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Maximize the Efficiency of a Rankine Cycle

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Maximizing the Efficiency of a Regenerative Rankine Cycle

Introduction

Rankine cycles are a thermodynamic process that turn heat into mechanical work. They're often employed in generating electrical power, with high pressure steam used to rotate a turbine.

The thermodynamic efficiency of a Rankine cycle is  where  is the net work done by the system, and Q is the heat added. Operating parameters are chosen to maximize efficiency - these may be the temperatures or pressures at various points in the system.

A typical regenerative Rankine cycle is illustrated below.

In this application, we will

 • define a procedure that calculates the cycle efficiency as a function of the pump outlet pressures at points 2 and 4
 • and then find the pump outlet pressures that maximize the efficiency of the cycle.

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Cycle Efficiency

This Code Edit region contains a procedure that calculates the cycle efficiency as a function of pump output pressures. The procedure calculates

 • the enthalpies, entropies, specific volumes and temperatures at every point,
 • the fraction of water removed at the high and low pressure turbine extraction points,
 • and the work done by the pumps.

The procedure can be modified to return any of these values; right now, it only returns the efficiency.

Procedure to Calculate Efficiency as a Function of Pressures at Points 2 and 4

Hence if both pumps output at 105 Pa, then the cycle efficiency is

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Optimization

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