Determine the dryness fractions at the high- and low-pressure turbine exit and the cycle efficiency.

Question

To avoid having addition inlet and outlet pipes through the wall of the pressure vessel of pressurized water nuclear reactors, it is usual to employ a steam – heated reheat cycle. Stem is bled from the boiler delivery main to reheat the steam leaving the high-pressure turbine before it enters the low-pressure turbine. The data for the cycle are as follows:

Boiler outlet condition – Saturated steam at 60 bar

LP turbine inlet pressure – 5 bar

Condenser pressure – 0.05 bar

HP turbine isentropic efficiency – 0.80 bar

LP turbine isentropic efficiency – 0.87 bar

Reheat temperature – 270 ⁰C

The feed pump terms can be neglected, and it may be assumed that the bled steam leaves the reheater at a temperature equal to that at the high-pressure turbine exit. Determine the dryness fractions at the high- and low-pressure turbine exit and the cycle efficiency.

Also determine these quantities if no reheating were used. Comment briefly on the result.             60