Abstract:
A fuel cell system includes a fuel cell which generates electric energy by an electro-chemical reaction, a water tank which stores water from the fuel cell, an intake pipe which has an inlet port for introducing moisture-containing exhaust gas from the fuel cell into the water tank and is connected with the water tank, an exhaust pipe which has an exhaust port for exhausting gas from the water tank and is connected with the water tank, and a partition member which is provided in the water tank at a position lower than the inlet port for partitioning an interior of the water tank into an upper space and the lower space. The fuel cell system is capable of collecting water from the fuel cell easily and efficiently without depending upon a large component or decreasing power generation efficiency.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a fuel cell system and a transportation apparatus including the same, and more specifically to a fuel cell system in which water from the fuel cell is stored in a water tank, and a transportation apparatus such as a two-wheeled vehicle including such a fuel cell system. 
         [0003]    2. Description of the Related Art 
         [0004]    Conventionally, in the field of fuel cell systems, proposals have been made for techniques to collect water that has been discharged from the fuel cell. 
         [0005]    For example, Japanese Unexamined Patent Application Publication No. 2002-124290 discloses a water collector. In the method described in Japanese Unexamined Patent Application Publication No. 2002-124290, moisture-containing fuel gas from the fuel cell is introduced to a tubular path where a number of partitioning plates are disposed. According to the water collector disclosed in Japanese Unexamined Patent Application Publication No. 2002-124290, moisture-containing fuel gas moves through the tubular path while contacting the partitioning plates whereby water is separated from the fuel gas. Thereafter, the water is collected in a water tank while the fuel gas is exhausted from an exhaust port. 
         [0006]    However, the technique according to Japanese Unexamined Patent Application Publication No. 2002-124290 requires a water collector which includes a tubular path in which a plurality of partitioning plates are disposed. This poses a problem of increasing the size of the water collector. 
         [0007]    Further, in order to move the moisture-containing fuel gas while contacting many partitioning plates, a greater output is required for an air pump which introduces the fuel gas into the tubular path. As a result, power consumption by the air pump increases, which decreases power generation efficiency of the fuel cell system. 
         [0008]    On the other hand, in direct methanol fuel cell systems in particular, it is necessary that a large amount of water which flows into the water tank is efficiently collected and supplied to an aqueous solution tank. If the water tank is small and exhaust gas from the fuel cell is introduced into the water tank, there is a problem that the gust of exhaust gas blows the water out of the tank, thereby decreasing water collection efficiency. 
       SUMMARY OF THE INVENTION 
       [0009]    In order to overcome the problems described above, preferred embodiments of the present invention provide a fuel cell system that is capable of collecting water from the fuel cell easily and efficiently without requiring a large component and without decreasing power generation efficiency, and to provide a transportation apparatus including such a fuel cell system. 
         [0010]    According to a preferred embodiment of the present invention there is provided a fuel cell system which includes a fuel cell which generates electric energy, a water tank which stores water from the fuel cell, an inlet port for introducing moisture-containing exhaust gas from the fuel cell into the water tank, an exhaust port for exhausting gas from the water tank, and a partition member which is provided in the water tank at a position lower than the inlet port for partitioning an interior of the water tank into an upper space and a lower space. 
         [0011]    In this preferred embodiment of the present invention, by providing a partition member which divides the interior of water tank, an upper space in which moisture-containing exhaust gas is introduced from the intake pipe, and a lower space in which water is stored, are provided. Most of the exhaust gas flowing into the water tank at a high velocity contacts the partition member and swirls in the upper space, and the lesser remaining portion of the exhaust gas contacts the water stored in the lower space. As a result, it becomes possible to prevent the water in the water tank from being blown upwardly by the whirling gust of exhaust gas and being discharged from the exhaust port. Therefore, water can be collected easily and efficiently without increasing the volume of the water tank to decrease the velocity of gust of exhaust gas. In other words, water can be collected easily and efficiently using only a small water tank. Further, since there is no need for a large water collector, nor electric power to drive the collector, there is no decrease in power generation efficiency. In addition, if the amount of water in the water tank exceeds the volume of the lower space, water which overflows into the upper space is blown upwardly by the swirling gust of exhaust gas circulating in the upper space and is discharged from the exhaust port. This provides virtual water level adjustment, and therefore there is no need for a device which prevents water in the water tank from overflowing, nor electricity to drive the device, and there is no decrease in power generation efficiency in this respect also. 
         [0012]    Preferably, the partition member has a plurality of through-holes. In this case, water which is introduced into the upper space can easily flow down to the lower space through these through-holes, allowing for highly efficient water collection. Exhaust gas introduced from the fuel cell into the upper space is hot and contains water vapor. The through-holes provided in the partition member increase the exhaust gas cooling space by the volumes of the holes, facilitating condensation of the water vapor contained in the exhaust gas, thereby enabling more water to be collected. 
         [0013]    Further preferably, the partition member is spaced by a gap from an inner wall of the water tank. In this case, it becomes possible for the water which is introduced in the upper space to readily fall through the gap into the lower space, enabling efficient collection of the water. 
         [0014]    Further preferably, the fuel cell system further includes a projection which is arranged in the water tank so as to be spaced a predetermined distance from the partition member, blocking the gap between the inner wall of the water tank and the partition member in a vertical view. In this case, even if the gust of exhaust gas comes into the lower space and blows the stored water, the projection prevents the water from being blown upwardly. Therefore, water in the lower space is not blown upwardly into the upper space, thereby facilitating efficient collection of water. 
         [0015]    Preferably, the inlet port and the exhaust port do not face each other in the water tank. By offsetting the inlet port from the exhaust port so that they will not face each other in the water tank, it becomes possible to prevent water which is introduced from the inlet port, from immediately being blown into the exhaust port and being discharged therefrom, making it possible to collect water efficiently. 
         [0016]    Further, the fuel cell system also preferably includes a water level sensor for detecting a level of water in the water tank, which is preferably disposed at a position lower than the partition member in the water tank. In this case, the water level sensor detects the level of water in the water tank in the lower space which is not really subject to the effects of the swirling gusts of exhaust gas and therefore is able to reliably store water in a stable manner. Thus, it is possible to detect the level of water in the water tank accurately. 
         [0017]    Further, the partition member preferably has an upper surface that is slanted with respect to a surface of the water in the water tank. In this case, water which is introduced in the upper space flows on the upper surface of the partition member down into the lower space more easily, making water collection even more efficient. 
         [0018]    According to another preferred embodiment of the present invention, there is provided a fuel cell system which includes a fuel cell which generates electric energy by an electro-chemical reaction, a water tank which stores water from the fuel cell, and an intake pipe which has a trumpet-shaped inlet port for introducing moisture-containing exhaust gas from the fuel cell into the water tank and is connected with the water tank. 
         [0019]    According to this preferred embodiment of the present invention, the moisture-containing exhaust gas from the fuel cell is introduced into the water tank via the intake pipe which has a trumpet-shaped inlet port. This reduces the velocity of the moisture-containing exhaust gas as it enters the water tank, and thus reduces the speed of swirling gusts of exhaust gas that occur in the water tank. Therefore, water in the water tank is not blown upwardly easily, thereby enabling easy and efficient collection of water. 
         [0020]    In direct methanol fuel cell systems, the fuel cell is supplied directly with methanol aqueous solution, so direct methanol fuel cell systems do not require a reformer, and can have a simplified system configuration. For this reason, direct methanol fuel cell systems are used suitably in an apparatus in which portability is essential and/or smallness in size is desired. For the sake of size reduction of the direct methanol fuel cell systems and thus the apparatus which utilizes the direct methanol fuel cell systems, water discharged from the fuel cell must be collected efficiently into a small water tank. The present invention enables efficient water collection even for a small water tank, and therefore is particularly advantageous in direct methanol fuel cell systems which are utilized suitably in an apparatus in which portability is essential and/or smallness in size is desired. 
         [0021]    Since the present invention enables a significant reduction in the size of the water tank, and thus the size of the entire fuel cell system, the fuel cell system can be suitably utilized in a transportation apparatus. 
         [0022]    The above described objects and other objects, features, elements, aspects and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention when taken in conjunction with the accompanying drawings. 
         [0023]    Other features, elements, steps, advantages and characteristics of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is a schematic diagram showing a primary portion of a fuel cell system according to a preferred embodiment of the present invention. 
           [0025]      FIG. 2  is a perspective view which shows the fuel cell system mounted on a frame of a motorcycle. 
           [0026]      FIG. 3  is an illustrative drawing which shows a primary portion of the fuel cell system. 
           [0027]      FIG. 4  is a block diagram which shows an electrical construction of the fuel cell system. 
           [0028]      FIG. 5  is a side view which shows a water tank and its surrounding elements. 
           [0029]      FIG. 6  is an illustrative sectional view which shows the water tank and its surrounding elements. 
           [0030]      FIG. 7  is a plan view which shows the water tank and its surrounding elements. 
           [0031]      FIG. 8  is a rear view which shows a water tank and its surrounding elements. 
           [0032]      FIG. 9  is a sectional view taken along line A-A in  FIG. 5 . 
           [0033]      FIG. 10  is a side view which shows a water tank with a partition member slanted therein, and the surrounding elements of the tank. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0034]    Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. 
         [0035]    As shown in  FIG. 1  through  FIG. 4 , a fuel cell system  10  according to a preferred embodiment of the present invention is provided as a direct methanol fuel cell system. Direct methanol fuel cell systems do not require a reformer, and therefore are used suitably in an apparatus in which portability is essential and/or smallness in size is desired. Here, description will be made for a case in which the fuel cell system  10  is used in a motorcycle as an example of a transportation apparatus. Note that in  FIG. 2 , the motorcycle will be represented only by a vehicle frame  200 . The fuel cell system  10  is disposed along the vehicle frame  200 . 
         [0036]    Referring mainly to  FIG. 1 , the fuel cell system  10  includes a fuel cell  12 . The fuel cell  12  is constructed as a fuel cell stack including a plurality of direct methanol fuel cells connected (laminated) in series, each of which includes an electrolyte  12   a , and a pair of an anode (fuel electrode)  12   b  and a cathode (air electrode)  12   c  which sandwich the electrolyte  12   a.    
         [0037]    The fuel cell system  10  includes a fuel tank  14  which holds highly concentrated methanol fuel (aqueous solution containing approximately 50 wt % of methanol, for example) F. The fuel tank  14  is connected, via a fuel supply pipe  16 , with an aqueous solution tank  18  which stores methanol aqueous solution S. The fuel supply pipe  16  is provided with a fuel pump  20 . The fuel pump  20  supplies the aqueous solution tank  18  with the methanol fuel F from the fuel tank  14 . 
         [0038]    The fuel tank  14  is provided with a water level sensor  15  for detecting the level of methanol fuel F in the fuel tank  14 . The aqueous solution tank  18  is provided with a water level sensor  22  for detecting the level of methanol aqueous solution S in the aqueous solution tank  18 . The aqueous solution tank  18  is connected, via an aqueous solution pipe  24 , with the anode  12   b  of the fuel cell  12 . The aqueous solution pipe  24  is provided with an aqueous solution pump  26 , a heat exchanger  30  equipped with a cooling fan  28 , and an aqueous solution filter  32 , respectively from the upstream side. The methanol aqueous solution S in the aqueous solution tank  18  is pumped by the aqueous solution pump  26  toward the anode  12   b , cooled by the heat exchanger  30  as necessary, and then purified by the aqueous solution filter  32  before being supplied to the anode  12   b.    
         [0039]    On the other hand, the cathode  12   c  in the fuel cell  12  is connected with an air pump  34  via an air pipe  36 . The air pipe  36  is provided with an air filter  38 . Thus, air which contains oxygen is sent from the air pump  34 , purified by the air filter  38  and then supplied to the cathode  12   c.    
         [0040]    The anode  12   b  and the aqueous solution tank  18  are connected with each other via a pipe  40 , so unused methanol aqueous solution S and produced carbon dioxide that is discharged from the anode  12   b  are supplied to the aqueous solution tank  18 . 
         [0041]    Further, the cathode  12   c  is connected with the water tank  44  via a pipe  42 . The pipe  42  is provided with a gas-liquid separator  48  equipped with a cooling fan  46 . Exhaust gas which is discharged from the cathode  12   c  and contains moisture (water and water vapor) is supplied to the water tank  44  via the pipe  42 . 
         [0042]    The aqueous solution tank  18  and the water tank  44  are connected with each other via the CO 2  vent pipe  50 . The CO 2  vent pipe  50  is provided with a methanol trap  52  which separates the methanol aqueous solution S. The carbon dioxide that is discharged from the aqueous solution tank  18  is thus supplied to the water tank  44 . 
         [0043]    The water tank  44  is provided with a water level sensor  54 , which detects the level of water in the water tank  44 . The water tank  44  is provided with an exhaust gas pipe  56 . The exhaust gas pipe  56  emits carbon dioxide and the exhaust gas from the cathode  12   c.    
         [0044]    The water tank  44  is connected with the aqueous solution tank  18  via a water return pipe  58 . The water return pipe  58  is provided with a water pump  60 . Water in the water tank  44  is returned to the aqueous solution tank  18  by the water pump  60  as necessary depending on the status of the aqueous solution tank  18 . 
         [0045]    In the aqueous solution pipe  24 , a bypass pipe  62  is provided between the heat exchanger  30  and the aqueous solution filter  32 . 
         [0046]    Referring also to  FIG. 4 , in the fuel cell system  10 , the bypass pipe  62  is provided with a concentration sensor  64  for detecting the concentration of methanol aqueous solution S. A temperature sensor  66  for detecting the temperature of the fuel cell  12  is attached to the fuel cell  12  whereas an ambient temperature sensor  68  for detecting the ambient temperature is provided near the air pump  34 . 
         [0047]    As shown in  FIG. 4 , the fuel cell system  10  includes a control circuit  70 . 
         [0048]    The control circuit  70  includes a CPU  72  which performs necessary calculations and controls operations of the fuel cell system  10 , a clock circuit  74  which supplies a clock to the CPU  72 , a memory  76  provided by e.g., an EEPROM which stores programs and data necessary for controlling the fuel cell system  10  as well as calculation data, etc, a reset IC  78  which prevents malfunction of the fuel cell system  10 , an interface circuit  80  for connections with external devices, a voltage detection circuit  84  which detects voltages in an electric circuit  82  to which the fuel cell  12  is connected to a motor  202  to drive the motorcycle, an electric current detection circuit  86  which detects electric current flowing in the electric circuit  82 , an ON/OFF circuit  88  which opens and closes the electric circuit  82 , a voltage protection circuit  90  which prevents an over voltage condition in the electric circuit  82 , a diode  92  provided in the electric circuit  82 , and a power source circuit  94  which supplies a predetermined voltage to the electric circuit  82 . 
         [0049]    In the control circuit  70  as described above, the CPU  72  is supplied with detection signals from the concentration sensor  64 , the temperature sensor  66  and the ambient temperature sensor  68 . Further, the CPU  72  is supplied with detection signals from a roll-over switch  96  which detects whether or not the vehicle has rolled over. Further, the CPU  72  is supplied with other signals from an input unit  98  for making various settings and information entry. Still further, the CPU  72  is supplied with detection signals from the water level sensors  15 ,  22  and  54  as well. 
         [0050]    The CPU  72  controls various components such as the fuel pump  20 , the aqueous solution pump  26 , the air pump  34 , the heat-exchanger cooling fan  28 , the gas-liquid separator cooling fan  46  and the water pump  60 . The CPU  72  also controls a display  100  which displays various information to notify the motorcycle rider. 
         [0051]    The fuel cell  12  has a parallel connection with a secondary battery  102 . The secondary battery  102  also has a parallel connection with the motor  202 . The secondary battery  102  supplements the output from the fuel cell  12 , is charged with electric energy from the fuel cell  12 , and discharges to provide the motor  202  and other components with electric energy. 
         [0052]    The motor  202  is provided with a meter  204  which makes measurements for various data concerning the motor  202 . These data and status information about the motor  202  measured by the meter  204  are supplied to the CPU  72  via the interface circuit  104 . 
         [0053]    Next, the water tank  44  will be described in detail. 
         [0054]    As shown in  FIG. 2  and  FIG. 3 , the water tank  44  is made of FRP for example, is small so as to fit within a predetermined region in the vehicle frame  200 , and has a lower portion that bulges more than the upper portion. 
         [0055]    Referring to  FIG. 5  through  FIG. 9 , intake pipes  106 ,  108 , an exhaust pipe  110  and a discharge pipe  112 , each made of SUS  304 , for example, are inserted into the water tank  44 . 
         [0056]    The intake pipe  106  has a cylindrical portion  106   a  which goes into the water tank  44  from the front and slightly upper position of the water tank  44 , and a generally trumpet-shaped (funnel-shaped) opening portion  106   b  which faces downward in the water tank  44 . The opening portion  106   b  has an inlet port  114   b  whose opening is greater than an entrance  114   a  of the cylindrical portion  106   a . The cylindrical portion  106   a  is connected with the pipe  42 . 
         [0057]    The exhaust pipe  110  is a cylindrical pipe which goes into the water tank  44  from the back of the water tank  44 , and is disposed so that its exhaust port  115  is above an opening portion  106   b  of the intake pipe  106  in the water tank  44 . As described, the opening portion  106   b  and the exhaust pipe  110  are arranged so that the inlet port  114   b  and the exhaust port  115  do not face each other in the water tank  44 . The exhaust pipe  110  is connected with the exhaust gas pipe  56 . 
         [0058]    The intake pipe  108  is preferably a cylindrical pipe which goes into the water tank  44  from the upper surface corner of the water tank  44 , and is disposed above the exhaust pipe  110  in the water tank  44 . The intake pipe  108  is connected with the CO 2  vent pipe  50 . 
         [0059]    The discharge pipe  112  is preferably a cylindrical pipe which goes into the water tank  44  from the back and near the bottom of the water tank  44 . The discharge pipe  112  is connected with the water return pipe  58 . 
         [0060]    Therefore, moisture-containing exhaust gas which comes from the cathode  12   c  flows through the pipe  42  and the intake pipe  106 , into the water tank  44 . Carbon dioxide which comes through the aqueous solution tank  18  and the CO 2  vent pipe  50  flows into the intake pipe  108  and then to the water tank  44 . Water in the water tank  44  goes into the discharge pipe  112  and then flows into the water return pipe  58 . Exhaust gas which contains carbon dioxide in the water tank  44  flows through the exhaust pipe  110  and the exhaust gas pipe  56  and then is released to the outside. 
         [0061]    Further, a partition member (wind shield member)  116  is provided inside the water tank  44 . The partition member  116  is preferably made of SUS 304  for example, and includes a generally rectangular and plate-like separator  116   a  and a mounting tab  116   b  which is bent generally squarely with respect to the separator  116   a . The partition member  116  is fixed inside the water tank  44  by attaching the mounting tab  116   b  to an inner wall of the water tank  44  so that the separator  116   a  becomes generally horizontal. The separator  116   a  partitions the interior of water tank  44  into an upper space  118   a  and a lower space  118   b . In the upper space  118   a , there are the intake pipes  106 ,  108  and the exhaust pipe  110 . In the lower space  118   b , there is the discharge pipe  112 . 
         [0062]    The partition member  116  is attached at a height that is high enough for the lower space  118   b  to hold a sufficient amount of water necessary to supply to the aqueous solution tank  18 . Further, as shown in  FIG. 9 , the partition member  116  is positioned so that no parts of the partition member other than the mounting tab  116   b  make contact with the inside walls of the water tank  44 , i.e., so that all three outer sides of the separator  116   a  are spaced from the corresponding three inside walls of the water tank  44 , by a gap  120 . 
         [0063]    The separator  116   a  is preferably provided with a plurality (for example, twenty one in this preferred embodiment) of small-diameter through-holes  122   a  and a plurality (for example, thirteen in this preferred embodiment) of large-diameter through-holes  122   b . The small-diameter through-holes  122   a  face the inlet port  114   b , and are concentrated in an area that is blasted by moisture-containing exhaust gas from the inlet port  114   b . Preferably, the small-diameter through-holes  122   a  have a diameter of about 4 mm, and the large-diameter through-holes  122   b  have a diameter of about 6 mm, for example. By providing the small-diameter through-holes  122   a  in such a location, it becomes possible to collect water efficiently while reducing entry of the exhaust gas into the lower space  118   b.    
         [0064]    Further, as shown in  FIG. 6 , a projection (obstruction plate)  124  is provided on a front inner wall in the lower space  118   b , below the separator  116   a  and at a predetermined gap from the separator  116   a . When viewed vertically, the projection  124  appears to block the gap  120  between the front inner wall of the water tank  44  and the separator  116   a.    
         [0065]    In the lower space  118   b , there is disposed a water level sensor  54  provided by a float sensor for detecting the water level in the water tank  44 . As shown in  FIG. 8 , the water level sensor  54  includes a sensor main body  54   a  and a float portion  54   b  attached to the sensor main body  54   a . The water level sensor  54  is able to detect the water level in the lower space  118   b  as the float portion  54   b  floats up and down when the water level changes in the lower space  118   b.    
         [0066]    An example of the operation of the fuel cell system  10  during power generation will be described. 
         [0067]    When power generation is started, a highly concentrated methanol aqueous solution S which is stored in the aqueous solution tank  18  is pumped by the aqueous solution pump  26  toward the fuel cell  12 . The solution is cooled as necessary by the heat exchanger  30 , purified by the aqueous solution filter  32 , and then supplied to the anode  12   b . On the other hand, air which contains oxygen is pumped by the air pump  34  toward the fuel cell  12 . The air is purified by the air filter  38  and then supplied to the cathode  12   c.    
         [0068]    On the anode  12   b  in the fuel cell  12 , methanol and water in the methanol aqueous solution S react electro-chemically with each other to produce carbon dioxide and hydrogen ions. The hydrogen ions move through the electrolyte  12   a  to the cathode  12   c , where the hydrogen ions react electro-chemically with oxygen in the air which is supplied to the cathode  12   c , to produce water and electric energy. 
         [0069]    Carbon dioxide which occurs on the anode  12   b  in the fuel cell  12  flows through the pipe  40 , the aqueous solution tank  18 , the CO 2  vent pipe  50  and the intake pipe  108 , then supplied to the water tank  44 , and then it is exhausted from the exhaust gas pipe  56  via the exhaust pipe  110 . 
         [0070]    On the other hand, most of the water vapor occurring on the cathode  12   c  in the fuel cell  12  is liquefied and discharged in the form of water, with saturated water vapor being discharged in the form of gas. Part of the water vapor which was discharged from the cathode  12   c  is liquefied by lowering the dew point in the gas-liquid separator  48 . Moisture (water and water vapor) and unused air from the cathode  12   c  are supplied to the water tank  44  via the pipe  42  and the intake pipe  106 . Also, water which has moved to the cathode  12   c  due to the water crossover is discharged from the cathode  12   c  and supplied to the water tank  44 . Further, water and carbon dioxide which occurred at the cathode  12   c  due to the methanol crossover are discharged from the cathode  12   c  and supplied to the water tank  44 . 
         [0071]    It should be noted here that the term water crossover is a phenomenon in which a few mols of water moves to the cathode  12   c , accompanying the hydrogen ions which occur at the anode  12   b  and are moving to the cathode  12   c . The term methanol crossover is a phenomenon in which methanol moves to the cathode  12   c , accompanying the hydrogen ions which move to the cathode  12   c . At the cathode  12   c , the methanol reacts with air supplied from the air pump  34 , and thereby decomposes into water and carbon dioxide. 
         [0072]    The exhaust gas which contains moisture (water and water vapor) from the cathode  12   c  are pumped by the air pump  34  into the upper space  118   a  via the inlet port  114   b  of the intake pipe  106  as indicated by arrow W in  FIG. 5 . This causes a strong gust of exhaust gas in the water tank  44 . Most of the exhaust gas hits the separator  116   a  of the partition member  116  and swirls in the upper space  118   a , and thus does not flow very much into the lower space  118   b . Water which has been introduced from the inlet port  114   b  into the upper space  118   a  flows down through the small-diameter through-holes  122   a  and large-diameter through-holes  122   b  of the separator  116   a , as well as through the gap  120  between the separator  116   a  and the inner walls of the water tank  44 , and is stored in the lower space  118   b . If the water in the lower space  118   b  is blown upwardly by the gust of exhaust gas, the blown water hits the projection  124  as indicated by the arrow X in  FIG. 5 , so the water does not flow back in the upper space  118   a.    
         [0073]    Water which was collected in the water tank  44  is pumped by the water pump  60  and returned to the aqueous solution tank  18  via the water return pipe  58 , where it is reused as water for the methanol aqueous solution S. 
         [0074]    If the amount of water in the water tank  44  exceeds the volume of the lower space  118   b , the excess water which comes in the upper space  118   a  is blown upwardly by the swirling gusts of exhaust gas and discharged from the exhaust port  115  together with the exhaust gas. Thus, the amount of water in the water tank  44  is always at an appropriate level. 
         [0075]    The water vapor liquefying operation in the gas-liquid separator  48  is achieved by operating the cooling fan  46  and thereby lowering the dew point. This operation may be controlled based on an output from the water level sensor  54  provided in the water tank  44 . Such an arrangement enables a significant reduction in power consumption by the cooling fan  46 . 
         [0076]    According to the fuel cell system  10  described above, by providing the partition member  116 , water in the lower space  118   b  becomes much less affected by the gust of exhaust gas in the upper space  118   a , and thus it becomes possible to prevent the water in the water tank  44  from being blown upwardly by the swirling gusts of exhaust gas and discharged from the exhaust port  115 . 
         [0077]    Particularly in motorcycles, a large amount of exhaust gas is supplied to a small water tank. This significantly increases wind velocity in the water tank, and thus the water in the water tank can easily be blown upwardly and discharged. However, according to the fuel cell system  10 , by using the partition member  116 , it is possible to keep the lower space  118   b  undisturbed. This makes it possible to prevent unnecessary discharge of water, and to collect water easily and efficiently in a small water tank  44 . 
         [0078]    Further, there is no need for devices or for electric power to drive the devices for controlling the speed of the moisture-containing exhaust gas which blows into the water tank  44 , and thus power generation efficiency does not decrease. 
         [0079]    Further, if the amount of water in the water tank  44  exceeds the volume of the lower space  118   b , water which overflows into the upper space  118   a  is blown upwardly by the swirling exhaust gas in the upper space  118   a  and discharged from the exhaust port  115 , which means that the water level in the water tank  44  is controlled automatically. 
         [0080]    In addition, by providing a plurality of small-diameter through-holes  122   a  and a plurality of large-diameter through-hole  122   b  in the separator  116   a  of the partition member  116 , water which is introduced in the upper space  118   a  can fall through the small-diameter through-holes  122   a  and the large-diameter through-holes  122   b  into the lower space  118   b , enabling efficient collection of water. Also, the small-diameter through-holes  122   a  and the large-diameter through-hole  122   b  increase the space of the upper space  118   a  or the cooling space by their volumes, facilitating liquefaction of water vapor contained in the exhaust gas thereby enabling a great amount of water to be collected. 
         [0081]    Further, by arranging the partition member  116  so that there is a gap  120  between the inner wall of water tank  44  and the separator  116   a , it becomes possible for the water which is introduced in the upper space  118   a  to fall through the gap  120  into the lower space  118   b , enabling efficient collection of the water. 
         [0082]    Further, even if the swirling gust of exhaust gas comes into the lower space  118   b  and blows the stored water, the projection  124  prevents the water from being blown upwardly. Therefore, water in the lower space  118   b  is not blown upwardly to be discharged from the exhaust port  115 , facilitating efficient collection of water. 
         [0083]    Further, by offsetting the inlet port  114   b  from the exhaust port  115  so that they will not face each other in the water tank  44 , it becomes possible to let the exhaust gas which is introduced in the water tank  44  turn around before it is discharged. This prevents the moisture-containing exhaust gas, which is introduced from the inlet port  114   b  into the upper space  118   a , from immediately being blown into the exhaust port  115  and being exhausted therefrom, thereby making it possible to collect water efficiently. 
         [0084]    Generally in a small water tank, it is impossible to precisely detect the level of water since the swirling gust of exhaust gas which is introduced in the water tank disturbs the surface of water in the water tank. However, according to the fuel cell system  10 , the partition member  116  prevents the lower space  118   b  from being affected by the swirling gust of exhaust gas, making it possible to store water stably in the lower space  118   b  and to allow the water level sensor  54  to detect the level of water accurately in the water tank  44 . 
         [0085]    Further, when introducing the moisture-containing exhaust gas from the fuel cell  12  through the intake pipe  106 , the gas flows out of the trumpet-shaped inlet port  114   b  into the water tank  44 . This reduces the velocity of moisture-containing exhaust gas as it enters the water tank  44 , and thus reduces the speed of the gusts of exhaust gas which occurs in the water tank  44 . Therefore, water in the water tank  44  is not spattered easily, enabling efficient collection of water. Especially in the case of a motorcycle, the fuel cell system  10  must be small and therefore the pipe  42  cannot have a large diameter, which increases the speed of the flow. However, by utilizing the intake pipe  106  having the inlet port  114   b  which is trumpet-shaped, the speed of the flow can be effectively reduced. 
         [0086]    Further, as shown in  FIG. 10 , a partition member  126  may be fixed in the water tank  44  so that an upper surface of a separator  126   a  is slanted with respect to the water surface in the water tank  44 . With this arrangement, water which is introduced in the upper space  118   a  flows on the upper surface of the separator  126   a  down into the lower space  118   b , making water collection even more efficient. 
         [0087]    The size and the number of through-holes to be formed in the separator may be adjusted in accordance with the rate of water contained in the exhaust gas so that the water can be collected efficiently. 
         [0088]    It should be noted that as far as it is possible to let water flow from the upper space  118   a  to the lower space  118   b  and to prevent the water in the lower space  118   b  from being blown upwardly by the gust of exhaust gas, the partition member may be made of a corrugated plate, fine-mesh net, coarsely woven cloth, etc. 
         [0089]    Further, the projection  124  may be provided below the separator  116   a  and spaced by a predetermined gap from the separator  116   a  in the water tank  44 , so that the projection  124  appears to block the gap  120  entirely when viewed vertically. 
         [0090]    An inlet port for introducing exhaust gas from the fuel cell  12  into the water tank  44  and an exhaust port for exhausting gas from the water tank  44  may be provided in the wall of the water tank  44 , respectively. 
         [0091]    The fuel cell system  10  is suitably applied not only to motorcycles but also to any transportation apparatuses such as automobiles and marine vessels. 
         [0092]    The present invention is also applicable to fuel cell systems which make use of a methanol-water-vapor reformer, or fuel cell systems in which hydrogen is supplied to the fuel cell. Further, the present invention is applicable to small-scale, stationary-type fuel cell systems. 
         [0093]    The present invention being thus far described and illustrated in detail, it is obvious that these description and drawings only represent examples of preferred embodiments of the present invention, and should not be interpreted as limiting the invention. The spirit and scope of the present invention is only limited by words used in the accompanied claims. 
         [0094]    While the present invention has been described with respect to preferred embodiments thereof, it will be apparent to those skilled in the art that the disclosed invention may be modified in numerous ways and may assume many preferred embodiments other those specifically set out and described above. Accordingly, it is intended by the appended claims to cover all modifications of the present invention which fall within the true spirit and scope of the present invention.