Fuel cell stack

A fuel cell stack formed by stacking a plurality of fuel cells in a stacking direction, the fuel cells each being formed by stacking a membrane electrode assembly and a separator together, the membrane electrode assembly including a pair of electrodes and an electrolyte membrane interposed between the electrodes, end plates being provided at both ends in the stacking direction of the fuel cells, a fluid passage extending through the fuel cells in the stacking direction for allowing at least one of reactant gases or a coolant to flow through the fluid passage, a connection pipe connecting the fluid passage and an external pipe being connected to at least one of the end plates,

• wherein the connection pipe integrally has one fluid outlet, only two intermediate pipe portions branched from the one fluid outlet at a branching point, and only two fluid inlets respectively provided for the two intermediate pipe portions,
• wherein a total intermediate opening cross sectional area that is a sum of cross sectional area of the two intermediate pipe portions is larger than an outlet opening cross sectional area of the one fluid outlet, the intermediate opening cross sectional area of the intermediate pipe portion being an area perpendicular to a flow direction of the fluid flowing through the intermediate pipe portion;
• and the outlet opening cross sectional area of the one fluid outlet being an area perpendicular to a flow direction of the fluid flowing through the one fluid outlet,
• wherein the total intermediate opening cross sectional area is larger than a total inlet opening cross sectional area that is a sum of cross sectional areas the two fluid inlets;
• the inlet opening cross sectional area of the fluid inlet being an area perpendicular to a flow direction of the fluid flowing through the fluid inlet,
• wherein said connection pipe has an inner wall surface over an area from the one fluid outlet to each of the two intermediate pipe portions, and over an area from each of the two fluid inlets to each of respective said intermediate pipe portions, and
• wherein the inner wall surface of the connection pipe is smooth and continuous as a whole, and only includes an outward curved surface which is curved outward in a length direction from the one fluid outlet towards a mid portion of the connection pipe, and also from each of the fluid inlets towards the mid portion of the connection pipe.

A fuel cell stack formed by stacking a plurality of fuel cells in a stacking direction, the fuel cells each being formed by stacking a membrane electrode assembly and a separator together, the membrane electrode assembly including a pair of electrodes and an electrolyte membrane interposed between the electrodes, end plates being provided at both ends in the stacking direction of the fuel cells, a fluid passage extending through the fuel cells in the stacking direction for allowing at least one of reactant gases or a coolant to flow through the fluid passage, at least one of the end plates being connected to a first connection pipe connecting the fluid passage and a first external pipe and a second connection pipe connecting the fluid passage and a second external pipe,

• wherein the first connection pipe integrally has one first fluid inlet, only two first intermediate pipe portions branched from the one first fluid inlet at a branching point, and only two first fluid outlets respectively provided for the two first intermediate pipe portions,
• wherein a first total intermediate opening cross sectional area that is a sum of cross sectional areas of the two first intermediate pipe portions is larger than a first inlet opening cross sectional area of the one first fluid inlet;
• the first intermediate opening cross sectional area of the first intermediate pipe portion being an area perpendicular to a flow direction of the fluid flowing through the first intermediate pipe portion;
• and the first inlet opening cross sectional area of the one first fluid inlet being an area perpendicular to a flow direction of the fluid flowing through the one first fluid inlet,
• wherein the first total intermediate opening cross sectional area is larger than a first total outlet opening cross-sectional area that is a sum of cross sectional areas of the two first fluid outlets;
• the first fluid outlet opening cross sectional area of the first fluid outlet being an area perpendicular to a flow direction of the fluid flowing through the first fluid outlet,
• wherein said first connection pipe has a first inner wall surface over an area from the one first fluid inlet to each of the two first intermediate pipe portions, and over an area from each of the two first fluid outlets to each of respective said two first intermediate pipe portions,
• wherein the first inner wall surface of the first connection pipe is smooth and continuous as a whole, and includes an outward curved surface which is curved outward in a length direction from the one first fluid inlet towards a mid portion of the first connection pipe, and also from each of the first fluid outlets towards the mid portion of the first connection pipe,
• wherein the second connection pipe integrally has one second fluid outlet, only two second intermediate pipe portions branched from the one second fluid outlet at a branching point, and only two second fluid inlets respectively provided for the two second intermediate pipe portions,
• wherein a second total intermediate opening cross sectional area that is a sum of cross sectional areas of the two second intermediate pipe portions is larger than a second outlet opening cross sectional area of the one second fluid outlet;
• the second intermediate opening cross sectional area of the second intermediate pipe portion being an area perpendicular to a flow direction of the fluid flowing through the second intermediate pipe portion;
• and the second outlet opening cross sectional area of the one second fluid outlet being an area perpendicular to a flow direction of the fluid flowing through the one second fluid outlet,
• wherein the second total intermediate opening cross sectional area is larger than a second total inlet opening cross sectional area that is a sum of cross sectional areas of the two second fluid inlets;
• the second fluid inlet opening cross sectional area of the second fluid inlet being an area perpendicular to a flow direction of the fluid flowing through the second fluid inlet,
• wherein said second connection pipe has a second inner wall surface over an area from the one second fluid outlet to each of the two second intermediate pipe portions, and over an area from each of the two second fluid inlets to each of respective said two second intermediate pipe portions, and
• wherein the second inner wall surface of the second connection pipe is smooth and continuous as a whole, and includes an outward curved surface which is curved outward in a length direction from the one second fluid outlet towards a mid portion of the second connection pipe, and also from each of the second fluid inlets towards the mid portion of the second connection pipe.