FLOW FIELD PLATE FOR FUEL CELL

Abstract

A flow field plate for a fuel cell, the flow field plate is provided with a plurality of fluid channels wherein at least one split block is provided between the fluid channels, at least one auxiliary microflow-channel is arranged in the split block, the microflow-channel changes flow rate and flow pressure of fluid at different sites along the fluid channel by having a depth and a width smaller than a depth and a width of the fluid channel at a confluent segment and also smaller than a depth and a width of the fluid channel at a diverging segment, so as to generate a pressure difference that forces fluid to flow into a diffusion layer. The flow field plate adjusts flow rate and pressure of fluid at different sites along the fluid channel, so as to transmit the reaction medium more effectively and removes generated water more effectively.

Claims

1. A flow field plate for a fuel cell, the flow field plate comprising a plurality of fluid channels, wherein at least one split block is provided between the fluid channels, at least one auxiliary microflow-channel is arranged in the split block, the microflow-channel changes flow rate and flow pressure of fluid at different sites along the fluid channel by having a depth and a width smaller than a depth and a width of the fluid channel at a confluent segment and also smaller than a depth and a width of the fluid channel at a diverging segment, so as to generate a pressure difference that forces fluid to flow into a diffusion layer.

2.-10. (canceled)

11. The flow field plate for a fuel cell of claim 1, wherein the diffusion layer is arranged at a bottom of the split block, when the fluid flows through the confluent segment and the diverging segment of the fluid channel, change in the flow rate causes pressure change of the fluid and forms the pressure difference, which forces the fluid to enter the diffusion layer in fitting contact with the flow field plate and removes water generated on a catalyst layer, thereby realizing a three-dimensional flow pattern related to x, y and z directions.

12. The flow field plate for a fuel cell of claim 11, wherein a guiding ramp or guiding groove is arranged at a fluidward side of the split block, when the fluid flows out the confluent segment and is about to hit the split block head-on, the fluid is guided into the diffusion layer under the split block by the guiding ramp or the guiding groove.

13. The flow field plate for a fuel cell of claim 12, wherein relation between a curvature radius R of a streamlined, curved profile at a front end of the split block and curvature radius r of a streamlined, curved profile at a rear end thereof is Rr, so that the split block divides the fluid channel into at least two diverging segments comprising an expansion part and a converging part, when the at least two diverging segments merge into a confluent segment at the rear end of the split block, an eddy that prevents retention of generated water around lateral walls of the fluid channel is formed at the rear end of the split block.

14. The flow field plate for a fuel cell of claim 1, wherein when the depth and/or width of the confluent segment and that of the diverging segment of the fluid channel are different, the fluid has a flow rate S.sub.L and a flow rate S.sub.P at the confluent segments as measured at cross sections thereof, respectively and has a flow rate S.sub.N at the diverging segment as measured at a cross section thereof, and S.sub.L and S.sub.P are smaller than or equal to S.sub.N.

15. The flow field plate for a fuel cell of claim 1, wherein the fluid channel adjusts the flow rate by having a wave-like, variant depth, wherein a depth H of a cross section of a confluent segment at the front end of the split block gradually decreases to a depth h of a cross section of the diverging segment, the depth of the cross section of the diverging segment gradually increases to a depth of a cross section at the rear end of the split block.

16. The flow field plate for a fuel cell of claim 1, wherein the split blocks in the adjacent fluid channels are arranged staggeredly, where the diverging segment of the fluid channel is in is defined as a divergence region, and where the confluent segment is in is defined as a conflux region, the divergence region of one fluid channel is adjacent to the conflux region of the adjacent fluid channel, a fluid pressure of the divergence region is different from that of the conflux region.

17. The flow field plate for a fuel cell of claim 1, wherein the diameter d of the auxiliary microflow-channel in the split blocks and the diameter D of the confluent segment of the fluid channel has a relationship of d= 1/10D.

18. The flow field plate for a fuel cell of claim 1, wherein the diameter or width D of the confluent segment of the fluid channel is greater than or equal to the sum of the diameters or widths of a plurality of the diverging segments.

19. The flow field plate for a fuel cell of claim 1, wherein the split block is a bump raised from the middle of the fluid channel, the fluid channels formed by the plurality of auxiliary microflow-channels in the split blocks form arched, I-shaped, Y-shaped and T-shaped patterns.

20. A flow guiding method for a fuel cell, wherein the flow guiding method comprises: arranging a plurality of fluid channels on a flow field plate, arranging at least one streamlined split block in the middle of the fluid channel, arranging a diffusion layer at the bottom of the split block, when a fluid flow through a confluent segment and a diverging segment along the fluid channel, change in flow rate leads to change in flow pressure and forms a pressure difference, which forces the fluid to enter the diffusion layer in fitting contact with the flow field plate and removes water generated on a catalyst layer, thereby realizing a three-dimensional flow pattern related to x, y and z directions.

21. The flow guiding method for a fuel cell of claim 20, wherein the method comprises: relation between a curvature radius R of a streamlined, curved profile at a front end of the split block and curvature radius r of a streamlined, curved profile at a rear end thereof is Rr, so that the split block divides the fluid channel into at least two diverging segments comprising an expansion part and a converging part, when the at least two diverging segments merge into a confluent segment at the rear end of the split block, an eddy that prevents retention of generated water around lateral walls of the fluid channel is formed at the rear end of the split block.

22. The flow guiding method for a fuel cell of claim 20, wherein a guiding ramp or guiding groove is arranged at a fluidward side of the split block, when the fluid flows out the confluent segment and is about to hit the split block head-on, the fluid is guided into the diffusion layer under the split block by the guiding ramp or the guiding groove.

23. A flow field plate for a fuel cell, wherein at least one streamlined split block is arranged in the middle of a fluid channel, a guiding ramp or guiding groove is arranged at a fluidward side of the split block, when a fluid flows out a confluent segment and is about to hit the split block head-on, the fluid is guided into a diffusion layer under the split block by the guiding ramp or the guiding groove.

24. The flow field plate for a fuel cell of claim 23, wherein the split block is provided with membrane electrode assemblies (MEA) at a bottom, which includes a diffusion layer, a membrane electrode and a catalyst layer applied at its two sides, wherein the diffusion layer is attached to the flow field plate, when a fluid flows through the confluent segment and the diverging segment of the fluid channel, variation of its flow rate causes change in the flow pressure of the fluid, and the pressure difference so generated forces the fluid to enter the diffusion layer attached to the flow field plate, and takes away water generated on the catalyst layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 is a schematic structural diagram of a known flow field plate;

[0028] FIG. 2 is a schematic structural diagram of a distributed/conflux region in a flow field plate according to a first aspect of the present invention;

[0029] FIG. 3 is a schematic structural diagram of a distributed/conflux region in a flow field plate according to a second aspect of the present invention;

[0030] FIG. 4 is a schematic structural diagram of a distributed/conflux region in a flow field plate according to a third aspect of the present invention;

[0031] FIG. 5 is a schematic structural diagram of a distributed/conflux region in a flow field plate according to a fourth aspect of the present invention;

[0032] FIG. 6 is a schematic drawing showing a fluid flowing through the distributed/conflux region;

[0033] FIG. 7 is a schematic structural diagram of plural adjacent fluid channels;

[0034] FIG. 8 is a schematic drawing showing a fluid flowing through the adjacent fluid channels according to the present invention;

[0035] FIG. 9 is a schematic drawing showing a fluid flowing through a split block according to the present invention;

[0036] FIG. 10 is a schematic structural diagram of a distributed/conflux region in a flow field plate according to a fifth aspect of the present invention; and

[0037] FIG. 11 is a cross-sectional view taken along Line I-I of FIG. 10.

DETAILED DESCRIPTION OF THE INVENTION

[0038] The invention as well as a preferred mode of use, further objectives and advantages thereof will be best understood by reference to the following detailed description of illustrative embodiments when read in conjunction with the accompanying drawings.

Embodiment 1

[0039] FIG. 1 is a schematic structural diagram of a known flow field plate with straight channels. The flow field plate 1 is provided with linear fluid channels 3. At the two ends of the flow field plate 1, there are a fuel port 4, a cooling fluid port 5 and an oxidant port 6, there is also a sealing groove 2.

[0040] The present invention modifies the fluid channel 3 into the structure as depicted in FIG. 2. A plurality of split blocks 7 are provided in each of the fluid channels 3, so that the fluid channel when meeting the split blocks 7 are divided into two (as shown in FIGS. 2-5. For example, the fluid channel 3 is divided into two at its cross section L, namely one sub-channel 3a and another sub-channel 3b), which are combined at the cross section P after the split block 7, thereby forming a wave-like, continuous, alternately divergent and convergent fluid channel Every fluid channel 3 is composed of a plurality of continuous distributed/conflux regions. Every distributed/conflux region comprises a expansion part A and a converging part B. The fluid channel 3 before and after each of the distributed/conflux regions is referred as a confluent segment and the fluid channel in the distributed/conflux regions is referred as diverging segments that are divided from the confluent segment. A fluid flows in the confluent segment with a flow rate S.sub.L and flows in the diverging segment with a flow rate S.sub.N, wherein S.sub.L<S.sub.N.

[0041] By choosing the width and/or depth of the fluid channel 3 in the confluent segments and in the diverging segments, the flow rate of a fluid at different sites along the fluid channel 3 can be set. For example, with the depth along the fluid channel 3 kept constant, by changing the relationship between the diameter D of the fluid channel 3 at the confluent segment and the diameters d1, d2 of the sub-channels in the diverging segment and making Dd1+d2 and having the diameters d1 and d2 of the two sub-channels the same or different, the fluid when entering the diverging segment from the confluent segment necessarily flows faster because of the reduced channel area, so that S.sub.L<S.sub.N. Afterward, at P downstream the split block 7, the two sub-channels are combined as they leave the diverging segment, so the flow rate of the fluid returns to S.sub.L.

[0042] In addition, by adjusting the depth H of the fluid channel 3 at the confluent segment and the depth h of the two sub-channels at the diverging segment, the flow rate can be changed, as shown in FIGS. 10-11. The fluid channel 3 has a wave-like profile, with gradually decreased depth from the depth H measured at the cross section L of the confluent segment to the depth h at the interface N, and then gradually increased depth from the depth at the interface N to the depth at the interface P.

[0043] The split block 7 is a bump raised from the fluid channel 3. The split block 7 has a streamlined, curved lateral profile. The curvature radius R at a front end of the streamlined, curved profile and the curvature radius r at a rear end of the streamlined, curved profile has a relationship of Rr, as shown in FIG. 4, so that the fluid forms an eddy at the rear end of the split block 7.

[0044] The split block 7 further has a plurality of auxiliary microflow-channel 8. The plurality of auxiliary microflow-channels 8 form passages of an arched pattern (as shown in FIG. 2), an I-shaped pattern (as shown in FIG. 3), a Y-shaped pattern (as shown in FIG. 4) and/or a T-shaped pattern (as shown in FIG. 5), or a pattern of any shape according to practical needs. The diameter d of the auxiliary microflow-channel 8 and the diameter D of the confluent segment of the fluid channel has a relationship of d= 1/10D. The auxiliary microflow-channels 8 are used as an additional means for changing the flow rate and flow pressure of fluid at different sites along the fluid channel, so as to form a flow pressure difference that forces the fluid to enter and flow in the diffusion layer smoothly. The depth of the auxiliary microflow-channel 8 is smaller than the depth of the fluid channel at the confluent segment, and is smaller than the depth of the fluid channel at the diverging segment, as shown in FIG. 6.

[0045] As shown in FIG. 6, the flow field plate 7 has its bottom provided with MEA membrane electrodes, which includes a diffusion layer 9, a membrane electrode 11 and a catalyst layer 10 applied at its two sides. The diffusion layer 9 is attached to the flow field plate 1. After fluid enters the fluid channel 3 of the flow field plate 1 through the fluid inlet port, and flows through the confluent segment and the diverging segment of the fluid channel 3, the variations of its flow rate cause change in the flow pressure of the fluid, and the pressure difference so generated forces the fluid to enter the diffusion layer 9 attached to the flow field plate 1, and takes away water generated on the catalyst layer 10. This creates a three-dimensional flow pattern related to x, y and z directions. For ensuring that the fluid enters the diffusion layer 9 smoothly, a guiding groove or guiding ramp 14 may be additionally provided at the upper surface of the split block 7 at the fluidward side of split block 7 that contacts the diffusion layer, as shown in FIG. 9. When the fluid flows out the confluent segment and is about to hit the split block 7, the guiding groove or the guiding ramp 14 serves to guide the fluid into the diffusion layer 9 under the split block.

[0046] As shown in FIG. 7, the split blocks 7 in the adjacent fluid channels 3 are arranged staggeredly. Meanwhile, the diverging segment of one fluid channel 3 is adjacent to the confluent segment of the adjacent fluid channel Where the diverging segment of the fluid channel is in is defined as a divergence region A, and where the confluent segment is in is defined as a conflux region B. The divergence region A of one fluid channel 3 is adjacent to the conflux region B of the adjacent fluid channel The flow pressure of the fluid in the divergence region A tends to increase, and the fluid flow pressure in the conflux region B tends to decrease. Such pressure variations form pressure difference across two sides of the lateral walls 12 of the adjacent diffusion and conflux regions. The pressure difference drives the fluid to spread and flow in the diffusion layer 9 at the lower parts of the lateral walls 12 (as shown in FIG. 8), and flow from an end of the fluid channel where the flow pressure is high to an adjacent fluid channel where the flow pressure is low through the diffusion layer at lower parts of lateral walls 12 of the fluid channel, thereby improving transmission of the reaction medium in the diffusion layer, and effectively removing water generated in the diffusion layer at the lower parts of the lateral walls of the channel, so as to prevent blockage of the porous diffusion layer, as indicated by the double-headed arrow 13 in FIG. 7. The double-headed arrow in FIG. 7 clearly shows that as the channel layout changes, the total flow pressure difference between the main flows in the adjacent channels may be different from the local flow pressure difference between the divergence and conflux regions, and therefore may counteract, reverse or amplify the flow pressure difference between the two sides of the lateral walls 12. The flow direction of the fluid depends on the magnitudes of the foregoing two kinds of flow pressure differences, and it is almost impossible that the difference can be completely cancelled out. According to actual design, both existence and complete prevention is possible. In either way, the fluid is driven to spread and flow in the diffusion layer at the lower parts of the lateral walls, and flow from an end of the fluid channel where the flow pressure is high to an adjacent fluid channel where the flow pressure is low through the diffusion layer at lower parts of lateral walls 12 of the fluid channel, thereby improving transmission of the reaction medium in the diffusion layer, and effectively removing water generated in the diffusion layer at the lower parts of the lateral walls of the channel, so as to prevent blockage of the porous diffusion layer.

Embodiment 2

[0047] In each fluid channel 3, plural of split blocks 7 are such arranged that a flow running along the fluid channel when encountering each split block 7 is divided into three flows and the three flows merge into one flow after passing the split block 7, so as to form a wave-like diverging and converging flow pattern. The rest of the present embodiment is identical to their counterparts in Embodiment 1.