Experimental investigation of inlet-temperature effects on energy separation in a Ranque–Hilsch vortex tube under pressure–temperature coupling

Inlet temperature directly determines the thermodynamic state of the working gas in a Ranque–Hilsch vortex tube (RHVT), but its role in pressure-driven energy separation remains insufficiently clarified, particularly under coupled variations in inlet pressure and cold mass fraction. In this study, a counter-flow RHVT using compressed air was experimentally investigated over inlet temperatures of 293.15–413.15 K, inlet pressures of 400–800 kPa, and cold mass fractions of 0.2–0.8. The results showed that, over this wide inlet-temperature range, the two outlet streams responded asymmetrically to inlet-temperature elevation. The cold-exit temperature drop increased monotonically at all pressures, whereas the hot-exit temperature rise responded much weaklier and even decreased at low pressure. Normalized analysis further confirmed that this difference was not a simple temperature-scale effect. The normalized cold-exit temperature drop increased with inlet temperature, while the normalized hot-exit temperature rise decreased. Energy-based analysis also revealed that the additional inlet thermodynamic potential was not distributed symmetrically, but was preferentially redirected toward the cold stream. Thermodynamic evaluation indicated that increasing inlet temperature increased the energy-balance residual but also improved the cold-exit efficiency. Based on the observed asymmetric response, a quadratic empirical correlation was developed for the normalized cold-exit temperature drop, with a maximum deviation of 5.58%. These results identified inlet temperature as an active operating parameter in RHVTs and provided guidance for the performance regulation and engineering application of RHVTs supplied by warm or hot compressed gas.