Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2001-08-10
2004-03-16
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C137S111000, C137S114000
Reexamination Certificate
active
06706438
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fluid supply device which is used in a supply system for fuel or the like to a fuel cell.
2. Description of the Related Art
A solid macromolecular membrane type fuel cell comprises a stack (called a fuel cell) which is made up of a plurality of cells laminated together, each comprising a solid macromolecular electrolyte membrane sandwiched between an anode and a cathode. Hydrogen is supplied as fuel to the anode and air is supplied as oxidizer to the cathode, and hydrogen ions which are generated by a catalytic reaction at the anode pass through the solid macromolecular electrolyte membrane and migrate as far as the cathode, where these hydrogen ions are subjected to oxidizing and electrochemical reaction by the cathode; and thereby generation of electricity is performed.
In order to maintain the ionic conductivity of a solid macromolecular electrolyte membrane, extra water is mixed into the hydrogen which is supplied to the fuel cell by a moisturizing device or the like. Due to this, water accumulates in the gas conduits in the electrode of the fuel cell, and, in order for these gas conduits not to become blocked up, a certain amount of the fuel flowing through these gas conduits is exhausted.
It is possible to make effective use of this exhaust fuel by recirculating it (hereinafter this fuel flow is also termed “recirculated hydrogen”) and mixing it into the fuel (i.e. the hydrogen) which is freshly being fed into the fuel cell, and thus it is possible to enhance the energy efficiency of a solid macromolecular membrane type fuel cell.
In the past, as a fuel cell of the type described above, there has been a known fuel cell device which recirculates the fuel in this manner by using an ejector, such as for example the fuel cell device disclosed in Japanese Patent Application, First Publication No. Hei 9-213353.
A typical prior art type ejector, as shown in
FIG. 19
, includes a recirculation chamber
2
which is connected to a base end aperture of a diffuser
1
and a recirculation conduit
3
which is connected to this recirculation chamber
2
, with a nozzle
4
which is arranged so as to be coaxial with the diffuser
1
projecting within the recirculation chamber
2
so that its end opposes the base end aperture of the diffuser
1
. With this ejector, when hydrogen which is freshly being fed into the fuel cell is injected from the nozzle
4
towards the diffuser
1
, a negative pressure is generated in the throat portion
5
of the diffuser
1
, and the recirculated hydrogen which has been conducted into the recirculation chamber
2
is sucked into the diffuser
1
by this negative pressure, so that the recirculated hydrogen and the hydrogen which is being injected from the nozzle
4
are mixed together and are then ejected from the outlet of the diffuser
1
.
FIG. 20
roughly shows the pressure distribution in the various regions of such a prior art ejector.
The sucking-in ratio provided by the ejector will be termed its “stoichiometry”. The meaning of the term “stoichiometry” is defined, in terms of this example, as being the ratio (Qt/Qa) of the flow Qt of the hydrogen which is ejected from the diffuser (in other words the total flow of hydrogen supply which is provided to the fuel cell) to the flow Qa of the hydrogen which is ejected from the nozzle (in other words the hydrogen consumption flow). Furthermore, if the flow of the recirculated hydrogen which is sucked in from the recirculation chamber to the diffuser is termed Qb, then, since Qt=Qa+Qb, the stoichiometry can be defined as (Qa+Qb)/Qa. When the stoichiometry is defined in this manner, it is possible to say that the greater is the value of the stoichiometry, the greater is the efficiency by which the ejector sucks in recirculated hydrogen.
Now, since with a prior art type ejector the diffuser diameter and the nozzle diameter of a particular ejector are fixed, it is usual to employ choices for the various diameters which are the most suitable for the fluid flow range which is being utilized. In this case, the fluid flow (in terms of this example, the hydrogen consumption flow Qa) is arranged to be a constant value for which the stoichiometry provided by the ejector is maximum.
FIG. 21
shows an example of experimental results which have been obtained with an ejector for fuel supply to a fuel cell for the relationship between stoichiometry value and hydrogen consumption flow Qa (hereinafter termed the “stoichiometry characteristic”) with the nozzle diameter as a parameter, and it will be clear from this figure that: on the one hand although the stoichiometry value is elevated when the nozzle diameter becomes small, the hydrogen consumption flow Qa becomes small; while on the other hand, although the hydrogen consumption flow Qa becomes large when the nozzle diameter becomes large, the stoichiometry value becomes small.
In the case of a fuel cell, the stoichiometry value which is required according to the operating state of the fuel cell (hereinafter termed the “required stoichiometry value”) is determined as shown in
FIG. 21
by the thick solid line, and, since in the case of a fuel cell automobile the hydrogen flow from idling to full output power varies by a factor of 10 to 20, therefore it has been difficult to satisfy the required stoichiometry value over the entire region of hydrogen flow with a single ejector.
In order to solve this problem, a two-stage changeover ejector system has been proposed by the present applicant (in Japanese Patent Application 2000-85291), which changes over between an ejector for small flow which includes a small diameter nozzle and a small diameter diffuser and an ejector for large flow which includes a large diameter nozzle and a large diameter diffuser, and which is fitted with a bypass conduit.
Although with this method it is possible to maintain the stoichiometry characteristic to be satisfactory over a comparatively wide range from a small flow to a large flow, it becomes necessary to provide two ejectors and a flow conduit changeover device; and additionally if, in order further to improve the stoichiometry characteristic, the number of ejectors is increased to 3 or 4, it becomes necessary to change over the fluid flow between these multiple ejectors, which leads to increase of the size and weight of the device, which is most disadvantageous.
Furthermore, in Japanese Patent Application, First Publications Hei 8-338398 and Hei 9-236013 there have been proposed variable flow ejectors, although these are not ejectors for fuel supply to fuel cells.
In the variable flow ejector disclosed in Japanese Patent Application, First Publication No. Hei 8-338398, a rod is included which can shift along its axial direction inside the nozzle, and the aperture area of the tip of the nozzle can be varied by shifting this rod along its axial direction. With this variable flow ejector, it is possible to vary the stoichiometry value by changing the aperture area of the tip of the nozzle in this manner, however, since the diffuser diameter is fixed, this restricts the correspondence relationship between the stoichiometry value and the flow. In this case, it is desirable to set the correspondence relationship which is required by the fuel cell (the correspondence relationship shown by the thick solid line in
FIG. 21
) in more detail, and to enhance progress in optimization of the stoichiometry value. Furthermore there is the problem that, if the aperture area is made small when the flow is small, the flow resistance due to the wall surface is increased, so that it becomes impossible to obtain the desired stoichiometry characteristic.
On the other hand, in the variable flow ejector disclosed in Japanese Patent Application, First Publication No. Hei 9-236013, the nozzle is made to be shiftable with respect to the diffuser along its axial direction, and a plurality of different nozzles which have different diameters are made available so that it is possible to change over between them. With
Fukuma Kazunori
Kasuya Kuri
Sahoda Katsumi
Takahashi Ryoichiro
Arent Fox Kintner & Plotkin & Kahn, PLLC
Honda Giken Kogyo Kabushiki Kaisha
Kalafut Stephen
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