A Sweep Study for the Intermediate Pressure in a Single-Reheat Steam Rankine Cycle

The general influence of the reheat pressure on the performance of the steam Rankine cycle with reheat, over a broad range from 0.1 to 12.5 MPa, is investigated. The response curves of several performance variables are computed as the reheat pressure changes while fixing some cycle parameters at reasonable reference values. The findings show that both the specific total input heat and the specific rejected heat monotonically decrease with the reheat pressure, approximately according to a logarithmic function; the specific net output shaft work has a peak value near the low reheat pressure of 0.2 MPa, and it can be approximated by a cubic function; the thermal cycle efficiency has an optimum peak value near a reheat pressure of 3.2 MPa, with a quartic regression expression for its natural-logarithm transformed quantity; the steam dryness fraction at the exit of the high-pressure turbine increases monotonically with the reheat pressure with a profile that closely a cubic polynomial; the steam dryness fraction at the exit of the intermediate-pressure turbine decreases monotonically with the reheat pressure, approximately according to a logarithmic profile; and the specific entropy generation decreases monotonically with the reheat pressure following nearly a power function. Also, our results show that there is a narrow range of reheat pressures during which the stream dryness fraction at the exit of both turbines is simultaneously above the acceptable threshold of around 90% (thus, 10% stream wetness fraction). This range does not include the optimal reheat pressure of maximum cycle efficiency.