In view of 3-D two-phase flow with spontaneous condensation in cryogenic turbo-expanders
a mathematical model of non-equilibrium condensation is employed to predict the condensation nucleation and droplet growth in gas repaid expansion
where the nucleation model corrected for non-isothermal effect and Gyarmathy droplet growth model are considered. Following the analysis for simulation results
the effects of inlet superheat degree and rotation on the spontaneous condensation in impeller flow passage are investigated
and the distributions of droplet number density
droplet diameter and wetness are obtained. A higher inlet superheat degree results in that repaid nucleation occurs in guiding section and consequently the process develops slowly
thus the gas remains in a higher supercooled state and the nucleation region is enlarged. Because of the interaction of condensation and secondary flow in impeller flow passage
the adverse temperature gradient causes an additional thermodynamic loss. Moreover
the strength of adverse pressure temperature gradient promotes the separation of boundary layer and further causes additional flow loss. For radial and mixed-flow turbines
the small droplets very likely gather and form bigger ones in the secondary flow region
wall of suction side and wake flow region
which leads to secondary nucleation
secondary droplets on a large-scale and the further additional mechanical loss.
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references
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