Experimental investigation of passive alternating flow heating strategies for PEMFC cold start

Abstract

International audiencePassive cold start remains a major challenge to Proton Exchange Membrane Fuel Cells (PEMFCs), with thermal imbalance during warm-up being a key challenge. Uneven temperatures can cause startup failure and long-term degradation. This study experimentally evaluates a new passive heating strategy using alternating coolant flow to improve thermal management. Experiments are conducted using a 3-cell thermal-emulation stack (100 cm2 per cell, ≈230 W thermal power), designed to replicate the edge and central-cell thermal behavior of real PEMFC stacks at −10 °C. The proposed method relies on alternating-flow operation, in which the coolant periodically reverses direction inside the cooling channels, enhancing heat retention and redistribution. This configuration is systematically compared with conventional no-flow (no coolant circulation) and unidirectional-flow (constant flow direction) using key thermal metrics, including temperature rise, vertical and horizontal uniformity, and forced-convection losses. Results show that the no-flow configuration enables rapid heating but induces significant inter-cell temperature differences, resulting in poor horizontal uniformity. Unidirectional configuration provides better horizontal uniformity but limits heating capability and leads to vertical temperature stratification at the cell level due to convective heat removal. The proposed alternating-flow strategy outperforms both reference cases, achieving a 32.3 °C temperature rise in 85 s, reducing vertical gradients by 90 %, and decreasing inter-cell temperature dispersion by more than 57 %. Under these conditions, the active surface exceeds 0 °C, enabling safe cold start. An adaptive strategy is proposed, dynamically switching flow modes based on internal thermal monitoring. This scalable approach offers a promising passive solution for cold-start management in PEMFCs