# SL: Real Power Cycles

### A more "realistic" power cycle: the ideal Rankine Cycle

The problem with compressing a mixture of liquid and vapor is that the work required to compress a liquid is considerably smaller than that of a vapor (or mixture). Why?

##### Note:

Again, the most convenient choice for the boiler operation is isobaric; therefore, the compression is typically to a sub-critical pressure.

##### Outcome:

Identify the key issues in choosing a working fluid

Obviously, the efficiency calculation used for a Carnot engine is no longer applicable. Why?

$\eta = \frac{\dot W_{net}}{\dot Q_H} = \frac{|\dot W_{turbine}| - |\dot W_{compressor}|}{\dot Q_H}$

##### Outcome:

Solve for the net power obtained and efficiency of reversible power cycles

##### Outcome:

Calculate the coefficient of performance of a reversible refrigeration cycle

##### Note:

An ideal Rankine cycle follows this (type of) path in reversible steps (hence the vertical lines). A real cycle would be irreversible so that we must also correct for the irreversibility.