Abstract:
A device includes a housing having a hollow center and a case having a hollow fiber membrane. The case is at least partially located inside the hollow center of the housing. A first gas flow flows to the hollow center through an introducing pipe and exits the housing via a discharging pipe. A second gas flow flows through the hollow fiber membrane in the case. The first gas flow enters the case through an inflow opening in the case from a gap between a wall of the housing and the case and exits the case through a discharging opening in the case to the gap between the wall of the housing and the case. The introducing pipe is located adjacent to a dividing wall. The device provides a humidifying property by transferring moisture from the first gas flow to the second gas flow or vice versa.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority to Japanese Patent Application No. 2005-228732, filed Aug. 5, 2005, the entire content of which is incorporated herein by reference. 
       TECHNICAL FIELD  
       [0002]    The invention relates to humidifying systems, and more particularly, but without limitation, to humidifying systems for fuel cells. 
       BACKGROUND 
       [0003]    Some fuel cells include a humidifying system to humidify inlet gasses. Humidifying systems are used in fuel cells to increase the average current density of a fuel cell. Inlet gasses require an optimal humidity level to produce the highest average current density possible for a particular fuel cell. One technique for increasing humidity of inlet gasses to reach an optimal level is to transfer moisture from the outlet gasses, which have high moisture content from water produced during the chemical reaction in the fuel cell, to the inlet gasses. 
         [0004]    A humidifying system used in a fuel cell system may use a hollow fiber membrane. A hollow fiber membrane provides pores on the inside of the hollow fiber membrane to separate moisture from a gas flow. The moisture of outlet gasses that flows inside the hollow fiber membrane is transferred to the outside of the hollow fiber membrane to humidify inlet gasses flowing on the outside of the hollow fiber membrane. 
       SUMMARY 
       [0005]    However, hollow fiber membranes are not particularly strong and are subject to fracture inside a humidifying system. Fracture of the hollow fiber membrane often occurs in areas of high airflow concentrations, such as at the inlets and outlets for gas flows through the humidifying system. 
         [0006]    To prevent the fracture of the hollow fiber membrane, high strength fibers may be located in areas of high airflow concentrations. However, high strength fibers tend to have a low humidifying property, which reduces the humidifying capacity of a humidifying system. 
         [0007]    In general, the invention provides a humidifying device that can effectively prevent the fracture of the hollow fiber membrane while maintaining a high humidifying property. According to time present invention, the humidifying device exchanges moisture between a gas flow that flows inside of the hollow fiber membrane and a gas flow that flows outside of the hollow fiber membrane. 
         [0008]    In one embodiment, the invention is directed to a device comprising a housing having an introducing pipe and a discharging pipe. A first gas flow flows into the housing through the introducing pipe. The first gas flow exits the housing through the discharging pipe. The device further comprises a fiber module that is covered by the housing, the fiber module having a case and a hollow fiber membrane stored in the case. The case includes an inflow opening through which the first gas flow flows into the case from a gap between a wall of the housing and the case, and a discharging opening through which the first gas flow flows from the case to the gap between the wall of the housing and the case, and a second gas flow flows through inside the hollow fiber membrane. The device further comprises a dividing wall that divides the gap into an introducing room and a discharging room. The inflow opening connects to the introducing room and the discharging opening connects to the discharging room. The position of the introducing pipe for the inflow opening is set toward the inside of the axial direction of the hollow fiber module or the position of the discharging pipe for the discharging opening is set toward the inside of the axial direction of the hollow fiber module. 
         [0009]    In another embodiment, the invention is directed to a device comprising a humidifying system and a fuel cell stack that receives a humidified gas flow from the humidifying system and outputs a humidifying gas flow gas flow to the humidifying system. The humidifying system includes a housing having a first hollow center and a case having a second hollow center. The housing includes an introducing pipe, wherein a first gas flow flows through the introducing pipe to the first hollow center, and a discharging pipe, wherein the first gas flow exits the first hollow center through the discharging pipe. The case is at least partially located inside the first hollow center of the housing. The case includes a hollow fiber membrane within the second hollow center, an inflow inlet connected to the hollow fiber membrane wherein a second gas flow flows through the inflow inlet to the hollow fiber membrane, a discharging outlet connected to the hollow fiber membrane wherein the second gas flow exits the hollow fiber membrane through the discharging outlet, an inflow opening through which the first gas flow flows into the case from a gap between a wall of the housing and the case, and a discharging opening through which the first gas flow flows from the case to the gap between the wall of the housing and the case. The humidifying system further includes a dividing wall that divides the gap into an introducing room and a discharging room. The inflow opening connects to the introducing room, and the discharging opening connects to the discharging room. The introducing pipe is located adjacent to the dividing wall. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0010]      FIG. 1  is an oblique perspective view illustrating a humidifying device of a first exemplary embodiment. 
           [0011]      FIG. 2   a  is a cross-sectional view illustrating a part of the inner structure of the humidifying device of the first exemplary embodiment. 
           [0012]      FIG. 2   b  is a partial cross-sectional view illustrating a hollow fiber module of the first exemplary embodiment. 
           [0013]      FIG. 3  is an oblique perspective view illustrating a humidifying device of a second exemplary embodiment. 
           [0014]      FIG. 4  is a cross-sectional view of the humidifying device of  FIG. 3 . 
           [0015]      FIG. 5   a  is an oblique perspective view illustrating a humidifying device of a third exemplary embodiment. 
           [0016]      FIG. 5   b  is an oblique perspective view illustrating the humidifying device of the third exemplary embodiment. 
           [0017]      FIG. 6  is an oblique perspective view illustrating a humidifying device of a fourth exemplary embodiment. 
           [0018]      FIG. 7  is an oblique perspective view illustrating a humidifying device of a fifth exemplary embodiment. 
           [0019]      FIG. 8  is an oblique perspective view illustrating a humidifying device of a sixth exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]      FIG. 1  is a perspective view illustrating the humidifying device  1  of a first exemplary embodiment. Also,  FIG. 2   a  is a cross-sectional view illustrating a part of the inner structure of the humidifying device  1 .  FIG. 2   b  is a partial cross-sectional view illustrating a hollow fiber module  2 . The humidifying device  1  may be used in a fuel cell system. 
         [0021]    A fuel cell system has a fuel cell, which produces electric power by generating an electrochemical reaction wherein hydrogen gas, which becomes the fuel, and air, which becomes oxidant, are supplied. The fuel cell has an electric power-generating unit including a cell with a fuel pole where hydrogen gas is supplied and an air pole where air is supplied. As the electrolyte of each cell, a solid high molecule type is often used considering densification of energy, decrease of the cost and reduction in weight. For example, a solid high molecular membrane may include an electrolyte made of an ion (proton)-conducting high molecular membrane such as fluorine resin group ion-exchange membrane and functions as the ion-conducing electrolyte by being saturated and hydroscopic. 
         [0022]    In the fuel cell system, hydrogen gas and air in a humidified state are inlet gasses to humidify the solid high molecular electrolyte membrane. Humidifying device  1  of the present embodiment is used for humidifying hydrogen gas and air, which are supplied to the fuel cell stack in the fuel cell system. 
         [0023]    Humidifying device  1  of the present embodiment humidities sweep gas D by exchanging water between humidified gas flow W, that is, hydrogen gas or air (hereinafter called off-gas) discharged from the fuel cell stack (not shown) and dry gas flow D, that is, hydrogen gas or air (hereinafter called sweep gas) supplied to the fuel cell stack. As shown in  FIG. 1 , humidifying device  1  comprises a hollow fiber module  2 , an introducing pipe  11 , which introduces gas (sweep gas D in the present embodiment) to the hollow fiber module  2 , and a discharging pipe  12 , which discharges gas (sweep gas D), which is humidified by passing through hollow fiber module  2  to the outside through hollow fiber module  2 . 
         [0024]    As shown in  FIG. 1 , hollow fiber module  2  includes water permeable hollow fiber membranes  3  stored in cylindrical case  4 . Case  4  is shaped as a cylinder with open edges, and inflow openings  5  and discharging openings  6  of sweep gas D are placed on the outer peripheral wall of the case in the vicinity of the edges in the axial direction. Hollow fiber membrane  3  has a number of microscopic capillary tubes, which reach from the inside to the outside. Gaps among each of the hollow fiber membranes  3  in both of the edges of case  4  are sealed by potting material (sealing material). 
         [0025]    In the hollow fiber module  2 , off-gas W, which is discharged from the fuel cell stack flows through inflow inlet  7  at one of the edges of hollow fiber module  2  and is discharged from discharging outlet  8  at the other edge of hollow fiber module  2 . In hollow fiber module  2 , the off-gas W flows to the inside of hollow fiber membrane  3 . Also, sweep gas D enters through inflow openings  5 , which are in one edge of hollow fiber module  2 , and is discharged from the other edge of discharging openings  6 . 
         [0026]    The humidifying device  1  exchanges water between a first gas flow (gas), which flows outside hollow fiber membrane  3  and humidifies the dried gas flow, and a second gas flow (gas), which flows inside hollow fiber membrane  3 . According to the present embodiment, sweep gas D, which flows outside hollow fiber membrane  3 , corresponds to the first gas flow, while off-gas W, which flows inside hollow fiber membrane  3 , corresponds to the second gas flow. 
         [0027]    The inflow opening  5  is the entrance of hollow fiber module  2  for sweep gas D, which is supplied to the fuel cell stack, and is located in the vicinity of one edge, which is the side of hollow fiber module  2  in which the off-gas is discharged. The inflow openings  5  are created at intervals on the outer circumferential wall of case  4  in the circumferential direction. Also, discharging opening  6  is the exit of the hollow fiber module  2  for sweep gas D and is located in the vicinity of the other edge, which is the side of hollow fiber module  2  in which the off-gas enters. The same number of discharging openings  6  as that of the inflow openings  5  is created on the outer circumferential wall of case  4 , 
         [0028]    Cylindrical housing  10  covers at least the outer circumference of the hollow fiber module  2 . Introducing pipe  11  and discharging pipe  12  are connected to the peripheral wall of the housing  10  in the position diagonal to the circumferential direction. Introducing pipe  11  is connected to the peripheral wall of housing  10  to connect to gap  15  between housing  10  and case  4 . Through the gap  15 , introducing pipe  11  introduces sweep gas D to the inside hollow fiber membrane  2  from inflow openings  5 . Also, discharging pipe  12  is connected to the peripheral wall of housing  10  so that it is connected with gap  15 . Through gap  15 , discharging pipe  12  discharges sweep gas D, which has passed through hollow fiber module  2 , to the outside of hollow fiber module  2 . 
         [0029]    Between housing  10  and case  4 , dividing wall  13  divides a circular space created by the gap  15  into an introducing side (introducing room  15   a ) where introducing pipe  11  and inflow openings  5  are placed and a discharging side (discharging room  15   b ) where discharging pipe  12  and discharging openings  6  are placed. 
         [0030]    Here, as shown in  FIG. 1 , in humidifying device  1  the position at which introducing pipe  11  is connected to housing  10  for inflow openings  5  is set towards the inside of the axial direction of hollow fiber module  2  (axial direction of case  4 ). In other words, the position at which introducing pipe  11  is connected to housing  10  for inflow openings  5  is set in the side of discharging openings  6  in the axial direction of hollow fiber module  2 . That is, the distance of the introducing pipe  11  and the discharging openings  6  along the axial direction of the case is shorter than the distance of the inflow openings  5  and the discharging openings  6  along the axial direction of the case. Also, the position at which discharging pipe  12  is connected to housing  10  for discharging openings  6  is set towards the inside of the axial direction of hollow fiber module  2 . In other words, the position at which discharging pipe  12  is connected to housing  10  for discharging openings  6  is set in the side of inflow openings  5  in the axial direction of hollow fiber module  2 . 
         [0031]    According to the present embodiment, since the position at which introducing pipe  11  is connected to housing  10  is set as described above, the flow path of sweep gas D from introducing pipe  11  to inflow openings  5  becomes curved. As a result, it is possible to uniformly disperse sweep gas D from introducing pipe  11  and to introduce the gas to each inflow opening  5 , thereby decreasing the likelihood of broken threads inside hollow fiber module  2 . At the same time, since it is possible to almost uniformly introduce sweep gas D to each inflow opening  5 , the flow path of sweep gas D inside hollow fiber module  2  is almost uniform, which provides good humidifying properties. 
         [0032]    Since the introducing pipe  11  can be placed away from inflow openings  5 , it is possible to increase the degree of freedom of the layout including introducing pipe  11 . It is also possible to apply the fact to the discharging side (discharging room  15   b ). That is, it is possible to increase the effect of preventing the broken thread caused by concentration of the inflow of sweep gas D not only in the side of introducing pipe  11  but also in the vicinity of discharging pipe  12 . Here, the present embodiment has a condition that the introducing pipe for the inflow openings is located in the side of the discharging openings along the axial direction of the hollow fiber module. 
         [0033]    Conversely, when the introducing pipe for the inflow openings is located in the side opposite to the discharging openings in the axial direction of the hollow fiber module, the flow from the introducing pipe to the inflow openings has the same direction as the flow inside the hollow fiber module. Therefore, dispersion of the gas is not effectively made while the gas flows from the introducing pipe to the inflow openings, the gas flow concentrates on the inflow openings, which are next to the introducing pipe and easier for the gas to flow in, and the gas flows linearly. As a result, the effective effect obtained in the present embodiment may not be obtained. 
         [0034]      FIG. 3  is an oblique perspective view illustrating the substantial part of the humidifying device of the second exemplary embodiment.  FIG. 4  is a cross-sectional view of the substantial part of  FIG. 3 . 
         [0035]    As shown in  FIGS. 3 and 4 , in humidifying device  11 B of the second exemplary embodiment, the positions of housing  10  and case  4  of hollow fiber module  2  in the radial direction are not coaxial. That is, by moving (decentering) the center axis of housing  10  and that of case  4 , the size of gaps  15  between housing  10  and case  4  is decreased in the side where introducing pipe  11  is connected and increased in other parts. As a result, the size of a part of circularly-continuing gaps  15 , which is closer to introducing pipe  11 , is minimum size d 1 , mid the size of its opposite side is maximum size d 2 . As a result, the cross-sectional area of the path from introducing pipe  11  to inflow opening  5 , which is located next to the introducing pipe  11 , is decreased, and as inflow opening  5  is located further from introducing pipe  11 , the cross-sectional area of the path from introducing pipe  11  is increased, 
         [0036]    According to humidifying device  1 B of the second exemplary embodiment, since gap  15  between housing  10  and case  4  is small in the vicinity of introducing pipe  11  compared with the structure where the size of the gap in the circumference is uniform as in the case of the humidifying device of the comparative example, it is possible to limit the flow of the gas flow to inflow opening  5 , which is located close to introducing pipe  11  where the flow of sweep gas D easily concentrates. Also, it is possible to almost uniformly disperse sweep gas D in each of inflow openings  5  and further improve the effect of preventing the broken thread caused by the concentration of the flow of sweep gas D. 
         [0037]    As for the discharging side, it is possible to obtain the same effect by placing the parts in a similar manner as described above. 
         [0038]    Moreover, when it is not possible to freely determine the offset amount of introducing pipe  11  to inflow opening  5  and that of discharging pipe  12  to discharging opening  6  due to conditions limiting the placement of the equipment, if the structure of the second exemplary embodiment is used, the degree of the decentering of the center axis of housing  10  to the center axis of case  4  can make it possible to supplement the shortness of the offset amount. 
         [0039]    Also, even when there is a condition limiting the placement of introducing pipe  11  as in the case of the third exemplary embodiment, if the structure of the second exemplary embodiment is used it is possible to effectively decrease the broken threads. 
         [0040]      FIG. 5   a  is ail oblique perspective view illustrating the substantial part of the humidifying device of the third exemplary embodiment, and  FIG. 5   b  is a cross-sectional view of its substantial part. 
         [0041]    In humidifying device  1 C of the third exemplary embodiment, due to the relation to the peripheral devices of humidifying device  1 C, introducing pipe  11  and discharging pipe  12  are placed in almost the same position in the circumferential direction of housing  10 . When introducing pipe  11  and discharging pipe  12  are placed in almost the same position in the circumferential direction of housing  10 , gas D easily flows into inflow openings  5  located next to introducing pipe  11  and at the same time gas is easily discharged from discharging openings  6  located next to discharging pipe  12 . As a result, the flow of gas inside hollow fiber module  2  becomes especially disproportionate. However, in the third exemplary embodiment, the same structure as that of the second exemplary embodiment is used to decenter the center axis of case  4  towards the side of introducing pipe  11  and discharging pipe  12  with respect to the center axis of housing  10 . As a result, it is possible to limit the inflow of gas D into inflow opening  5 , which is located closer to introducing pipe  11  where gas D easily concentrates, and to limit the flow of gas D from discharging opening  6 , which is located closer to discharging pipe  12 , thereby effectively decreasing the broken thread even in the case where there is limitation in placing introducing pipe  11  and discharging pipe  12 . 
         [0042]      FIG. 6  is an oblique perspective view illustrating the substantial part of the humidifying device of the fourth exemplary embodiment. 
         [0043]    In humidifying device  1 D of the fourth exemplary embodiment, the position of dividing wall  13  is moved from the position that evenly divides inflow openings  5  and discharging openings  6 . For example, when the average flow rate in the introducing side where sweep gas D is introduced through introducing pipe  11  is faster than in the discharging side where sweep gas D is discharged through discharging pipe  12 , dividing wall  13  is located towards the discharging side in the axial direction of hollow fiber module  2 . Conversely, when the average flow rate in the discharging side is faster than in the introducing side, dividing wall  13  is located towards the introducing side in the axial direction of hollow fiber module  2 . The example shown in  FIG. 6  illustrates the latter case. 
         [0044]    Due to the differences in the temperature and pressure conditions before and after hollow fiber module  2 , the average flow rate of the gas flow in the introducing side and discharging side does not always coincide. As a result, the frequency of the broken thread in the introducing side may be different from that of the discharging side. In humidifying device  1 D of the present embodiment, the position of dividing wall  13  between housing  10  and case  4  is moved in the axial direction as described above. As a result, it is possible to distribute the load to the part where the flow rate is faster and the part where the flow rate is slower, thereby improving the anti-thread breakage in the entire humidifying device. 
         [0045]      FIG. 7  is an oblique perspective view illustrating the substantial part of the humidifying device of the fifth exemplary embodiment. 
         [0046]    In humidifying device  1 E of the fifth exemplary embodiment, dividing wall  13  is located diagonally to the axial direction of hollow fiber module  2 . By diagonally placing dividing wall  13 , the distance between inflow opening  5  and dividing wall  13  or the distance between discharging opening  6  and dividing wall  13  is enlarged both in the side where introducing pipe  11  is connected and the side where discharging pipe  12  is connected. 
         [0047]    Therefore, it is possible to increase the offset amount when introducing pipe  11  and discharging pipe  12  are connected to housing  10 . By increasing the offset amount both in the introducing side (introducing room  15   a ) and discharging side (discharging room  15   b ), it is possible to further improve the anti-thread breakage. As a result, the humidifying device is effective when the target life span to the average flow rate of sweep gas and the strength of the thread is high. 
         [0048]      FIG. 8  is an oblique perspective view illustrating the substantial part of the humidifying device of the sixth exemplary embodiment. 
         [0049]    In humidifying device  1 F of the sixth exemplary embodiment, introducing pipe  11  is located opposite to discharging pipe  12  in the circumferential direction of housing  10 . Introducing pipe  11  and inflow openings  5  are placed in the same side, and discharging pipe  12  and discharging openings  6  are placed in the same side. Introducing pipe  11  and inflow openings  5  are placed opposite to discharging pipe  12  and discharging openings  6  in the axial direction. 
         [0050]    Dividing wall  13  is located almost parallel to the axial direction of hollow fiber module  2  and, by dividing the space created by gap  15  between housing  10  and case  4  in the direction of the diameter of housing  10  and case  4 , the dividing wall  13  creates the introducing side (introducing room  15   a ), which contains introducing pipe  11  and inflow openings  5 , and the discharging side (discharging room  15   b ), which contains discharging pipe  12  and discharging openings  6 . 
         [0051]    In humidifying device  1 F, by placing dividing wall  13  almost parallel to the longitudinal direction of the housing (almost parallel to the axial direction of hollow fiber module  2 ), introducing pipe  11  and inflow openings  5  are placed in both sides of housing  10  in the longitudinal direction and at the same time discharging pipe  12  and discharging openings  6  are placed in both sides of housing  10  in the longitudinal direction, thereby simultaneously securing the maximum offset amount both in the side of introducing pipe  11  and that of discharging pipe  12 . As described above, since the maximum offset amount of introducing pipe  11  and discharging pipe  12  can be secured, in the present embodiment it is possible to further increase the anti-thread breakage. Here, it is preferable to use the sixth exemplary embodiment when inflow openings  5  and discharging openings  6  can be placed in an area that is half the area of the circumference of case  4 ; each individual inflow opening  5  and discharging opening  6  can be made in a large size, and its necessary circulating ability can be secured. 
         [0052]    As another embodiment, for example, when the pipe diameter of introducing pipe  11  and that of discharging pipe  12  are different, the offset length of inflow opening  5  or discharging opening  6  with a smaller pipe diameter is made larger than the offset length of inflow opening  5  or discharging opening  6  with a larger pipe diameter. The offset length of inflow opening  5  is the distance between inflow opening  5  and introducing pipe  11 . Similarly the offset length of discharging opening  6  is the distance between discharging opening  6  and discharging pipe  12 . 
         [0053]    By increasing the offset length of introducing pipe  11  or discharging pipe  12  in the side where the flow rate around the pipe entrance is fast, it is possible to decrease the diameter of introducing pipe  11  and discharging pipe  12  without increasing the distribution of the flow of the gas flow in hollow fiber module  2  as a whole while maintaining the anti-bread breakage. 
         [0054]    When the cross-sectional shapes of introducing pipe  11  and discharging pipe  12  are different, the offset length of inflow opening  5  or discharging opening  6  with a faster flow rate is made larger than the offset length of inflow opening  5  or discharging opening  6  with a slower flow rate. 
         [0055]    By increasing the offset length of the introducing pipe or the discharging pipe in the side where the flow rate around the pipe entrance is fast, it is possible to make introducing pipe  11  and discharging pipe  12  in shapes other than the cylindrical shape, for example an ellipse, without increasing the distribution of the gas flow in hollow fiber module  2  as a whole while maintaining the anti-thread breakage properties. 
         [0056]    Here it is described that the second gas flow, which flows inside hollow fiber membrane  3 , is a humidifying gas flow (off-gas W), and the first gas flow, which flows outside hollow fiber membrane  3 , is a dry gas flow (sweep gas D). Conversely, the second gas flow, which flows inside hollow fiber membrane  3 , may be a dry gas flow (sweep gas D), and the first gas flow, which flows outside hollow fiber membrane  3 , may be a humidified gas flow (off-gas W). In this case, it is possible to obtain the similar effect. 
         [0057]    In a structure where the introducing pipe is connected towards the inflow opening in the axial direction, and where the offset length is L 1 , the maximum offset length is L 1 max, and the minimum offset length is L 1 min, it is preferable to set the range as L 1 max&gt;L 1 &gt;L 1 min. When the position where the introducing pipe is connected to the housing is set so that the range is L 1 min&gt;L 1 , the gas flow from the introducing pipe may concentrate on the inflow opening, which is close to the introducing pipe. 
         [0058]    On the other hand, when the position where the introducing pipe is connected to the housing is set so that the range is L 1 &gt;L 1 max, another gas flow is generated in the process where, after the gas flow enters the inside of the housing, it flows to the inflow openings. As a result, a large dispersing effect may not be obtained. Also, it is preferable to use the offset length with which the gas flow introduced through the introducing pipe does not directly enter the inflow openings, that is, the offset length with which the side edge of the inflow opening of the introducing pipe does not coincide with the side edge of the introducing pipe of the inflow opening. 
         [0059]    Based on the same reason described below, in the structure where the discharging pipe is connected towards the discharging opening in the axial direction, and where the offset length is L 2 , the maximum offset length is L 2 max, and the minimum offset length is L 2 min, it is preferable to set the range as L 2 max&gt;L 2 &gt;L 2 min. Also, it is preferable to use the offset length with which the gas flow discharged from the discharging openings is not directly discharged to the discharging pipe, that is, the offset length with which the side edge of the discharging pipe of the discharging opening does not coincide with the side edge of the discharging opening of the discharging pipe.