Pore-scale investigation of non-isothermal liquid water transport in gas diffusion layers with temperature-dependent surface tension

A stochastic reconstruction method and the Volume of Fluid (VOF) model are combined to investigate non-isothermal liquid water transport in a Toray-060 gas diffusion layer (GDL). The equilibrium water-air surface tension is prescribed as a function of temperature, and conjugate heat transfer is solved in the fluid and carbon-fiber domains. Compared with a constant-surface-tension case, temperature-dependent surface tension produces only a small change in overall liquid saturation but alters local water pathways in the front and middle regions. This response combines changes in the normal capillary force caused by the local magnitude of surface tension and tangential thermocapillary stresses caused by interfacial surface-tension gradients. The redistribution becomes more evident as the imposed temperature difference increases. Inlet velocities of 0.01, 0.02, and 0.04 m s⁻¹ correspond to capillary numbers of approximately 5.5 × 10⁻⁵, 1.1 × 10⁻⁴, and 2.2 × 10⁻⁴, respectively, using the liquid-water properties at 80 °C. All investigated cases remain capillary dominated; increasing velocity changes breakthrough pathways and retained water, but the present range does not establish a universal transition threshold.