KR20240015775A - Fuel cell stack having enhanced uniformity of temperature distribution - Google Patents

Abstract

The present invention relates to a fuel cell stack with improved temperature uniformity. The fuel cell stack with improved temperature uniformity according to the present invention includes a plurality of cooling plates stacked with unit cells between end plates on both sides of the fuel cell stack; a coolant supply manifold that supplies coolant supplied inside the fuel cell stack to a central cooling plate located in the central area of the fuel cell stack among the plurality of cooling plates; and a coolant discharge manifold that moves coolant passing through the central cooling plate out of the stack, and a coolant channel of an end cooling plate disposed close to an end plate of the fuel cell stack among the plurality of cooling plates is connected to the coolant discharge manifold. It is characterized in that the flow of coolant is allowed only in the direction in which coolant is supplied and flows out to the coolant inlet manifold.

Description

Fuel cell stack having enhanced uniformity of temperature distribution}

The present invention relates to a fuel cell stack in which temperature uniformity is improved. More specifically, the temperature distribution of the fuel cell stack is uniformized by passing high temperature coolant that has passed through the central cooling plate through end cooling plates disposed close to the end plates. However, it relates to a fuel cell stack with improved temperature uniformity that can improve the durability of the device by arranging a coolant channel in the end cooling plate that allows only flow from the lower coolant outlet manifold to the upper coolant supply manifold. .

Polymer Electrolyte Membrane Fuel Cells (PEMFC) or Proton Exchange Membrane Fuel Cells are devices that generate electricity by electrochemically reacting hydrogen and oxygen to produce water. Compared to fuel cells, it has the advantages of high efficiency, high current density and power density, short start-up time, and quick response characteristics to load changes.

The composition of the fuel cell stack is as follows. Inside, the main component, the Membrane-Electrode Assembly (MEA), is located. This membrane-electrode assembly includes a solid polymer electrolyte membrane that can move hydrogen protons, and hydrogen and hydrogen on both sides of the electrolyte membrane. It consists of a cathode and an anode, which are electrode layers coated with a catalyst so that oxygen can react.

In addition, a gas diffusion layer (GDL) and a gasket are laminated on the outer part of the membrane electrode assembly, that is, the outer part where the cathode and anode are located, and the reaction gas (hydrogen as fuel and oxygen or oxidant as an oxidizing agent) is placed on the outside of the gas diffusion layer. A bipolar plate is located where air is supplied and a flow field is formed through which coolant passes.

Using this configuration as a unit cell, a plurality of unit cells are stacked and then an end plate is attached to the outermost part to support the unit cells. By arranging and fastening the unit cells between the end plates, fuel A battery stack is formed.

Looking at the operating principle of a polymer electrolyte membrane fuel cell, hydrogen as a fuel and oxygen (air) as an oxidizing agent are supplied to the anode and cathode of the membrane electrode assembly through the flow path of the separator, respectively. The hydrogen supplied to the anode, which is the oxidizing electrode, is supplied to the electrode layer. It is separated into hydrogen ions (protons, H+) and electrons (electrons, e-) by a catalyst, and only hydrogen ions are selectively transferred to the cathode through the electrolyte membrane, which is a cation exchange membrane. At the same time, electrons are transferred to the gas diffusion layer, which is a conductor. It is transmitted to the cathode through the separator plate and external conductor. At this time, current is generated by the flow of electrons through the external conductor.

At the cathode, which is the cathode, hydrogen ions supplied through the electrolyte membrane and electrons transferred through the separator meet with oxygen supplied to the cathode, causing a reaction that generates heat and water.

These unit cells maintain a low voltage (usually 1V or less) during operation, so to increase the voltage, tens to hundreds of cells are stacked in series to form a stack and then used as a power generation device.

Meanwhile, polymer electrolyte membrane fuel cells generally exhibit high performance between room temperature and 80°C, but as the temperature decreases, performance may decrease due to decreased reaction activation and ion conductivity of the electrolyte membrane.

In particular, when the external temperature drops below 0℃, such as in winter, and the temperature of the fuel cell stack mounted on the vehicle falls below the freezing point of water, not only does the activity of the electrode decrease, but the water that transfers hydrogen ions in the electrolyte membrane freezes, causing the conductivity to decrease. falls, resulting in low performance.

Additionally, if the temperature is low while supplying humidifying gas, flooding problems may occur due to water condensation, which can have a fatal impact on performance and durability.

Therefore, in order to operate a fuel cell stack composed of hundreds of unit cells stacked at an appropriate temperature, it is important to maintain uniform temperature distribution throughout the stack within a certain range.

Due to the structure of the fuel cell stack, end plates containing current collectors are located at both ends to maintain fastening force and collect current. In many experiments and papers, it has been confirmed that the temperature of cells near the end plate is lower than that of other cells. .

FIG. 1 is a diagram showing the coolant flow state in a typical fuel cell stack. The separator plates constituting each unit cell 11 of the fuel cell stack 10 are stacked, and a coolant inlet manifold 13 is placed on one side of the stack, and the coolant inlet manifold 13 is installed on one side of the stack. A coolant outlet manifold (15) is formed on the side, and the coolant supplied to the inlet manifold (13) passes through each cell (11) and is collected to the outlet manifold (15) on the other side before being discharged to the outside.

That is, the coolant flowing into the inlet manifold 13 is distributed to the coolant channel 11b formed in the separator plate of each cell 11, cools each cell as it passes through, and then is collected in the outlet manifold 15, The cooled water collected in the outlet manifold (15) is finally discharged to the outside of the stack.

In this way, while the coolant moves from the inlet manifold 13 through the cell 11 to the outlet manifold 15, it receives heat generated from the electrochemical reaction of the stack, thereby cooling the stack.

Accordingly, the coolant collected in the outlet manifold (15) receives heat during the cooling process, and thus becomes coolant at a relatively high temperature compared to the coolant initially supplied to the inlet manifold (13).

Meanwhile, in a conventional fuel cell stack, cells near the end plate 19 and the current collector 18 show relatively low temperatures at the beginning of startup. Figure 2 is a diagram showing the coolant temperature distribution in the outlet manifold. Within the fold, it can be seen that the temperature decreases toward the downstream side based on the coolant flow direction.

Figure 3 is a diagram showing the results of a one-dimensional heat transfer model analysis during cold start of the stack. This also shows that the temperature of cells closer to the end plate is lower during cold start, and the temperature of all cells is adjusted uniformly to distribute the temperature within the stack. A plan to improve is needed.

Conventionally, a thick insulation or heating device is inserted between the end plate and the stacked cells to prevent temperature decrease.

For example, in the case of U.S. Patent 6,824,901, a method of insulating the area where the actual reaction occurs is applied by inserting a thick insulator between the end plate and the separator plate, or by inserting a flat heater between the end plate and the separator plate, the stack is insulated during cold start. The problem of temperature unevenness is solved by keeping the temperature of all parts constant.

In addition, in Korean Patent No. 747865 (2007.08.08), the current collector is composed of one or more materials with different thermal expansion coefficients, and the thickness change according to temperature, that is, the difference in contact resistance according to temperature, is used. When the temperature is low, the contact resistance increases due to the contraction of a material with a high thermal expansion coefficient, allowing the current collector to function not only as a current collector but also as a heater by resistance. When the temperature is high, the contact resistance decreases and only serves as a current collector. The stack is open.

In addition, Korean Patent No. 747869 (2007.08.08) discloses a fastening structure for a fuel cell stack that forms an air layer for insulation by attaching a device that can cover the outside of the end plate to enable cold starting of the fuel cell. .

However, in the case of insulating the entire end plate, the insulator must be thick for insulation, which has the disadvantage of increasing the thickness of the entire fuel cell stack. In the case of attaching a cover to the outside of the current collector, the heat generated from the electrode is transferred to the end plate. It has the disadvantage of not being able to prevent it from being taken away.

In addition, when inserting a heater between the end plate and the separation plate, a separate power supply for heater operation must be supplied from the outside, so an accessory device for power supply must be installed, and the heater operation must be controlled, which has the disadvantage of complicating the control system. There is.

US Patent 6,824,901 Korean Patent No. 747865 Korean Patent No. 747869

Therefore, the purpose of the present invention is to solve this conventional problem, by passing the high temperature coolant passing through the central cooling plate through the end cooling plates disposed close to the end plates to equalize the temperature distribution of the fuel cell stack, The aim is to provide a fuel cell stack with improved temperature uniformity that can improve the durability of the device by arranging a coolant channel in the end cooling plate that only allows flow from the lower coolant outlet manifold to the upper coolant supply manifold.

The above object is, according to the present invention, a plurality of cooling plates stacked together with the unit cells between end plates on both sides of the fuel cell stack; a coolant supply manifold that supplies coolant supplied inside the fuel cell stack to a central cooling plate located in the central area of the fuel cell stack among the plurality of cooling plates; and a coolant discharge manifold that moves coolant passing through the central cooling plate out of the stack, and a coolant channel of an end cooling plate disposed close to an end plate of the fuel cell stack among the plurality of cooling plates is connected to the coolant discharge manifold. This is achieved by a fuel cell stack with improved temperature uniformity, which allows the flow of coolant only in the direction in which coolant is supplied and flows out to the coolant inlet manifold.

The coolant channels of the end cooling plate include a plurality of main channels that are inclined in opposite directions and connected in series to form a zigzag-shaped flow path between the coolant inlet and outlet, and are each disposed on one side of the main channel and pass through the main channel. It is preferable to include a loop channel that does not provide resistance to the forward flow of the coolant, but provides resistance to the main channel to restrict the reverse flow of the coolant, thereby limiting the reverse flow of the coolant.

In addition, the loop channel has one opening disposed parallel to the inclined direction of the adjacent upper first unit channel and connected to the upper end of the first unit channel, and the other opening is disposed parallel to the inclined direction of the adjacent lower first unit channel. It is preferable that it is connected to the lower end of the first unit channel.

Additionally, the loop channel preferably forms a curved flow path between one side opening and the other side opening.

According to the present invention, the temperature distribution of the fuel cell stack is equalized by passing the high temperature coolant that has passed through the central cooling plate through the end cooling plates disposed close to the end plates, and the temperature distribution of the fuel cell stack is uniformized from the lower coolant outlet manifold within the end cooling plate to the upper coolant outlet manifold. A fuel cell stack is provided with improved temperature uniformity that can improve device durability by arranging coolant channels that only allow flow toward a coolant supply manifold.

1 is a diagram showing the coolant flow state in a typical fuel cell stack;
2 is a diagram showing the coolant temperature in the outlet manifold;
Figure 3 is a diagram showing the results of a one-dimensional heat transfer model analysis during stack cold start;
4 is a cross-sectional view showing the configuration of a fuel cell stack with improved temperature uniformity according to the present invention;
Figure 5 is a front view of the central cooling plate according to the fuel cell stack in which temperature uniformity is improved according to the present invention;
6 is a front view of an end cooling plate according to the fuel cell stack in which temperature uniformity is improved according to the present invention;
Figure 7 is a diagram showing a state in which coolant flows in the forward direction within the end cooling plate shown in Figure 6;
FIG. 8 is a diagram showing a state in which coolant flows in the reverse direction within the end cooling plate shown in FIG. 6.

Prior to explanation, in various embodiments, components having the same configuration will be representatively described in the first embodiment using the same symbols, and in other embodiments, configurations different from the first embodiment will be described. do.

Hereinafter, a fuel cell stack with improved temperature uniformity according to a first embodiment of the present invention will be described in detail with reference to the attached drawings.

Among the accompanying drawings, FIG. 4 is a cross-sectional view showing the configuration of a fuel cell stack with improved temperature uniformity according to the present invention, FIG. 5 is a front view of the central cooling plate according to the fuel cell stack with improved temperature uniformity according to the present invention, and FIG. 6 is a front view showing the configuration of a fuel cell stack with improved temperature uniformity according to the present invention. This is a front view of an end cooling plate according to the fuel cell stack in which temperature uniformity is improved according to the present invention.

The fuel cell stack with improved temperature uniformity according to the present invention includes a plurality of cooling plates 110 stacked with unit cells 101 between end plates 102 on both sides of the fuel cell stack 100, and a coolant supply manifold. (120) and a coolant discharge manifold 130, and the plurality of cooling plates 110 are disposed close to the central cooling plate 110a and the end plate 102 located in the center of the fuel cell stack 100. It is divided into an end cooling plate (110b).

In this embodiment, among the plurality of cooling plates 110, one cooling plate 110 closest to the end plate 102 is selected as the end cooling plate 110b, and the remaining cooling plates 110 are selected as the central cooling plate 110a. ) has been selected as an example, but is not limited thereto. In order to equalize temperature distribution, a plurality of cooling plates 110 adjacent to the end plate 102 may be selected as the end cooling plate 110b.

The central cooling plate 110a includes a coolant inlet connected to the coolant supply manifold 120, a coolant outlet connected to the coolant discharge manifold 130, and a plurality of coolant channels connecting the coolant inlet and the coolant outlet ( 111). The low-temperature coolant flowing in through the coolant inlet of the central cooling plate 110a cools the central cooling plate 110a while passing through the coolant channel 111, and then flows through the outlet at an increased temperature to the coolant discharge manifold 130. ) to exit. Here, the coolant channel 111 of the central cooling plate 110a is preferably designed to minimize flow resistance of coolant and improve heat exchange efficiency.

The end cooling plate 110b has an inlet connected to the coolant discharge manifold 130, an outlet connected to the inlet of the coolant supply manifold 120 or the adjacent central cooling plate 110a, and a connection between the inlet and the outlet. It includes a plurality of coolant channels 111.

In particular, the coolant channel 111 of the end cooling plate 110b is disposed inclined in opposite directions to form a zigzag flow field between the coolant inlet and outlet and has a plurality of main channels 111a connected in series. ) and one side opening is arranged parallel to the inclined direction of the adjacent upper main channel 111a and connected to the upper end of the main channel 111a, and the other opening is arranged parallel to the inclined direction of the adjacent lower first unit channel. It includes a loop channel (111b) that is connected to the lower end of the first unit channel in a closed state and forms a curved flow path between the one side opening and the other side opening. This loop channel (111b) does not provide resistance to the forward flow of coolant passing through the main channel (111a) and provides resistance to the main channel (111a) to reverse flow, thereby limiting the reverse flow of coolant. there is.

The coolant supply manifold 120 is for supplying coolant to the central cooling plate 110a, and includes one end plate 102, a plurality of unit cells 101, and a plurality of cooling plates at the top of the fuel cell stack 100. It may be provided in a form that penetrates the plate 110.

The coolant discharge manifold 130 is for recovering coolant heat-exchanged in the process of passing through the central cooling plate 110a, and is connected to one end plate 102 and a plurality of unit cells ( 101) and may be provided in a form that penetrates a plurality of cooling plates 110.

Meanwhile, in this embodiment, the flow path of the central cooling plate 110a is described as an example in the form of a general cooling water channel allowing two-way flow, but cooling water is supplied using the same principle as the end cooling plate 110b. It may also be possible to provide a form that only allows flow in the direction from the manifold 120 toward the coolant discharge manifold 130, but does not allow flow in the reverse direction.

Among the accompanying drawings, FIG. 7 is a view showing a state in which coolant flows in the forward direction within the end cooling plate shown in FIG. 6, and FIG. 8 shows a state in which coolant flows in the reverse direction within the end cooling plate shown in FIG. 6. This is the drawing shown.

First, as shown in FIG. 7, when coolant flows in the forward direction from the coolant discharge manifold 130 toward the coolant supply manifold 120 within the coolant channel 111 of the end cooling plate 110b, the coolant inlet The coolant flowing in from the coolant discharge manifold 130 flows along a plurality of main channels 111a connected in a zigzag shape and flows out to the coolant supply manifold 120 connected to the coolant outlet. At this time, the loop channel (111b) disposed on one side of the main channel (111a) has the other opening located on the lower side parallel to the upper part of the lower main channel (111a) and one opening located on the upper side of the upper main channel (111a). It is placed parallel to the lower part. Therefore, the coolant passing through the loop channel (111b) moves in a direction parallel to the flow direction of the main channel (111a) and therefore does not provide resistance to the forward flow of the coolant passing through the main channel (111a).

Meanwhile, as shown in FIG. 8, when coolant flows in the reverse direction from the coolant supply manifold 120 toward the coolant discharge manifold 130 within the coolant channel 111 of the end cooling plate 110b, the coolant outlet The coolant flowing in from the coolant supply manifold 120 is mixed with the coolant passing through the loop channel (111b) in the process of passing through the main channel (111a), and in this process, counterflow and eddy current prevent reverse flow. It provides resistance.

That is, as the coolant flowing in through the coolant outlet passes through the upper part of the main channel (111a) forming a zigzag-shaped flow path, some of the coolant flows into the loop channel (111b) arranged in a direction parallel to the upper main channel (111a). flows into one opening of the loop channel (111b) and then from the lower part of the main channel (111a) to the lower part of the main channel (111a) through the other opening arranged in a direction parallel to the lower main channel (111a). The remaining coolant that is discharged and does not flow into one opening of the loop channel (111b) moves to the lower main channel (111a) via the main channel (111a). At this time, the moving directions of the coolant moving from the lower part of the main channel 111a to the lower main channel 111a and the coolant discharged to the lower part of the main channel 111a through the other opening of the loop channel 111b are opposite to each other. Therefore, resistance to the coolant passing through the main channel 111a is provided by countercurrent and eddy current effects caused by the coolant passing through the loop channel 111b at the lower end of the main channel 111a. Since the countercurrent and eddy current effects caused by the coolant passing through the loop channel 111b act in each of the plurality of main channels 111a constituting the zigzag-shaped flow path, the coolant actually flows in the reverse direction within the coolant channel 111. It becomes unable to move.

As described above, when the high-temperature coolant stored in the coolant discharge manifold 130 passes through the end cooling plate 110b disposed close to the end plate 102, the high-temperature coolant stored in the coolant discharge manifold 130 is close to the end plate 102 of the fuel cell stack 100. It is possible to prevent the temperature of the area from being relatively low compared to the temperature of the center.

That is, considering that the amount of heat emitted from the unit cell 101 in the end area close to the end plate 102 is greater than that of the unit cell 101 in the central area, the end area in contact with the unit cell 101 in the end area is cooled. As high-temperature coolant passes through the plate 110b, the amount of heat lost to the coolant from the unit cell 101 in the end area decreases compared to the unit cell 101 in the central area, so the central unit cell 101 and the end unit cell ( 101) can be reduced as much as possible to prevent damage to the unit cell 101, and the temperature distribution of the fuel cell stack 100 can be improved to improve power generation efficiency.

In addition, the coolant channel 111 of the end cooling plate 110b allows coolant to flow only in the direction from the coolant discharge manifold 130 to the coolant supply manifold 120, and the coolant supply manifold 120 Since the flow of coolant is restricted in the direction from the coolant discharge manifold 130, there is no need for a separate structure to guide the supply of coolant to the coolant channel 111 of the end cooling plate 110b. When a structure for guiding the supply of coolant to the coolant channel 111 of the end cooling plate 110b is placed within the coolant discharge manifold 130, the cross-sectional area of the coolant discharge manifold 130 is reduced, and the coolant As flow resistance increases, a larger capacity coolant pump may be required. However, when the coolant channel 111 that allows flow in only one direction is arranged as in the present embodiment, a separate structure that reduces the cross-sectional area or increases flow resistance may not be placed within the coolant discharge manifold 130. Therefore, a relatively small capacity coolant pump can be applied.

The scope of the present invention is not limited to the above-described embodiments, but may be implemented in various forms of embodiments within the scope of the appended claims. It is considered to be within the scope of the claims of the present invention to the extent that anyone skilled in the art can make modifications without departing from the gist of the invention as claimed in the claims.

100: fuel cell stack, 101: unit cell, 102: end plate,
110: cooling plate, 110a: central cooling plate,
110b: end cooling plate, 111: coolant channel, 111a: main channel,
111b: loop channel, 120: coolant supply manifold,
130: Coolant discharge manifold

Claims (4)

A plurality of cooling plates stacked together with the unit cells between end plates on both sides of the fuel cell stack;
a coolant supply manifold that supplies coolant supplied inside the fuel cell stack to a central cooling plate located in the central area of the fuel cell stack among the plurality of cooling plates;
It includes a coolant discharge manifold that moves coolant that has passed through the central cooling plate out of the stack,
Among the plurality of cooling plates, the coolant channel of the end cooling plate disposed close to the end plate of the fuel cell stack receives coolant from the coolant discharge manifold and allows the flow of coolant only in the direction in which it flows out to the coolant inlet manifold. A fuel cell stack with improved temperature uniformity. According to clause 1,
The coolant channels of the end cooling plate include a plurality of main channels that are inclined in opposite directions and connected in series to form a zigzag-shaped flow path between the coolant inlet and outlet, and are each disposed on one side of the main channel and pass through the main channel. A fuel cell stack with improved temperature uniformity including a loop channel that limits the reverse flow of coolant by providing resistance to the main channel for reverse flow of coolant without providing resistance to the forward flow of coolant. According to clause 2,
The loop channel has one opening disposed parallel to the inclined direction of the adjacent upper first unit channel and connected to the upper end of the first unit channel, and the other opening is disposed parallel to the inclined direction of the adjacent lower first unit channel. A fuel cell stack with improved temperature uniformity connected to the lower part of the first unit channel. According to clause 3,
The loop channel is a fuel cell stack in which temperature uniformity is improved by forming a curved flow path between one opening and the other opening.

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