The effects of rate of expansion and injection of water droplets on the entropy generation of nucleating steam flow in a Laval nozzle |
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Authors: | A R Teymourtash Javad Abolfazli Esfahani S A Mousavi Shaegh |
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Institution: | (1) Mechanical Engineering Department, Ferdowsi University of Mashhad, P.O. Box 91775-1111, Mashhad, Iran |
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Abstract: | The entropy generation due to irreversible heat transfer between vapor and liquid phases in a nucleating steam flow in a Laval
nozzle is studied. To calculate the entropy generation due to self-condensation in transonic steam flow, a thermodynamic model
is presented. The calculations of nucleating steam flow and the predictions of entropy generation rely on one-dimensional
two-phase model. This model shows that the most of the thermodynamic losses take place during the nucleation phenomena. The
effect of rate of expansion on the exergy losses is considered by decreasing the divergent angle of nozzle. Also micro-sized
pure water droplets is injected theoretically to supercooled steam right after the nozzle throat at the onset of divergent
section and the effects of injected droplets on thermodynamic losses and nucleation phenomena are investigated. The results
indicate that decreasing the divergent angle and also injection of droplets diminishes the pressure rise in transonic steam
flow and decreases the thermal entropy generation due to nucleation. |
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