Thermodynamics: An Engineering Approach
9th Edition
ISBN: 9781259822674
Author: Yunus A. Cengel Dr., Michael A. Boles
Publisher: McGraw-Hill Education
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Textbook Question
Chapter 11.10, Problem 13P
An ice-making machine operates on the ideal vapor-compression cycle, using refrigerant-134a. The refrigerant enters the compressor as saturated vapor at 20 psia and leaves the condenser as saturated liquid at 80 psia. Water enters the ice machine at 55°F and leaves as ice at 25°F. For an ice production rate of 15 lbm/h, determine the power input to the ice machine (169 Btu of heat needs to be removed from each l bm of water at 55°F to turn it into ice at 25°F).
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An ideal vapor-compression refrigeration cycle that uses refrigerant-134a as its working fluid maintains a condenser at 800 kPa and the evaporator at 15 kPa. Given 300 kW of cooling load, determine the following: 1. Construct didactic sketches, showing the operating principles of a refrigeration system.2. When you select a refrigerant for a certain application, what qualities would you look for in the refrigerant?3. Estimate the reversible COP values, if the low and high medium temperature are as for the evaporator and condenser.
a) A freezer working on an ideal vapour-compression refrigeration cycle uses refrigerant R-
134a with a mass flow rate of 0.10 kg/s. The refrigerant leaves the evaporator as saturated
vapour at a temperature of -8 °C. It leaves the condenser as saturated liquid at a pressure of
0.8 MPa. Determine the power required to drive the compressor.
Note that the thermodynamic properties of R-134a are attached at the end of the paper.
0.8 MPa
A
Figure Q4
b) A freezer wall is made of a composite material with a thickness of 20 mm and a
conductivity of 0.03 W/m-K. Air temperatures inside and outside the freezer are -6 °C and
20 °C, respectively. The convection coefficient is 2 W/m² K on both the inner and outer
surfaces of the freezer wall. Determine the heat flux through the freezer wall.
-8 C
An ideal ammonia (R – 717) vapor-compression refrigeration cycle has an evaporator temperature of –20 C and a condenser pressure of 12 bar. Saturated vapor enters the compressor, and saturated liquid exits the condenser. The mass flow rate of the refrigerant is 3 kg/min. Determine the compressor work, kW.
Chapter 11 Solutions
Thermodynamics: An Engineering Approach
Ch. 11.10 - Why do we study the reversed Carnot cycle even...Ch. 11.10 - Why is the reversed Carnot cycle executed within...Ch. 11.10 - A steady-flow Carnot refrigeration cycle uses...Ch. 11.10 - Refrigerant-134a enters the condenser of a...Ch. 11.10 - Does the ideal vapor-compression refrigeration...Ch. 11.10 - Why is the throttling valve not replaced by an...Ch. 11.10 - In a refrigeration system, would you recommend...Ch. 11.10 - Does the area enclosed by the cycle on a T-s...Ch. 11.10 - Consider two vapor-compression refrigeration...Ch. 11.10 - It is proposed to use water instead of...
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