Chapter 6, Problem 6.12P

2. An ideal gas undergoes a process from state 1 ( T1= 300 K, P1= 100 kPa) to state 2 ( T2= 600 K, P2 500 kPa). The specific heats of the ideal gas are : c, = 1 kJ/kg-K and c, = 0.7 kJ/kg-K. The change in specific entropy of the ideal gas from state 1 to state 2 (in kJ/kg-K) is (correct to two decimal places).

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T-9

Steam enters a turbine operating at a steady state at a pressure of 4 MPa, at temperature of 400 degrees Celcius, and a velocity of 200m/s . Saturated vapor exits at 100 degrees Celcius with a velocity of 100 m/s. Heat transfer from the turbine to its surroundings takes place at the rate of 20 kJ/kg of steam at a location where the average surface temperature is 350K. (a) Write the energy and entropy balance equations for a control volume the includes only the turbine and its contents (b) Determine the work produced, in kJ/kg of steam flowing. (c) For a control volume that includes only the turbine and its contents, calculate the rate of entropy production in kJ/kg*K (d) Assume the turbine described above is located in a factory where  the ambient temperature is 27 degrees Celcius. Determine the rate of entropy production in kj/kg*Kof steam, for an inlarged control volume that included the turbine and enough of its immediate surroundings so that heat transfer takes place from the…

20 kg of water substance at 10 bar and 500 K is contained in a piston-cylinder apparatus. The system does work and the pressure fall to 1 bar, heat being transferred from a reservoir at 600 K. It is stated that when 3400 kJ of work is done by the apparatus, the final internal energy of the water sustance is 40000 kJ. (a) What is the entropy change (kJ/K) of the water substance? (b) How much heat (kJ) is transferred?

No entropy accompanies work as it crosses the system boundary. But entropy may be generated within the system as work is dissipated into a less useful form of energy.

A rigid cylindrical tank stores 80 kg of a substance at 400 kPa and 480 K while the outside temperature is 290 K. A paddle wheel stirs the system transferring shaft work at a rate of 0.7 kW. At the same time an internal electrical resistance heater transfers electricity at the rate of 1.6 kW. A. Do an energy analysis to determine the rate of heat transfer for the tank. B. Determine the absolute value of the rate at which entropy leaves the internal system (at a uniform temperature of 480 K). Answer in kW/K C. Determine the rate of entropy increase in the system's surroundings. Answer in kW/K

Air is compressed adiabatically in a piston-cylinder assembly from 1 bar, 300 K to 6 bar, 600 K. The air can be modeled as an ideal gas and kinetic and potential energy effects are negligible. Determine the amount of entropy produced, in kJ/K per kg of air, for the compression. What is the minimum theoretical work input, in kJ per kg of air, for an adiabatic compression from the given initial state to a final pressure of 6 bar? Note that work is positive into the compressor. Part A Determine the amount of entropy produced, in kJ/K per kg of air, for the compression. o/m = i kJ/K

Steam enters a turbine operating at steady state at 1 MPa, 200°C and exits at 40°C with a quality of 83%. Stray heat transfer and kinetic and potential energy effects are negligible. Determine (a) the power developed by the turbine, in kJ. per kg of steam flowing, (b) the change in specific entropy from inlet to exit, in kJ/K per kg of steam flowing.