ME235_Exam1_W08_version_A

ME235_Exam1_W08_version_A - ME 235 Thermodynamics I Exam #1...

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ME 235 Thermodynamics I Exam #1 February 8, 2008 2:40pm – 3:30pm Instructor: Kevin Pipe (Sec. 002) Exam Rules: Open Book, Calculator, No Laptops, No Notes Write your final answers in the blanks provided below . When you are done, staple your work pages to these sheets, with this cover page on top. Name __________________________________ Problem 1 50 Points Problem 2 50 Points I have observed the honor code and neither given nor received aid on this exam . ____________________________________________ Signature
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Problem 1 (50 pts). A piston/cylinder system as shown contains air at 227 o C and 500 kPa. The piston, which is initially floating, has a cross- sectional area of 0.1 m 2 . The piston is restrained by a total external force that is directly proportional to the cylinder volume. Heat is removed from the air until its temperature reaches 27 o C. Neglect the thicknesses of the piston and stops. a) Plot the process on P vs. V and T vs. V diagrams below, with the beginning and end of the process clearly labeled. Show any phase boundaries, and also label the axes with numerical values for P , V , and T at the beginning and end of the process. In your work pages, CLEARLY justify the shapes of the P - V and T - V curves for every step in the process, using QUANTITATIVE reasoning. V P V T b) How much work is done on the air during the process? Answer: Work = __________________________________ c) How much heat is removed from the air during the process? Answer: Heat = __________________________________ 2 z [m] 0 10 F ext
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Problem 2 (50 pts). A piston/cylinder system as shown contains R-12 at 10 o C and x = 0.1, with the piston resting on the lower set of stops. The cross-sectional area of the cylinder is 0.01 m 2 , and the mass of the piston is such that a pressure of 500 kPa will float it. The linear spring is initially in equilibrium (unstretched) and has a spring constant k of 5000 N/m. Heat is added until the temperature of the R-12 reaches
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ME235_Exam1_W08_version_A - ME 235 Thermodynamics I Exam #1...

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