previous prelim problems

previous prelim problems - A. A 50 kg block of cast iron...

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Unformatted text preview: A. A 50 kg block of cast iron casting at 500 K is thrown into a large lake that is at a temperature of 285 K. The iron block eventually reaches thermal equilibrium with the lake water. Assuming 1) an average specific heat of 0.45 kJ/(kg K) for the iron and iron and 2) iron as incompressible substance, determine: a) The entropy change of the iron block b) The entropy change of the lake water c) The entropy generated during the process B. An open feedwater heater for preheating the water before entering a boiler operates on the principle of mixing (no work involved) the water with the steam that has been bled from the turbine. For the state as shown in the figure below, calculate the rate of net entropy production for the process, assuming the process to be steady flow and adiabatic. p1 = 1 MPa p3 = 1 MPa Feedwater Heater T3 = 160 oC T1 = 40 C o m = 4 kg/s 3 • C. Consider the turbocharger of an internal combustion engine. The exhaust gases enter the turbine at 450 oC at a rate of 0.02 kg/s and leave at 400 oC. Air enters the compressor at 70 oC and 95kPa at a rate of 0.018 kg/s and leaves at 135 kPa. The mechanical efficiency between the turbine and the compressor is 95% (5% of turbine work is lost during its transmission to the compressor). Air is modeled as ideal gas. Using air properties (ideal gas) for the exhaust gases, determine: (a) The air temperature at the compressor exit (b) The isentropic efficiency of the compressor 400 oC Air, 70 oC, 95 kPa, 0.018 kg/s Exhaust gas 450 oC, 0.02kg/s 135 kPa Turbine Compressor ...
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This note was uploaded on 03/15/2010 for the course ENGRD 2210 at Cornell.

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