Final answer:
The mass fraction and overall cycle efficiency require additional thermodynamic data, which is not provided, thus we cannot calculate precise values. Principles and formulas involving energy balances and efficiency calculations could be applied if the necessary details were known.
Step-by-step explanation:
To determine the mass fraction (y) extracted in the turbine and fed to the feedwater heater (FWH) as well as the overall cycle efficiency for a power plant using ammonia as the working fluid, we need to analyze the thermodynamic cycle. Unfortunately, without additional information such as the energy added in the boiler, specific enthalpies at various states, and the details of the turbine work, we cannot numerically calculate these values. However, we can discuss the principles and formulas that would be used if these details were provided.
The overall cycle efficiency would be calculated based on the net work output of the cycle divided by the heat input at the boiler. For an ideal Rankine cycle with a feedwater heater, the mass fraction y can be found using energy balance equations around the feedwater heater and turbine, considering the enthalpies at the various states of the cycle.
The Carnot cycle efficiency can be estimated assuming the plant operates between the given temperatures, which would be calculated using the Carnot efficiency formula: Effc = 1 - (Tc/Th), where Tc and Th are the absolute (Kelvin) temperatures of the cold and hot reservoirs, respectively. In the provided case, the temperatures would first need to be converted from Celsius to Kelvin before applying the formula.