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Consider a combined gas–steam power plant that has a net power output of 450 MW. The pressure ratio of the gas-turbine cycle is 14. Air enters the compressor at 300 K and the turbine at 1400 K. The combustion gases leaving the gas turbine are used to heat the steam at 8 MPa to 4008C in a heat exchanger. The combustion gases leave the heat exchanger at 460 K. An open feedwater heater incorporated with the steam cycle operates at a pressure of 0.6 MPa. The condenser pressure is 20 kPa. Assuming all the compression and expansion processes to be isentropic, determine

(a) the mass flow rate ration of air to steam,
(b) the required rate of heat input in the combustion chamber, and
(c) thermal efficiency of the combined cycle.

User Harben
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2 Answers

5 votes

Final answer:

To find the maximum theoretical efficiency for a heat engine, like in a nuclear power plant scenario, one applies the Carnot efficiency formula by converting the high and low operational temperatures to Kelvins and then following the formula Effc = 1 - (Tc/Th). For temperatures of 300°C and 27°C, this results in an efficiency of 47.65%.

Step-by-step explanation:

The question revolves around the concept of thermodynamics and how it applies to practical heat engines and electrical power generation. By considering a nuclear power reactor with water at high temperature and steam condensing at a lower temperature, the maximum theoretical efficiency for a heat engine can be calculated.

In general, the Carnot efficiency formula, which is Effc = 1 − (Tc/Th), where Tc is the temperature of the cold reservoir and Th is the temperature of the hot reservoir in Kelvins, can be used to calculate the maximum theoretical efficiency of a heat engine. To get the efficiency, we first convert the temperatures from degrees Celsius to Kelvins (by adding 273.15 to each temperature). For a nuclear reactor operating between a high temperature of 300°C (573.15K) and a low temperature of 27°C (300.15K), the theoretical efficiency is calculated using the Carnot efficiency formula.

The calculation would result in the following:

  1. Convert temperatures from Celsius to Kelvin: Th = 300 + 273.15 = 573.15 K, Tc = 27 + 273.15 = 300.15 K.
  2. Plug into the Carnot efficiency formula: Effc = 1 − (Tc/Th) = 1 − (300.15/573.15).
  3. Calculate the efficiency: Effc = 1 − 0.5235 = 0.4765 or 47.65%.

This would be the maximum theoretical efficiency of the cycle, not accounting for real-world losses that would make actual efficiency lower.

User Prakhar Trivedi
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4 votes

Answer: the correct answer is b

Step-by-step explanation:

B is goin to be your best bet

User Haseeb Wali
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5.7k points