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Modern Engineering Thermodynamics

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146 CHAPTER 4: The First Law of <strong>Thermodynamics</strong> and Energy Transport Mechanisms<br />

74. You are designing a new mechanical transmission large rock<br />

crusher used in the mining industry. The transmission is driven<br />

by a 300. hp engine but transmits only 290. hp to the rock<br />

crusher. You need to prevent the transmission from overheating,<br />

so how much cooling is needed to keep it at ambient<br />

temperature?<br />

75.* Dave, your boss, wants you to estimate the amount of heat that<br />

has to be removed from an iron ingot to cool it from 900ºC to<br />

150ºC. Make this request into a thermodynamic problem<br />

statement and solve it.<br />

76.* You are a new engineer at a company that manufactures<br />

gas-filled shock absorbers for racing cars. The chief engineer<br />

wants to understand the relation between the gas pressure inside<br />

the shock absorber and the compression of the gas. The shock<br />

absorbers are essentially piston-cylinder devices that are initially<br />

filled with nitrogen gas at 0.345 MPa and 20.0ºF. When the<br />

piston compresses the gas by 20%, the pressure increases to<br />

0.414 MPa. You think this is a polytropic compression process.<br />

Write and solve a thermodynamics problem to determine the<br />

polytropic exponent for this process.

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