ENGR225Spring2014 - Homework 2 (1)

ENGR225Spring2014 - Homework 2 (1) - ENGR 225 Spring 2014...

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ENGR 225 Spring 2014 Homework #2 due by recitation week of 1/27 1. During a boiling process, why does the temperature of the liquid/vapor mixture stay constant? 2. A perfectly fitting pot and its lid often stick after cooling, and it becomes very difficult to open the lid when the pot cools down. Explain why this happens and what you would do to open the lid. 3. Complete this table for water – use the tables in the back of the book. T (°C) P (kPa) ν (m 3 /kg) Phase description 50 7.72 110 350 400 Saturated vapor 250 500 4. Complete this table for refrigerant-134a – use the tables in the back of the book. T (°C) P (kPa) u (kJ/kg) Phase description -12 320 30 150 550 Saturated vapor 60 600 5. 100 kg of R-134a at 200kPa are contained in a piston-cylinder device whose volume is 12.322 m 3 . The piston is now moved until the volume is one-half its original size. This is done such that the pressure of the R-134a does not change. Determine the final temperature
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Unformatted text preview: and the change in the total internal energy of the R-134a. Answers: -10°C, -110 kJ/kg 6. Water initially at 300 kPa and 250°C is contained in a piston-cylinder device fitted with stops. The water is allowed to cool at constant pressure until it exists as a saturated vapor and the piston rests on the stops. Then, the water continues to cool until the pressure is 100 kPa. Find the overall change in internal energy between the initial and final states per unit mass of water. Answers: 1566 kJ/kg 7. Determine the specific volume and internal energy of compressed liquid water at 80°C and 20 MPa using the saturated liquid approximation. Compare these values to the ones obtained from the compressed liquid tables....
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