Charge-discharge cycle thermodynamics for compression hydrogen storage system

• A uniform thermodynamic model expresses for all processes in charge-discharge cycle.
• The model is solved analytically under constant/variable inlet/outlet temperatures.
• New concepts of characteristic time, temperature and mass flow rate are proposed.
• The solution provides good benchmarks for multi-dimensional or system level models.
• Analytical formula fits experimental or simulated hydrogen temperatures very well.

Knowledge of the evolution of the thermodynamic properties of hydrogen storage systems, such as temperature and pressure, is required in order to evaluate and optimize their performance. The thermodynamic models of hydrogen storage systems are based on the mass and energy balance equations. They can be expressed, for high level analysis, as lumped parameter or zero-dimensional models, which are represented as a set of ordinary differential equations. We present a simple thermodynamic model that can predict the charging and discharging of gaseous hydrogen, which allows, in specific situations, for analytical solutions of the temperature and the pressure as a function of time, and can be used to validate more detailed numerical models. From the analytical solution, the final hydrogen temperature of refueling can be expressed as a weighted average of initial, inflow and ambient temperatures. The weighted factors are related to other refueling parameters, such as initial mass, initial pressure, refueling time, refueling mass rate, average pressure ramp rate (APRR), final mass, final pressure, etc. This work may be extended to adsorption-based or metal hydride hydrogen storage system. The analytical solutions can be used for sensitivity studies of hydrogen fueling standard.