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Modern Engineering Thermodynamics

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56 CHAPTER 2: Thermodynamic Concepts<br />

Each inlet<br />

has twice<br />

the mass<br />

flow rate of<br />

the previous<br />

inlet.<br />

Inlets 1−5<br />

Hydraulic<br />

reaction<br />

multiplexer<br />

Outlets 1−8<br />

Each outlet<br />

has half the<br />

mass flow<br />

rate of the<br />

previous<br />

outlet.<br />

FIGURE 2.16<br />

Problem 67.<br />

FIGURE 2.15<br />

Problem 60.<br />

61.* Say you consume about 1.5 kg of solid food and about 1.0 kg<br />

of liquid beverage per day. If you do not produce any waste<br />

material during this time, draw a sketch of this system (you)<br />

and use Eq. (2.21) to determine the increase in your mass at the<br />

end of the day.<br />

62.* The combustion chamber on a jet engine has air entering at a<br />

rate of 2.0 kg/s while the fuel enters through a fuel injector at a<br />

rate of 0.07 kg/s. Draw a sketch of this system and use Eq.<br />

(2.22) to determine the mass flow rate of exhaust gases from<br />

the engine.<br />

63.* As your automobile travels down the highway, it consumes fuel<br />

at a rate of 2.0 × 10 –3 kg/s and it consumes 20. kg of air for<br />

every kg of fuel burned. Draw a sketch of this system and use<br />

Eq. (2.22) to determine the mass flow rate of exhaust gases out<br />

the tail pipe of your automobile.<br />

64.* A rigid tank is being filled with high-pressure oxygen gas at a<br />

rate of 1.3 lbm/h from an external source. Taking the tank as<br />

your system, draw a sketch of the system being filled and use<br />

Eq. (2.22) to determine the rate of gain in mass of the tank.<br />

65.* A chemical reaction vessel has chemical A entering at a rate of<br />

0.51 kg/m through a 0.020 m diameter pipe, chemical B<br />

entering at a rate of 0.75 kg/m through a 0.050 m diameter<br />

pipe, and chemical C entering at a rate of 0.011 kg/m through a<br />

0.015 m diameter pipe. The reaction products are drawn off<br />

through two pipes at the bottom of the vessel at a rate of<br />

0.35 kg/m in a small 0.015 m diameter pipe and 0.67 kg/m<br />

in a large 0.085 m diameter pipe. Determine the net rate of<br />

accumulation of chemicals in the vessel.<br />

66. A new water spray nozzle head has 15 holes. If the mass flow<br />

rate of water into the nozzle head is 0.13 lbm/s, determine the<br />

mass flow rate of water through each hole.<br />

67. A creative young engineer designed a hydraulic reaction multiplexer<br />

that contains a constant mass. The unit has five inlet pipes,<br />

numbered Inlet 1 through Inlet 5, and eight outlet pipes, numbered<br />

Outlet 1 through Outlet 8. Each inlet pipe has twice the mass flow<br />

rate of the previous numbered pipe (i.e., Inlet 2 has twice the mass<br />

flow rate of Inlet 1 and so forth), and each outlet pipe has half the<br />

mass flow rate of the previous numbered pipe (Figure 2.16). If the<br />

mass flow rate in Inlet 1 is 10. lbm/s, determine the mass flow rates<br />

in all the remaining inlet and outlet pipes.<br />

68.* 2.0 kg of hydrogen (H 2 ) reacts with 16 kg of oxygen (O 2 )to<br />

yield water (H 2 O). Determine the chemical equation for this<br />

reaction on a kgmole basis, and find the amount of water<br />

formed in kg.<br />

69. 12 lbm of carbon (C) reacts with 24 lbm of oxygen (O 2 )to<br />

form 22 lbm of carbon dioxide (CO 2 ) plus an unknown<br />

amount of carbon monoxide (CO). Determine the amount of<br />

carbon monoxide formed in lbm, and find the chemical<br />

equation for this reaction on a lbmole basis.<br />

Writing to Learn Problems<br />

The following questions are designed to assist in the learning process<br />

through the development of writing skills. For these problems, you<br />

should develop a written answer containing an opening thesis sentence<br />

followed by the presentation of several supporting statements,<br />

ending with a concluding section that supports the thesis. Equations<br />

should be used only to supplement your written statements. Limit<br />

your response to about two double-spaced pages per question. You<br />

will need to find additional material in your library to complete<br />

these assignments.<br />

70. Write a set of instructions to an engineering student friend defining<br />

a thermodynamic state and describing how to determine it from<br />

its thermodynamic properties. Illustrate your instructions with<br />

specific examples dealing with water.<br />

71. Provide a detailed written explanation of a thermodynamic<br />

cycle. Give three specific examples of thermodynamic cycles.<br />

Chapter 9 contains numerous practical thermodynamic cycles<br />

from which you may choose.<br />

72. Write a letter to a nontechnical friend in which you explain the<br />

zeroth law of thermodynamics. Define the law and create three<br />

nontechnical examples where it applies.<br />

73. Write a short science fiction story based on the continuum<br />

hypothesis. First, describe the hypothesis as it is currently<br />

understood, then create an imaginary scenario where it does not<br />

work. Describe the consequences your new theory may have on<br />

world order.<br />

74. Write a short science fiction story based on the balance concept.<br />

First, describe the concept as it is currently understood, then<br />

create an imaginary scenario in which a new, as yet undiscovered,<br />

term must be added to create a true balance. Describe the<br />

consequences your new theory has on physics today.<br />

75. Write a 500 word article for your high school newspaper on the<br />

conservation of mass law. Is this a truly valid law or are there<br />

cases in which mass is not conserved? If it is not a truly valid<br />

law of physics, then why do we treat mass as conserved in most<br />

engineering applications?

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