Plot the Rankine cycle on T-S diagram and derive an expression for thermal efficiency of the cycle. List different methods of improving the performance of the cycle. Discuss any one method in brief.
1 Answer

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Work done on pump, per kg of water, $W_P= h_2 - h_1$

Energy added in steam generator, $q_1= h_3 - h_2$

Work delivered by turbine, $WT= h_3 - h_4$

Energy rejected in the condenser, $q_2= h_4 - h_1$

The thermal efficiency of the Rankine cycle is given by,

$η = \frac{q_1 - q_2}{q_1} = \frac{(h_3 - h_2) - (h_4 - h_1)}{h3 - h2} = \frac{(h_3 - h_4) - (h_2 - h_1)}{h3 - h2}$

Methods to increase efficiency

  1. Lowering the condenser Pressure:-

  2. Superheating the steam to high temperatures:-

    The average temperature at which heat is added to the steam can be increased without increasing the boiler pressure by superheating the steam to high temperatures.

    Superheating the steam to higher temperatures has another very desirable effect: It decreases the moisture content of the steam at the turbine exit.

  3. Increasing the Boiler pressure

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