6.79 Air enters a turbine operating at steady state at 8 bar, 1400 K and expands to 0.8 bar. The turbine is well insulated, and kinetic and potential energy effects can be neglected. Assuming ideal gas behavior for the air, what is the maximum theoretical work that could be developed by the turbine in kJ per kg of air flow? . . . evaluate the thermodynamic performance of the system.97 An inventor has provided the steady-state operating data shown in Fig. P6. The ideal gas model applies to the air. . The system receives and discharges energy by heat transfer at the rates and temperatures indicated on the figure. Using energy and entropy rate balances. All heat transfers are in the directions of the accompanying arrows.97 for a cogeneration system producing power and increasing the temperature of a stream of air. Kinetic and potential energy effects are negligible.6. in kW/K. the pressure and temperature of the air are 475 kPa and 450 K. (a) the rate of heat transfer. At the pipe exit. Determine at steady state.101 Air at 500 kPa. Kinetic and potential energy effects can be ignored. 300 K.6.39. and (b) the rate of entropy production. Air can be modeled as an ideal gas with k 5 1. for an enlarged control volume that includes the pipe and enough of its surroundings that heat transfer occurs at the ambient temperature. in kW. 500 K and a mass flow of 600 kg/h enters a pipe passing overhead in a factory space. for a control volume comprising the pipe and its contents. respectively. . .6. determine the rate of entropy production. in kW. The mass flow rate of refrigerant entering the compressor is 7 kg/min. to 10 bar. (b) If the heat transfer occurs at an average surface temperature of 508C. in kW/K. Kinetic and potential energy effects can be neglected. saturated vapor. and the power input is 10. (a) Determine the rate of heat transfer.85 kW. in kW/K. (c) Determine the rate of entropy production. 908C in a compressor operating at steady state. for an enlarged control volume that includes the compressor and its immediate surroundings such that the heat transfer occurs at 300 K.103 Refrigerant 134a is compressed from 2 bar. Assuming the ideal gas model for air with cp 5 0.107 shows data for a portion of the ducting in a ventilation system operating at steady state. determine (a) the temperature of the air at the exit.107 Figure P6. in 8F.6. in ft. and ignoring kinetic and potential energy effects.24 Btu/lb _ 8R. in Btu/min _ 8R. . and (c) the rate of entropy production within the duct. The ducts are well insulated and the pressure is very nearly 1 atm throughout. (b) the exit diameter. . Determine the mass flow rate of air entering the compressor. The compressor power input is 6700 kW. in kW/K.6.110 shows an air compressor and regenerative heat exchanger in a gas turbine system operating at steady state. and a separate stream of air passes though the regenerator in counterflow.110 Figure P6. Air flows from the compressor through the regenerator. in K. Operating data are provided on the figure. the temperature of the air exiting the regenerator at state 5. and the rates of entropy production in the compressor and regenerator. Stray heat transfer to the surroundings and kinetic and potential energy effects can be neglected. in kg/s. place the components in rank order. (e) If the goal is to increase the power developed per kg of steam flowing. beginning with the component contributing the most to inefficient operation of the overall system. evaluate the rate of entropy production. 5408C and undergoes a throttling process to 40 bar before entering the turbine.111 shows several components in series. which of the components (if any) might be eliminated? Explain. 2408C. Kinetic and potential energy effects can be ignored.111 Figure P6. . and then undergoes a throttling process to 1 bar before entering the condenser. Steam exits the boiler at 60 bar. all operating at steady state. (d) Using the result of part (c).6. in kJ per kg of steam flowing. (b) Determine the power developed by the turbine. (a) Locate each of the states 2–5 on a sketch of the T–s diagram. Steam expands adiabatically through the turbine to 5 bar. Liquid water enters the boiler at 60 bar. (c) For the valves and the turbine. each in kJ/K per kg of steam flowing. (c) the rates of entropy production. Determine (a) temperature T3.112. (d) Using the result of part (c). . P6. (b) the power output of the second turbine. beginning with the component contributing most to inefficient operation of the overall system. Stray heat transfer and kinetic and potential energy effects can be ignored. in kW. each in kW/K. place the components in rank order.112 Air as an ideal gas flows through the turbine and heat exchanger arrangement shown in Fig.6. Steady-state data are given on the figure. for the turbines and heat exchanger. in K. 5 lbf/in.114.2 Assuming no heat transfer and neglecting kinetic and potential energy effects. and the amount of entropy produced. determine the final mass of refrigerant in the cylinder. The surrounding atmospheric pressure is 14. as illustrated in Fig. P6. . 508F.5-ft3 cylinder that is initially evacuated to take on a service call. in Btu/8R. in lb.2.5 lbf/in.2 (gage). The technician opens a valve and lets refrigerant from the storage tank flow into the cylinder until the pressure gage on the cylinder reads 25.6. A technician fills a 3.116 A two-phase liquid–vapor mixture of Refrigerant 134a is held in a large storage tank at 100 lbf/in.