Modern Engineering Thermodynamics

56 CHAPTER 2: Thermodynamic Concepts
Each inlet
has twice
the mass
flow rate of
the previous
inlet.
Inlets 1−5
Hydraulic
reaction
multiplexer
Outlets 1−8
Each outlet
has half the
mass flow
rate of the
previous
outlet.
FIGURE 2.16
Problem 67.
FIGURE 2.15
Problem 60.
61.* Say you consume about 1.5 kg of solid food and about 1.0 kg
of liquid beverage per day. If you do not produce any waste
material during this time, draw a sketch of this system (you)
and use Eq. (2.21) to determine the increase in your mass at the
end of the day.
62.* The combustion chamber on a jet engine has air entering at a
rate of 2.0 kg/s while the fuel enters through a fuel injector at a
rate of 0.07 kg/s. Draw a sketch of this system and use Eq.
(2.22) to determine the mass flow rate of exhaust gases from
the engine.
63.* As your automobile travels down the highway, it consumes fuel
at a rate of 2.0 × 10 –3 kg/s and it consumes 20. kg of air for
every kg of fuel burned. Draw a sketch of this system and use
Eq. (2.22) to determine the mass flow rate of exhaust gases out
the tail pipe of your automobile.
64.* A rigid tank is being filled with high-pressure oxygen gas at a
rate of 1.3 lbm/h from an external source. Taking the tank as
your system, draw a sketch of the system being filled and use
Eq. (2.22) to determine the rate of gain in mass of the tank.
65.* A chemical reaction vessel has chemical A entering at a rate of
0.51 kg/m through a 0.020 m diameter pipe, chemical B
entering at a rate of 0.75 kg/m through a 0.050 m diameter
pipe, and chemical C entering at a rate of 0.011 kg/m through a
0.015 m diameter pipe. The reaction products are drawn off
through two pipes at the bottom of the vessel at a rate of
0.35 kg/m in a small 0.015 m diameter pipe and 0.67 kg/m
in a large 0.085 m diameter pipe. Determine the net rate of
accumulation of chemicals in the vessel.
66. A new water spray nozzle head has 15 holes. If the mass flow
rate of water into the nozzle head is 0.13 lbm/s, determine the
mass flow rate of water through each hole.
67. A creative young engineer designed a hydraulic reaction multiplexer
that contains a constant mass. The unit has five inlet pipes,
numbered Inlet 1 through Inlet 5, and eight outlet pipes, numbered
Outlet 1 through Outlet 8. Each inlet pipe has twice the mass flow
rate of the previous numbered pipe (i.e., Inlet 2 has twice the mass
flow rate of Inlet 1 and so forth), and each outlet pipe has half the
mass flow rate of the previous numbered pipe (Figure 2.16). If the
mass flow rate in Inlet 1 is 10. lbm/s, determine the mass flow rates
in all the remaining inlet and outlet pipes.
68.* 2.0 kg of hydrogen (H 2 ) reacts with 16 kg of oxygen (O 2 )to
yield water (H 2 O). Determine the chemical equation for this
reaction on a kgmole basis, and find the amount of water
formed in kg.
69. 12 lbm of carbon (C) reacts with 24 lbm of oxygen (O 2 )to
form 22 lbm of carbon dioxide (CO 2 ) plus an unknown
amount of carbon monoxide (CO). Determine the amount of
carbon monoxide formed in lbm, and find the chemical
equation for this reaction on a lbmole basis.
Writing to Learn Problems
The following questions are designed to assist in the learning process
through the development of writing skills. For these problems, you
should develop a written answer containing an opening thesis sentence
followed by the presentation of several supporting statements,
ending with a concluding section that supports the thesis. Equations
should be used only to supplement your written statements. Limit
your response to about two double-spaced pages per question. You
will need to find additional material in your library to complete
these assignments.
70. Write a set of instructions to an engineering student friend defining
a thermodynamic state and describing how to determine it from
its thermodynamic properties. Illustrate your instructions with
specific examples dealing with water.
71. Provide a detailed written explanation of a thermodynamic
cycle. Give three specific examples of thermodynamic cycles.
Chapter 9 contains numerous practical thermodynamic cycles
from which you may choose.
72. Write a letter to a nontechnical friend in which you explain the
zeroth law of thermodynamics. Define the law and create three
nontechnical examples where it applies.
73. Write a short science fiction story based on the continuum
hypothesis. First, describe the hypothesis as it is currently
understood, then create an imaginary scenario where it does not
work. Describe the consequences your new theory may have on
world order.
74. Write a short science fiction story based on the balance concept.
First, describe the concept as it is currently understood, then
create an imaginary scenario in which a new, as yet undiscovered,
term must be added to create a true balance. Describe the
consequences your new theory has on physics today.
75. Write a 500 word article for your high school newspaper on the
conservation of mass law. Is this a truly valid law or are there
cases in which mass is not conserved? If it is not a truly valid
law of physics, then why do we treat mass as conserved in most
engineering applications?