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This set of Engineering Thermodynamics Multiple Choice Questions & Answers (MCQs) focuses on Engineering Thermodynamics Set 9
Q1 | Examine follwing two statements & choosethe correct relationshipi) for a steam power plant Rankine cycle is preferred over Carnot cycleii) a pump which will handle the mixture of vapour & liquid is difficult to construct
- a) both i) ii) are correct & i) is the consequence of ii)
- b) both i) & ii) are independently correct
- c) i) is correct but ii) is not
- d) ii) is correct but i) is not
Q2 | Considerfollowing options for a simple Rankine cyclei) increasing pressure at exist of turbineii) increasing average temperature of heat additioniii) decreasing pressure at exit of turbineiv) superheating of steamv) decreasing pressure during superheating. Which combination of above will increase Rankine efficiency?
- i), ii) & iv)
- i), ii) & v)
- iii), iv) & v)
- ii), iii) & iv)
Q3 | Higher dryness fraction of steam at turbine exit in aRankine cycle
- a) will increase cycle efficiency
- b) will increase turbine work
- c) will protect turbine blading
- d) will reduce pump work
Q4 | The main purpose of reheat Rankine cycle is
- a) to reduce moisture in steam & thus to protect turbine blading
- b) to obtain significant gain in efficiency
- c) to obtain significant gain in net work
- d) to reduce heat supplied & yet maintain turbine work
Q5 | 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
- a) i) is preferred over ii) for higher efficiency
- b) ii) is preferred over i) for reduced moisture content of steam in l.p side
- c) only i) is implemented in actual practice
- d) by preferring ii) overi) significant gain in efficiency results
Q6 | In a steam power plant which cycle requires two or more feed pumps
- a) regenerative rankine cycle
- b) reheat rankine cycle
- c) simple rankine cycle
- d) idealized regenerative rankine cycle
Q7 | In a regenerative Rankine cycle as compared to simple Rankine cycle
- a) the pump work is smaller
- b) the addition of heat is smaller
- c) the superheat is to lesser extent
- d) the heat rejected in condenser is smaller
Q8 | A Rankine cycle is lessefficient than Carnot cycle because
- a) the working fluid is steam
- b) heat is not added athighest temperature of cycle
- c) condensation processis extended into liquid phase
- d) superheating occurs at constant pressure
Q9 | A regenerative Rankine cycle may approach efficiency of a Carnot cycle between sametemperature by
- a) reducing heat to condenser
- b) reducing volume of steam passed into condenser
- c) increasing turbine work
- d) adding heat a highest temp.
Q10 | Average temp.at which heat is supplied isincreased in
- a) simple rankine cycle
- b) reheat rankine cycle
- c) regenerative rankine cycle
- d) modified rankine cycle
Q11 | A power cycle using steam as working fluid consist ofi) constant pressure heat additionii)adiabatic expansioniii) constant pressure heat rejection &iv) adiabatic compression. The cycle is
- simple rankine cycle
- modified rankine cycle
- carnot cycle
- regenerative rankine cycle
Q12 | 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
- a) 0.79
- b) 0.815
- c) 0.84
- d) 0.86
Q13 | A Rankine cycle has efficiency of 19.4%. The steam enters the turbine with enthalpy of 32.85 kJ/Kg while heat of water entering the boiler is 423.6 kJ/Kg.the work of the turbine is 560 kJ/ Kg. the pump work is
- a) 3.5 kj/kg
- b) 5 kj/kg
- c) 6.5 kj/kg
- d) 7 kj/kg
Q14 | A steam power plant working on Rankine cycle produces steam in the boiler at a rate of 100 kg/s with enthalpy of 3280 kJ/kg from water whose total heat content is 420 kJ/kg. The plant has Rankine efficiency of 24.65 while pump requires 5 kJ/kg of work. The turbine generates power of
- a) 71 mw
- b) 71.5 mw
- c) 72 mw
- d) 72.5 mw
Q15 | In a simple Rankine cycle steam was expanded from 100 bar & 380°C to 1 bar0.8 dry state. The pump motor consumes 10 kJ/kg of energy. The efficiency of cycle is
- a) 31%
- b) 34%
- c) 29.8%
- d) 30.6%
Q16 | In a reheat Rankine cycle steam with enthalpy of 3300 kJ/kg is expanded inh.p turbine to a state where enthalpy is 2650 kJ/kg. The steam is further expnaded from a state where enthalpy is 2950 kJ/kg to enthalpy of 2525 kJ/kg & latent heat of 2201 kJ.kg. The work of the cycle & amount of reheat respectively are
- a) 1075 kj/kg,300 kj.kg
- b) 1399 kj/kg, 300 kj/kg
- c) 1075 kj/kg, 324 kj/kg
- d) 1399 kj/kg, 324 kj/kg
Q17 | In above question the heat supplied & efficiency respectively are
- a) 3276 kj/kg, 42.7%
- b) 2976 kj/kg, 36.12%
- c) 3300 kj/kg, 32.6%
- d) 330 kj/kg, 42.4%
Q18 | Due to which of the following reasons the Carnot cycle cannot be realised in actual practice?
- a) high volume ratios in the cylinder
- b) very high pressure developed in the cylinder
- c) both a & b
- d) none of the above
Q19 | The flow through turbine on a Mollier chart isrepresented by
- a) vertical line
- b) horizontal line
- c) curved line convex up
- d) curved line convex down
Q20 | The latent enthalpy of vapourisation at criticalpoint is
- a) zero
- b) minimum
- c) maximum
- d) none of the above
Q21 | Above critical point, asubstance exists as
- a) vapour
- b) liquid
- c) gas
- d) supersaturated fluid
Q22 | Triple point of a pure substance is a point atwhich
- a) solid & vapour exist together
- b) solid & liquid exist together
- c) liquid & vapour exist together
- d) solid, liquid & vapour phases existtogether
Q23 | Which of the following cycles is used in thermalpower plants?
- a) brayton
- b) carnot
- c) ericsson
- d) rankine
Q24 | In a Carnot engine, when the working substance rejects its heat to sink, the temperature of sink
- a) remains same
- b) decrease
- c) increases
- d) becomes 0??k
Q25 | Which of the following is used as a working substance for a Carnotcycle?
- a) ideal gas
- b) real gas
- c) steam
- d) atmospheric air