Consider the situation described in Problem 7.112. How does the thermal efficiency change if the high-temperature heat-addition process is now conducted at 15MPa instead of 6 MPa? Be quantitative. How does the net work produced per unit mass of steam (Ẇ_net=ṁ) compare for the two cycles?

Problem 7.112

Consider a steady-flow ideal Carnot cycle, using steam as the working fluid, in which the high-temperature, constant-pressure heat-addition process starts with a saturated liquid and ends with a saturated vapor.

A. Plot this cycle in T–s coordinates showing the steam dome.

B. Calculate the thermal efficiency for this cycle if the pressure of the high temperature steam is 6 MPa and the low-temperature heat-rejection process occurs at 300 K. Calculate the values of the quality at the beginning and end of the heat-rejection process.

C. Explain why it is difficult to operate a practical steam power plant on the ideal Carnot cycle of part A.

Saturated liquid (P = 6 MPa) Win OL Saturated vapor (P = 6 MPa) W out TL = 300 K