To combat climate change successfully, enhancing existing processes is imperative alongside exploring new regenerative technologies. For this purpose, new components must be considered to improve the efficiency of thermodynamic processes. A promising candidate is the Ranque–Hilsch vortex tube due to its low investment cost and maintenance. Previous research has highlighted the thermodynamic advantages of employing a vortex tube in various applications, such as Brayton cycles or as a replacement for conventional expansion valves. However, to assess the potential of the vortex tube within a thermodynamic process, a computationally efficient but precise model of the vortex tube is required. Existing modeling approaches often fail to accurately predict experimental trends or require information such as geometry data that are not available for potential analyses. Thus, the present study proposes a novel thermodynamic-based black-box modeling approach: the vortex tube efficiency is introduced by incorporating operating and geometrical conditions into a single parameter. The vortex tube efficiency is systematically investigated for different operating conditions and various fluids and compared with available experimental results. The resulting modeling approach allows the qualitative and quantitative prediction of vortex tube behavior for air at various operating pressures and cold gas fractions. Further experimental investigations are required for a comprehensive quantitative description of vortex tubes with different geometries and working fluids.