Unsteady Leakage Flow Through Axial Clearance of an ORC Scroll Expander

As the scroll-type expander (STE) becomes an attractive expansion device for small-scale organic Rankine systems, performance enhancement of STE could achieve a further improvement of the energy efficiency of ORC system. The gas leakages through the axial and radial clearances have a great effect on the overall performance of STE. The present work proposed a three-dimensional numerical technique available for modeling the radial leakage flows through the axial clearances at the tip and root of scroll wrap. The radial leakage flow patterns of both axial clearances are investigated. Asymmetrical distribution of the radial leakage flow through the axial clearances at both sides of working chambers are revealed. Leakage flow difference between the top and bottom axial leakage clearances is comparatively discussed. The effects of radial leakage on the flow fields in the working chambers are also analyzed. The results show the radial leakage flows occur at the axial clearances of both the scroll segments between asymmetrical working chambers and those between symmetrical working chambers. Radial leakage flows through the top and bottom axial clearances are approximately symmetrical about the meshing line. Pressure distribution in the axial clearance passage is uneven along the scroll involute direction, especially in the axial clearance passages between asymmetric chambers. Pressure distortion occurs in the downstream of the axial clearance passage between asymmetric working chambers nearby the mesh point of the scroll wraps. Radial leakage flow leads to the secondary vortex flows and non-uniform pressure distributions in the working chambers.