Session: 30-09 Systems 1 and Components

Submission Number: 176639

One-Dimensional Design of Supercritical Carbon Dioxide Brayton TAC Units With Axial Thrust Balance 

Supercritical carbon dioxide (sCO2) Brayton cycles are gaining attention as next-generation power-conversion systems because of the high thermal efficiency, small number of components, and compact system layout. To reduce mechanical losses and overall volume, many designs adopt a coaxial layout in which the turbine, alternator, and compressor share a common shaft, hereafter referred to as the turbine-alternator-compressor (TAC) unit. While this packaging is attractive, it introduces a key challenge: managing axial thrust across the coupled compressor-turbine rotor. In TAC units, the impellers are overhung at both ends of the common shaft and sealed at their back faces with dry gas seals. The combined action of impeller aerodynamic loads and the seal balancing diameter can impose unequal axial forces at the two shaft ends. If not actively balanced, the compressor and turbine can exhibit inconsistent thrust evolution during startup and off-design operation, altering axial clearances and potentially driving axial migration. In severe cases, this may precipitate rotor-stator rub or casing contact, compromising the safety and reliability of the TAC unit.

Conventional practice evaluates axial thrust only after preliminary sizing has been completed and then iteratively adjusts geometry and seal features until specifications are met. This late-stage loop is time-consuming and can obscure performance and safety trade-offs. This work proposes an integrated one-dimensional (1D) TAC design framework that embeds axial thrust prediction directly into the primary sizing loop. The method couples 1D turbomachinery sizing with seal force estimation and explicit thrust-balance constraints, so that feasible shaft-end load distributions are obtained during preliminary design rather than deferred to late checks. The framework targets both design point and part-load conditions relevant to practical sCO2 installations, with the objective of (i) enforcing thrust balance, (ii) minimizing impact on cycle performance, and (iii) reducing the number of geometry and seal-parameter iterations. By unifying performance sizing and axial-force control within a single workflow, the proposed approach provides a clearer and more efficient path to TAC configurations that are compact, robust, and ready for subsequent detailed analysis and validation.

Presenting Author: Mingxiang Lin Institute of Engineering Thermophysics, Chinese Academy of Sciences; University of Chinese Academy of Sciences

Presenting Author Biography: Lin Mingxiang is currently a doctoral candidate at the Institute of Engineering Thermophysics, Chinese Academy of Sciences. His research focuses on the design optimisation, dynamic characteristics, and control strategies of supercritical carbon dioxide Brayton cycle systems.

Authors:

Mingxiang Lin Institute of Engineering Thermophysics, Chinese Academy of Sciences; University of Chinese Academy of Sciences
Chaohong Guo Institute of Engineering Thermophysics, Chinese Academy of Sciences; University of Chinese Academy of Sciences
Yuming Zhu Institute of Engineering Thermophysics, Chinese Academy of Sciences; University of Chinese Academy of Sciences
Haikun Ren Institute of Engineering Thermophysics, Chinese Academy of Sciences; University of Chinese Academy of Sciences
Haisong Zhang Institute of Engineering Thermophysics, Chinese Academy of Sciences; University of Chinese Academy of Sciences
Yong Tian Institute of Engineering Thermophysics, Chinese Academy of Sciences; University of Chinese Academy of Sciences
Bo Wang Institute of Engineering Thermophysics, Chinese Academy of Sciences; University of Chinese Academy of Sciences
Xiang Xu Institute of Engineering Thermophysics, Chinese Academy of Sciences; University of Chinese Academy of Sciences