Method for Determining the Characteristics of a Radial Turbo Expander for Mixed Working Fluids in Nondesign Modes

Abstract

The work is devoted to determining the characteristics of turbine stages in off-design modes that arise when pressures and temperatures change before or after the stage, a transition to a different rotation speed, or, for example, when the composition of the working fluid changes. As part of the project, a quasi-one-dimensional method for calculating the characteristics of a turboexpander assembly (TEA) stage when changing operating parameters and/or working fluid has been developed, which differs from known methods by using the equations of the state of real gas, adaptation to purely radial stages, and a simplified approach to determining the pressure at the outlet of the guide vane for assessing the degree of reactivity and the ability to switch to another working fluid, including a mixed one. The analytical methodology was verified by comparison with the experimental data of other authors and the results of calculations using CFD methods for radial-axial stages as well as with approaches to the calculation of purely radial turbomachines due to the lack of experimental data for this type of TEA in the public domain. An extended characteristic of a radial stage operating in air (turbo map) was constructed, and the dependences of the isentropic efficiency, degree of reactivity, mass flow and power of the stage on the relative circumferential speed were assessed. An assessment was made of the impact of switching to another working fluid (for example, switching from air to methane was chosen). It is shown that the characteristics do not change qualitatively but they shift from one another along the axis of the relative peripheral velocity. Further development of the technique involves taking into account possible phase transitions (volume condensation) in the flow part.