Modern Engineering Thermodynamics

Problems 317
The cavitation process is the formation of these vapor bubbles.
Carry out the preliminary thermodynamic design of a closed
loop apparatus that illustrates this phenomenon by having a
liquid pumped through a transparent nozzle wherein the
pressure drops below the local saturation pressure and the
vapor bubbles become visible. Choose a suitable liquid and
provide an engineering sketch containing all the major
dimensions and materials of your system. Estimate the pump
size and power required, and the entropy production rate of
your nozzle.
73. The Engine Test Facility at the Arnold Air Force Base in Tennessee
requires a test cell 48.0 ft in diameter and 85.0 ft long with an air
flow rate of 4300. ft 3 /s at atmospheric pressure and temperature.
Carry out the preliminary thermodynamic design of a
compressor-nozzle system that meets these requirements. The
compressor inlet is at atmospheric conditions, and the inlet
temperature of the nozzle must be 70.0°F (this means an
intercooling system must be used). Determine the horsepower
required to drive the compressor, the nozzle outlet temperature,
and the entropy production rate of your nozzle. Assume the
compression process is polytropic with n = 1.30 and the pressure
loss through the nozzle is 15.0% of the inlet pressure.
74. The Aeropropulsion System Test Facility at the Arnold Air Force
Base in Tennessee requires a heat exchanger capable of cooling
2750. lbm/s of gas turbine exhaust from 3500. to 80.0°F before
discharging it to the atmosphere. Carry out a preliminary
thermodynamic design of a suitable heat exchanger using water
as the second fluid. Determine the amount of cooling water
needed and recommend an appropriate source. Also determine
the entropy production rate of your heat exchanger.
75.* Carry out the preliminary thermodynamic design of a fuel
mixing valve for a furnace that efficiently mixes inlet flow
streams of air at 2.50 kg/s and methane at 0.500 kg/s, both at
atmospheric pressure and temperature, and produces one outlet
flow stream. Assume these gases behave as constant specific heat
ideal gases. Provide a dimensioned engineering sketch and
estimate the entropy production rate of your valve.
76.* Carry out the preliminary thermodynamic design of a system
that uses a vortex tube to cool a full body suit for a firefighter.
The suit must be able to reject up to 1300. kJ/h, and this
cooling rate must be easily adjustable by the wearer. Use the
data given in Case Study 9.1 or from appropriate industrial
literature.
77. Carry out the preliminary thermodynamic design of a system
that uses a vortex tube to heat a skintight suit for an underwater
diver by bleeding off part of the air supply to the diver. The suit
must be able to supply 800. Btu/h, and this heating rate must
be easily adjustable by the diver. Use the data given in Case
Study 9.1 or from appropriate industrial literature.
78.* Carry out the preliminary thermodynamic design of a system that
isothermally fills an initially evacuated, rigid, cylindrical tank with
air at 20.0°C to 20.0 MPa with a minimum amount of entropy
production. The tank is 0.250 m in diameter and 1.50 m high.
Assume the air behaves as a constant specific heat ideal gas.
Discuss the technology and economics of how the tank is
maintained isothermal during the filling process. Note that there
will beentropy production in the pipes and valves used to connect
the tank to the air supply.
79. The Von Karman Gas Dynamics Facility at the Arnold Air Force
Base in Tennessee has need of a blowdown wind tunnel, to be
supplied from a tank containing compressed air initially at
1000. psia and 70.0°F. The wind tunnel is to be at the end of
a nozzle attached to the tank and must be 8.00 ft in diameter
and have a velocity of 10.0 × 10 3 ft/s at 2000. R. The tank must
be of sufficient size to sustain these wind tunnel conditions for
a minimum of 30.0 min of testing. Carry out the preliminary
thermodynamic design of such a facility and estimate the size of
the storage tank required and the power required to compress the
air in filling the tank if it must be done overnight (i.e., in 8.00 h).
Determine the entropy production associated with both the filling
and emptying of the tank if both are done isothermally.
Computer problems
The following computer assignments are designed to be carried out
on a personal computer using a spreadsheet or equation solver. They
are meant to be exercises using some of the basic formulae of
this chapter. They may be used as part of a weekly homework
assignment.
80.* Develop a program that allows you to plot the entropy
production rate discussed in Example 9.1 vs. the heat transfer
rate. Let the heat transfer rate range from 100. to 1000. watts.
Assume all the remaining variables are as given in Example 9.1.
81. Develop a program that determines the entropy production rate
of an incompressible fluid or a constant specific heat ideal gas
of your choice flowing through an adiabatic nozzle. Input all
the variables with proper units. Allow the choice of working in
either Engineering English or SI units.
82. Develop a program that determines the entropy production rate
of an incompressible fluid or constant specific heat ideal gas of
your choice from an adiabatic diffuser. Input all the variables
with proper units. Allow the choice of working in either
Engineering English or SI units.
83. Develop a program that determines the entropy production
inside a heat exchanger having two inlets and two outlets, when
the mass flow rates, temperatures, and fluid properties of both of
the flow stream fluids are known. Assume the fluids do not mix
inside the heat exchanger, and allow either flow stream to be an
incompressible liquid or a constant specific heat ideal gas at the
user’s discretion. Input all the variables with proper units. Allow
the choice of working in either Engineering English or SI units.
84. Develop a program that performs an energy rate balance on a
gas turbine engine. Input the appropriate gas properties (in the
proper units), the turbine’s heat loss or gain rate, and the input
mass flow rate, and the inlet and exit temperatures. Output to
the screen the turbine’s output power. Assume the gas behaves
as a constant specific heat ideal gas, and neglect all kinetic and
potential energy terms. Allow the choice of working in either
Engineering English or SI units.
85. Curve fit the hot and cold vortex tube outlet temperature data
given in Case Study 9.1 vs. the inlet absolute pressure. Then
develop a program that returns these outlet temperatures plus
the COP of this device when it is used as a Carnot heat pump
and when it is used as a Carnot refrigerator or air conditioner
when the user inputs the inlet pressure. Use this program to
generate enough data to plot the values of these two COPs vs.
the inlet absolute pressure.
86. Develop a program that outputs the entropy production rate for
the filling of an initially evacuated rigid vessel with an