WO1996034421A1

WO1996034421A1 - Fluid distributing device

Info

Publication number: WO1996034421A1
Application number: PCT/NL1996/000180
Authority: WO
Inventors: Reinder Jacobs Boersma; Franciscus Georgius Hubertus Koene
Original assignee: Stichting Energieonderzoek Centrum Nederland
Priority date: 1995-04-25
Filing date: 1996-04-24
Publication date: 1996-10-31
Also published as: AU5409796A; NL1000218C2

Abstract

Fluid distributing device, wherein a fluid comes into exchanging contact with a surface. The fluid can be, for example, a gas in an electrochemical cell, such as a fuel cell. In order to produce complicated channels in a particularly simple and inexpensive manner, in order to distribute a fluid of this kind as evenly as possible over the exchanging surface, it is proposed to construct channels of this type from a number of perforated plates (3, 4). In this case, the openings (8) are arranged such that, when the plates are positioned accurately on top of one another, the openings overlap partially. These channels are laterally sealed, so that accurate metering of the gases through the various channels is ensured and a sufficient pressure drop is ensured to discharge any moisture which may form.

Description

Fluid distributing device

The present invention relates to a fluid distributing device according to the preamble of Claim 1.

A fluid distributing device of this kind is disclosed by the 'Abstract' of Japanese Patent Application 58-155666. In this device, two grids provided with diamond-shaped meshes are placed on top of one another. The mesh width of the various grids differs, so that the reactant (gas) can spread across the electrode in all directions. For fuel cells, consisting at least of an anode, cathode, electrolyte and separator plate, it is important to provide the electrodes with gas which takes part in the reaction leading to the generation of electricity, and to discharge gas which is formed during the reaction. To this end, the gas should be spread over the active surface of the anode or cathode in a manner which is as evenly distributed as possible. In certain applications, there is moreover the problem of the formation of water vapour, which condenses to form water droplets which have to be blown off.

With the design according to Japanese Patent Application 58- 155666, owing to the uncontrolled distribution of the reactant across the grid, it cannot be ensured that there is a sufficient pressure drop at every location, so that it cannot be prevented that water droplets remain at certain locations.

In order to avoid this problem, the prior art, for example US Patent 5,108,849, proposes designs having channels, in order to distribute the gas as evenly as possible and to provide a sufficient pressure drop to remove the water droplets.

A pressure drop of this kind can be realized, in particular, by means of long channels.

In the design according to the abovementioned US Patent, the channels are produced by milling channels from a solid block of graphite, which is particularly complicated and time-consuming.

This is true in particular if a number of parallel channels are used, which is important for the purpose of limiting as far as possible the effect of one of the channels becoming blocked. When used in the fuel cells, the boundaries of the channels are required to be electrically conductive, because the current generated in the electrodes has to be conducted to the separator plate. Moreover, the boundary of the channels has to be resistant to the fluid used, which can be aggressive under certain circumstances.

For this reason, graphite is used in the US Patent 5,108,849.

If fuel cells of this kind are used for special applications, such as in space technology or submarines, the high price of cells of this kind is of subordinate importance, so that the use of graphite is not a problem.

However, efforts are being made to limit the cost price of fuel cells, and more particularly of SPFC cells (Solid Polymer Fuel Cell).

It is the object of the present invention to provide a fluid distributing device which can be produced in a simple manner and by means of which it is easily possible to design all sorts of channel configurations comprising a number of parallel channels situated next to one another.

This object is achieved in the case of a device as described above by means of the characterizing features of Claim 1. Because of the fact that the openings are basicly arranged with the same spacing and are positioned accurately above one another, the lateral boundaries of the openings form a seal. As a result, a number of well-defined flow channels are obtained, each having a pressure drop which can be determined in advance. As a result, moisture can be discharged.

By means of the above-described design, on the one hand, sufficient contact with the exchanging surface, such as an electrode, is provided by means of the material which bounds the channels, in order, for example, to be able to take off current, while, on the other hand, a sufficiently large surface is exposed to be able to take up or give off the gases in question.

In this way, the channel can be led across the electrode surface in any chosen manner, starting at the inlet opening and ending at the outlet. By means of this design, connections between channels are possible at any desired location, as well as at the inlet and outlet openings.

According to a preferred embodiment of the invention, two adjacent channels are connected to one another at the point which is situated furthest from the inlet opening, so that a serpentine-like channel is formed.

It will be understood that plates of this kind, from which a channel is constructed, are particularly easy to manufacture. If the plates comprise, for example, metal plates, the openings can be produced in a particularly simple manner by punching or (electrochemical) etching.

By using two metal plates provided with a series of openings, a serpentine-like channel can be formed.

The fluid distributing device according to the invention can be used in all exchanging surfaces. This means heat exchangers and electrochemical cells in general.

The above-described plates which form the channels can be produced from any material known from the prior art, such as graphite. Preferably, however, stainless steel is used. This is a comparatively inexpensive material which can be readily provided with openings by punching.

One of the plates can comprise the backing of the electrode. By making openings therein, a continuous channel can be obtained. A backing of this kind generally has a thickness of a few tenths of a millimetre. The openings which are to be made can have any form known from the prior art, but are preferably of essentially rectangular design, the longest side of the rectangle extending in the direction of flow of the fluid in question.

To provide a complete seal, a sealing ring can be arranged around the plates which form the channels.

The plates may optionally be firmly connected to one another.

The invention will be explained in more detail below, with reference to an exemplary embodiment depicted in the drawing, in which:

Fig. 1 shows, in perspective view, a cut-away part of a fuel cell;

Fig. 2 shows a top view of the structure according to Fig. 1;

Fig. 3 shows the bottom plate of the structure according to Figs. 1 and 2; and

Fig. 4 shows the top plate of the structure according to Figs. 1 and 2.

Fig. 1 shows part of a fuel cell, specifically the part which adjoins an electrode, for example the anode 2. The electrolyte, cathode and the current collector which adjoins the cathode are not shown. The part which is connected to the cathode can, in principle, be designed in the same way as the part which is arranged on the anode, which will be explained in more detail below.

For the purpose of sealing, a ring 1 is placed on the anode 2. Plate 3 is arranged inside the ring, followed by plate 4. Details of plate 3 emerge from Fig. 3, while details of plate 4 emerge from Fig. 4. In Fig. 3, the first, or bottom, plate 3 is shown. This consists of a number of perforations 8a,b, which are made by punching. The plate itself preferably consists of a stainless steel material, βa indicates perforations which ensure the transportation of the fluid in the longitudinal direction, in a manner which will be described in more detail hereinbelow. 8b indicates punched-out pieces, which provide the connection between the channels which have been formed.

Fig. 4 shows the second, or top, plate 4. It will be seen that a pattern of perforations is likewise present. This pattern differs from the pattern shown in Fig. 3.

When these plates are placed in the correct position on top of one another, the pattern as is shown cut away in Fig. 1 and in top view in Fig. 2, will be formed.

As is shown by arrow 13, a zigzag-like channel is formed. This must be differentiated from the meander or serpentine curve which is shown by arrow 14.

It can be seen that a number of parallel channels are formed, indicated by 9-12. These are connected, on the one hand, to an opening 6 in ring 1 as inlet, and, on the other hand, to opening 7 of the same ring as outlet. These openings form part of gas-lead-through channels.

It emerges from the figures that the openings can have different dimensions. It will be understood that, in addition to the dimensions shown, numerous other dimensions are possible.

As an example of the length of the openings, mention may be made of a range between 1 and 200 mm, more particularly between 2 and 100 mm, and preferably between 2 and 50 mm.

The width of the openings is preferably between 0.5 and 10 mm, in particular between 1 and 5 mm, and more particularly between 2 and 4 mm. The width of the areas between the perforations is likewise important, in order to provide the contact surface between electrode and separator plate 5 in electrochemical cells. Preference is given to a width lying between 0.2 and 10 mm, in particular between 0.5 and 5 mm, and more particularly between 0.5 and 2 mm. The thickness of the plates can vary within a range of values, and is, inter alia, dependent on the material used and the fluid which flows through them. This thickness can lie between, for example, 0.05 and 5 mm, in particular between 0.1 and 2 mm, and more particularly between 0.2 and 1 mm.

In the examples shown, the channels interact on one side with the anode 2 and are enclosed on the other side by partition or separator plate 5. It will be understood that this plate 5 can be replaced by another electrode or an actively exchanging part.

If electrical conductivity is not important, the plates can likewise consist of plastic material. Naturally, the plastic can be made conductive.

Although the invention is described above with reference to a preferred embodiment, it will be understood that numerous modifications can be made thereto without departing from the scope of the present application. Many forms are conceivable for those skilled in the art and fall within the scope of the appended claims.

Claims

1. Fluid distributing device for a fuel cell arranged, on the one hand, adjoining a surface (2) of the cell which is reactive with or interacts with the fluid, and, on the other hand, adjoining a surface of this kind or a partition (5), and comprising at least two plates (3, 4) provided with openings, the openings (2) of these plates being arranged with respect to one another such that a continuous flowpath is created, characterized in that the shape and the position of the openings placed on top of one another is such that a number of parallel channels which extend in one direction and are sealed on both sides are formed, and wherein the part of the material of the plates between these channels is designed as a lateral seal.

2. Fluid distributing device according to Claim 1 , wherein at least two adjacent channels are coupled to form a serpentine curve at an end boundary in the direction of flow.

3. Fluid distributing device according to one of the preceding claims, wherein the openings are essentially rectangular, with the longest side extending parallel to the direction of flow of the fluid.

4. Fluid distributing device according to one of the preceding claims, wherein these plates comprise metal plates and these openings are produced by punching.

5. Fluid distributing device according to one of the preceding claims, wherein this partition for the channel which is remote from the electrode comprises a plate (5) which is produced from the same material as these at least two plates.

6. Fluid distributing device according to one of the preceding claims, wherein these plates comprise a stainless steel material.

7. Fluid distributing device according to one of the preceding claims, wherein a packing ring (1) is provided, which surrounds at least one of these two plates.

8. Fluid distributing device according to Claim 7, wherein said packing ring is provided with supply/discharge openings or lead-through openings (6, 7) for the fluid.

9. Fluid distributing device according to one of the preceding claims, wherein said at least two plates are electrically connected to one another.

10. Fluid distributing device according to one of the preceding claims, wherein one of the plates comprises an electrode backing.

11. Electrochemical cell comprising a layer of electrolyte which is bounded by electrodes, wherein at least one of these electrodes is bounded on the other side by one or more gas feed/discharge channels according to one of the preceding claims.