Unformatted text preview: EML 3100 Practice Exam 2 In the actual exam, either property values or tables will be provided. 1. (15%) In engineering thermodynamics, we have learned both the first law and the second law. For the following heat engine system, please first answer the questions and then use this heat engine system to illustrate the physical meanings of both laws. In a steam power plant 1 MW of heat is added to the boiler to generate steam, 0.58 MW is taken out of the condenser for rejecting to the river, and 0.02 MW is consumed by the pump. Find the power output of the turbine and the thermal efficiency. 2. (20%) In a piston‐cylinder device, the piston that can impose a pressure of 200 kPa is floating without any restriction during the process. The 2 kg of water with a quality of 25% initially inside the cylinder is heated until its temperature is raised by 20 oC when the process is completed. What are the heat transfer and work done in the process. Also indicate the process path on a P‐
v and a T‐v diagram. 3. (15%) A piston/cylinder system contains 1.5 kg of air at 300 K and 150 kPa. It is now heated in a two‐step process : First by a constant‐volume process to 1000 K (state 2) followed by a constant‐pressure process to 1500 K (state 3). Find the total heat transfer for the process from state 1 to state 3. 4. (20%) A steam turbine receives superheated steam at 15 MPa and 600 oC at a mass flow rate of 100 kg/s. At middle section, 20 kg/s is withdrawn at 2 MPa and 350 oC and the rest exits the turbine at 75 kPa and 95% quality. Assume an adiabatic turbine and negligible KE and PE changes between the inlet and two outlets. Under a steady state operation, what is the power delivered by the turbine ? 5. (20%) In a large gas–turbine power plant, process air is pre‐heated by the turbine exhaust gas in a cross‐flow heat exchanger called regenerator before it enters the combustion chamber. Air enters the regenerator at 1 MPa and 550 K with a mass flow rate of 800 kg/min. Total heat transfer from the exhaust gas to the air is at a rate of 3200 KW. Exhaust gas enters the regenerator at 140 kPa and 800 K and leaves at 130 kPa and 600 K. Also treat the exhaust gas as air and then determine (a) the exit enthalpy of air and (b) the mass flow rate of the exhaust air. You may assume both process air and exhaust gas are ideal gases. 6. (10%) A self‐proclaimed innovative engineer announced that a super engine has been developed and it can produce 250 KW of net power while receiving 750 KW of heat from a burner at 400 K while rejecting heat to the environment at 300 K. Is this a reasonable claim ? Please substantiate your answer. ...
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 Fall '08
 Sherif
 Dynamics, Sort, 10%, 25%, 300 K, 2 kg, 1 MW

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