This application claims priority of application No. 096142944 filed in Taiwan R.O.C on Nov. 14, 2007 under 35 U.S.C. §119; the entire contents of which are hereby incorporated by reference.
The invention relates to a fuel cell circulation system and its fluid management method, particularly to a fuel cell circulation system and its fluid management method capable of facilitating miniaturization and preventing water leakage.
A fuel cell has advantages of high efficiency, low noise and pollution-free and thus is a popular fuel technology conforming to the trend of environmental protection. The most commonly seen fuel cell is a PEMFC (proton exchange membrane fuel cell) or a DMFC (direct methanol fuel cell). Taking the DMFC as an example, a fuel (methanol solution) reacts with a catalyst at the anode side to produce hydrogen ions and electrons, with the electrons being transported to the cathode side via a circuit and the hydrogen ions penetrating through a proton exchange membrane to react with oxygen and the electrons to produce reaction water at the cathode side. During the operation of the DMFC, the concentration of the methanol solution supplied to the anode side of the DMFC should maintain at an allowable range, such as 5%-10%. Specifically, a methanol concentration of lower than 5% may result in insufficient fuel supply; in contrast, a methanol concentration of higher than 10% may cause excess methanol to penetrate through a membrane electrode assembly (MEA) and arrive at the cathode side. Each of them deteriorates the performance of a fuel cell. In addition, the reaction water produced at the cathode side may be recycled to mix with the highly-concentrated methanol to achieve the allowable range of the concentration, thus improving the utilization efficiency of fuels.
Further, a circulation pump 208 pumps the fuel in a mixing tank 212 to an anode side of the fuel cell 202, and the residue of fuel after reaction is transported back to the mixing tank 212. When the concentration of the methanol solution stored in the mixing tank 212 decreases, a dosing pump 216 is used to transport highly-concentrated methanol in the fuel tank 218 into the mixing tank 212, and the reaction water in the water tank 206 is naturally dropped into the mixing tank 212 by the force of gravity.
Though in the above-mentioned conventional design the reaction water is collected by the force of gravity to enable the water pump (shown in
In addition, the water tank is typically provided with an air inlet through which outside air flows to condense evaporated water. Hence, if the fuel cell circulation system is adapted for a portable device, the reaction water may leak from the air inlet of the water tank to the outside of the portable device to wet a user.
The invention provides a fuel cell circulation system and its fluid management method capable of reducing occupied space and fabrication cost, simplifying the fuel concentration control, and preventing water leakage.
According to an embodiment of the invention, a fuel cell circulation system, which is used for controlling the concentration of a fuel supplied to at least one fuel cell and for recycling reaction water produced by an electrochemical reaction of the fuel cell, includes a fuel tank a water tank, a mixing tank, a first pump, a second pump, and an on/off valve. The fuel tank is used for storing the fuel, the water tank is used for storing the reaction water, and the mixing tank is in fluid communication with the fuel tank and the water tank. The first pump in fluid communication with the fuel tank, the water tank and the mixing tank is used for pumping the fuel in the fuel tank and the reaction water in the water tank into the mixing tank to form a mixed fluid. The second pump in fluid communication with the fuel cell and the mixing tank is used for cyclically pumping the mixed fluid to the fuel cell to cause the electrochemical reaction and sending the reacted mixed fluid back to the mixing tank. The on/off valve is provided on the flow path between the fuel tank and the first pump to control the fluid communication between the fuel tank and the mixing tank.
In one embodiment, the flow path between the fuel tank and the first pump is merged with the flow path between the water tank and the first pump at a merged point.
In one embodiment, the flow path between the fuel tank and the first pump is separated from the flow path between the water tank and the first pump.
In one embodiment, a three-way valve in fluid communication with the fuel tank is provided on the flow path between the first pump and the mixing tank. Under the circumstance, when the fuel circulation system begins to shutdown, the first pump may pump the reaction water in the water tank into the fuel tank instead of the mixing tank to prevent the initial concentration of the methanol solution in the mixing tank from being too low for the next run of the circulation system.
In one embodiment, a three-way valve in fluid communication with the fuel cell is provided on the flow path between the first pump and the mixing tank. Under the circumstance, when the fuel circulation system begins to shutdown, the water pumped into the flow channel at the anode side of the fuel cell may force the residue of methanol to be transported to the mixing tank, so that the methanol is not left in the MEA and a wet state of the MEA is also maintained.
According to each of the embodiments above, the on/off valve provided on the flow path between the fuel tank and the first pump allows for an adjustment for the concentration of fuels in the mixing tank. Compared with the conventional design, in each of the embodiments above the water pump is no longer needed for the recycling of water, so that the occupied space, fabrication cost and power dissipation of the circulation system are all reduced. Besides, since the reaction water is not collected by the force of gravity, the height difference provided in the circulation system is no longer needed to allow for a reduced occupied space. In addition, the circulation system may operate no matter whether reaction water exists in the water tank, so the control for the fuel concentration is simplified, and additional processes, such as monitoring the fluid level in the mixing tank or the water tank, are no longer needed.
Further, since the water tank and the mixing tank are separately arranged in two sides of the first pump, the possibility that fuels leak into the water tank is eliminated.
According to another embodiment of the invention, a fluid management method for a fuel cell circulation system includes the steps of detecting the fuel concentration of the fluid in the mixing tank; pumping the fuel in the fuel tank and the reaction water in the water tank into the mixing tank by a pump when the detected fuel concentration is lower than a preset value, wherein the pump is not turned off until the fuel concentration of the fluid in the mixing tank reaches the preset value; and blocking off the flow path between the fuel tank and the mixing tank immediately after the fuel cell circulation system receives a shutdown signal, wherein the pump is turned on to pump the reaction water out of the water tank for a predetermined period of time and then turned off to remove the reaction water in the water tank.
In one embodiment, the flow path between the fuel tank and the mixing tank is blocked off, and the pump is turned on to pump the reaction water out of the water tank at regular time intervals before the reception of the shutdown signal.
In one embodiment, whether the fuel concentration of the fluid in the mixing tank continuously decreases is detected to determine the time span for pumping the reaction water out of the water tank after the reception of the shutdown signal.
In one embodiment, whether the dissipation power of the pump obviously changes is detected to determine the time span for pumping the reaction water out of the water tank when the shutdown signal is received.
According to each of the embodiments above, it is ensure that no water is allowed to leak through any opening of the water tank after the shutdown of the fuel cell circulation system.
Other objectives, features and advantages of the present invention will be further understood from the further technological features disclosed by the embodiments of the present invention wherein there are shown and described preferred embodiments of this invention, simply by way of illustration of modes best suited to carry out the invention.
In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology is used with reference to the orientation of the Figure(s) being described. The components of the present invention can be positioned in a number of different orientations. As such, the directional terminology is used for purposes of illustration and is in no way limiting. On the other hand, the drawings are only schematic and the sizes of components may be exaggerated for clarity. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms “connected,” and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings. Similarly, “adjacent to” and variations thereof herein are used broadly and encompass directly and indirectly “adjacent to”. Therefore, the description of “A” component facing “B” component herein may contain the situations that “A” component directly faces “B” component or one or more additional components are between “A” component and “B” component. Also, the description of “A” component “adjacent to” “B” component herein may contain the situations that “A” component is directly “adjacent to” “B” component or one or more additional components are between “A” component and “B” component. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive.
According to an embodiment of the invention,
Referring to
Hence, according to each of the embodiments above, it is clearly seen that the on/off valve provided on the flow path between the fuel tank 26 and the dosing pump 24 allows for an adjustment for the concentration of fuels in the mixing tank 22. Compared with the conventional design, in each of the embodiments above the water pump shown in
Further, since the water tank 16 and the fuel tank 26 are arranged in parallel at the inlet of the dosing pump 24 in each of the embodiments above, the circulation system may operate no matter whether reaction water exists in the water tank 16. Specifically, when the on/off valve 28 is turned on, the dosing pump 24 pumps both reaction water and highly-concentrated methanol into the mixing tank 22 as the reaction water exists in the water tank 16, or the dosing pump 24 pumps only highly-concentrated methanol into the mixing tank 22 as no reaction water exist in the water tank 16. Under the circumstance, the control for the fuel concentration is simplified, and additional processes, such as monitoring the fluid level in the mixing tank 22 or the water tank 16, are no longer needed.
Further, in one embodiment, even the concentration of the fuel in the mixing tank 22 is not lower than the preset value and thus the dosing pump 24 and the on/off valve 28 do not need to be turned on, the dosing pump 24 still is turned on at regular time intervals while the on/off valve 28 is turned off to pump the water in the water tank 16 to the mixing tank 22 (step S70). This step S70 may ensure that the water tank 16 is kept dry to avoid the leakage of water due to overturn or other factor. Certainly, the step S70 is not necessary and should be performed according to the actual demand, and the reaction water in the water tank 16 may be transported into the mixing tank 22 as only highly-concentrated fuel is needed.
Referring to
In one embodiment, the dosing pump 24 may, immediately after the circulation system 10 receives a shutdown signal and the on/off valve 28 is turned off, be turned on to pump the water out of the water tank 16 for a predetermined period of time and then be turned off to ensure all water is cleaned off the water tank 16.
In an alternate embodiment, the dosing pump 24 may, immediately after the circulation system 10 receives a shutdown signal and the on/off valve 28 is turned off, be turned on to pump the water out of the water tank 16 and then be turned off as the fuel concentration reaches a fixed value. Specifically, it is clearly seen that the concentration of the fuel in the mixing tank 22 gradually decreases once water is continuously added therein, and that the fuel concentration will reach a fixed value when all the reaction water in the water tank 16 is pumped out. Thus, the concentration of the fuel in the mixing tank 22 may be monitored to recognize whether all water is cleaned off the water tank 16, and the dosing pump 24 is turned off as the fixed fuel concentration is detected.
In an alternate embodiment, the dissipation power of the dosing pump 24 is monitored to recognize whether all water in the water tank 16 is pumped out, because the dissipation power for pumping water is completely different to the dissipation power for pumping air by the dosing pump 24.
Further, though each of the embodiments above uses the methanol solution as a liquid fuel and a working fluid circulating in the circulation system, this is not limited. Instead, a variety of liquid fuels containing molecular hydrogen are available, such as light oil or ethanol solution.
The foregoing description of the preferred embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form or to exemplary embodiments disclosed. Accordingly, the foregoing description should be regarded as illustrative rather than restrictive. Obviously, many modifications and variations will be apparent to practitioners skilled in this art. The embodiments are chosen and described in order to best explain the principles of the invention and its best mode practical application, thereby to enable persons skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use or implementation contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents in which all terms are meant in their broadest reasonable sense unless otherwise indicated. Therefore, the term “the invention”, “the present invention” or the like does not necessarily limit the claim scope to a specific embodiment, and the reference to particularly preferred exemplary embodiments of the invention does not imply a limitation on the invention, and no such limitation is to be inferred. The invention is limited only by the spirit and scope of the appended claims. The abstract of the disclosure is provided to comply with the rules requiring an abstract, which will allow a searcher to quickly ascertain the subject matter of the technical disclosure of any patent issued from this disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Any advantages and benefits described may not apply to all embodiments of the invention. It should be appreciated that variations may be made in the embodiments described by persons skilled in the art without departing from the scope of the present invention as defined by the following claims. Moreover, no element and component in the present disclosure is intended to be dedicated to the public regardless of whether the elements or component is explicitly recited in the following claims.
Number | Date | Country | Kind |
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096142944 | Nov 2007 | TW | national |