What is the effect of accounting for friction in steam nozzles at constant pressure ratios_________?
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Answer: A. increase in dryness fraction of exit steam
Explanation
Friction in steam nozzles generates internal irreversibilities that reheat the flowing working fluid. This frictional reheat effect increases the dryness fraction of the exit steam compared to isentropic expansion. Entropy generation shifts the expansion path to the right on a standard Mollier enthalpy entropy diagram. Steam nozzles convert thermal energy into kinetic energy as high-pressure steam expands rapidly outward. The dryness fraction represents the mass proportion of vapor present in a saturated liquid vapor mixture. Isentropic expansion assumes idealized reversible conditions without any frictional losses or fluid turbulence.
Engineers must account for nozzle friction to accurately predict turbine stage performance and power output. Excessive moisture droplet formation in low-pressure turbine stages causes severe blade erosion and pitting. Understanding exit quality changes helps designers select appropriate materials for advanced steam turbine blading. A decrease in dryness fraction would incorrectly imply that friction removes heat rather than generates it. Assuming no quality change ignores the fundamental thermodynamic reality of irreversible frictional heating effects. Depending on inlet quality is incorrect because friction consistently increases the relative exit vapor proportion.
- Subject
- Engineering
- Category
- Electrical Engineering
- Topic
- —
- Difficulty
- medium
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