Influence of sealing cavity geometries on flank clearance leakage and pressure imbalance of micro-scale transcritical CO2 scroll expander by CFD modelling

For a micro-scale (< 10 kW) transcritical CO2 waste heat recovery power system, the scroll-type expander is a potential candidate. However, the scroll expander suffers from leakage and pressure imbalance issues because of the high-pressure working conditions. The current study designs twelve different sealing cavities based on the reference of labyrinth seals and presents a transient CFD analysis to investigate the flow behaviors. The results show that the sealing cavity has a positive impact on the machinery performance, where the isentropic efficiency improves from 0.907 % to 0.952 % for the single group. Increasing the height and cavity number of single-group sealing can improve the performance while enlarging the cavity spacing shows the opposite. There is no significant difference between the three different shapes of RST, ITST and RTST. However, the improvement in the instantaneous leakage ratio is remarkable, the leakage reduces from 55.3 % to 70.2 %. For the multi-group sealing cavity, the isentropic efficiency slightly improves to 0.982 %, and the pressure imbalance gets partially optimized. The locations of the sealing cavity are important to solve the pressure imbalance between two symmetrical working chambers. The paper suggests designing the upstream sealing cavity for a lower-pressure working process and downstream for a higher-pressure working process, which can ideally achieve the maximum pressure balance.

Automated summary

This study investigates the impact of sealing cavities on the performance of scroll-type expanders in transcritical CO2 waste heat recovery power systems. The results show that sealing cavities can improve machinery performance, reduce leakage, and optimize pressure imbalance issues. Different shapes of sealing cavities have similar effects in enhancing isentropic efficiency and reducing leakage ratio.