exam1_sol_2006

exam1_sol_2006 - ENGRD 221 Thermodynamics (Prof. N....

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ENGRD 221 –Thermodynamics (Prof. N. Zabaras) Prelim I 10/12/2006 Page 2 of 9 b) negative and zero, respectively. c) positive and negative, respectively. d) positive and zero, respectively. e) all of the above. Answer: (a) negative and positive respectively; σ is always positive for this process. (4) (3 points) Air (considered an ideal gas) is compressed from room conditions to a specified pressure in a reversible manner by two compressors: one isothermal and the other adiabatic. If the entropy change of air is Δ s isothermal during the reversible isothermal compression and Δ s adiabatic during the reversible adiabatic compression, the correct statement regarding the entropy change of air per unit mass is a) Δ s isothermal = Δ s adiabatic = 0 b) Δ s isothermal = Δ s adiabatic > 0 c) Δ s adiabatic > 0 d) Δ s isothermal < 0 e) Δ s isothermal = 0 Answer: (d) Δ s isothermal < 0; For the reversible adiabatic compression process, Δ s adiabatic = 0. However, for the reversible isothermal compression process for an ideal gas, Δ s isothermal = -Rln(p 2 /p 1 ) < 0,
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This note was uploaded on 07/09/2009 for the course M&AE 326 taught by Professor Psiaki during the Spring '08 term at Cornell.

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exam1_sol_2006 - ENGRD 221 Thermodynamics (Prof. N....

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