engr2010-exam1-rev-ans

engr2010-exam1-rev-ans - . 8 kJ 7. m = P 1 V 1 /RT 1 , and...

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ENGR 2010: Thermodynamics I Exam I Study Guide: answers to problems. Disclaimer: I have made every effort to accurately calculate the answers to the problems. I cannot guarantee that the answers are absolutely correct. 1. You can use the H2O.EXE code on the website to check the numbers. 2. Constant–pressure process: Q 1 - 2 = m ( h 2 - h 1 ). Properties P 2 = P 1 and h 2 fix state 2. T 2 52 C. 3. Free expansion, so W 1 - 2 = 0 and Q 1 - 2 = m ( u 2 - u 1 ). Properties v 2 = 10 v 1 and P 2 fix state 2. Q 1 - 2 = - 13 . 24 kJ. 4. Use the formula for polytropic process work and the ideal gas law. T 2 = 395 . 9 K, P 2 = 316 . 6 kPa, W 1 - 2 = - 9 . 58 kJ. 5. Since pressure is constant and air is an ideal gas: T 2 /T 1 = V 2 /V 1 and T 2 = 900 K. For the constant pressure process Q 1 - 2 = m ( h 2 - h 1 ) mc P ( T 2 - T 1 ) (assuming specific heat is constant). Constant pressure: W 1 - 2 = P ( V 2 - V 1 ) = 86 . 1 kJ. Using the tables for h values: Q 1 - 2 = 316 . 3 kJ. 6. The process is constant volume until P = 1 MPa, then constant pressure until x = 1. Q 1 - 2 = 2567
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Unformatted text preview: . 8 kJ 7. m = P 1 V 1 /RT 1 , and V 2 = mRT 2 /P 2 . Since P varies linearly with V , W 1-2 = Z V 2 V 1 P dV = 1 2 ( P 1 + P 2 ) ( V 2-V 1 ) = 37 . 5kJ and Q 1-2 = m ( u 2-u 1 ) + W 1-2 = 304 . 9 kJ (tables). 8. The process is constant volume. At state 2: v 2 = v g (250 C), and m = V/v 2. v 1 = v 2 and P 1 = 100 kPa x state 1. x 1 = 0 . 029, Q 1-2 = 4240 . 3 kJ. 9. Same as the given info in the previous problem. 10. For water the initial state is a saturated mixture. A constanttemperature compression will therefore correspond to a constantpressure compression, until the water becomes a pure liquid phase. For air the work can be calculated from the ideal gas law. Water: W 1-2 =-26 . 25 kJ, Q 1-2 =-336 . 4 kJ. O 2 : W 1-2 = Q 1-2 =-50 . 76 kJ....
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This note was uploaded on 09/24/2011 for the course ENG 2010 taught by Professor Staff during the Fall '11 term at Auburn University.

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