Modern Engineering Thermodynamics

590 CHAPTER 14: Vapor and Gas Refrigeration Cycles
75. Develop a computer program that provides data to plot (either
manually or with a computer) the coefficient of performance of
a vapor-compression cycle heat pump, refrigerator, or air
conditioner vs. the throttling valve outlet quality, x 4h . Prompt
the user for all the relevant input information, including the
compressor’s isentropic efficiency.
76. Develop an interactive computer program that determines
either the system’s coefficient of performance or its cooling
capacity in tons (allow the user to choose which) of a vaporcompression
cycle air conditioner, refrigerator, or heat pump
(again allow the used to choose which). Prompt the user for
all necessary information (in proper units) and produce a
screen diagram of the system with all the variables and the
unknowns shown.
77.* Develop an interactive reversed Brayton ASC computer program
that utilizes constant specific heat ideal gas equations of state as
the source of the enthalpy values. Allow the user to select either
a refrigeration, air conditioning, or heat pump application. Have
the user input the appropriate gas constants (or choose the gas
from a screen menu), the source and sink temperatures, the
mass flow rate of the gas, and the isentropic pressure ratio, PR.
Output the coefficient of performance, the source and sink heat
transfer rates, and the net power input. Use this program to plot
the coefficient of performance vs. the PR for a reversed Brayton
cycle refrigerator operating between 20.0°C and −14.0°C. Allow
the PR to range from 1.00 to 14.0.
78.* Expand Problem 77 by replacing the ideal gas properties with a
gas menu that contains a computerized version of the isentropic
gas tables as the source of the enthalpy values.
79. Develop an interactive computer program that determines the
coefficient of performance of a Joule-Thomson refrigeration
system using air or carbon dioxide (allow the user to choose
which). Curve fit the information given in Figure. 6.6 as the
source of the proper Joule-Thomson coefficient. Prompt the user
for the appropriate temperatures, pressures, and isentropic
compressor efficiency.
80. Develop an interactive computer program that determines the
coefficient of performance of a reversed Stirling ASC
refrigerator or heat pump (allow the user to choose which).
Prompt the user for all necessary input information (in the
proper units).
Writing to Learn Problems
Provide a coherent 500-word written response to the following questions
on 8 1 2
by 11 in paper, double spaced, 12 point font, with 1 in
margins on all sides. Unless your instructor indicates otherwise, your
response should include the following:
a. An opening thesis statement containing the argument you wish
to support.
b. A body of supporting material.
c. A conclusion section in which you use the supporting material
to substantiate your thesis statement.
81. Describe how you think the introduction of food refrigeration
by artificial ice used in kitchen iceboxes in the mid 19th century
could improve the standard of living in a society.
82. While water makes a very good working fluid for power cycles,
it does not make a good refrigerant. Describe the reasons for
this and discuss the evolution of refrigerant working fluids.
What problems are produced by leaking refrigerants?
83. Describe the controversy over CFCs and the ozone layer. Do you
believe it is true?
84. Describe the assumptions behind the air standard cycle. Which
are the most severe and which are the least severe?
85. Describe what you see as future refrigeration needs in the next
100 years (i.e., what will the refrigeration need be 100 years
from now, in your opinion)?