Question 167Steam Plants - Assistant Engineer
70% to passWhy does air entry into the main condenser reduce the efficiency of the steam cycle?
ASteam flow rate through the main turbine increases
BCondensate sub cooling in the main condenser increases
CThe air mixes with the steam and enters the condensate
DLow-pressure turbine exhaust steam enthalpy value increases
AI Explanation
The correct answer is D) Low-pressure turbine exhaust steam enthalpy value increases. Air entry into the main condenser reduces the efficiency of the steam cycle because it increases the enthalpy (heat content) of the low-pressure turbine exhaust steam. The presence of air in the condenser increases the total pressure in the condenser, raising the condensation temperature and pressure. This, in turn, increases the enthalpy of the low-pressure turbine exhaust steam, reducing the amount of work that can be extracted from the steam in the turbine. The other answer choices are incorrect because they do not directly address the impact of air entry on the efficiency of the steam cycle.
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