POWER PLANT/MISCELLANEOUS PROBS) 10. A superheat steam Rankine cycle has turbine inlet conditions of 17.5 MPa and 530°C expands in a turbine to 0.007 MPa. The turbine and pump polytropic efficiencies are 0.85 and 0.75 respectively, pressure losses between pump and turbine inlet are 1.5 MPa. What should be the pump work in kJ/kg? A. 17.34 B. 27.32 Answer: C C. 25.32 D. 47.33 11. In an open feedwater heater for a steam plant, saturated steam at 7 bar is mixed with subcooled liquid at 7 bar and 25°C. Just enough steam is supplied to ensure that the mixed steam leaving the heater will be saturated liquid at 7 bar when heater efficiency is 95%. Calculate the mass flow rate of subcooled liquid if steam flow rate is 0.865 kg/s. Steam properties are:At 7bar, saturated vapor:h, = 2763.5 kJ/kg + At 7 bar and 25°C:hr = 105.5 kJ/kg At 7 bar, saturated liquid: h697.22 kJ/kg A. 2.725 kg/s B. 3.356 kg/s Answer: C C. 2.869 kg/s D. 3.948 kg/s 12. Steam expands adiabatically in a turbine from 2000 kPa, 400°C to 400 kPa, 250°C. What is the effectiveness of the process in percent assuming an atmospheric pressure of 18°C. Neglect changes in kinetic and potential energy. Steam properties are:At 2000 kPa and 400°C:h = 3247.6 kJ/kg s = 7.1271 kJ/kg-K At 400 kPa and 250°C:h =2964.2 kJ/kgs = 7.3789 kJ/kg-K A. 82 B. 84 Answer: D C. 79.60 D. 79.46 13. A heat exchanger was installed purposely to cool 0.50 kg of gas per second. Molecular weight is 32 and k = 1.32. The gas is cooled from 150°C to 80°C. Water is available at the rate of 0.30 kg/s and at a temperature of 15°C. Calculate the exit temperature of the water in °C. A. 44.86 B. 42.86 C. 46.45 D. 40.34 Answer: A