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TEST_1_F95

# 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: _______________________________________________ 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.) (b): State 1 is in saturation region, so cannot treat as ideal gas: x 1 =(v 1 -v 1,l )/v lg,1 = (0.2-0.001002)/57.777=0.00344 (Table D.10) and u 1 =u l,1 +x 1 u lg,1 = 83.833+0.00344x2318.2 = 91.8kJ/kg u 2 is in superheat region, and Table D.12 gives u 2 =2653.9 kJ/kg, so u 2 -u 1 =2653.9-91.8=2562.1 kJ/kg . 3) (20%) Find the specific volume at T=50°C and u= 300 kJ/kg for: a) water c) ammonia

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SOLUTION: (a): at 50°C, this u is in saturation region, so, from Table D.12,
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