Optimization and flow field analysis of a helium turbo-expander impeller for a 5 TPD hydrogen liquefier using a cylindrical projection based parametric approach.

Improving the efficiency of hydrogen liquefaction cycles is essential for reducing costs and promoting clean hydrogen energy. As the core refrigeration component, the helium turbo-expander (HTE) experiences significant efficiency losses within the impeller passage. However, current design methodologies often involve complex manual iterations that can limit systematic 3D optimization. This paper explores a parametric approach for 3D impeller design based on cylindrical projection (Cylindrical Projection based Parametric Impeller Design). This method allows for the definition of blade profiles at the hub, mid span, and shroud sections using projection parameters (Tu, Tr), facilitating smooth geometric transitions. To evaluate the approach, a final stage HTE impeller for a 5 TPD hydrogen liquefier was analyzed. Numerical simulations indicate that adjusting the flow path geometry using these parameters can lead to significant performance variations: Case C1 showed a calculated 16.58% reduction in helium mass flow at a constant refrigeration power of 30,551.4 W, while Case C2 yielded a predicted isentropic efficiency of 92.33% (a 2.81% absolute increase) with a 3.5% reduction in required inlet pressure. Flow field analysis using the Ω vortex identification method suggests that these improvements are associated with the suppression of high loss vortex structures. Specifically, the concave blade profiles appear to mitigate transverse pressure differences, reducing the intensity of passage vortices. These results demonstrate that the parametric projection method offers a useful alternative for the geometric optimization of cryogenic turbo-expander impellers.