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ME 104 Thermodynamics [F23]

Homework Assignment 10

[Due Mon 11/06]

Text: Thermodynamics: An Engineering Approach, Y. Çengel and M. Boles, McGraw-Hill, 10th Edition, 2024. The link to the book is provided on the course site.

Problem 1: [8–21E] Steam at 100 psia and 650°F is expanded adiabatically in a closed system to 10 psia. Determine the work produced, in Btu/lbm, and the final temperature of steam for an isentropic expansion efficiency of 80 percent.

Problem 2: [8–26] Refrigerant-134a enters an adiabatic compressor as saturated vapor at 100 kPa at a rate of 0.7 m3/min and exits at 1-MPa pressure. If the isentropic efficiency of the compressor is 87 percent, determine (a) the temperature of the refrigerant at the exit of the compressor and (b) the power input, in kW. Also, show the process on a T-s diagram with respect to saturation lines.

Problem 3: [10–18E] An air-standard cycle with variable specific heats is executed in a closed system and is composed of the following four processes:

1-2 V = constant heat addition from 14.7 psia and 80°F in the amount of 300 Btu/lbm

2-3 P = constant heat addition to 3200 R

3-4 Isentropic expansion to 14.7 psia

4-1 P = constant heat rejection to initial state

(a) Show the cycle on P-v and T-s diagrams.

(b) Calculate the total heat input per unit mass.

(c) Determine the thermal efficiency.

Problem 4: [10–36] An ideal Otto cycle has a compression ratio of 8. At the beginning of the compression process, air is at 95 kPa and 27°C, and 750 kJ/kg of heat is transferred to air during the constant-volume heat-addition process. Taking into account the variation of specific heats with temperature, determine (a) the pressure and temperature at the end of the heat-addition process, (b) the net work output, (c) the thermal efficiency, and (d) the mean effective pressure for the cycle.