Engineering thermodynamics MCQ Mechanical Engineering

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About Engineering thermodynamics

Following are some of the multiple choice questions on the Engineering thermodynamics with answers that will help the students in developing their knowledge.

Engineering thermodynamics MCQ

1. Rankine cycle efficiency of a good steam power plant may be in the range of

  • 15 to 20%
  • 35 to 45%
  • 70 to 80%
  • 90 to 95%

2. The efficiency of an ideal Carnot engine depends on

  • working substance
  • on the temperature of the source only
  • on the temperature of the sink only
  • on the temperatures of both the source & the sink

3. Which of the following contributes to the improvement of efficiency of Rankine cycle in a Thermal Power Plant?

  • reheating of steam at intermediate stage
  • regeneration use of steam for heating boiler feed water
  • use of high pressures
  • all of the mentioned

4. A regenerative Rankine cycle may approach efficiency of a Carnot cycle between sametemperature by

  • reducing heat to condenser
  • reducing volume of steam passed into condenser
  • c) increasing turbine work
  • adding heat a highest temp.

5. The temperature of feed water can be increased in following two ways in a regenerative Rankine cyclei) by passing feed water around turbine casing in direction opposite to flow of steamii) by bleeding certain portion of steam at the end of h.p expansion & mixing with condensate to make feed water at the temperature of boiler

  • i) is preferred over ii) for higher efficiency
  • ii) is preferred over i) for reduced moisture content of steam in l.p side
  • only i) is implemented in actual practice
  • by preferring ii) overi) significant gain in efficiency results

6. The____________obtainable from a certain heat input in a cyclic heat engine is called          

  • minimum work output, available energy
  • maximum work output, available energy
  • minimum work input, unavailable energy
  • none of the mentioned

7. Efficiency of a heat engine is defined as

  • total heat output / net work input
  • total heat input / net work output
  • net work output / total heat input
  • net work input / total heat output

8. The universal gas constant will be equal to difference between specific heats at constant pressure & constant volume for

  • 1 kg mass of gas
  • 1 molecule of gas
  • 1 kg molecule of gas
  • any mass of gas

9. Air expands from initial condition of p1, v1 to final condition of 1/2 p1, 2v1.Choose the correct statement

  • a) no work is performed during expansion
  • expansion is isothermal
  • expansion is polytropic with n= 1.2
  • expansion is adiabatic

10. Steam enters the turbine at 5.44 bar with dryness fraction of 0.9 & is expanded adiabatically to a pressure of 0.68 bar. It will enter the condenser with a quality very close to

  • 0.79
  • 0.815
  • 0.84
  • 0.86

11. A power cycle using steam as working fluid consist ofi) constant pressure heat addition ii)adiabatic expansioniii) constant pressure heat rejection & iv) adiabatic compression. The cycle is

  • simple rankine cycle
  • modified rankine cycle
  • carnot cycle
  • regenerative rankine cycle

12. Which of the following remains constant during an adiabatic expansion

  • entropy
  • temperature
  • internal energy
  • none of the above

13. According to Carnot’s theorem, all heat engines operating between a given constant temperature source and sink, none has a higher efficiency than a reversible engine.

  • true
  • false

14. Relative humidity is defined as

  • (saturation pressure of pure water) / pw
  • pw / (saturation pressure of pure water)
  • (saturation pressure of pure water) / p
  • p / (saturation pressure of pure water)

15. The efficiency and work ratio of a simple gas turbine cycle are

  • low
  • very low
  • high
  • very high

16. In a steam power plant which cycle requires two or more feed pumps

  • regenerative rankine cycle
  • reheat rankine cycle
  • simple rankine cycle
  • idealized regenerative rankine cycle

17. The entropy __________ in an irreversible cyclic process.

  • remains constant
  • decreases
  • increases
  • none of the above

18. Which of the following is an example of high grade energy?

  • mechanical work
  • electrical energy
  • water power and wind power
  • all of the mentioned

19. Processes inside a thermal energy reservoir are quasi-static.

  • true
  • false

20. Entropy principle is the quantitative statement of the second law of thermodynamics.

  • true
  • false

21. Which of the following represents the latent heat of vaporization at a particular pressure.

  • hf-hg
  • hg-hf
  • hf+hg
  • none of the mentioned

22. Which of the following can be considered as an application of entropy principle?

  • transfer of heat through a finite temperature difference
  • mixing of two fluids
  • maximum temperature obtainable from two finite bodies
  • all of the mentioned

23. Which of the following processes exhibit external mechanical irreversibility?

  • isothermal dissipation of work
  • adiabatic dissipation of work
  • both of the mentioned
  • none of the mentioned

24. Which of the following is an example of low grade energy?

  • heat or thermal energy
  • heat from nuclear fission or fusion
  • heat from combustion of fossil fuel
  • all of the mentioned

25. Which of the following is a type of energy?

  • high grade energy
  • low grade energy
  • both of the mentioned
  • none of the mentioned

26. When considering a finite energy source, its working fluid expands,

  • reversibly
  • adiabatically
  • reversibly and adiabatically
  • none of the mentioned

27. The superheat or degree of superheat is given by

  • difference between the temperature of saturated liquid and saturation temperature
  • difference between the temperature of superheated vapour and saturation temperature
  • sum of the temperature of superheated vapour and saturation temperature
  • none of the mentioned

28. Which of the following exists in a p-V diagram for water?

  • saturated solid line
  • saturated liquid lines
  • saturated vapour line
  • all of the mentioned

29. Entropy increase dS of the system can be expressed as

  • ds=ds(due to external heat interaction)- ds(due to internal irreversibility)
  • ds=ds(due to external heat interaction)+ds(due to internal irreversibility)
  • ds=-ds(due to external heat interaction)- ds(due to internal irreversibility)
  • ds=-ds(due to external heat interaction)+ds(due to internal irreversibility)

30. Which if the following statements are true for a mechanical energy reservoir(MER)?

  • it is a large body enclosed by an adiabatic impermeable wall
  • stores work as ke or pe
  • all processes within an mer are quasi- static
  • all of the mentioned

31. A pure substance which exists in a single phase has____________independent variables.

  • zero
  • one
  • two
  • three

32. Water____________on melting and has the fusion curve with a____________slope.

  • contracts, negative
  • contracts, positive
  • expands, negative
  • expands, positive

33. The properties of liquid__________with pressure.

  • do not vary
  • vary largely
  • vary little
  • none of the mentioned

34. The slope of sublimation curve is_________the slope of the vaporization curve at triple point.

  • equal to
  • less than
  • greater than
  • none of the mentioned

35. The total entropy of a mixture of gases is the___________of the partial entropies.

  • average
  • weighted mean
  • sum
  • difference of the highest and the lowest

36. When humidity ratio of air___________air is said to be dehumidified.

  • increases
  • decreases
  • remains constant
  • none of the mentioned

37. At any dbt, the___________the difference of wbt reading below below dbt,______________is the amount of water vapour held in mixture.

  • smaller, smaller
  • greater, greater
  • greater, smaller
  • smaller, greater

38. The optimum reheat pressure for most of the power plants is how many times of the initial steam pressure?

  • 0.1-0.15
  • 0.2-0.20
  • 0.2-0.25
  • 0.1-0.10

39. Which of the following cycles is used in thermalpower plants?

  • brayton
  • carnot
  • ericsson
  • rankine

40. By reducing the condenser pressure in Rankine power plant

  • heat supplied increases & work of cycle decreases
  • work of cycle & moisture content of steam in l.p side ofturbine increase
  • heat supplied & efficiency of cycle increase
  • work of cycle increases but heat supplied decreases

41. Essential parts of a power plant operating on aRankine cycle are

  • engine or turbine
  • engine or turbine & conderser
  • engine or turbine, condenser, pump &boiler
  • engine or turbine & boiler

42. Most of the fossil fuelbased power plants operate on

  • rankine cycle
  • brayton cycle
  • carnot cycle
  • either rankine or brayton cycle

43. When unsaturated air flows over a sheet of water in an insulated chamber

  • specific humidity of air decreases
  • the water evaporates
  • both air and water are cooled during evaporation
  • all of the mentioned

44. The degree of saturation is the ratio of

  • (saturated specific humidity / actual specific humidity)^2
  • 1/(saturated specific humidity * actual specific humidity)
  • saturated specific humidity / actual specific humidity
  • actual specific humidity / saturated specific humidity

45. The expression which represents the pressure exerted by a gas is

  • nvrt
  • nrt/v
  • v/nrt
  • 1/nvrt

46. An application requires R-12 at −140°C. The triple-point temperature is −157°C. Find the pressure of the saturated vapour at the required condition.

  • 0.0058 kpa
  • 0.0098 kpa
  • 0.0068 kpa
  • 0.0088 kpa

47. At the triple point, l(sublimation) = l(vaporization) – l(fusion).

  • true
  • false

48. When does a vapour become superheated?

  • when the temperature of vapour is less than the saturation temperature at given pressure
  • when the temperature of vapour is more than the saturation temperature at given pressure
  • when the temperature of vapour is equal to the saturation temperature at given pressure
  • none of the mentioned

49. The slopes of sublimation and vaporization curves for all substances are

  • negative
  • positive
  • zero
  • none of the mentioned

50. The Clausius-Clapeyron equation is given by

  • dp/dt = l / t(vf+vi)
  • dp/dt = l / t(vf-vi)
  • dt/dp = l / t(vf+vi)
  • dt/dp = l / t(vf-vi)

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