Name:_______________________________
ME 305 Thermodynamics II
Woodbury/Hewitt
Çengel & Boles, 7th Edition July 14, 2011 Homework #3
Summer 2011
These problems are due Monday, July 18. 1. At the beginning of the compression process of an cold air‐standard Otto cycle, p1 = 1 bar and T1 = 290K, and V1= 400 cm3. The maximum temperature in the cycle is 2200 K and the compression ratio is 8. Assume constant specific heats at room temperature(300K). a) What is the heat addition in kJ? b) What is the net work in kJ? c) What is the thermal efficiency of the cycle? d) What is the mean effective pressure in bar? e) If this engine operates at 3600 RPM, how much power is delivered (in kW)? Note that one cycle requires two revolutions of the crankshaft. 2. The pressure and temperature at the beginning of compression in an air‐standard Diesel cycle are 95 kPa and 300K. At the end of the heat addition process, the pressure is 7.2 MPa and 2150 K. Assume variable specific heats. a) What is the compression ratio? b) What is the cutoff ratio? c) What is the thermal efficiency of the cycle? d) What is the mean effective pressure? 3. Repeat problem 2 assuming constant specific heats at room temperature (300K). 4. An ideal dual cycle has a compression ratio of 16 and a cutoff ratio 1.15. The pressure ratio during the constant volume portion of the heating is 2.2. At the beginning of the cycle the air is 95 kPa and 300 K. Assume variable specific heats. a) The heat addition at constant volume and at constant pressure in kJ/kg. b) The net work of the cycle in kJ/kg. c) The heat rejection in kJ/kg. d) The thermal efficiency. 5. Air enters the compressor of an ideal air‐standard Brayton cycle at 100 kPa and 300 K with a volumetric flow rate of 5 m3/s. The compressor ratio is 10. Assume variable specific heats. The turbine inlet temperature is 1600 K a) The thermal efficiency of the cycle b) The back work ratio (wcompressor/wturbine) c) The net power developed, in kW.