BME Thermodynamics 3

Question 1

For a steam power plant operating as a Rankine cycle, the purpose of the feedwater pump is to:

Accepted Answer

Increase pressure of the liquid condensate

Answer

The feedwater pump increases the pressure of the liquid water from condenser pressure to boiler pressure, requiring relatively little work.

Question 2

Maxwell's relations in thermodynamics are derived from which thermodynamic potentials?

Accepted Answer

Internal energy, enthalpy, Helmholtz, and Gibbs functions

Answer

Maxwell's relations are derived from the exactness of the differentials of the four thermodynamic potentials: U, H, A, and G.

Question 3

In a refrigeration system using the vapor-compression cycle, the throttling device (expansion valve) reduces pressure by:

Accepted Answer

An irreversible isenthalpic process

Answer

The expansion valve is an isenthalpic (constant enthalpy) throttling device where pressure drops irreversibly without work or heat transfer.

Question 4

The triple point of water is approximately:

Accepted Answer

0.01°C and 611.7 Pa

Answer

The triple point of water occurs at approximately 0.01°C (273.16 K) and 611.7 Pa, where all three phases coexist.

Question 5

For an Otto cycle (ideal spark-ignition engine), thermal efficiency depends on:

Accepted Answer

Compression ratio and specific heat ratio γ

Answer

Otto cycle efficiency η = 1 - (1/r^(γ-1)), where r is the compression ratio and γ is the specific heat ratio.

BME - Bachelor of Mechanical Engineering Practice Test