Abstract A 3D numerical study was carried out to analyze flow, heat and mass transfer first in a single half-cell cathode channel of proton exchange mem- brane (PEM) fuel cell. From practical point of view, it is necessary to put the appropriate number of cells in a stack. Hence, the above study on a single half-cell is extended to a stack of channels. Due to stacking, the assumption of uniform flow distribution would no longer hold true. Therefore, the channel flow-maldis- tribution is considered. The water formed at the active surface due to the electrochemical reaction diffuses through the porous layer and eventually enters the gas flow duct. The higher gas velocities in the duct result in faster water vapour removal which leads to a lower value of water vapour into the duct and hence a lower Nusselt number. Keywords Fuel cell  PEM fuel cell stack  Maldistribution  Membrane electrode assembly List of symbols a Width of the lower wall (m) A Cross section area of the port (m 2 ) A c Cross section area of the duct (m 2 ) A active Control volume surface area at active site (m 2 ) B Microscopic inertial coefficient (m –1 ) C i Concentration of species I in (mol/m 3 ) C w Water concentration (mol/m 3 ) D h Hydraulic diameter of the duct (m) f app Apparent Fanning friction factor f d Fully developed Fanning friction factor F Faraday constant (96,487 C/mol) h Height of the duct (m) h b Heat transfer coefficient (W/m 2 K) I Current density (A/m 2 ) k Thermal conductivity (W/mK) K Permeability (m 2 ) l c Length of the duct m 2 Maldistribution parameter Eq. 15 M Molecular weight (kg/kmol) n Number of ducts N Duct number Nu Local Nusselt number P Pressure (Pa) q¢¢ Heat flux (W/m 2 ) Re Reynolds number (wD h /nu) S Source term T Temperature (K) u, v, w Velocity components in x, y, and z directions, respectively (m/s) _ v Non-dimensional volume flow rate V Volume of the control volume at the active surface (m 3 )  v Velocity vector (m/s) V cell Cell voltage (V) x,y,z Cartesian coordinates (m) x* Non-dimensional x coordinate Greek symbols a Net water transport coefficient per proton e Porosity A. S. Bansode  S. Patel  T. Rajesh Kumar  B. Muralidhar  T. Sundararajan  S. K. Das (&) HTTP Lab, Room 203, Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600 036, India e-mail: skdas@iitm.ac.in Heat Mass Transfer (2007) 43:1037–1047 DOI 10.1007/s00231-006-0191-x 123 ORIGINAL Numerical simulation of effects of flow maldistribution on heat and mass transfer in a PEM fuel cell stack A. S. Bansode Æ Siddharth Patel Æ T. Rajesh Kumar Æ B. Muralidhar Æ T. Sundararajan Æ Sarit Kumar Das Received: 1 February 2006 / Accepted: 12 September 2006 / Published online: 6 October 2006 Ó Springer-Verlag 2006