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Unformatted text preview: Test #1 Elements of Thermo EML 3007 February 5, 2009 Open book (class text only), open notes (prepared by you, class site downloads). 2 hours. Problem 1 (40). Nitrogen gas at 300 K and 0.5 MPa (State 1) flows steadily through a heat exchanger, then through a turbine. In the heat exchanger, heat is supplied to the nitrogen at a rate of 1.kW. The heat exchanger exit temperature is 400 K (State 2). The flow then enters the turbine, exiting at State 3. The turbine produces power at a rate of 1 kW and is adiabatic. For nitrogen, you may take the specific heats to be constant: C v =743 J/kg K and C p =1041 J/kg K. a) Show that the N 2 gas can be considered an ideal gas. The critical state for N 2 is - 147 C and 3.4 MPa. b) By analyzing the heat exchanger, determine the mass flow rate. c) Find the temperature at the turbine exit (State 3). Problem 2 (60). A piston/cylinder device contains 0.2 kg of water, pressurized to 200 kPa by the weight of the piston acting downward on the water. The initial quality of the water is 0.5 (State 1). Heat is then added slowly until the piston rises 0.2 m (State 2). The piston area is 0.1 m 2 . The surrounding air is at 1 atm and 310 K. a) Find the temperature and specific volume at State 2. b) Find the heat transferred in the process from State 1 to 2. c) Find the work done by the water in the process. d) Considering the water and piston combined as the system, find the work done in the process. Why is it different from the previous answer? Test #1 Elements of Thermo EML 3007 October 10, 2003 Open book (class text only), open notes (in your handwriting, homework solutions). 1 hr. Problem 1 (40). Ten kg of water is contained in a piston-cylinder device arranged so as to keep the pressure constant. The water is initially at a temperature of 400 C and a quality of 0.1. a) Heat is added until all of the water is just vaporized. Determine the heat input required and the work performed on the piston by the water. b) Now, addition force is gradually applied to the piston so that it moves back to its initial position. This compression process is adiabatic. Find the work performed by the water. c) Do the answers in parts a and b depend on the order of the steps? In other words, if the additional force had been added before the heat had been added, would the answers have changed? Justify your answer. Problem 2 (30). Air enters a turbine steadily at a temperature of 500 K and a pressure of 3 atm. The turbine efficiency is 80% and the exit temperature is 400 K. a) Find the exit pressure. b) Find the change in specific entropy. c) Find the exit pressure that would occur if the efficiency were 100%. Problem 3 (30). Liquid water at 300 K and 1 atm is pumped by an ideal pump to 2 atm, then heated in an ideal heat exchanger to produce saturated steam....
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This note was uploaded on 09/06/2011 for the course EML 3100 taught by Professor Sherif during the Spring '08 term at University of Florida.
- Spring '08