Test_1_F95 - ME 326 THERMODYNAMICS I Test 1 October 6 1995...

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ME 326: THERMODYNAMICS I Test 1, October 6, 1995 1) (20%)  Argon  gas is maintained  at 127 ° C inside a piston-cylinder  apparatus. Originally, the gas is at 1 atm and  occupies a volume  of 10  m 3 . The piston  is moved, compressing  the gas isothermally to a gas  pressure of 5 atm. How  much  work is done (kJ) to compress the gas? SOLUTION: 1 W 2 = PdV = mRT V 1 V 2 dV V = P 1 V 1 dV V V 1 V 2 V 1 V 2 = P 1 V 1 ln V 2 V 1 P 1 V 1 = mRT = P 2 V 2 ; so V 2 V 1 = P 1 P 2 and 1 W 2 = P 1 V 1 ln P 1 P 2 =101.32kN/m 2 × 10m 3 ln 1 5 = -1630kJ _______________________________________________ 2) (20%)  A substance is initially at a temperature  of 20 ° C and  a specific  volume  of 0.2 m 3 /kg.  The state is then changed  to T 2 =200 ° C, v 2 =1.0803  m 3 /kg.  Find the change in the specific internal energy of the substance  if it is: (a) Argon (b) Steam SOLUTION: (a): For ideal gas, u F(v), so u 2 -u 1 =c v (T 2 -T 1 = 0.3124(kJ/kg•K)(200-20) ° C = 56.2 kJ/kg  (cv from Table D.3 or C.2.)
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