Performance prediction and experimental verification of high flow rate cryogenic helium turbine expander

The helium reverse Brayton cycle is a highly efficient cryogenic refrigeration cycle suitable for small and medium-sized hydrogen liquefaction plants. The helium turbine expander is a key component providing cryogenic cooling capacity, and its efficiency and stability are crucial to system performance. This study investigates the performance prediction methodology and off-design characteristics of a helium turbine expander for a 2 t/d hydrogen liquefaction system. To mitigate experimental expenditures while accurately forecasting the expander's off-design efficiency, a loss-model-based performance prediction framework is proposed. Through incorporation of real helium thermophysical properties and heat leakage corrections, this approach enables precise prediction of turbine thermodynamic performance predicated on inlet and outlet boundary conditions. Experimental validation demonstrates prediction errors within ±5% relative to actual cryogenic operational data, substantiating the methodology's robust applicability and accuracy across an extensive temperature spectrum. Concurrently, the cooldown dynamics of the 2 t/d hydrogen liquefaction system are analyzed across variable operating conditions. The findings reveal that during turbine expander cooldown, isentropic efficiency exhibits a positive correlation with decreasing temperature, while the cooling rate progressively accelerates under invariant inlet/outlet boundary conditions. The study establishes the characteristic ratio as a critical parameter for turbine thermodynamic performance analysis. Within the design operating temperature regime, the experimental turbine's isentropic efficiency manifests a non-monotonic relationship with characteristic ratio, attaining a high-performance plateau exceeding 75% efficiency within the characteristic ratio range of 0.60—0.75. This research furnishes an efficacious and computationally efficient predictive tool, establishing a theoretical foundation for optimal design and performance analysis of helium turbine expanders across broad operating envelopes.