CN2886817Y - Current-guiding pole plate for self-drained fuel cell - Google Patents

Abstract

The utility model discloses a diverting polar plate of gravity drainage fuel battery, comprising a plate body, on which a first fluid channel and a second fluid channel are arranged. The channels are respectively arranged with entrances and exits, and the first channel is communicated with the second one by a diverting slot. When the utility is working, because of the different flow rates of two fluid channels, the water resulted from reaction is absorbed from one fluid channel to another fluid channel via the diverting slot for draining the water in this fluid channel or another. According to the different positions where the flow field is located, the diverting slot can keep an ideal pressure distribution and the flow of reacting gas flow in each fluid channel. The invention can push the left water in the fluid channels to flow, and stop the partial oxygen from loss when the oxidant is oxygen in the air.

Description

Self-draining fuel cell flow guide polar plate

One, the technical field

The utility model relates to a fuel cell, specific fuel cell water conservancy diversion polar plate that uses among the fuel cell that says so.

Second, background Art

A pem fuel cell stack is a device that generates electrical energy by the electrochemical reaction of a fuel and an oxidant. The core component of the device is a Membrane Electrode (MEA), which is composed of two porous gas diffusion layers and a proton exchange Membrane sandwiched therebetween. An electrochemical catalyst is attached to the interface of the proton exchange membrane and a gas diffusion layer (e.g., carbon paper).

Another important component of a pem fuel cell stack is the flow-guide plates. The anode and cathode reactions respectively occur at two sides simultaneously, which is called bipolar plate. One side of the plate is close to the current collector, and the other side is connected with the membrane electrode, and the reaction only occurs on one side, so the plate is called a unipolar plate. The bipolar or unipolar plates contain channels for the passage of a gas (e.g., hydrogen or air) and fluid flow channels for the passage of a coolant (e.g., air or water).

In a hydrogen fuel cell, hydrogen enters the hydrogen flow channels of a bipolar or monopolar plate from the hydrogen inlet of the fuel cell stack and then permeates through a porous gas diffusion layer (e.g., carbon paper) to the surface of the catalyst. Under the action of the catalyst, hydrogen gas is electrochemically reacted, and hydrogen atoms lose electrons to become positive ions (protons). The electrons reach the electric appliance through a porous gas diffusion layer (such as carbon paper) and a bipolar plate or a unipolar plate, and then reach the catalyst surface on the other side of the membrane electrode through the bipolar plate or the unipolar plate and the porous gas diffusion layer (such as carbon paper). Under the action of the catalyst, the electrons electrochemically react with an oxidant (e.g., oxygen) that reaches the catalyst surface through a porous gas diffusion layer (e.g., carbon paper) and protons that reach the catalyst surface through a proton exchange membrane to generate a reaction product (e.g., water). The electrochemical reaction that occurs in a hydrogen fuel cell can be represented by the following reaction equation:

and (3) anode reaction:

and (3) cathode reaction:

a membrane electrode is clamped between two flow guide polar plates to form a single cell of the fuel cell. The voltage that the single cell can provide in the reaction is lower than 1.0V. In order to increase the output of a fuel cell stack, more than one cell is assembled in series in one stack, the output voltage of the fuel cell stack being the sum of the voltages of all the cells in the fuel cell stack.

The ideal operating condition for a fuel cell is to provide each membrane electrode with the correct and continuous supply of fuel or oxidant. During operation, the proton exchange membrane must be saturated with water to meet its adequate electrogenic properties and to minimize its electrical resistivity. The reaction product of the fuel cell is water, and due to normal diffusion, the movement of water molecules carried by ions in the proton exchange membrane occupies the main flow, and water tends to gather toward the cathode side of the membrane electrode. As the current density increases, the amount of water produced on a certain membrane electrode area also increases. Whether for the purpose of satisfying the flow of the reaction gas or for the purpose of saturating the water in the proton exchange membrane, it is necessary to properly manage the water, that is, to remove excessive water when the water content is high and the reaction gas starts to be prevented from stably passing through the gas diffusion layer, and to supply sufficient water when the water content in the proton exchange membrane is not saturated.

In the existing fuel cell, the structure of the fluid flow channel on the flow guide polar plate is divided into a single reaction gas fluid flow channel bent flow field, a multi-reaction gas fluid flow channel bent flow field and a multi-reaction gas fluid flow channel parallel flow field. In operation, reactant gases and reaction products, water, flow along the fluid channels in the plates, and the design of the plate fluid channels affects the distribution of reactant gases, as well as the electrical contact and oxygen consumption between the plates and the membrane electrode. Reactant gases are humidified before entering the fuel cell stack and if not, once heated to operating temperature, have a low relative humidity, but as they move down the fluid flow channels, they may rise to a saturation point and excess water will generally collect or condense in the channels of the plates and pores of the gas diffusion layers, a condition known as flooding which prevents the passage of reactant gases through the gas diffusion layers, reducing the performance of the fuel cell. When the flow channels are completely blocked by water, the electrochemical reaction on the affected local active area of the fuel cell will be severely weakened or stopped, and the diverted reactant gas will also deteriorate the flow conditions of other flow channels, and more flow channels will be blocked one by one. As water continues to accumulate in the fluid flow channels, the overall performance of the fuel cell decreases significantly as its effective active area decreases, and none of the above three fluid flow channel configurations solves this problem well.

Third, the invention

1. The purpose of the invention is as follows: the utility model aims at providing a from drainage type fuel cell water conservancy diversion polar plate, it makes to get rid of this problem of surplus water in the fluid flow channel from the flow field and becomes simple and convenient.

2. The technical scheme is as follows: the utility model relates to a from drainage type fuel cell water conservancy diversion polar plate, it includes the polar plate body, is equipped with first fluid runner and second fluid runner on the polar plate body, first fluid runner and second fluid runner have import and export, characterized by respectively: the first fluid flow channel and the second fluid flow channel are communicated with each other through the diversion trench.

When water collects in a certain fluid flow channel region to partially or completely block the fluid flow channel (hereinafter, this phenomenon is referred to as a fluid flow channel blocking region), the flow velocity of the reaction gas in the fluid flow channel is reduced as compared with a fluid flow channel region that is not blocked or is only partially blocked (hereinafter, this phenomenon is referred to as a fluid flow channel non-blocking region). When the diversion trench is used to connect the fluid flow channel blocking area and the fluid flow channel unblocking area, the flow rates of gas near the end opening of the diversion trench in the fluid flow channel blocking area and near the end opening of the diversion trench in the fluid flow channel unblocking area are different, resulting in different pressures near the end openings of the two diversion trenches. The pressure near the end of the channel at regions of relatively low flow velocity (blocked regions of the fluid flow path) is higher than the pressure near the end of the channel at regions of relatively high flow velocity (unblocked regions of the fluid flow path). Generally, the pressure near the end opening of the guide channel with high relative flow rate is lower than the pressure at the blockage. When the flow guide groove is used for connecting the fluid flow passage blocking area and the fluid flow passage unblocking area, the pressure of gas in the fluid flow passage of the blocking area is higher than that of gas in the fluid flow passage of the unblocking area, and under the action of pressure difference, moisture accumulated in the fluid flow passage of the blocking area flows into the fluid flow passage of the unblocking area from the flow guide groove and is discharged out of the fuel cell stack by reaction gas. Depending on the location of the end openings of the channels and the general flow field pattern, the channels may deliver water to the fluid flow channel regions where the mea is too dry.

The location and number of channels in the flow field required to achieve effective water removal depends on many different factors. For example, in an air-cooled fuel cell, the region of the fluid flow channels near the inlet to the fluid flow channels is entirely likely to condense the water produced by the reactants, particularly if the reactant gases are humidified, which can produce an imperceptible accumulation of water in the upflow of the fluid flow channel region. It may be desirable to provide a channel near the inlet of the fluid flow channels in a gas cooled fuel cell. However, in general, overflow typically occurs in the portion of the fluid flow path in the downflow, so it is generally advisable to locate the flow leader near the outlet of the fluid flow path rather than the inlet, and typically in the third of the downflow of the fluid flow path. The channels may be connected to the fluid flow path in a variety of ways, for example, more channels may be spaced along two adjacent fluid flow paths, or the channels may be used to connect fluid flow paths in many other areas. The number of channels required along the flow channels and the appropriate channel locations depend in large part on the operating current density of the fuel cell (which determines the amount of water produced), the flow rates of the fuel and oxidant, the pressure and humidity, the cross-sectional area of the flow channels, the number of flow channels, and the smoothness of the wall surfaces of the flow channels. The number and location of channels can be determined by pressure drop calculations or CFD simulations (sizing of fluid flow channels and fuel cell testing).

One or more channels connecting the fluid flow channels may effectively reduce flooding in this region and improve fuel cell performance. In general, for a multi-fluid flow channel flow field, when one fluid flow channel is blocked, thereby impeding the flow of reactant gas, the reactant gas will instead flow to another or more unblocked fluid flow channels, thereby increasing the flow of gas within the unblocked fluid flow channels. Since the change in flow rate can cause a change in pressure differential, an increase in flow rate in an unobstructed fluid flow channel will cause an increase in pressure differential between the vicinity of the opening at the end of the flow channel duct that obstructs the fluid flow channel and the vicinity of the opening at the end of the flow channel duct that does not obstruct the fluid flow channel, thereby dynamically increasing the water drive effect of the flow duct connecting the two fluid flow channels due to the obstruction of gas flow in the obstructed fluid flow channels. Therefore, the guide grooves connecting the two fluid flow channel areas in the flow field can automatically remove accumulated water, thereby reducing overflow in the area.

The channels connecting the flow channels in the flow field may also slow down the formation of water blockage in the flow channels because the channels may balance the pressure of the reactant gases in the region when the flow rates in the region of the flow channels connected by the channels are not identical. According to the number of the diversion trenches and the positions of the openings at the tail ends of the diversion trenches, the pressure balance can ensure that the fluid flow channel in the flow field has enough pressure at the key position of the flow field and enough pressure drop along the length of the whole fluid flow channel. Thus, the pressure balance created by the channels helps maintain the desired flow of reactant gas along each fluid flow path, and also prevents oxygen loss in this region if the oxidant is oxygen-containing air.

To achieve the desired water driving effect and to avoid undesirable shunting of reactant gases through the shortcut fluid flow channels, the cross-sectional area of the smallest of the channels is preferably smaller than the cross-sectional area of the fluid flow channels at the opening near the end of the channels. And the cross-sectional area of each channel at the channel end opening is preferably less than the cross-sectional area of its fluid flow path. The relative cross-sectional areas of the appropriate fluid flow channels and channels depend on a number of factors including the form of the flow field, the length of the channels, and the flow rate of operation.

The method of increasing the reactant gas flow rate (i.e., decreasing the pressure) near the opening at the end of the channel is associated with the opening at the end of the channel. More preferably, the fluid flow path is shaped as a venturi or cone, and the opening at the end of the flow channel is positioned at or near the narrowest point of the venturi (at its throat). When the flow rates in the two fluid flow channel regions connected by the guide grooves are not exactly the same, the venturi tube at the opening at the end of the guide groove increases the flow rate in each venturi tube, thereby reducing the pressure at the end of each guide groove by a slight flow balance, so that no flow is generated between the fluid flow channels through the guide grooves. When the flow rate in one of the fluid flow channel regions is lower than in the other fluid flow channel region due to the obstruction of water in one of the fluid flow channels, the increase in flow rate and the pressure drop caused by the venturi in the high flow rate fluid flow channel region increases the ability to drive water from the low flow rate fluid flow channel region. The increase in water transport through the flow channels caused by the venturi is very significant when the flow velocity in the low flow velocity fluid flow path region approaches zero. However, the increase in flow rate (pressure drop) caused by the venturi is proportional to the flow rate of the ascending flow in the venturi. Therefore, the Venturi tube at the opening at the tail end of each guide groove can amplify the flow speed difference (or pressure difference) between the two fluid flow passages connected by the guide grooves. Also, the combination of the channel/venturi is more sensitive to flow rate reduction due to clogging than the channel alone. The introduction of a venturi increases the flow field plate production cost and so a trade-off must be made between increased cost and improved performance of the fuel cell by introducing a venturi, which depends primarily on the flow field configuration of the fuel cell.

The liquid in the diversion trench flows in and out of the diversion trench; the blocking position of the fluid flow channel wall is the tail end opening of the diversion trench; the venturi enhances the flow mechanism of the reactant gases, particularly oxidizing gases-these structural and operational features are intended to disrupt the laminar flow of air and thereby create a mixed gas stream that helps prevent oxygen loss at the air/membrane electrode assembly interface.

3. Has the advantages that: the electrochemical reaction performance of the fuel cell is enhanced by the introduction of a (typically a plurality of) flow channels between the fluid flow channels within the flow field. The use of a channel/venturi combination is not limited to pem fuel cells only, nor is the reactant limited to a gas, and fluid flow paths blocked by any blocking substance can be prevented or removed by the channel/venturi combination.

Fourthly, explanation of the attached drawings:

fig. 1 shows a schematic view of the present invention, which is a partial area of a two-flow field fluid flow path with a combination of flow channels/venturi;

FIG. 2 is a schematic illustration of the first embodiment showing the removal of water from the fluid flow path;

fig. 3 shows a multi-parallel fluid flow channel flow field with the channel/venturi combination of fig. 1 at the exit of each pair of fluid flow channels.

FIG. 4 illustrates a two-fluid flow channel bending flow field with a channel/venturi combination at the fluid flow channel exit;

fig. 5 illustrates a two-fluid flow channel serpentine flow field with a channel/venturi combination atthe fluid flow channel outlet and between the fluid flow channel inlet and outlet.

The fifth embodiment is as follows:

as shown in fig. 1, is a portion of a two-flowfield fluid flow path region with a channel/venturi combination 12. The first fluid flow channel 10 is a longitudinally extending concave surface on the surface of the flow field plate which connects to land 14. The guide groove 16 connects the fluid flow passage 10 and the second fluid flow passage 11. Channel 16 is a concave surface with an open channel end at each end. Each fluid flow path is provided with a venturi tube 20 which becomes a conical building part of the fluid flow path 10. Each of the baffle slot end openings 18 is located at the throat 22 or narrowest portion of the respective venturi.

In use, lands 14 abut the electrode plates to seal the fluid flow paths one by one except, of course, where the fluid flow is provided by channels 16. The cross-sectional area of the fluid passageway formed by channels 16 and the membrane electrode surfaces is less than the cross-sectional area formed by each fluid flow channel and the membrane electrode surfaces, whether at the widest dimension of the fluid flow channel or at the narrowest venturi 22. The appropriate relative cross-sectional areas of the fluid flow path, the channels 16 and the venturi 20 depend on many factors including the form of the flow field, the length of the channels 16, the operating flow rate, etc.

In use, as shown in fig. 1, when the first fluid flow channel 10 and the second fluid flow channel 11 are not blocked, the flow rates of the reactant gases through the two fluid flow channels are substantially the same, as indicated by the thick arrows in fig. 1, so that little or no pressure differential exists at the end opening 18 of the channel, and thus little or no fluid flows between the two fluid flow channels through the channel 16.

As shown in fig. 2, when the first fluid flow path 10 is blocked by the accumulation of water 26, the flow rate of the reactant gas near the distal opening 18 of the channel 16 of the blocked first fluid flow path 10 will be less than the flow rate near the distal opening 18 of the channel of the unblocked second fluid flow path 11. The difference in flow velocities at the openings 18 at the ends of the two channels will be amplified by the venturi 20. Depending on the configuration of the fluid flow channel inlet and the reactant gas supply, the flow velocity difference may also be amplified at the fluid flow channel inlet (not shown in fig. 1 and 2) by the transfer of gas from the blocked first fluid flow channel 10 to the unblocked second fluid flow channel 11.

The difference in flow velocity at the channel end opening 18 causes a pressure differential which causes the water 26 in the blocked first fluid flow path 10 to flow under pressure through the channel 16 to the unblocked second fluid flow path 11. By this means, the accumulated water 26 is removed by being transferred, and the flow rate of the reaction gas in the first fluid flow path 10 can be restored to the original state.

The deflector channel/venturi combination 12 may be used on a variety of different flow fields. For example, the deflector/venturi combination shown in fig. 3 may be used in a multi-parallel fluid flow channel flow field 30 having first and second fluid flow channels 10, 11 on the multi-parallel fluid flow channel flow field 30, the first and second fluid flow channels 10, 11 having an inlet 34 and an outlet 32, respectively. As shown in fig. 3, the baffle/venturi combination may be positioned adjacent the fluid flow path outlet 32.

Fig. 4 illustrates an example of the use of the baffle/venturi combination 12 for a two-fluid flow channel serpentine flow field 36. Each pair of fluid flow channels in the two-fluid flow channel serpentine flow field 36 is comprised of more than one flow channel/venturi combination 12 as shown in fig. 5.

Claims (5)

1. The utility model provides a from drainage type fuel cell water conservancy diversion polar plate, it includes polar plate body (1), is equipped with first fluid flow way (10) and second fluid flow way (11) on polar plate body (1), first fluid flow way (10) and second fluid flow way (11) have import (34) and export (32), characterized by respectively: the first fluid flow channel (10) and the second fluid flow channel (11) are communicated with each other through a diversion trench (16).

2. The flow guide plate for a self-draining fuel cell of claim 1, wherein: the flow guide groove (16) is arranged at the outlet (32) of the first fluid flow channel (10) and the second fluid flow channel (11).

3. The flow guide plate for a self-draining fuel cell of claim 1, wherein: the minimum cross-sectional area of the flow channel (16) is less than the minimum cross-sectional area of the fluid flow path adjacent the flow channel (16).

4. The flow guide plate for a self-draining fuel cell of claim 1, wherein: venturi tubes (20) are arranged in the first fluid flow channel (10) and the second fluid flow channel (11) and correspond to openings on two sides of the guide groove (16).

5. The self-draining fuel cell flow-guiding plate of claim 4, wherein: the openings of the guide grooves (16) are positioned nearthe narrowest part of the corresponding Venturi tube (20).

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