane  220  to cover the dry airflow path  134 . The extension plate  240  is coupled to and in close contact with the end of the flow path dividing plate  135  that separates the wet airflow path  133  and the dry airflow path  134  from each other. Accordingly, the dry air that has passed through the hollow fiber membrane  220  and the wet air that has entered the wet airflow path  133  may not come into direct contact with each other. 
     Meanwhile, when wet air is in indirect contact with dry air with the hollow fiber membrane  220  therebetween and the wet air and the dry air exchange moisture, moisture condenses in the interior of the hollow fiber membrane  220  and falls down, and accordingly, condensed water may be deposited on the bottom of the dry airflow path  134 . When the flow rate of condensed water collected at the bottom of dry airflow path  134   increases above a certain level, humidity exchange between wet air and dry air may not be performed normally, and the membrane humidifier may be damaged. 
     Therefore, the membrane humidifier for fuel cell according to the present disclosure may include a bypass flow path for discharging the condensed water collected at the bottom of the dry airflow path  134  to the space between the cartridge housing  210  and the membrane humidifier housing  100 . The bypass flow path may have one end that is located near the bottom of the dry airflow path  134 , and another end that is located above the cartridge housing  210 . 
     At this time, since the pressure of the interior of the dry airflow path  134  is higher than the pressure of the interior of the wet airflow path  133 , the condensed water collected at the bottom of the dry airflow path  134  goes up along the bypass flow path and is discharged to the space between the cartridge housing  210  and the membrane humidifier housing  100 . The bypass flow path applied to this disclosure is not manufactured as a separate metal tube, but is integrally molded with the cartridge housing  210 . Accordingly, separate manufacturing costs or assembly costs may not occur. 
     The other side of the cartridge housing  210  in the longitudinal direction thereof (the right side in this embodiment) may be mounted directly on the third housing  130  rather than on the third housing  130  through a separate bulkhead  500  as a coupling medium. That is, the cartridge flange  215  located on the other longitudinal side of the cartridge housing  210  is in close contact with the end of the flow path dividing plate  135  as illustrated in  FIG.  10   , and to seal the contact portion between the cartridge flange  215  and the flow path dividing plate  135 , the O-ring  300  may be provided between the cartridge flange  215  and the flow path dividing plate  135 . Similarly, the head seal  400  may be provided at a portion where the first housing  110  contacts the third housing  130 , and the head seal  400  may be connected to and integrally formed with the O-ring  300  to increase the convenience of the assembly process. 
     Hereinafter, a membrane humidifier for a fuel cell according to another embodiment of the present disclosure will be described in detail with reference to  FIGS.  11  to  19   . 
       FIGS.  11  and  12    are a perspective view and a cross-sectional perspective view of a membrane humidifier for a fuel cell according to the present disclosure,  FIGS.  13  and  14    are a perspective view and an exploded perspective view showing a structure in which the bulkhead is coupled to opposite ends of the hollow fiber membrane cartridge  200 , and  FIG.  15    is a partial perspective view of the cartridge housing  210  included in the present disclosure. 
     The membrane humidifier for fuel cell according to the present disclosure is a type of humidifier configured such that moisture of wet air passing outside a hollow fiber membrane  220  is transferred to dry air passing through the inside of the hollow fiber membrane  220 , and the hollow fiber membrane  220  is not integrally coupled to the membrane humidifier housing  100 , but is placed inside the hollow fiber membrane cartridge  200  that is detachably coupled to the membrane humidifier housing  100 , wherein a plurality of hollow fiber membrane cartridges  200  are provided in the interior of a single membrane humidifier housing  100 . 
     That is, the membrane humidifier for fuel cell according to the present disclosure includes: a plurality of hollow fiber membrane cartridges  200 , each including a cartridge housing  210  formed in the shape of a hollow tube having openings facing opposite sides in the longitudinal direction and having a plurality of vent holes  212  on the side wall, the hollow fiber membrane  220  inserted into the interior of the cartridge housing  210  such that opposite ends thereof in the longitudinal direction face the openings of the cartridge housing  210 , and a resin layer  230  filling the inner space of the cartridge housing  210  on opposite sides thereof in the longitudinal direction such that opposite ends of the hollow fiber membrane  220  in the longitudinal direction thereof are exposed to the outside; a membrane humidifier housing  100  in which the hollow fiber membrane cartridges  200  are provided and which includes a wet air inlet  111  and a wet air outlet  112  communicating with the vent holes  212 , and a dry air inlet  121  and dry air outlet  132  communicating with the hollow fiber membrane  220 ; and a pair of bulkheads  500  which have edges that are mounted so as to be in close contact with the inner surfaces of opposite sides of the membrane humidifier housing  100  in the longitudinal direction thereof, and each of which has a plurality of mounting holes  510  which is formed in the central portion thereof and into which ends of the cartridge housings  210  in the longitudinal direction thereof are inserted. 
     As described above, when the hollow fiber membrane cartridges  200  are provided in the membrane humidifier housing  100  using the bulkhead  500  as a coupling medium, since the number of the hollow fiber membrane cartridges  200 , which are mountable, may be increased or decreased by increasing or decreasing the number of mounting holes  510  formed in the bulkhead  500 , the degree of freedom of the specification and number of the hollow fiber membrane cartridges  200  can be increased while commonly using the membrane humidifier housing  100 . In this embodiment, only a case in which three hollow fiber membrane cartridges  200  are provided on a pair of bulkheads  500  is illustrated, but the number of hollow fiber membrane cartridges  200  provided on a pair of bulkheads  500  may be 2 or 4 or more. 
     In addition, when the opposite ends of the hollow fiber membrane cartridge  200  in the longitudinal direction thereof are provided on the bulkhead  500  in the fitting manner, the assembly of the hollow fiber membrane cartridge  200  is facilitated and productivity is improved, and the replacement of the hollow fiber membrane cartridge  200  is simplified and thus the use thereof is convenient. 
     In addition, regarding the membrane humidifier for fuel cell according to the present disclosure, instead of completely filling the inner space of opposite sides of the membrane humidifier housing  100  in the longitudinal direction thereof with the resin layer  230 , only the inner space of opposite sides of the cartridge housing  210  in the longitudinal direction thereof is filled with the resin layer  230 . Accordingly, the use of resin layer  230 , which is expensive, can be significantly reduced, and the manufacturing costs of the product can be reduced. 
     Meanwhile, the membrane humidifier housing  100  includes: a first housing  110  which is formed in a hollow tube shape with open opposite sides in the longitudinal direction thereof and into which the hollow fiber membrane cartridge  200  is inserted; a second housing  120  coupled to cover one side (left side in this embodiment) of the first housing  110  in the longitudinal direction thereof; and a third housing  130  coupled to cover the other side in the longitudinal direction (the right side in this embodiment) of the first housing  110 . The wet air inlet  111  and the wet air outlet  112  may be formed in the first housing  110 , the dry air inlet  121  may be formed in the second housing  120 , and the dry air outlet  132  may be formed in the third housing  130 . 
     Therefore, the dry air introduced into the second housing  120  through the dry air inlet  121  passes through the cartridge housing  210  along the flow path inside the hollow fiber membrane  220  and is delivered to the interior of the third housing  130  and then is drawn out through the dry air outlet  132  (see the dotted arrow). In addition, the wet air flowing into the interior of the rear side (right side in this embodiment) of the first housing  110  through the wet air inlet  111 , enters the interior of the hollow fiber membrane cartridge  200  through the vent holes  212  and flows while being in contact with the outer surface of the hollow fiber membrane  220 , and is discharged to the outside through the wet air outlet  112 . 
     Meanwhile, protruding ribs  213  may be formed on an outer surface of a middle portion of the cartridge housing  210  in the longitudinal direction thereof and may divide the inner space of the membrane humidifier housing  100  into a front portion and a rear portion of the membrane humidifier housing  100 , and the vent holes  212  are formed on one side wall of the cartridge housing  210  in the longitudinal direction thereof and another side wall opposite to the side wall in the longitudinal direction thereof with respect to the protruding rib  213 . The wet air introduced through the wet air inlet  111  is not directly discharged through the wet air outlet  112 . Instead, the wet air may be introduced into the interior of the cartridge housing  210  through the vent holes  212  formed on the side wall of rear portion of the cartridge housing  210  (right side in this embodiment) and may flow toward the frontward, and then, passing through the vent holes  212  formed on the side wall of the front portion of the cartridge housing  210  (left side in this embodiment), the wet air is discharged through the wet air outlet  112 . 
     As such, when the dry air flows while in contact with the inner surface of the hollow fiber membrane  220  and the wet air flows while in contact with the outer surface of the hollow fiber membrane  220 , the moisture in the wet air is transferred to the dry air so that the dry air may be humidified. This humidification principle is the same as of the related art, and thus a detailed description thereof will be omitted. 
     In this regard, in this embodiment, the membrane humidifier housing  100  includes three housings, that is, the first housing  110 , the second housing  120 , and the third housing  130 . However, in one or more embodiments, the membrane humidifier housing  100  may consist of two housings or four or more housings, or a single housing. 
     Meanwhile, to prevent the resin layer  230  coupled to the cartridge housing  210  from being easily removed from the cartridge housing  210 , the cartridge housing  210  includes a locking protrusion  214  and a cartridge flange  215 . The locking protrusion  214  may be formed entirely over opposite ends of the cartridge housing  210  in the longitudinal direction and protrudes outward (specifically, toward the direction in which the protrusion is made along the lateral direction of the cartridge housing  210 ), and the cartridge flange  215  may be formed at a point spaced a certain distance from the locking protrusion  214 . 
     At this time, the locking protrusion  214  is provided to be completely embedded in the resin layer  230 . Accordingly, even when the resin layer  230  is not fixed on the surface of the cartridge housing  210  and peeled off, as long as the locking protrusion  214  is damaged, the coupling of the resin layer  230  to the cartridge housing  210  may be maintained. 
     Furthermore, of the side wall of the cartridge housing  210 , in a portion between the locking protrusion  214  and the cartridge flange  215 , a plurality of through-holes  216 , which is to be filled with the resin layer  230 , may be formed. The resin layer  230  is initially in a liquid state, and when in contact with the cartridge housing  210 , undergoes a curing process to be integrally coupled to the cartridge housing  210 . As described above, when the through-holes  216  are formed in a portion of the side wall of the cartridge housing  210  surrounded by the resin layer  230 , the resin layer  230 , which is a liquid state, fills the through-holes  216  in the process in which the resin layer  230  is brought into contact with the cartridge housing  210 . As a result, the bonding strength between the resin layer  230  and the cartridge housing  210  is very high. 
     In addition, the cartridge flange  215  formed on opposite sides of the cartridge housing  210  in the longitudinal direction thereof is a component for limiting the distance by which the hollow fiber membrane cartridge  200  is inserted into the bulkhead  500 , and the seating structure and function of the cartridge flange  215  will be separately described in detail with reference to different drawings. 
       FIG.  16    is a vertical cross-sectional view showing a structure in which a hollow fiber membrane cartridge  200  and a membrane humidifier housing  100  are coupled to each other using the bulkhead  500  as a coupling medium,  FIG.  17    is a perspective view of the O-ring  300  and the head seal  400  included in the present disclosure,  FIG.  18    is a perspective view of a pair of bulkheads  500  according to the present disclosure, and  FIG.  19    is a horizontal cross-sectional perspective view of the first housing  110  included in the present disclosure. 
     The hollow fiber membrane cartridge  200  is coupled to the bulkhead  500  in such a manner that opposite ends of the hollow fiber membrane cartridge  200  in the longitudinal direction thereof are inserted into the mounting holes  510  of the bulkhead  500 . In this regard, to limit the distance by which the hollow fiber membrane cartridge  200  is inserted, the cartridge flange  215  is formed on each of the opposite sides of the cartridge housing  210  in the longitudinal direction thereof. The cartridge flange  215  is in close contact with the surface of the bulkhead  500  (the right surface in this embodiment) when the end of the hollow fiber membrane cartridge  200  is inserted by a certain depth into the mounting holes  510 . Accordingly, the hollow fiber membrane cartridge  200  may not be more inserted into the mounting holes  510 . 
     At this time, the O-ring  300  may be press-fitted between the contact surface between the cartridge flange  215  and the bulkhead  500  to prevent the air from leaking at the contact surface of the cartridge flange  215  and the bulkhead  500 . The O-ring  300  is provided for each of the cartridge flange  215 . Accordingly, when three hollow fiber membrane cartridges  200  are provided as in this embodiment, a total of six O-rings  300  may be required. 
     In addition, the pair of bulkheads  500  each have a head flange  520  extending from a portion of the outer surface thereof being adjacent to the hollow fiber membrane cartridge  200 , and the second housing  120  and the third housing  130  each have a flange seating groove in which the head flange  520  is seated. The end of the first housing  110  in the longitudinal direction thereof is coupled to cover the head flange  520  seated in the flange seating groove, the head seal  400  is press-fitted at a point where the first housing  110 , the second housing  120 , and the head flange  520  meet, and a point where the first housing  110 , the third housing  130 , and the head flange  520  meet. 
     When the head seal  400  is provided at the point where the three components meet as described above, sealing is performed at once in-between the first housing  110  and the second housing  120 , in-between the first housing  110  and the head seal  400 , and in-between the second housing  120  and the head seal  400 . Accordingly, the number of parts for the membrane humidifier housing  100  is reduced and the interior configuration may be simplified. 
     At this time, in this embodiment, only the structure in which the first housing  110  is coupled to cover the head flange  520  seated in the flange seating groove of the second housing  120  is illustrated. However, a structure in which the first housing  110  is coupled to cover the head flange  520  seated in the flange seating groove of the third housing  130  is substantially the same as the structure of  FIG.  16   , except that only the direction is opposite. Accordingly, a detailed description thereof will be omitted. 
     At this time, when the O-ring  300  and the head seal  400  are manufactured and installed as separate components, the O-ring  300  and the head seal  400  need to be installed separately, which results in a long assembling time. Also, during the O-ring  300  is installed, the location of the head seal  400  may be changed, and during the head seal  400  is installed, the location of the O-ring  300  may be changed, which leads to an assembly defect problem. Therefore, three O-rings  300  and one head seal  400  may be integrally connected by a plurality of bridges  410  as shown in this embodiment. In one or more embodiments, when two hollow fiber membrane cartridges  200  are provided in the interior of one membrane humidifier housing  100 , two O-rings  300  and one head seal  400  are connected by bridges  410 , and when four hollow fiber membrane cartridges  200  are provided in the interior of the membrane humidifier housing  100 , four O-rings  300  and one head seal  400  may be connected by bridges  410 . That is, the number of O-rings  300  connected to one head seal  400  by bridges  410  may vary depending on the number of the hollow fiber membrane cartridges  200 . 
     In this regard, to allow the head seal  400 , the O-ring  300 , and the bridges  410  to be stably seated in the bulkhead  500 , a head seal seating groove  530 , an O-ring seating groove  540 , and a bridge seating groove  550  may be separately formed on a surface of the outer surface of the bulkhead  500  facing the center of the hollow fiber membrane cartridge  200 . 
     The hollow fiber membrane cartridges  200  are provided in the interior of the membrane humidifier housing  100  in such a manner that protruding ribs  213  are arranged in a stacked structure in close contact with each other. When, as illustrated in the present embodiment, the cross section of the protruding ribs  213  is formed in an elliptical shape and the inner surface of the first housing  110  is formed to be flat, the outer surface of the protruding ribs  213  and the inner surface of the first housing  110  may not be sealed. 
     Accordingly, hollow blocks  113  may be formed in a portion of the inner surface of the first housing  110  corresponding to the protruding ribs  213  in such a manner that the protruding ribs  213  stacked in close contact with each other are inserted thereinto in a fitting manner. The inner surface of the hollow block  113  may be conformed to the shape of the protruding ribs  213 . Accordingly, when the protruding ribs  213  are inserted into the hollow blocks  113  in the fitting manner, the outer surface of the protruding ribs  213  may be completely pressed on the inner surface of the hollow blocks  113 . 
     Hereinafter, a membrane humidifier for a fuel cell according to another embodiment of the present disclosure will be described in detail with reference to  FIGS.  20  to  28   . 
       FIG.  20    is a perspective view of a membrane humidifier for a fuel cell according to the present disclosure,  FIGS.  21  and  22    are an exploded perspective view and a perspective cross-sectional view of the hollow fiber membrane cartridge  200  and a fuel cell membrane humidifier having the same according to the present disclosure, and  FIG.  23    is a perspective cross-sectional view of a housing included in a membrane humidifier for a fuel cell according to the present disclosure. 
     The membrane humidifier for fuel cell according to the present disclosure is a humidifier configured such that moisture of wet air passing outside a hollow fiber membrane  220  is transferred to dry air passing through the inside of the hollow fiber membrane  220 , and the hollow fiber membrane  220  is not integrally coupled to the membrane humidifier housing  100 , but the hollow fiber membrane  220  is provided in a separate hollow fiber membrane cartridge  200 , and the hollow fiber membrane cartridge  200  is detachably coupled to the cartridge housing  210 . 
     The hollow fiber membrane cartridge  200  according to the present disclosure is formed in the shape of a hollow tube having openings facing the front and rear directions, and is detachably provided in the interior of the membrane humidifier housing  100 , and includes: one or more cartridge housings  210  each having a side wall with a plurality of vent holes  212  therein; a hollow fiber membrane  220  inserted into the interior of each of the cartridge housing  210 ; and a resin layer  230  which fills the inner space of opposite sides of the cartridge housing  210  in the longitudinal direction thereof so as to allow opposite ends of the hollow fiber membrane  220  in the longitudinal direction thereof to be exposed to the outside, and which covers the opposite ends and outer surfaces of opposite sides of the cartridge housing  210  in the longitudinal direction thereof. 
     In addition, the membrane humidifier for fuel cell according to the present disclosure includes, as basic components, a hollow fiber membrane cartridge  200  configured as described above, and the membrane humidifier housing  100  which is formed in the shape of a hollow tube having openings facing the front and rear directions, and which has the wet air inlet  111  and the wet air outlet  112  on side walls on opposite sides thereof in the longitudinal direction thereof. 
     As described above, in the membrane humidifier for fuel cell according to the present disclosure, a plurality of hollow fiber membrane cartridges  200  are detachably coupled to the membrane humidifier housing  100 . Accordingly, when the hollow fiber membrane  220  included in any one of the hollow fiber membrane cartridges  200  is damaged, only the corresponding hollow fiber membrane cartridge  200  is replaced and all other parts can be utilized. That is, the maintenance costs are significantly reduced. 
     In addition, regarding the membrane humidifier for fuel cell according to the present disclosure, instead of completely filling the inner space of opposite sides of the membrane humidifier housing  100  in the longitudinal direction thereof with the resin layer  230 , only the inner space of opposite sides of the cartridge housing  210  in the longitudinal direction thereof is filled with the resin layer  230 . Accordingly, the use of resin layer  230 , which is expensive, can be significantly reduced, and the manufacturing costs of the product can be reduced. 
     The membrane humidifier housing  100  is formed in a hollow tube shape in which opposite sides thereof in the longitudinal direction thereof are open, a pair of bulkheads  500  are coupled to the openings on opposite sides of the membrane humidifier housing  100 , and a pair of caps  600 , respectively having a dry air outlet  620  and a dry air inlet  610 , are coupled to cover the outside of the pair of bulkheads  500 . At this time, the bulkheads  500  are each formed with the mounting holes  510  into which the end of the cartridge housing  210  in the longitudinal direction thereof is inserted. 
     Therefore, the dry air introduced into each of the interior of the caps  600  through the dry air inlet  610  passes through the cartridge housing  210  along the flow path of the interior of the hollow fiber membrane  220  and is delivered to the interior of the other cap  600  through the cartridge housing  210 , and then, discharged to the outside through the dry air outlet  620 . 
     In addition, since protruding ribs  213  that divide the inner space of the membrane humidifier housing  100  into front and rear portions thereof, are formed on the outer surface of the middle portion of the cartridge housing  210  in the longitudinal direction thereof, the wet air introduced into the wet air inlet  111  is not discharged directly through the wet air outlet  112 , but flows into the interior of the cartridge housing  210  through the vent holes  212  formed on the side wall of the front side (left in this embodiment) of the cartridge housing  210  to flow the rearwards, and then drawn out to the interior of the cap  600  on the rear side through the vent holes  212  formed on the side wall of the rear side (right side in this embodiment) of the cartridge housing  210  and then discharged to the outside through the wet air outlet  112 . 
     As such, when the dry air flows while in contact with the inner surface of the hollow fiber membrane  220  and the wet air flows while in contact with the outer surface of the hollow fiber membrane  220 , the moisture in the wet air is transferred to the dry air so that the dry air may be humidified. This humidification principle is the same as of the related art, and thus a detailed description thereof will be omitted. 
     In this embodiment, only the structure in which the openings on opposite sides of the membrane humidifier housing  100  are closed with a pair of caps  600 . However, the structure of the membrane humidifier housing  100  is not limited as long as the membrane humidifier housing  100  includes the hollow fiber membrane cartridge  200  and the inside and outside thereof can be isolated from each other. 
     Even when a plurality of hollow fiber membrane cartridges  200  are provided in the interior of the membrane humidifier housing  100 , a partition wall  137  may be provided in the middle portion of interior of the membrane humidifier housing  100  in the longitudinal direction thereof so as to completely isolate the inner space of the membrane humidifier housing  100  into a front portion and a rear portion. The partition wall  137  is erected to cross the middle portion of the longitudinal direction of the membrane humidifier housing  100 , and insertion holes  139  are formed to allow the cartridge housing  210  to be inserted. Accordingly, the cartridge housing  210  is inserted into the insertion holes  139  in a fitting manner. At this time, the protruding ribs  213  formed on the outer surface of the middle portion of the cartridge housing  210  are in close contact with the inner surface of the mounting holes  510 , so that the wet air flowing into the inner space on the front side of the membrane humidifier housing  100  may not be delivered to the inner space of the rear side of the membrane humidifier housing  100  without passing through the interior of the cartridge housing  210 . 
     In addition, the head seal  400  sealing the gap between the outer surface of the bulkhead  500  and the inner surface of the caps  600  may be provided to prevent dry air from leaking in between the bulkhead  500  and the caps  600 . The coupling structure of the head seal  400  and the effects thereof will be described in detail with reference to  FIG.  28   . 
     In this embodiment, only the case where three hollow fiber membrane cartridge  200  are provided in the interior of one membrane humidifier housing  100 , the number, shape, and arrangement pattern of the hollow fiber membrane cartridge  200  provided in the interior of the membrane humidifier housing  100  may vary depending on the designer’s choice. 
     When manufacturing a membrane humidifier for fuel cell according to the present disclosure, first, a cartridge housing  210  which is formed in the shape of a hollow tube having openings facing opposite sides in the longitudinal direction and which has a side wall having a plurality of vent holes  212 , and a plurality of hollow fiber membranes  220  are inserted into the interior of the cartridge housing  210  in such a manner that the opposite ends of the cartridge housing  210  in the longitudinal direction thereof face the openings of the cartridge housing  210 , and then, the inner space of opposite sides of the cartridge housing  210  in the longitudinal direction thereof is filled with the resin layer  230  to expose the opposite ends of the hollow fiber membrane  220  in the longitudinal direction thereof to the outside, thereby completing the manufacture of the hollow fiber membrane cartridge  200 . When the hollow fiber membrane cartridge  200  is completely manufactured, the hollow fiber membrane cartridge  200  is inserted into the interior of the membrane humidifier housing  100  in which the wet air inlet  111  and the wet air outlet  112   communicating with the vent holes  212  are formed on opposite sides thereof in the longitudinal direction thereof, and the dry air inlet  610  and the dry air outlet  620  communicating with the hollow fiber membrane  220  are formed on opposite sides thereof in the longitudinal direction thereof, thereby completing the manufacture of a membrane humidifier for a fuel cell. 
     When the hollow fiber membrane cartridge  200  manufactured as described above is detachably provided in the interior of the membrane humidifier housing  100 , only the hollow fiber membrane cartridge  200  can be replaced, making maintenance and repairing easy, and by filling the resin layer  230  in the interior of the cartridge housing  210 , the resin layer  230  may be less used. In addition, since the hollow fiber membrane cartridge  200  can be manufactured in advance, the time required for manufacturing the membrane humidifier for fuel cell can be reduced. 
       FIG.  24    is a partial perspective view of a cartridge housing  210  included in a membrane humidifier for a fuel cell according to the present disclosure, and  FIGS.  25  and  26    are perspective and cross-sectional views illustrating a structure in which a hollow fiber membrane  220  and a resin layer  230  are coupled to the cartridge housing  210 . 
     In the membrane humidifier for fuel cell according to the present disclosure, the resin layer  230  not only fills the inner space on opposite sides of the cartridge housing  210  in the longitudinal direction, but also covers the ends of the cartridge housing  210  in the longitudinal direction thereof and some of the outer surfaces of opposite sides thereof in the longitudinal direction thereof. As such, when the resin layer  230  is coupled to cover the ends of the cartridge housing  210  in the longitudinal direction thereof and some of the outer surfaces of opposite sides thereof in the longitudinal direction, even when the membrane humidifier housing  100 , the cartridge housing  210 , and the resin layer  230  undergo thermal expansion and contraction repeatedly so that a gap may be formed between respective components, the wet air may not leak into the gap between the components. This will be described in detail with reference to  FIG.  28   . 
     Meanwhile, to prevent the resin layer  230  coupled to the cartridge housing  210  from being easily removed from the cartridge housing  210 , the cartridge housing  210  includes a locking protrusion  214  and a cartridge flange  215 . The locking protrusion  214  may be formed over the entire opposite ends of the cartridge housing  210  in the longitudinal direction thereof and projects outward (more specifically towards the inner surface of the mounting holes  510 ), and the cartridge flange  215  is spaced a distance from the locking protrusion  214 . 
     At this time, the locking protrusion  214  is provided to be completely embedded in the resin layer  230 . Accordingly, even when the resin layer  230  is not fixed on the surface of the cartridge housing  210  and peeled off, as long as the locking protrusion  214  is damaged, the coupling of the resin layer  230  to the cartridge housing  210  may be maintained. 
     Furthermore, of the side wall of the cartridge housing  210 , in a portion between the locking protrusion  214  and the cartridge flange  215 , a plurality of through-holes  216 , which is to be filled with the resin layer  230 , may be formed. The resin layer  230  is initially in a liquid state, and when in contact with the cartridge housing  210 , undergoes a curing process to be integrally coupled to the cartridge housing  210 . As described above, when the through-holes  216  are formed in a portion of the side wall of the cartridge housing  210  surrounded by the resin layer  230 , the resin layer  230 , which is a liquid state, fills the through-holes  216  in the process in which the resin layer  230  is brought into contact with the cartridge housing  210 . As a result, the bonding strength between the resin layer  230  and the cartridge housing  210  is very high. 
     In addition, when the resin layer  230  is provided to cover not only the locking protrusion  214  but also the cartridge flange  215 , when the cartridge housing  210  is inserted into the mounting holes  510  of the bulkhead  500 , the cartridge housing  210  may not directly contact the inner surface of the mounting holes  510 , so the bonding strength may be decreased slightly. Therefore, in the membrane humidifier for fuel cell according to the present disclosure, the protrusion height of the cartridge flange  215  is greater than the protrusion height of the locking protrusion  214 , and the resin layer  230  may cover up to a point where the cartridge flange  215  is formed from the outer surfaces of the opposite sides of the cartridge housing  210  in the longitudinal direction thereof. 
     When the end of the cartridge flange  215  is configured to be exposed to the outside as described above, since the end of the cartridge flange  215  is in close contact with the inner surface of the mounting holes  510 , when the cartridge housing  210  is coupled to the bulkhead  500 , the bonding strength between the cartridge housing  210  and the bulkhead  500  can be increased. 
       FIG.  27    is an exploded perspective view illustrating the coupling of the bulkhead  500  and the caps  600 , and  FIG.  28    is a vertical cross-sectional view of the membrane humidifier for a fuel cell according to the present disclosure, showing the directions in which the wet air and the dry air flow. 
     In the membrane humidifier for fuel cell according to the present disclosure, the gap between the resin layer  230  and the mounting holes  510  may be completely sealed. For example, the bulkhead  500  may include a protrusion  525  protruding from the entire outer end (left end in  FIG.  28   ) of the mounting holes  510 . 
     When the protrusion  525  is formed in the mounting holes  510  as described above, when the cartridge housing  210  is coupled to the bulkhead  500 , the outer edge of the resin layer  230  is in close contact with the protrusion  525 , so that the sealing force between the resin layer  230  and the mounting holes  510  may be increased. Furthermore, the O-ring  300  to seal between the protrusion  525  and the resin layer  230  may be additionally provided so as to more securely seal the gap between the resin layer  230  and the mounting holes  510 . 
     In addition, in order to further increase the adhesion between the resin layer  230  and the protrusion  525 , the resin layer  230  may have an outer edge that has the stepwise and bent shape, and the protrusion  525  may be mounted in such a way that an edge thereof is in close contact with the bent portion of the resin layer  230 . As described above, when the edge of protrusion  525  is coupled to be press-fitted to the stepped bent portion of the resin layer  230 , even when an external force and vibration are applied to the resin layer  230  or the bulkhead  500 , the coupling portion does not shake and the fixed state thereof can be maintained. In addition, the area in which the resin layer  230  contacts the bulkhead  500  may be increased and thus, the sealing force may be further enhanced. 
     Meanwhile, since the cartridge housing  210 , the resin layer  230 , and the bulkhead  500  have different coefficients of thermal expansion, when the cartridge housing  210 , the resin layer  230  and the bulkhead  500  are repeatedly heated and cooled, a fine gap may be formed at the contact surfaces of components, and accordingly, the wet air may enter the contact surfaces of respective components. At this time, in the case of the membrane humidifier for fuel cell according to the present disclosure, even when the wet air enters the contact surfaces of respective components, the wet air may be blocked by the O-ring  300  and the head seal  400 . Accordingly, the wet air may not flow toward the caps  600 , but return to the interior of the cartridge housing  210 . 
     That is, in the membrane humidifier for fuel cell according to the present disclosure, even when gaps are formed among components, the wet air and the dry air do not directly contact each other. Accordingly, the moisture transmission using the hollow fiber membrane  220  as a medium can be stably maintained. 
     In the membrane humidifier for fuel cell according to the present disclosure, since a plurality of hollow fiber membrane cartridges are detachably mounted in one membrane humidifier housing, the assembly and replacement of components are very easy, and since the resin layer is configured to fill only opposite sides of the hollow fiber membrane cartridge, the amount of the resin layer used can be reduced, leading to lower manufacturing costs. Also, since the airtightness of the wet air flow path and the dry air flow path is increased and thus, the humidification efficiency may be increased. 
     As described above, although the present disclosure has been described in detail using preferred embodiments, the scope of the present disclosure is not limited to specific embodiments, and should be interpreted by the appended claims. In addition, those skilled in the art should understand that many modifications and variations can be made without departing from the scope of the present disclosure.