Patent Publication Number: US-2012036869-A1

Title: Portable refrigerator with fuel cell system and operating method thereof

Description:
CROSS-REFERENCE TO A RELATED APPLICATION 
     Pursuant to 35 U.S.C. §119(a), this application claims the benefit of earlier filing date and right of priority to Korean Application 10-2010-0079005, filed on Aug. 16, 2010, the content of which is incorporated by reference herein in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a portable refrigerator with a fuel cell system and an operating method thereof, and particularly, to a portable refrigerator is using a fuel cell as an energy source. 
     2. Background of the Invention 
     A portable refrigerator is configured to be easily carried with a smaller volume than a general refrigerator for home or commercial uses. This portable refrigerator is being used as a refrigerator for leisure or medical uses. 
     The portable refrigerator may be classified according to a cooling method. The cooling method may include a method using a vapor compression type cooling cycle, and a method using a thermoelectric element. The method using a vapor compression type cooling cycle has an advantage of high energy efficiency. However, the method has disadvantages such as a complicated structure and a large volume. Accordingly, the method using a thermoelectric element is being widely adopted. 
     The method using a thermoelectric element adopts the Peltier effect that heat absorption and heat release (dissipation) simultaneously occur from contact points between two conductors when a current flows. Here, a heat absorption phenomenon is applied to a cooling operation. The method using a thermoelectric element has a lower energy efficiency than the method using a vapor compression type cooling cycle. However, the method using a thermoelectric element implements a simplified structure and a small size due to no additional components, and can precisely control a cooling capacity. 
     Furthermore, the method using a thermoelectric element is not influenced by a gravitational direction when a cooling system is applied. Besides, the method using a thermoelectric element has an eco-friendly characteristic due to no refrigerant. Accordingly, the method using a thermoelectric element is suitable for is medical uses, especially. 
     In order to operate a portable refrigerator using a thermoelectric element, a battery is generally used as a power source. However, the conventional portable refrigerator using a battery has the following problems. Firstly, when a battery of a large capacity is used to supply high power for operating the thermoelectric element, the entire system has a large volume to degrade a portable characteristic. Secondly, when the battery is consumed up, it takes a lot of time to charge the battery. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide a portable refrigerator capable of supplying a sufficient amount of power and capable of being easily carried. 
     Another object of the present invention is to provide an operating method of a portable refrigerator. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a portable refrigerator with a fuel cell system, comprising: a case having a storage space; a fuel cell stack disposed in the case; a gas tank configured to store gas necessary to operate the fuel cell stack; a fan configured to cool the fuel cell stack and supply air to the fuel stack; a thermoelectric cooling means disposed in the case, and configured to cool the storage space; a battery charged by the fuel cell stack, and configured to supply power to the thermoelectric cooling means; and a controller configured to control the fuel cell is stack and the thermoelectric cooling means. 
     As a power source of the portable refrigerator, a fuel cell may be used. Inside of the case may be divided into two spaces. One space may be utilized as a storage space, and another space may be utilized as a space for each component necessary to drive the fuel cell and cooling means for cooling the storage space. This may allow the portable refrigerator to have a compact and portable structure. 
     The fuel cell may include PAFC (Phosphoric Acid FC), MCFC (Molten Carbonate FC), SOFC (Solid Oxide FC), DMFC (Direct Methanol FC) and PEMFC (Proton Exchange Membrane FC) according to a type of an electrolyte and a fuel. In the present invention, the PEMFC may be used as a driving source. 
     The PEMFC may be operated by a principle that electricity is generated by a catalytic reaction between hydrogen of an anode side and oxygen of a cathode side, and water and heat are generated by a chemical reaction between the hydrogen and the oxygen. This PEMFC may have a high output density, a low operation temperature less than 100° C., less restrictions on an installation place, and a small size due to a simplified configuration. The PEMFC may be a fuel cell system that can be applied for the purposes of carrying, living and transferring, due to high endurance, a short initial-driving time, an operation at a room temperature and under an atmospheric pressure, a rapid response speed, etc. Especially, the PEMFC having a flexible configuration due to an energy conversion function and a storage function separate from each other, a long lifespan due to high durability, and a relatively low cost may be suitable for a driving source of the portable refrigerator. 
     Heat generated while the stack is operated may be removed by the cooling fan. Air having passed the stack by the cooling fan may have temperature is increment due to heat transfer, and may be exhausted from the stack in the high-temperature state. The exhausted air may be blown to the gas tank. Here, the gas tank may store hydrogen therein. The air blown to the gas tank may heat the gas tank to exhaust the hydrogen stored in the gas tank to outside. 
     The fuel cell stack may be arranged below the gas tank, and a plurality of through holes may be formed at a gas tank fixing plate disposed between the gas tank and the fuel cell stack. This may allow air having temperature increment to be transferred to the gas tank via the through holes. 
     The thermoelectric cooling means may be operated by power of the battery. However, when the voltage of the battery is not sufficient, the thermoelectric cooling means may be operated by directly receiving power from the fuel cell stack. For selective power supply to the thermoelectric cooling means, the fuel cell stack and the battery may be controlled by the controller. 
     The thermoelectric cooling means may include a thermoelectric device disposed such that a low temperature side is towards the storage space, a radiating means connected to a high temperature side of the thermoelectric device, and a fan provided at the radiating means. The air having temperature increment may be blown to the gas tank by the fan for cooling the radiating means. 
     A flow path for collecting condensed water may be formed on a bottom surface of the storage space, and a condensed water reservoir for storing the condensed water collected in the flow path may be provided. Condensed water generated in the storage space during the operation of the refrigerator may be collected to the bottom surface of the storage space. Here, the condensed water may be collected in one spot due to the flow path, and then may be moved to the condensed water reservoir. This may minimize collection of condensed water in is the storage space. 
     Here, the condensed water stored in the condensed water reservoir may be supplied to the stack. For this, a moisture supplying means may be further provided. 
     The moisture supplying means may include a non-woven fabric covering one side surface of the stack, and having one end extending to inside of the condensed water reservoir. Air introduced by the cooling fan may be blown to the stack via the non-woven fabric. Once air passes through the non-woven fabric by the cooling fan, moisture contained in the non-woven fabric may be evaporated to be supplied into the stack. The moisture supplied to the stack may allow the stack to be smoothly operated. 
     The condensed water reservoir may be disposed at a position lower than the bottom surface of the storage space. 
     The portable refrigerator with a fuel cell system according to the present invention may further comprise a pump configured to transfer condensed water collected in the storage space to the condensed water reservoir. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is also provided an operating method of a portable refrigerator comprising a fuel cell stack, a battery configured to store power generated from the fuel cell stack, and a thermoelectric cooling means operated by receiving power from the battery or the fuel cell stack, the method comprising: checking an output voltage of the battery; when the output voltage is less than a predetermined value, charging the battery by operating the fuel cell stack; and when the thermoelectric cooling means needs to be operated in the process of charging the battery, directly is supplying power to the thermoelectric cooling means from the fuel cell stack. 
     When the thermoelectric cooling means needs to be operated in a state that the output voltage of the battery is not sufficient, power may be directly supplied to the battery and the thermoelectric cooling means from the fuel cell stack, respectively. This may always provide a cooling function, thereby enhancing a user&#39;s convenience. 
     Since a fuel cell may be used as a power source of the portable refrigerator, the portable refrigerator according to the present invention may have a more compact structure and an enhanced portable characteristic. 
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. 
       In the drawings: 
         FIG. 1  is a perspective view of a portable refrigerator according to a first embodiment of the present invention; 
         FIG. 2  is a perspective view of the portable refrigerator of  FIG. 1 , which shows a state that handgrips have been lifted up; 
         FIG. 3  is a perspective view of the portable refrigerator of  FIG. 1 , which shows a state that first and second covers have opened; 
         FIG. 4  is a longitudinal section view taken along line A-A′ in  FIG. 3 ; 
         FIG. 5  is a planar view of a bottom surface of a storage space in the portable refrigerator of  FIG. 1 ; and 
         FIG. 6  is a view schematically showing each component of the portable refrigerator of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Description will now be given in detail of the present invention, with reference to the accompanying drawings. 
     For the sake of brief description with reference to the drawings, the same or equivalent components will be provided with the same reference numbers, and description thereof will not be repeated. 
     Hereinafter, a portable refrigerator according to the present invention will be explained in more detail with reference to the attached drawings. 
       FIG. 1  is a perspective view of a portable refrigerator according to a first embodiment of the present invention,  FIG. 2  is a perspective view of the portable refrigerator of  FIG. 1 , which shows a state that handgrips have been lifted up, and  FIG. 3  is a perspective view of the portable refrigerator of  FIG. 1 , which shows a state that first and second covers have opened. 
     Referring to  FIGS. 1 to 3 , the portable refrigerator  100  is provided with a first cover  102  and a second cover  104  mounted at an upper part thereof so as to be open and closed. The first cover  102  is configured to a cover a refrigerating chamber, and the second cover  104  is configured to cover a mechanical chamber having a fuel cell stack, etc. to be later explained. 
     Handgrips  106  are slidably installed at both side surfaces of the portable refrigerator so as to enhance a portable characteristic. As shown in  FIG. 2 , the handgrips  106  are configured to be usable after being upwardly slid. When not used, the handgrips  106  are downwardly slid to be in an accommodated state as shown in  FIG. 1 . 
     A plurality of slits  108  are formed on the side surface adjacent to the mechanical chamber, through which external air can be easily introduced into the mechanical chamber. The slits  108  may be provided on a front surface or a rear surface of the portable refrigerator  100 . An LCD  110  is provided on the front surface of the portable refrigerator  100 , through which an operation state of the portable refrigerator  100  is informed to a user. 
     Referring to  FIG. 3 , the refrigerating chamber open and closed by the first cover  102  is divided into a first space  112  and a second space  114  by a partition wall  116 . Here, the number of partitioned spaces of the refrigerating chamber may be arbitrary. Furthermore, the partition wall  116  may not be fixed, but may be configured to vary an area of each space by being slid. 
     At an upper part of the mechanical chamber open and closed by the second cover  104 , installed are two canisters  120  and  122  configured to store gas required to operate a fuel cell stack. The canisters  120  and  122  are charged with hydrogen, and are stably fixed to an upper side of the mechanical chamber by a canister fixing plate  124 . Solenoid valves  126  and  128  are respectively installed at outlets of the canisters  120  and  122  for control of gas supply. 
       FIG. 4  is a longitudinal section view taken along line A-A′ in  FIG. 3 , and  FIG. 5  is a planar view of a bottom surface of a storage space in the portable refrigerator of  FIG. 1 . 
     Referring to  FIGS. 4 and 5 , condensed water channels  112   a  and  114   a  are formed on bottom surfaces of the first and second spaces  112  and  114 . Each of the condensed water channels  112   a  and  114   a  is formed in a zigzag form, and is configured to have a height gradually lowered toward ‘b’ from ‘a’ in  FIG. 5 . Accordingly, condensed water generated from each storage space is collected in the condensed water channels by gravity, and then is finally collected in the region of ‘b’. 
     Here, the condensed water channel may not be limited to the illustrated form, but may have any form to collect condensed water to one spot. For instance, the condensed water channel may have a lattice form. 
     Referring to  FIG. 4  back, the mechanical chamber is divided into three spaces by an upper plate  107  and a lower plate  109 . As aforementioned, the condensed water collected in the region of ‘b’ moves to outside the space along a transfer pipe  114   b . Then, the condensed water is stored in a condensed water reservoir  130  installed at a lowermost part of the mechanical chamber. The condensed water reservoir  130  is installed at a position lower than the bottom surface of each storage space, so that collected condensed water can be introduced into the condensed water reservoir without an additional pump. Here, an additional pump may be installed. 
     A lower end of the non-woven fabric  132  extending in upper and lower directions is immersed in the condensed water reservoir  130 . The non-woven fabric  132  is installed on one side surface of the portable refrigerator  100  so as to cover the slits  108  on an inner side surface. Under this configuration, condensed is water stored in the condensed water reservoir  130  is absorbed to the non-woven fabric  132 . 
     The canister fixing plate  124  is fixed to the upper plate  107 , and the upper plate  107  is provided with a plurality of through holes  107   a . The lower plate  109  is also provided with a plurality of through holes  109   a , and a fuel cell stack  140  is mounted above the lower plate  109 . 
     The fuel cell stack  140  generates power by using hydrogen stored in the canisters, and oxygen provided through the cooling fan  142  arranged to be adjacent thereto. The cooling fan  142  for removing heat generated during the operation of the fuel cell stack  140  is provided on one side surface of the fuel cell stack  140 . Here, air introduced by the cooling fan  142  passes through the non-woven fabric  132 . Accordingly, condensed water soaked into the non-woven fabric  132  is evaporated by flow of the air thus to be supplied to the fuel cell stack  140 . The air exhausted to outside via the fuel cell stack  140  has temperature increment due to heat from the fuel cell stack  140 . The high-temperature air is supplied to the canisters  120  and  122  through the through holes  107   a.    
     Accordingly, the canisters  120  and  122  are heated by relatively-high temperature air. This may allow hydrogen stored in the canisters  120  and  122  to be in a state suitable for operating the fuel cell stack  140 . Furthermore, air is exhausted to outside of the portable refrigerator  100  after transferring heat to the canisters  120  and  122  to some degrees. This may minimize increase of an indoor temperature due to exhausted air when the portable refrigerator  100  is used for a long time. 
     A thermoelectric cooling means  150  is installed at one side of the storage space. More concretely, the thermoelectric cooling means  150  includes a is thermoelectric device  151  arranged so that a low temperature side thereof can be toward the storage space. A heat sink  152  having a plurality of radiating fins on the surface thereof is attached to the low temperature side of the thermoelectric device  151 . Referring to  FIG. 4 , the heat sink  152  is configured to cool the storage space by natural convection. However, the present invention is not limited to this. That is, an additional fan may be provided to heat-exchange air inside the storage space with the heat sink  152 . 
     A heat sink  153  is also provided at a high temperature side of the thermoelectric device  151 . The heat sink  153  is thermally connected to a radiating plate  156  provided below the mechanical chamber by a heat pipe  154 . The radiating plate  156  is provided with a cooling fan  157 . Accordingly, heat generated from the high temperature side of the thermoelectric device  151  is transferred to the heat sink  153 , the heat pipe  154  and the radiating plate  156 , and then is transferred to indoor air by the cooling fan  157 . 
     The exhausted high-temperature air sequentially passes through the through holes  109   a  of the lower plate  109  and the through holes  107   a  of the upper plate  107 , thereby heating the canisters  120  and  122 . 
     Hereinafter, the operation of the portable refrigerator  100  will be explained with reference to  FIG. 6 . 
       FIG. 6  is a view schematically showing each component of the portable refrigerator of  FIG. 1 . 
     Referring to  FIG. 6 , hydrogen stored in the two canisters  120  and  122  is supplied to the fuel cell stack  140  according to an open or closed state of the solenoid valves  126  and  128 . Here, the solenoid valves  126  and  128  are controlled so that the hydrogen can be supplied to the fuel cell stack  140  only when the fuel cell stack  140  is operated by the controller  160 . 
     Here, the hydrogen can be supplied to the fuel cell stack  140  by directly supplying reformed hydrogen, or by reforming a hydrocarbon-based material by including a reformer in the system. The method using a reformer has an advantage that many types of hydrocarbon-based fuels being used as an energy source can be directly used. However, the method using a reformer has a problem that a reformer has to be included in the entire system. Therefore, hydrogen is stored in the canisters  120  and  122  thus to be directly supplied to the fuel cell stack  140 . 
     The hydrogen from the canisters is reacted via the fuel cell stack, and then is operated by a dead end method without being exhausted to the outside. A purging valve  144  is mounted to a rear end of the fuel cell stack  140 . The purging valve  144  is operated in a predetermined period, thereby removing water or impurities remaining in the fuel cell stack  140 . Here, the purging valve  144  is operated for about 0.5 seconds in a period of 10 seconds. 
     The hydrogen exhausted from the canisters cannot be directly supplied to the fuel cell stack due to instability and high pressure. Accordingly, the hydrogen needs to be uniformly depressurized into a pressure suitable for the fuel cell stack  140 . For this, a regulator  129  is disposed between the solenoid valves and the fuel cell stack. 
     The thermoelectric cooling means  150  is operated by power supplied from a battery  147 . The battery  147  is charged by power generated by the fuel cell stack  140 , and an output voltage thereof is periodically checked by the controller. If the battery has a voltage less than a lower limit value, the fuel cell stack  140  is operated to charge the battery. On the other hand, if the battery has a voltage more than a higher limit value, the fuel cell stack  140  is stopped to maintain a suitable voltage range of the battery. 
     A DC-DC converter  145  is disposed between the fuel cell stack  140  and the battery  147 . The controller  160  real time checks a voltage of the DC-DC converter  145 , thereby checking an output voltage from the fuel cell stack  140 . If the hydrogen remaining in the canisters is deficient, the DC-DC converter  145  has a lowered voltage. Accordingly, upon detection of a lowered voltage, the controller informs, through the LCD  110 , a time point when the canisters are to be replaced. 
     Driving conditions of the fuel cell stack  140  according to a charged state of the battery and a load will be explained with reference to  FIGS. 7A to 7D . In  FIGS. 7A to 7D , the solid line indicates an electrically-connected state, whereas the dotted line indicates an electrically-disconnected state. 
     Once the portable refrigerator is operated, the controller real time checks a voltage of the battery. If the voltage of the battery is less than a predetermined value, the controller charges the battery by driving the fuel cell stack  140  as shown in  FIG. 7A .  FIG. 7A  shows a state that a load is applied even from the thermoelectric cooling means, i.e., cooling power is supplied even to the thermoelectric device. Electricity generated from the fuel cell stack is supplied to the thermoelectric cooling means via the DC-DC converter  145  and a diode  146  as well as the battery. 
     If cooling power is not required any more, the current state of the system is converted into a state of  FIG. 7B . Under the sate of  FIG. 7B , power is not supplied to the thermoelectric cooling means, but electricity generated from the fuel cell stack is used only to charge the battery until the output voltage of the battery reaches the higher limit value.  FIGS. 7C and 7D  show that the fuel cell stack is not operated. More concretely,  FIG. 7C  shows that a load is not applied to the battery and the thermoelectric cooling means, and  FIG. 7D  shows that a load is applied only to the thermoelectric cooling means. That is, when the battery has a sufficient capacity, the thermoelectric cooling means is driven just by power of the battery in a state that the fuel cell stack is not driven. 
     On the contrary, when the voltage of the battery is lowered to a voltage less than the lower limit value, the current state of the system is re-converted into the state of  FIG. 7A . 
     The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present disclosure. The present teachings can be readily applied to other types of apparatuses. This description is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. The features, structures, methods, and other characteristics of the exemplary embodiments described herein may be combined in various ways to obtain additional and/or alternative exemplary embodiments. 
     As the present features may be embodied in several forms without departing from the characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalents of such metes and bounds are therefore intended to be embraced by the appended claims.