Consider a simple ideal Rankine cycle with

QUESTION:

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A rankine steam cycle modified with two closed feedwater heaters and one open feedwater heater is considered. The T-s diagram for the ideal cycle is to be sketched. The fraction of mass extracted for the open feedwater heater y and the cooling water flow temperature rise are to be determined. Also, the rate of heat rejected in the condenser with the thermal efficiency of the plant is to be determined.

Assumptions are

1. Steady operating conditions exist

2. kinetic and potential energy changes are negligible.

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(a)Sketch the T-s diagram for the ideal cycle as below.

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(b) Using the data from the problem statement, the enthalpies at various states are

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An energy balance on the open feedwater heater gives

Where $$y$$ is the fraction of steam extracted from the low-pressure turbine. Solving for y,

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( C) An energy balance on the condenser gives

Solving for the temperature rise of cooling water, and substituting with correct units,

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(d) The rate of heat rejected in the condenser is

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The rate of heat input in the boiler is

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The thermal efficiency is then