MEEN 315, SECTION 503 PRINCIPLES OF THERMODYNAMICS Spring 2013 Homework #6 DUE March 5, 2013 N.B.: The enhancement lectures “Example_Isentropic Efficiency” and “Example_SS Work Device” may be helpful on this homework. They are located on the elearning website LecturesEnhancement LecturesExample_Isentropic Efficiency and Example_SS Work Device, respectively. 1. A steam turbine receives steam from two boilers, as shown below. One flow is 5 kg/s at 3 MPa and 700°C, and the other flow is 15 kg/s at 800 kPa and 500°C. The exit state is 10 kPa, with a quality of 96%. Find the total power out of the adiabatic turbine. 2. An air turbine with an isentropic efficiency of 80% actually produces 120 Btu/lbm of work. The inlet temperature is 1800 R, and it exhausts to the atmosphere (Pe = 14.7 psia). Find the required inlet pressure and the exhaust temperature. Draw the actual and ideal processes on P-v and T-s diagrams. 3. A steam turbine inlet is at 1200 kPa, 500°C. The exit is at 200 kPa. For an adiabatic turbine, what is the lowest possible exit temperature of the steam? What is the isentropic efficiency of the turbine for that exit condition? 4. A compressor in a refrigeration cycle elevates R-134 from an initial state of 50 psia pressure, saturated vapor to a final state of 180 psia pressure and temperature of 140 F. The compressor can be assumed to be adiabatic (no heat transfer). a. Determine the specific work of the compressor and the amount of specific entropy generation during the process. b. Suppose the compressor now operates as an ideal turbine (reversible and adiabatic) where initial pressure is 180 psia, initial temperature is temperature of 140 F, and the ideal exit state is 50 psia. What is the maximum work the turbine can make? c. What does the difference between the work into the compressor and the work out of the ideal turbine represent? 5. An air compressor used in an industrial facility is constantly monitored for faults to ensure it is operating at optimal efficiency. Further, air compressors are generally cooled (e.g., exterior fins) to effect as much heat transfer as possible so that the air temperature remains roughly constant through the compressor (i.e., it’s desired for the air to have high pressure, but not necessarily high temperature). Suppose air is initially at P = 14.7psia and T = 80F. The air compressor increases the pressure to 190 psia. The air flow rate into the compressor is 44.1 ft3/min and the compressor uses 13.5 kW electric power (assume the electric-to-mechanical efficiency is 100%). According to the fault monitoring, the temperature gauge providing the exit air temperature reads 80F. Is this process possible? Regardless of your answer, if the process were not possible what might be wrong?A steam turbine receives steam from two boilers, as shown below. 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