single-screw expander, ORC, CFD
Organic Rankine Cycle (ORC) systems rely on the expander performance to generate power output in an efficient manner. Especially in the low power range (below 100 kWe), positive displacement (PD) expanders (e.g. scroll, twin-screw, reciprocating, vane, spool, etc.) result to be cost-effective. However, commercially available PD expanders are still limited and, in many cases, the existing PD compressors are operated in reversed mode by introducing design modifications to sealing, bearings, port sizes, lubrication requirements to increase both their performance and reliability. Computational fluid dynamics (CFD) as a design and analysis tool of positive displacement machine has been proven to be viable. Challenges arise when CFD is applied to PD machines due to the dynamics of the expansion (or compression) process, presence of internal leakages and heat transfer mechanisms, as well as deforming working chambers. Different grid generation methods and solution schemes have been successfully implemented to scroll, twin-screw and reciprocating machines (Rane et al. 2012, Rane et al. 2013). The limitation of such methodologies to be applied directly to complex multi-rotor machines has been highlighted by Rane et al. (Rane at al. 2012). In this paper, a single-screw expander is used as benchmark to evaluate different grid generation methodologies (dynamic remeshing and Chimera strategy overlapping grid) and commercial software, in terms of computational resources required, accuracy of the results and limitations. The calculations have been performed with air to reduce the complexity of the problem. Â Â Â Â REFERENCES Rane S., Kovacevic A., Kethidi M., â€œCFD Modeling in Screw Compressors with complex multi rotor configurationsâ€(2012), Int. Compressor Engineering Conference at Purdue Univ. Paper 2141. Rane S., Kovacevic A., Stosic N., Kethidi M., â€œGrid deformation strategies for CFD analysis of screw compressorsâ€, Int. J. Refrigeration, 36(2013), 1883-1893.