the turbine where it expands, consequently undergoing a temperature reduction. The power thus produced turns the compressor (which moves the gas around the loop) and the generator which produces the electrical power. After leaving the turbine considerable energy remains in the gas; some energy is transferred to the "cold side" gas flow in the recuperator (a gas-to-gas plate/fin heat exchanger). The minimum gas temperature occurs in the cooler (a gas-to-liquid metal heat exchanger). Here cool liquid metal (NaK) from the radiator system absorbs heat energy from the gas. With the gas at minimum temperature it is ready for compression (the lower the gas temperature the lower the energy required to achieve a given temperature rise). After compression the gas flows through the recuperator, picking up the thermal energy from the "hot side" at the cycle, and again enters the cavity heat exchanger. Maximum gas pressure occurs at the compressor outlet. 4.8.2 Brayton Cycle Design Equations Figure 4-33 is an approximate temperature-entropy (T-S) diagram for the closed Brayton cycle. The Fig 4-33. Cycle State Diagram temperature (T) and pressure state points around the cycle are identified by the following subscripts: 0 Compressor inlet (cooler outlet) 1 Compressor outlet (recuperator cold side inlet) 2 Recuperator cold side outlet (cavity heat absorber inlet) 3 Cavity heat absorber outlet (turbine inlet) 4 Turbine outlet (recuperator hot side inlet) 5 Cooler inlet (recuperator hot side outlet) Thus T3 is the maximum gas temperature in the cycle. Other state points associated with the cooler are: Some fundamental relationships for the closed Brayton cycle are given below:
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