Paragraph Styles Shape Effects Select- Drawing Editing EXAMPLE 9-5 The Simple Ideal Brayton Cycle A gas-turbine power plant operating on an ideal Brayton cycle has a pressure ratio of 8. The gas temperature is 300 K at the compressor inlet and 1300 K at the turbine inlet. Utilizing the air-standard assumptions, determine (a) the gas temperature at the exits of the compressor and the turbine, (b) the back work ratio, and (c) the thermal efficiency. SOLUTION A power plant operating on the ideal Brayton cycle is considered. The compressor and turbine exit temperatures, back work ratio, and the thermal efficiency are to be determined. Assumptions 1 Steady operating conditions exist. 2 The air-standard assumptions are applicable. 3 Kinetic and potential energy changes are negligible. 4 The variation of specific heats with temperature is to be considered. T, KA 1300 300 1 9in P = const. 5=8 P = const. 4o Wcomp 5 Notes A tes Font Paragraph Drawing EXAMPLE 9-6 An Actual Gas-Turbine Cycle T. KA Assuming a compressor efficiency of 80 percent and a turbine efficiency of 85 percent, determine (a) the back work ratio, (b) the thermal efficiency, and (c) the turbine exit temperature of the gas-turbine 1300 cycle discussed in Example 9-5. SOLUTION The Brayton cycle discussed in Example 9-5 is reconsidered. For specified turbine and compressor efficiencies, the back work ratio, the thermal efficiency, and the turbine exit temperature are to be determined. Analysis (a) The 7-s diagram of the cycle is shown in the figure opposite. The actual compressor work and turbine work are determined by using the definitions of compressor and turbine efficiencies, Eqs. 9-19 and 9-20: 300 25 gin, 43 2a Yout 8 Notes B EXAMPLE 9-7 Actual Gas-Turbine Cycle with Regeneration Determine the thermal efficiency of the gas-turbine described in Example 9-6 if a regenerator having an effectiveness of 80 percent is installed. SOLUTION The gas-turbine discussed in Example 9-6 is equipped with a regenerator. For a specified effectiveness, the thermal efficiency is to be determined. Analysis The T-s diagram of the cycle is shown in the figure opposite. We first determine the enthalpy of the air at the exit of the regenerator, using the definition of effectiveness: -N T. KA 1300 300 2a 4a regen saved (-605.39) kJ/kg 0.80- h, 825.37 kJ/kg (880.36-605.39) kJ/kg 11 ASUS Notes