Porous inserts for improved coolant distribution in bipolar plate assemblies for fuel cells

Abstract

Certain fuel cell designs employ bipolar plate assemblies with internal coolant flow fields which comprise a coolant channel region and transition regions adjacent the coolant channel region. The temperature and/or pressure drop, and hence flow, of coolant over the coolant channel region can be non-uniform however, and this can have an adverse effect on cell performance. The coolant flow and temperature distribution can be modified and made more uniform by inserting an appropriate non-uniform porous insert in one or more of the coolant transition regions.

What is claimed is: 
     
         1 . A method of improving coolant distribution in a fuel cell stack, the fuel cell stack comprising a series stack of fuel cells and a plurality of bipolar plate assemblies having internal coolant flow fields, each plate assembly comprising:
 an anode plate comprising:
 inlet and outlet ports for each of fuel, oxidant, and coolant fluids; 
 a fuel flow field comprising an active region on the anode side of the anode plate wherein the active region comprises a plurality of fuel channels whose inlets and outlets are fluidly connected to the inlet and outlet fuel ports respectively; and 
 a coolant flow field comprising a coolant channel region, an inlet transition region, and an outlet transition region on the coolant side of the anode plate, wherein the inlet and outlet transition regions each comprise at least one transition coolant duct, the coolant channel region comprises a plurality of coolant channels whose inlets and outlets are fluidly connected to the inlet and outlet transition coolant ducts in the inlet and outlet transition regions respectively, and the inlet and outlet coolant ducts are fluidly connected to the inlet and outlet coolant ports respectively; 
 wherein the length direction of the plate assembly is defined by the length direction of the coolant channels and the width direction of the plate assembly is perpendicular to the length direction of the plate assembly in the plane of the plate; 
   a cathode plate comprising:
 inlet and outlet ports for each of fuel, oxidant, and coolant fluids; 
 an oxidant flow field comprising an active region on the cathode side of the cathode plate wherein the active region comprises a plurality of oxidant channels whose inlets and outlets are fluidly connected to the inlet and outlet oxidant ports respectively; and 
 a coolant flow field comprising a coolant channel region, an inlet transition region, and an outlet transition region on the coolant side of the anode plate, wherein the inlet and outlet transition regions each comprise at least one transition coolant duct, the coolant channel region comprises a plurality of coolant channels whose inlets and outlets are fluidly connected to the inlet and outlet transition coolant ducts in the inlet and outlet transition regions respectively, and the inlet and outlet coolant ducts are fluidly connected to the inlet and outlet coolant ports respectively; 
   wherein the coolant side of the anode plate is bonded to the coolant side of the cathode plate to form the internal coolant flow field; and   
       the method comprising: 
       determining the flow, pressure drop, or temperature distribution of the coolant in the coolant channel region of the coolant flow field; 
       preparing a porous insert, wherein the porous insert is non-uniform over the width of the plate assembly; wherein the porous insert is characterized by length and width dimensions in the length and width directions of the plate assembly respectively; and wherein the length of the porous insert varies over the width of the porous insert, such that the flow, pressure drop, or temperature distribution of the coolant is more uniform in the coolant channel region with the porous insert inserted in at least one of the inlet and outlet transition coolant ducts; and 
       inserting the porous insert in one of the inlet and outlet transition coolant ducts in the internal coolant flow field of at least one plate assembly in the stack. 
     
     
         2 . The method of  claim 1  wherein the porous insert is in the inlet transition coolant duct. 
     
     
         3 . The method of  claim 2  comprising an additional porous insert in the outlet transition coolant duct. 
     
     
         4 . The method of  claim 1  wherein the porous insert is made of metal foam. 
     
     
         5 . The method of  claim 1  wherein the inlet coolant port is not aligned with the coolant channels in the coolant channel region. 
     
     
         6 . The method of  claim 1  wherein the length of the porous insert is smaller near the middle than at the ends over the width of the porous insert. 
     
     
         7 . The method of  claim 6  wherein the length of the porous insert near the middle is about half of the length near the ends over the width of the porous insert. 
     
     
         8 . The method of  claim 1  wherein the permeability of the porous insert is in the range from about 250 to 300 millidarcies. 
     
     
         9 . The method of  claim 1  wherein the plurality of coolant channels are essentially parallel and straight. 
     
     
         10 . A fuel cell stack comprising a series stack of solid polymer electrolyte fuel cells and a plurality of the bipolar plate assemblies of  claim 1 . 
     
     
         11 . A method of improving coolant distribution in a fuel cell stack, the fuel cell stack comprising a series stack of fuel cells and a plurality of bipolar plate assemblies having internal coolant flow fields, each plate assembly comprising:
 an anode plate comprising:
 inlet and outlet ports for each of fuel, oxidant, and coolant fluids; 
 a fuel flow field comprising an active region on the anode side of the anode plate wherein the active region comprises a plurality of fuel channels whose inlets and outlets are fluidly connected to the inlet and outlet fuel ports respectively; and 
 a coolant flow field comprising a coolant channel region, an inlet transition region, and an outlet transition region on the coolant side of the anode plate, wherein the inlet and outlet transition regions each comprise at least one transition coolant duct, the coolant channel region comprises a plurality of coolant channels whose inlets and outlets are fluidly connected to the inlet and outlet transition coolant ducts in the inlet and outlet transition regions respectively, and the inlet and outlet coolant ducts are fluidly connected to the inlet and outlet coolant ports respectively; 
 wherein the length direction of the plate assembly is defined by the length direction of the coolant channels and the width direction of the plate assembly is perpendicular to the length direction of the plate assembly in the plane of the plate; 
   a cathode plate comprising:
 inlet and outlet ports for each of fuel, oxidant, and coolant fluids; 
 an oxidant flow field comprising an active region on the cathode side of the cathode plate wherein the active region comprises a plurality of oxidant channels whose inlets and outlets are fluidly connected to the inlet and outlet oxidant ports respectively; and 
 a coolant flow field comprising a coolant channel region, an inlet transition region, and an outlet transition region on the coolant side of the anode plate, wherein the inlet and outlet transition regions each comprise at least one transition coolant duct, the coolant channel region comprises a plurality of coolant channels whose inlets and outlets are fluidly connected to the inlet and outlet transition coolant ducts in the inlet and outlet transition regions respectively, and the inlet and outlet coolant ducts are fluidly connected to the inlet and outlet coolant ports respectively; 
   wherein the coolant side of the anode plate is bonded to the coolant side of the cathode plate to form the internal coolant flow field; and   
       the method comprising: 
       determining the flow, pressure drop, or temperature distribution of the coolant in the coolant channel region of the coolant flow field; 
       preparing a porous insert non-uniformly over its width, wherein the average pore size of the porous insert is less than about 200 micrometers, such that the flow, pressure drop, or temperature distribution of the coolant is more uniform in the coolant channel region with the porous insert inserted in at least one of the inlet and outlet transition coolant ducts; and 
       inserting the porous insert in one of the inlet and outlet transition coolant ducts in the internal coolant flow field of at least one plate assembly in the stack. 
     
     
         12 . The method of  claim 11  wherein the porous insert is in the inlet transition coolant duct. 
     
     
         13 . The method of  claim 12  comprising an additional porous insert in the outlet transition coolant duct. 
     
     
         14 . The method of  claim 11  wherein the porous insert is made of metal foam. 
     
     
         15 . The method of  claim 11  wherein the inlet coolant port is not aligned with the coolant channels in the coolant channel region. 
     
     
         16 . The method of  claim 14  wherein the porous insert is in the inlet transition coolant duct. 
     
     
         17 . The method of  claim 16  comprising an additional porous insert in the outlet transition coolant duct. 
     
     
         18 . A method of improving coolant distribution in a fuel cell stack, the fuel cell stack comprising a series stack of fuel cells and a plurality of bipolar plate assemblies having internal coolant flow fields, each plate assembly comprising:
 an anode plate comprising:
 inlet and outlet ports for each of fuel, oxidant, and coolant fluids; 
 a fuel flow field comprising an active region on the anode side of the anode plate wherein the active region comprises a plurality of fuel channels whose inlets and outlets are fluidly connected to the inlet and outlet fuel ports respectively; and 
 a coolant flow field comprising a coolant channel region, an inlet transition region, and an outlet transition region on the coolant side of the anode plate, wherein the inlet and outlet transition regions each comprise at least one transition coolant duct, the coolant channel region comprises a plurality of coolant channels whose inlets and outlets are fluidly connected to the inlet and outlet transition coolant ducts in the inlet and outlet transition regions respectively, and the inlet and outlet coolant ducts are fluidly connected to the inlet and outlet coolant ports respectively; 
 wherein the length direction of the plate assembly is defined by the length direction of the coolant channels and the width direction of the plate assembly is perpendicular to the length direction of the plate assembly in the plane of the plate; 
   a cathode plate comprising:
 inlet and outlet ports for each of fuel, oxidant, and coolant fluids; 
 an oxidant flow field comprising an active region on the cathode side of the cathode plate wherein the active region comprises a plurality of oxidant channels whose inlets and outlets are fluidly connected to the inlet and outlet oxidant ports respectively; and 
 a coolant flow field comprising a coolant channel region, an inlet transition region, and an outlet transition region on the coolant side of the anode plate, wherein the inlet and outlet transition regions each comprise at least one transition coolant duct, the coolant channel region comprises a plurality of coolant channels whose inlets and outlets are fluidly connected to the inlet and outlet transition coolant ducts in the inlet and outlet transition regions respectively, and the inlet and outlet coolant ducts are fluidly connected to the inlet and outlet coolant ports respectively; 
   wherein the coolant side of the anode plate is bonded to the coolant side of the cathode plate to form the internal coolant flow field; and   
       the method comprising: 
       determining the flow, pressure drop, or temperature distribution of the coolant in the coolant channel region of the coolant flow field; 
       preparing a porous insert non-uniformly over its width such that the flow, pressure drop, or temperature distribution of the coolant is more uniform in the coolant channel region with the porous insert inserted in at least one of the inlet and outlet transition coolant ducts; and 
       inserting the porous insert in one of the inlet and outlet transition coolant ducts in the internal coolant flow field of at least one plate assembly in the stack, wherein the porous insert is in contact with the ends of the plurality of coolant channels; and wherein the porous insert is impressed from about 1 to 3 mm into the ends of the plurality of coolant channels. 
     
     
         19 . The method of  claim 18  wherein the porous insert is made of metal foam. 
     
     
         20 . The method of  claim 18  wherein the inlet coolant port is not aligned with the coolant channels in the coolant channel region.