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Unformatted text preview: ME 326H: THERMODYNAMICS I Test 1, Feb. 23, 1996 1) (28%) A substance is inside a piston/cylinder system. Initially, the substance is at T 1 =150C and P 1 =10 kPa. The piston is moved to compress the substance isothermally until P 2 =100 kPa. a) If the substance is argon, what is the change in the specific internal energy of the argon, u 2-u 1 (kJ/kg)? b) If the substance is argon, how much heat transfer 1 q 2 (kJ/kg) occurred? c) If the substance is steam, what is the change in the specific internal energy of the steam, u 2-u 1 (kJ/kg)? d) If the substance is steam, describe in a few sentences how you could calculate how much heat transfer 1 q 2 (kJ/kg) occurred. SOLUTION: a): Argon acts as an ideal gas, for which u=u(T only), so for an isothermal process, u=0 . b): First Law for CM is 1 q 2- 1 w 2 =u 2-u 1 =0, so 1 q 2 = 1 w 2 so 1 q 2 = 1 w 2 = Pdv v v = RT dv v v v = RT ln v 2 v 1 = RT ln P 1 P 2 = 0.20813 423 ln0.1 =-202.7 kJ/kg c): From Table D.12, u 1 =2587.4 kJ/kg; u 2 =2582.4 kJ/kg, so u 2- u...
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