Question

Consider a regenerative steam Rankine cycle with a single open feedwater heater. At the entrance to the turbine the steam is at 17.5MPa and 650∘

C.20% of the steam is extracted from the turbine at 1.4MPa and directed to the open feedwater heater directly, while the remaining steam is further expanded to 20kPa before being sent to the condenser unit. The steam is condensed at 20kPa to saturated liquid conditions before being pumped to higher pressure and directed to the open feedwater heater. After mixing in the open feedwater heater, the combined stream is pumped to high pressure and directed to the boiler to vaporize the steam. (a) What is the degree of sub-cooling of the liquid at the exit to the open feedwater heater (i.e. what is the temperature difference between the liquid leaving the open feedwater heater and a saturated liquid at the same temperature)?

Answer 1

The degree of sub-cooling in a regenerative steam Rankine cycle with a single open feedwater heater can be calculated by finding the temperature difference between the liquid leaving the open feedwater heater and a saturated liquid at the same pressure.

Step-by-step explanation:

The degree of sub-cooling of the liquid at the exit to the open feedwater heater can be determined by finding the temperature difference between the liquid leaving the open feedwater heater and a saturated liquid at the same temperature. Since the steam is condensed at 20kPa to saturated liquid conditions before being pumped to higher pressure and directed to the open feedwater heater, the temperature of the liquid leaving the open feedwater heater will be higher than that of a saturated liquid at the same pressure. Therefore, the degree of sub-cooling is equal to the temperature difference between the liquid at the exit and the saturation temperature at the same pressure.