Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
1999-03-16
2001-08-21
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000
Reexamination Certificate
active
06277511
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application No. HEI 10-192833 filed on Jul. 8, 1998 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fuel cell formed by stacking a plurality of unit cells.
2. Description of the Related Art
Fuel cells are known as devices for converting energy of a fuel into electric energy. A typical fuel cell has a stack structure formed by stacking a plurality of unit cells. Normally, each cell has a pair of electrodes that are disposed so as to sandwich an electrolyte member. An electrochemical reaction occurs when a hydrogen-containing reaction gas (fuel gas) contacts a surface of one of the pair of electrodes in each cell and an oxygen-containing gas (air) contacts a surface of the other electrode. By utilizing this electrochemical reaction, each fuel cell generates electric energy.
Japanese Patent Application Laid-open No. HEI 2-226669 discloses a fuel cell system having a plurality of fuel cell stacks divided into a plurality of blocks, with the flow rates of the gasses supplied to the fuel cells in each block being controlled.
This fuel cell system uses flow rate regulating valves to control the gas flow rates to the individual blocks. Therefore, a great number of flow rate regulating valves are required, so that the cost of the fuel cell system increases.
Furthermore, the aforementioned fuel cell system has stacks that are formed by stacking a plurality of cells, and generates electric energy by utilizing the chemical reaction occurring in each cell. Therefore, in order to optimize the power generating efficiency of the fuel cell system, it is preferable to optimize the power generating efficiency (reaction efficiency) in each fuel cell stack. However, the aforementioned system does not allow control to be performed in accordance with a parameter other than the gas flow rates to the individual fuel cell stacks, so that it is difficult to optimize the power generating efficiency in the fuel cell system.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a fuel cell capable of achieving an optimal performance in accordance with an operating condition of the fuel cell.
According to the invention, there is provided a fuel cell including a stack formed of a plurality of cells, a plurality of first passages for a first fluid that flows in the stack, and a passage changer that changes a connection state of the first passages in accordance with an operating condition of the fuel cell.
Therefore, this fuel cell makes it possible to change the connection state of the passages in the stack provided in the fuel cell in accordance with the operating condition of the fuel cell, so as to change the fluid flow velocity distribution and the fluid passage sequence in accordance with the operating condition. That is, it becomes possible to control the fluid flow rate required in the stack. As a result, an optimal performance of the fuel cell can be achieved.
According to the invention, the passage changer may change the connection state of the first passages so that a passage resistance of the first passages changes. For example, if the fluid that flows in the stack is a reaction gas, the connection state of the passages may be changed so that the passage resistance decreases as the output of the fuel cell increases. As a result, a gas flow rate required for high output operation can reliably be attained, so that favorable progress of reactions in the fuel cell can be maintained.
If the fluid that flows in the stack is a coolant, for example, cooling water or the like, the connection state of the passages may be changed so that the flow velocity increases as the output of the fuel cell increases. An increased flow velocity causes turbulence of the coolant, so that the cooling performance during high output operation can be enhanced.
If in addition to the first passages for the first fluid that flows in the stack, a plurality of second passages for a second fluid that flows in the stack are provided. The connection state of the second passages may be changed synchronously with a timing of changing the connection state of the first passages. For example, by changing the connection state of a plurality of cooling water passages synchronously with the changing of the connection state of a plurality of gas passages, cooling can be performed in accordance with the gas flow rate.
Furthermore, the fuel cell of the invention may also have a construction as follows. That is, an upstream-side portion of each of the first passages located at an inlet side is formed on a dry-type electrolyte membrane, and a downstream-side portion of each first passage located at an outlet side is formed on a wet-type electrolyte membrane. This construction will further optimize the chemical reactions in the fuel cell.
The plurality of cells may be divided into a first group and a second group. In this case, the number of passages divided in each cell of the first group may be different from the number of passages divided in each cell of the second group. This construction increases the variations of passages and therefore increases the freedom in design and the like, in comparison with a construction in which all the cells of a stack have the same number of divided passages.
If a passage in the stack is divided into a plurality of passages in a cell, inlets and outlets of the divided passages may be formed near a predetermined side of the cell. This arrangement makes it possible to reduce dead spaces related to portions required for gas manifolds or sealing. Therefore, the output density per unit volume of the fuel cell can be increased.
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Hamada Hitoshi
Iwase Masayoshi
Kalafut Stephen
Kenyon & Kenyon
Toyota Jidosha & Kabushiki Kaisha
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