Sample_Problems_4

# Sample_Problems_4 - Engi2800 Engineering Thermodynamics I...

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Sample Problems #4 (Chapter 5) Ismet Ugursal, J.M. Chuang Dalhousie University Dept. of Mechanical Engineering October 3, 2009 Engi2800 Engineering Thermodynamics I

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Problems (Textbook 7 th Ed.) Questions Page Topics 5.5 162 Concept-Study Guide 5.23 163 Kinetic and Potential 5.75 167 5.76 168 5.89 168 Energy Equation: Solids and Liquids 5.101 169 Energy Equation: Solids and Liquids 5.103 169 Energy Equation: Ideal Gas Energy Equation: Multistep Solution Energy Equation: Multistep Solution
3 CV A is the mass inside a piston-cylinder, CV B is that plus the piston outside, which is the standard atmosphere. Write the energy equation and work term for the two CVs assuming we have a non-zero between state 1 and state 2. Solution: CV A: CV B: Notice how the P inside CV A is i.e. the first work term is larger than the second. The difference between the work terms is exactly equal to the potential energy of the piston sitting on the left hand side in the CV B energy Eqn. The two equations are mathematically identical. Prob. 5.5 Concept-Study Guide piston E 2 ¡ E 1 = m A ( e 2 ¡ e 1 ) + m pist ( e 2 ¡ e 1 ) = m A ( u 2 ¡ u 1 ) + m pist ( gZ 2 ¡ gZ 1 ) P = P 0 + m pist g=A cyl ( P = P 0 + m pist g=A cyl ) E 2 ¡ E 1 = m A ( e 2 ¡ e 1 ) = m A ( u 2 ¡ u 1 ) = 1 Q 2 ¡ 1 W A 2 Q 1 W A 2 = Z P dV = P ( V 2 ¡ V 1 ) 1 Q 2 ¡ 1 W B 2 = 1 W B 2 = Z P 0 dV = P 0 ( V 2 ¡ V 1 ) 1 W A 2 = P ( V 2 ¡ V 1 ) = f P 0 + m pist g=A cyl g ( V 2 ¡ V 1 ) = 1 W B 2 + m pist g ( V 2 ¡ V 1 ) =A cyl = 1 W B 2 + m pist g ( Z 2 ¡ Z 1 ) Note :( V 2 ¡ V 1 ) =A cyl = ( Z 2 ¡ Z 1 )

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4 Prob. 5.23 Kinetic and Potential A 25 kg piston is above a gas in a long vertical cylinder. Now the piston is released from rest and accelerates up in the cylinder reaching the end 5 m higher at a velocity of 25 m/s. The gas pressure drops during the process so the average is 600 kPa with an outside atmosphere at 100 kPa. Neglect the change in gas kinetic and potential energy, and find the needed change in the gas volume. Solution: C.V. Piston Energy equation for the piston is: Remark: so the two work terms are of opposite sign. = 0 + 25
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Sample_Problems_4 - Engi2800 Engineering Thermodynamics I...

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