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# HW11_Solutions.pdf

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University of Michigan - Ann Arbor

Mechanical Engineering

MECHENG 235

Donald Siegel

Winter

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THE UNIVERSITY OF MICHIGAN
Department of Mechanical Engineering
ME 235 Thermodynamics I / Winter 2014 / Section 002
HW 11 Solutions
Due date: Apr. 17 2014
7.96 Methane at 1 MPa, 300 K is throttled through a valve to 100 kPa. Assume no change in the kinetic
energy and ideal gas behavior. What is the specific entropy generation?
Solution:
7.125 Air from a line at 12 MPa, 15°C, flows into a 500-L rigid tank that initially contained air at ambient
conditions, 100 kPa, 15°C. The process occurs rapidly and is essentially adiabatic. The valve is closed
when the pressure inside reaches some value2 P . The tank eventually cools to room temperature, at which
time the pressure inside is 5 MPa. What is the pres2ure P ? What is the net entropy change for the overall
process? 7.127 A balloon is filled with air from a line at 200 kPa, 300 K to a final state of 110 kPa, 300 K with
a mass of 0.1 kg air. Assume the pressure is proportional to the balloon volume as: P = 100 kPa + CV.
Find the heat transfer to/from the ambient at 300 K and the total entropy generation.
Solution: 7.148 Air enters an insulated turbine at 50°C, and exits

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