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Homework #7 MEMS 0051 – Introduction to Thermodynamics solved

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Problem #1
A high-temperature reservoir at 800 K dissipated 2,000 [kJ] of heat to a low-temperature thermal reservoir
of a) 500 K and b) 750 K. Determine which of these two processes is the least reversible, i.e. which has the
greatest change of entropy.
Problem #2
A rigid tank contains R-134a in the quantity of 5 [kg] initially at 293 K and 140 [kPa]. The refrigerant is
cooled in a process until the pressure within the tank reaches 100 [kPa]. Determine the change of entropy
during this process.
Problem #3
A mass-less piston-cylinder device contains 1.36 [kg] of water at 138 [kPa] and 21 ◦C. 3,700 [kJ] of thermal
energy is supplied to the water. Determine the change of entropy of the water during this process.
Problem #4
Liquid methane is the main undergoes a process from 100 K and 1,000 [kPa] to 120 K and 5,000 [kPa].
Determine the change of entropy for this process using:
a) tabulated values;
b) T dS equations for incompressible substances.
Problem #5
Air at STSP conditions is compressed to 600 [kPa] and 300 K. Determine the change of entropy using:
a) tabulated values;
b) T dS equations for compressible substances.
Problem #5
Consider an automobile engine with a compression ratio of 8, i.e. ∀1/∀2=8. If State 1 exists at STSP,
determine the final temperature of the air.
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