Fuel cell stack

Abstract

A fuel cell stack is formed by stacking a plurality of fuel cells in a stacking direction, and at both ends in the stacking direction of the fuel cells, a first end plate and a second plate are provided. An oxygen-containing gas supply connection pipe connected to an oxygen-containing gas supply passage is attached to the first end plate. In the oxygen-containing gas supply connection pipe, the opening cross sectional area of an intermediate pipe portion is larger than the opening cross sectional area of an oxygen-containing gas inlet and the opening cross sectional area of an oxygen-containing gas outlet.

What is claimed is: 
     
         1 . 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 and 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 in the connection pipe, an opening cross sectional area of an intermediate pipe portion is larger than an opening cross sectional area of a fluid inlet and an opening cross sectional area of a fluid outlet. 
     
     
         2 . The fuel cell stack according to  claim 1 , wherein the connection pipe has a smoothened inner wall surface over an area from the fluid inlet to the intermediate pipe portion, and over an area from the fluid outlet to the intermediate pipe portion; and
 the inner wall surface is formed only by an outward-curved surface which is curved outward in a pipe length direction.   
     
     
         3 . The fuel cell stack according to  claim 1 , wherein the connection pipe includes two intermediate pipe portions, two fluid outlets, and one fluid inlet; and
 a total opening cross sectional area of the intermediate pipe portions calculated by summing the opening cross sectional areas of the two intermediate pipe portions is larger than the opening cross sectional area of the fluid inlet, and the total opening cross sectional area of the intermediate pipe portions is larger than a total opening cross sectional area of the fluid outlets calculated by summing the opening cross sectional areas of the two fluid outlets.   
     
     
         4 . The fuel cell stack according to  claim 1 , wherein the connection pipe includes the fluid inlet connected to the external pipe, the fluid outlet connected to the fluid passage, and an intermediate pipe portion curved between the fluid inlet and the fluid outlet;
 the opening cross sectional area of the intermediate pipe portion is larger than the opening cross sectional area of the fluid outlet; and   the intermediate pipe portion includes an expanded portion expanded toward an opposite side of the fluid inlet from an opening area of the fluid outlet in a front view.   
     
     
         5 . The fuel cell stack according to  claim 4 , wherein a fluid flow direction at the fluid inlet is perpendicular to a fluid flow direction in the fluid passage.