Evaluation of Direct Cooling Strategies for Hydrogen Refueling Stations

This study investigates the potential for reducing or eliminating conventional pre-cooling requirements in hydrogen refueling stations (HRS) through the integration of turboexpanders, using a combined thermodynamic modeling and Computational Fluid Dynamics (CFD) approach. A key novelty of the present work is the explicit comparison between constant and variable isentropic efficiency formulations, enabling a more realistic representation of turboexpander performance under the highly transient operating conditions characteristic of hydrogen refueling processes. A simplified thermodynamic model is first used to estimate the transient inlet conditions associated with different pressure-reduction strategies, which are subsequently imposed as boundary conditions for three-dimensional CFD simulations of the fast filling of a 70 MPa Type III hydrogen cylinder. The CFD methodology is validated against experimental data for conventional refueling under prescribed inlet-temperature conditions, while the sensitivity of the predictions to turbulence modeling is also assessed. The validated framework is then applied to compare conventional throttling, a single turboexpander with constant isentropic efficiency, and a parallel-expander configuration accounting for variable off-design efficiency. The CFD predictions indicate that turboexpander-assisted refueling can reduce hydrogen heating, with the parallel-expander configuration yielding a final average hydrogen temperature approximately 15 K lower than that predicted for conventional throttling.