KR20080070124A - Fuel cell stack with converging channels - Google Patents

Abstract

A fuel cell stack structure having an asymmetric fine flow path between a cooling water flow path and a fuel gas flow path is provided to maximize humidifying efficiency without using an additional humidifier, and to reduce the volume and weight of a fuel cell stack. A fuel cell stack structure comprises: a cooling water flow path(40) for introducing/discharging cooling water; a fuel gas flow path(70) formed in the cooling water flow path while being spaced apart therefrom by a uniform distance; and a fine flow path(55) connecting a first connection hole(50) formed in the cooling water flow path and a second connection hole(60) formed in the fuel gas flow path. In the fine flow path, the first connection hole is larger than the second connection hole in diameter.

Description

Fuel cell stack structure with asymmetrical micro flow paths {Fuel cell stack with converging channels}

1A and 1B are cross-sectional views of a separator plate having a humidifying part of a conventional fuel cell.

2 is a top and bottom plan view of a separator according to a preferred embodiment of the present invention.

3 is an enlarged view illustrating main parts of the micro channel according to the present invention.

Figure 4 shows the flow of cooling water at the time of forming a micro channel passage in contrast to the present invention.

Figure 5 illustrates the flow of cooling water in a preferred embodiment according to the present invention.

** Specific Names of Main Parts of Drawings **

1: Separator 10: Cooling water inlet hole 11: Cooling water outlet hole

20: fuel gas inlet hole 21: fuel gas outlet hole 30: oxidizing gas inlet hole

31: oxidizing gas outlet hole 40: cooling water flow path 50: first connection hole

55: micro-channel passage 60: second connection hole 70: fuel gas channel

The present invention relates to a stack structure of a fuel cell, and more particularly, an asymmetric micro flow path structure between a cooling water flow path and a fuel gas flow path can maximize a humidification efficiency without a separate humidification device. The present invention relates to a stack structure of a fuel cell capable of reducing volume and weight.

 A fuel cell is a device that converts chemical energy of a fuel into electrochemical energy directly in a cell without converting it into heat by combustion, and is a pollution-free power generation device that is researched with interest as a power source of an automobile or a power supply of a laser electric appliance. The hydrogen of the fuel gas is supplied to the anode of the fuel cell and the oxygen of the oxidant is supplied to the cathode. A humidifier for supplying moisture to the hydrogen and oxygen to separate the electrons from the hydrogen and oxygen to promote ionization is fuel. It is mounted on the anode and cathode of the battery, respectively. The fuel cell may be directly connected to a solid oxide fuel cell, a molten carbonate fuel cell, a polymer electrolyte fuel cell, and the like depending on the operating temperature and the type of electrolyte. It is divided into direct methanol fuel cell.

Polymer Electrolyte Membrane Fuel Cell (PEMFC for short), which has been studied a lot recently, shows relatively high output, fast start-up and response characteristics, in particular, low operating temperature (80 ~ 100 ℃).

In the PEMFC structure, the electrolyte membrane of the membrane-electrode assembly (Membrane Electrode Assembly) that generates electricity has a structure in which an electrolyte membrane is attached between an electrode consisting of a catalyst layer and a gas diffusion layer. In this electrolyte membrane, in order to increase the conductivity of hydrogen ions, the membrane surface needs to be humidified. To this end, a humidifier is installed externally or configured to have a separate humidifying part inside the stack.

The solid polymer fuel cell uses a cation exchange membrane as an electrolyte. In order to cause a fuel cell reaction in the cation exchange membrane, supply of water is essential. This means that hydrogen is separated into hydrogen ions and electrons by the catalyst at the anode, and the hydrogen ions move through the cation exchange membrane to the catalyst of the cathode, where the cathode reacts with oxygen and hydrogen ions in the air and electrons passing through the external conductor. At this time, the movement of hydrogen ions in the cation exchange membrane is related to the SO 3 H- group of the polymer material constituting the cation exchange membrane, and the amount of water in the cation exchange membrane is dependent on the amount of migration of these. Therefore, it can be said that the role of humidification that can maintain an appropriate amount of moisture in the cation exchange membrane for the performance of the solid polymer fuel cell is very large.

The separator (or bipolar plate) of the polymer electrolyte fuel cell supplies oxidizing gas, cooling water and fuel gas to the membrane-electrode junction structure, and drains water generated after the electrochemical reaction between hydrogen and oxygen. It also serves as a path through which the generated electrons move. The separator consists of an anode-side separator having a fuel gas flow path, a cathode separator designed with an oxidizing gas flow path, and coolant flows between the two separation plates, and mainly composed of metal or graphite. Are manufactured.

Looking at the prior art for such a humidification with reference to Figure 1a, a humidified integrated separator (Korea Patent Publication No. 10-2006-0004269), which is a humidification unit integrated fuel cell separator in the separator 100 is fuel cell separation In the plate, the fuel cell unit 110 and the membrane humidifying unit 130 are formed in one separator plate 100, and the membrane-electrode assembly (MEA) is formed in the fuel cell unit 110. In the membrane humidifying unit 130, various kinds of humidification membranes 150 including an ion exchange membrane for humidifying the reactor are formed. On the side of the membrane humidifier 130, a fuel gas inlet 450 through which fuel gas is supplied, a coolant outlet 550 through which coolant is discharged, and an oxidant outlet 300 through which oxidant is discharged are disposed. On the branch 110 side, a fuel gas outlet 400 through which fuel gas is discharged, a coolant inlet 500 through which coolant is supplied, and an oxidant inlet 350 through which oxidant gas is supplied are disposed. The fuel cell unit 110 and the membrane humidifying unit 130 are simultaneously configured on one separator plate, and heat and moisture generated from the cathode are supplied to the fuel gas inlet unit in a dry state through the humidifying membrane. In addition, the separation wall is installed between the fuel cell unit and the humidifying unit so that the generated water does not flow into the fuel cell unit.

However, since a part of the flow path inside the stack is divided into humidifying parts, a bonding area of the fuel gas and the membrane-electrode assembly is reduced, and a separator having a relatively long horizontal axis is required. In addition, since a separate humidification membrane is required, the total area of the membrane to be manufactured is increased along with the area of the electrolyte membrane of the fuel unit, thereby increasing the efficiency and manufacturing cost of the fuel cell.

In addition, referring to FIG. 1B, in Korean Laid-Open Publication No. 2003-0018078, oxygen inlet and outlet holes 253b and 255b, coolant inlet and outlet holes 253c and 255c, hydrogen inlet and outlet holes 253a and 255a are disclosed. And it provides a humidifying structure consisting of a drain hole 258, a microtubule 257. Through this, a plurality of microtubules were formed in the cooling water inlet hole and the fuel gas inlet hole of each separation plate to provide a space-saving fuel jersey stack without a separate humidifier.

However, in this humidification structure, the diameter of the microtube 257 is too small compared to the fuel gas and the coolant inlet hole 253c of the separator plate, so that the flow of the fluid cannot occur actively, and thus the coolant cannot flow. The problem of inferior humidification efficiency, the temporary supply of moisture at the inlet, does not sufficiently humidify hydrogen, and low heat recovery rate of the fuel cell.

The present invention has been made to solve the above problems, an object of the present invention is to provide an asymmetric micro-channel passage structure between the cooling water flow path and the fuel gas flow path can maximize the humidification efficiency without a separate humidification device, fuel It is to provide a stack structure of a fuel cell that can reduce the volume and weight of the cell stack.

In order to solve the above technical problem, the fuel cell stack structure according to the present invention, a cooling water channel for introducing the cooling water; A fuel gas flow path spaced apart from the cooling water flow path at uniform intervals; And a fine flow path connecting the first connection hole formed in the cooling water flow path and the second connection hole formed in the fuel gas flow path.

In another aspect, the present invention provides a fuel cell stack structure characterized in that the diameter of the first passage hole is larger than the diameter of the second connection hole to pass through the cooling water passage without the configuration of a separate humidifier. Cooling water alone allows efficient humidification.

In addition, the present invention is the cooling water flow path and the fuel gas flow path is formed in one of the separation plate, a plurality of cooling water flow path connecting the cooling water inlet hole and the outlet hole for entering the cooling water formed on the upper surface of the separation plate; A plurality of fuel gas flow paths connecting the fuel gas inlet and outlet holes through which the fuel gas formed on the lower surface of the separation plate is introduced; And a plurality of micro passages connecting the plurality of first connection holes formed in the cooling water flow path and the plurality of second connection holes formed in the fuel gas flow path, wherein the micro flow paths have a diameter of the first connection hole. It is characterized in that the larger than the diameter of the second connection hole to enable efficient humidification through the micro-channel passage in the cooling water flow path without the presence of a separate external humidification. .

In addition, the present invention provides a fuel cell stack structure characterized in that the diameter of the cooling water flow path is larger than the diameter of the fuel gas flow path to facilitate the flow of cooling water to increase the humidification efficiency.

In addition, the present invention provides a fuel cell stack structure characterized in that the interval between each of the micro-channel passage is formed in a ratio of a uniform interval to adjust the interval according to the specification or user's intention of the fuel cell. By controlling the flow of cooling water to control the degree of humidification.

In addition, the present invention provides a stack structure of a fuel cell, characterized in that the micro-channel passage is formed in one or more of the cooling water passage and the fuel gas passage to provide a micro-channel passage in a separate channel according to the needs of the degree of cooling It can be further formed to control the cooling efficiency.

In addition, in the present invention, the diameter of the first connector is 30 to 60% of the diameter of the cooling water flow path, and the diameter of the second connector is a fuel cell stack, characterized in that 20 to 30% of the diameter of the fuel gas flow path. By providing a structure, it is possible to realize the optimum effect that the cooling water can be supplied to the fuel gas flow path by the micro flow path.

Hereinafter, with reference to the accompanying drawings will be described in detail the configuration and operation of the present invention.

One preferred embodiment of the present invention is to provide a micro-channel passage 55 having an asymmetrical structure connecting the coolant passage 40 and the fuel gas passage 70 in the stack structure of the fuel cell shown in FIG. The asymmetrical structure of the microchannel passage 55 has a different diameter between the first connection hole 50 formed in the cooling water flow path and the second connection hole 60 formed in the fuel gas flow path 70. (More precisely, the diameter of the first connection hole 50 is larger than the diameter of the second connection hole 60), and thus the conical shape in which the micro flow paths connecting the different diameters become narrower toward one side is obtained. The structure that you have. The micro-channel passage 55 having such a structure allows the flow of the cooling water of the cooling-water passage to flow smoothly into the micro-channel passage, and further allows the cooling water to be injected in a manner sprayed by the nozzle to the fuel gas passage.

Looking at the configuration of a preferred embodiment of the present invention to which the micro-channel passage of the asymmetric structure is applied with reference to Figure 2, Figure 2- (a) is a planar cross-sectional view of the surface formed with a cooling water flow path of the separator plate, Figure 2 -(b) is a plan sectional view of the part in which the fuel gas flow path in which the cooling water flow path was formed was formed.

Referring to FIG. 2- (a), the upper surface of the separator 1 on which the coolant flow path is formed may include a coolant inlet hole 10, a coolant outlet hole 11, a fuel gas inlet hole 20, and a fuel gas outlet hole ( 21, an oxidant gas inlet hole 30 and an oxidant gas outlet hole 31 are formed, and the coolant inlet hole 10 and the coolant outlet hole 11 are connected by a coolant flow path 40, in particular, a coolant flow path. Consists of a number of channels (paths). One channel (path) of the cooling water channel 40 is formed with a plurality of first connection holes 50 to which the micro channel path is connected.

Referring to Fig. 2- (b), it is a figure showing a fuel gas flow path 70 formed on the back surface of the separator plate on which the cooling water flow path is formed, which is the back surface of the separation plate on which the cooling water flow path is formed, each of which has a corresponding configuration. However, the fuel gas inlet hole 20 and the fuel gas outlet hole 21 are connected by a fuel gas flow path 70 in a serpentine type to which the fuel gas inlet hole 20 and the fuel gas inlet hole 21 are connected. One of the flow paths is formed with a second connection hole 60 which is connected to the first connection hole 50 on the rear surface, so that the fine flow path (55 in FIG. 3A) is formed with the first connection hole 50 and the first connection hole 50. 2 Connect the connection hole (60).

With reference to this, the operation of the present invention will be described.

A plurality of coolant flow passages 40 and fuel gas flow passages 70 are formed on the upper and rear surfaces of the separator, respectively, and a first connection is connected to one of several channels of the cooling water passage in one corresponding channel of each of the plurality of flow passages. A hole 50 is formed, and a second connection hole 60 is formed in one of the fuel gas flow paths on the opposite side of the corresponding position, thereby forming the first connection hole 50 and the second connection hole 60. The connecting micro flow path is formed. In this case, the diameter of the first connection hole and the second connection hole is greater than that of the first connection hole 50 and the second connection hole 60. Therefore, the microchannel passage connecting the two holes has a first connection. The cross section of the diameter of the passage from the hole 50 toward the second connection hole 60 has an asymmetrical structure gradually narrowing. In addition, the diameter of the cooling water flow path is formed to be two to three times larger than the diameter of the fuel gas flow path. In this case, the coolant flowing through the coolant flow path easily passes through the first connection hole under pressure, and passes through a relatively narrow second connection hole to humidify the fuel gas flow path in the form of spraying the coolant in a spray form.

Referring to Figure 3 (a), in more detail, a fine flow passage 55 is formed between the cooling water flow path 40 and the serpentine-shaped fuel gas flow path 70. At this time, the diameter of the end surface of the micro-channel passage 55 connected to the cooling water flow path 40 (the first connection hole 50) and the end surface of the micro-channel passage connected to the fuel gas flow path (the second connection hole 60). When comparing the size of the, the diameter of the first connection hole 50 is formed larger, so that the shape of the micro-channel passage 55 connected as a whole is designed to be asymmetrically designed like a cone shape. This is to prevent the flow of the coolant through the micro-channel passage to move to the fuel gas flow path tube much instantaneously, and further to spray the coolant efficiently.

The cross section (circular shape) connected to the fine flow path in the cooling water flow path preferably maintains 30 to 60% of the diameter of the cooling water flow path tube 40. In addition, the cross-sectional diameter of the fine flow path connected to the fuel gas flow path on the opposite side is preferably designed to be 23 to 30% of the diameter of the fuel gas flow path pipe (70). In the present invention, the width of the cooling water flow path tube is designed to be 2-3 times wider than the width of the fuel gas flow path tube. If the diameter of the micro connection passage is too small when the coolant flows, it is to overcome the conventional problem that the flow of the coolant inside the micro passage is not observed.

In the case of Figure 3 (b) it is shown that the spacing of the micro channel path 55 can be adjusted uniformly. This can be adjusted by the user according to the user's intention or the need for cooling efficiency of the fuel cell. This may not only design the positions of the micro flow path 55 at regular intervals, but also may form the micro flow path at a higher rate so as to be closer to the cooling water inlet hole. This is because the coolant flows in the coolant flow path, and the pressure gradient gradually decreases. Therefore, when the microfluidic pipe is designed at equally wide intervals, the flow of the coolant flowing into the fuel gas flow path flows in the fine connection passage at the latter position. Weakens. In comparison, when the spacing between the asymmetrical micro-converging channels is set narrow (the location of the micro-channel passage is located close to the coolant inlet hole), the amount of coolant flow is larger than when the micro-channel passage is arranged at a wide interval. Lose. However, depending on the structure and characteristics of the fuel cell to be designed, the spacing and diameter of the microchannel passages that are connected can be adjusted.

In addition, since the temperature inside the stack of the driven fuel cell is maintained at 80 to 100 ° C., some of the coolant injected through the micro connection passage is converted into steam, thereby increasing the wetting effect of the fuel gas. This is because the heat of reaction from the electrochemical reaction between hydrogen and oxygen may cause the cooling water to vaporize when some fluid flow enters the fuel gas flow path through the micro-connected flow path.

4 and 5, Figure 4 is the flow of the cooling water when the configuration of the micro-channel passage in a cylindrical uniform shape, Figure 5 implements the shape of the asymmetrical micro-channel according to the present invention The flow of coolant in the case of adjusting the interval is shown as an image on COMSOL. (The COMSOL is a computer simulation program capable of analyzing multiple physical phenomena.)

4 (a) and 4 (b) show streamline simulation results using COMSOL in the case where the inlet and outlet cross-sections of the microchannel passages connected between the coolant channel and the fuel gas channel are the same. In this case, the widths of the cooling water flow paths and the fuel gas flow paths are 2000 μm and 1000 μm, respectively. 200 μm. In addition, the space | interval between the microchannel passages in FIG. 4- (a) is 500 micrometers, and the space | interval between the microchannel passages in FIG. In the fluid flow simulation results, almost no flow from the cooling water flow path to the fuel gas flow path occurs. In addition, regardless of the proximity to the position of the coolant inlet hole, it can be seen that a change in the flow of the coolant is hardly found inside the microchannel passage. This is because the width of the microchannel passage is narrower than that of the cooling water and flows with the same effect as in the case where there is no micropath. Looking at the flow inside the coolant and fuel gas channels, there is no change in the flow pattern. The equation applied to the COMSOL simulation was applied to the condition of incompressible fluid in the Navier Stokes Equation as follows.

As shown in FIGS. 5- (a) and (b), in the COMSOL simulation, when the width of the inlet (first connection hole) of the micro flow path is increased from 200 μm to 1000 μm, the closer to the coolant inlet hole, The flow phenomenon to the fuel gas is easily observed. FIG. 5- (a) shows the flow rate when the gap between the microchannel passages is narrow (500 μm), and FIG. 5- (b) shows the gap when the gap is wide (2000). μm). As shown in the above two figures, the closer the position of the fine flow path is closer to the cooling water inlet hole, the more the flow of the cooling water to the fuel gas flow path is observed. This increases the humidification of the membrane of the membrane-electrode assembly (MEA) through the fuel gas. Unlike the case of FIG. 4, the change in the shape of the flow inside the cooling water flow path and the fuel gas flow path is observed by the influence of the flow path of the fine flow path of the cooling water. That is, as shown in FIG. 4, more flows are flowing into the fuel gas flow pipe.

Table 1 below shows the data for measuring the flow velocity at each position (①, ②, ③) of the four embodiments of FIGS. 4- (a), (b) and 5- (a), (b). In the results, the FIG. 5 embodiment shows a faster flow rate than the FIG. 4 embodiment. This means that there is more flowing flow. In particular, it can be seen that the case of Figure 5 (a) is the optimal case. As a result, asymmetric microconverging channels can be more humidified when the initial flow rates of cooling water and fuel gas are the same.

In view of the above-described effects of the structure of the present invention, in order to facilitate the movement of hydrogen ions generated in the fuel gas and to humidify the membrane of the membrane-electrode junction structure, a separate humidifier or Unlike the existing structure in which an integral humidification part is built and performs its function, it moves directly from the flow path of the cooling water to the fuel gas flow path, so that the membrane of the membrane-electrode assembly is uniformly and continuously humidified. do. Therefore, it is possible to implement the advantage of reducing the volume and weight of the fuel cell stack and reducing the manufacturing cost.

Furthermore, in the flow through the microchannel of uniform size in the existing cooling water and fuel gas inlet hole (manifold), it is difficult to flow the uniform flow due to the microchannel having a very small diameter compared to the manifold. A fine flow passage having a diameter comparable to that of the cooling water flow passage is connected to the cooling water flow passage, and an end portion of the flow passage having a smaller width than the portion connected to the cooling water flow passage is formed at a connection portion of the fuel gas opposite to the cooling flow passage. . This can increase the efficiency of humidification by smoothly flowing the cooling water flowing to the fuel gas flow path as compared to the existing micro-channel passage. (These asymmetrical converging channels can be adjusted according to the stack of fuel cells to be sought. Also, the optimum ratio of microchannel passages through which coolant can flow is obtained.) When the coolant flows into the fuel gas flow path through the micro-channel passage, it is vaporized by the heat (80-100 ° C) generated by the electrochemical reaction of hydrogen and oxygen, and the flow of the coolant in the fuel gas flow path is accelerated, so that the membrane is humidified. You can increase the effect.

In the detailed description of the invention as described above, specific embodiments have been described. However, various modifications are possible within the scope of the present invention without departing from the scope of the present invention. The technical idea of the present invention should not be limited to the described embodiments of the present invention, and the claims are equivalent to the claims. It must be decided by things.

According to the present invention, an asymmetric microchannel passage structure is provided between the cooling water channel and the fuel gas channel to maximize the humidification efficiency without a separate humidifier.

In addition, it is also possible to reduce the volume and weight of the fuel cell stack by implementing the humidification only by the asymmetrical micro-channel passage.

Claims (7)

A cooling water channel for introducing cooling water; A fuel gas flow path spaced apart from the cooling water flow path at uniform intervals; A fine flow passage connecting the first connection hole formed in the cooling water flow path and the second connection hole formed in the fuel gas flow path; A fuel cell stack structure comprising a. The method according to claim 1, The micro channel has a fuel cell stack structure, characterized in that the diameter of the first connection hole is larger than the diameter of the second connection hole . The method according to claim 1, The cooling water flow path and the fuel gas flow path are formed in one separation plate, A plurality of cooling water flow paths connecting the cooling water inlet hole and the outlet hole for introducing the cooling water formed on the upper surface of the separator; A plurality of fuel gas flow paths connecting the fuel gas inlet and outlet holes through which the fuel gas formed on the lower surface of the separation plate is introduced; And And a plurality of fine flow paths connecting the plurality of first connection holes formed in the cooling water flow path and the plurality of second connection holes formed in the fuel gas flow path. The micro channel passage is a fuel cell stack structure, characterized in that the diameter of the first connection hole is larger than the diameter of the second connection hole. The method according to claim 3, And a diameter of the cooling water flow path is larger than a diameter of the fuel gas flow path. The method according to claim 4, The fuel cell stack structure, characterized in that formed in a structure in which the interval between each of the micro-channel passage is arranged at a ratio of the uniform interval. The method according to claim 5,  And the micro channel is formed in at least one of the cooling water channel and the fuel gas channel. The method according to any one of claims 1 to 6, The diameter of the first connection portion is 30 to 60% of the diameter of the cooling water flow path, the diameter of the second connection portion of the fuel cell stack structure, characterized in that 20 to 30% of the diameter of the fuel gas flow path.

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