UPSSSC JE'21 ME: Daily Practices Quiz. 18-Sep-2021

Quiz: Mechanical Engineering
Exam: UPSSSC
Topic: Power Plant

Each question carries 1 mark
Negative marking: 1/4 mark
Time: 8 Minutes

Q1. The factor(s) on which the reheat factor depend(s) upon
(a) initial pressure and super-heat
(b) exit pressure
(c) turbine stage efficiency
(d) All of the above

Q2. In a power plant, the efficiency of the electric generator, turbine, boiler, cycle and the overall plant are 0.97, 0.95, 0.92, 0.42 and 0.33 respectively. In the generated electricity, the auxiliaries will consume nearly
(a) 7.3%
(b) 6.5%
(c) 5.7%
(d) 4.9%

Q3. The function of the air preheater is to _____ the temperature for air before it enters the furnace.
(a) Increase
(b) Decrease
(c) Either (a) or (b)
(d) None of these

Q4. Which among the following is the boiler mounting?
(a) Blow off cock
(b) Feed pump
(c) Economizer
(d) Superheater

Q5. The degree of reaction is the ratio of
(a) Actual enthalpy changes in rotor to actual enthalpy change in stator
(b) Actual enthalpy changes in rotor to actual enthalpy change in state
(c) Actual enthalpy changes in state to actual enthalpy change in rotor
(d) Actual enthalpy changes in stator to actual enthalpy change in rotor

Q6. Which of the following is the formula for efficiency of Brayton cycle?
(a) ɳ=1-1/r^γ
(b) ɳ=1-1/r^(γ-1)
(c) ɳ=1-1/r^(1-γ)
(d) ɳ=1-1/r^((γ-1)/γ)

Solutions
S1. Ans. (d)
Sol. The reheat factor (R.F.) is defined as the ratio of cumulative heat drop to
Isentropic heat drop
It depends on
Initial pressure and superheat
Exit pressure
Turbine stage efficiency.
Reheat factor increases with the increase in number of stages.
The numerical value of reheat factor varies from 1.02 to 1.06

S2. Ans. (a)
Sol. Efficiency of overall plant can be defined as
ɳ_o=ɳ_b×ɳ_t×ɳ_e×ɳ_g×ɳ_a
0.33=0.92×0.95×0.42×0.97×ɳ_a
ɳ_a=0.0733=7.33%
S3. Ans. (a)
Sol. The function of air preheater is to increase the temperature of air before it enters the furnace.

S4. Ans. (a)
Sol. Boiler mountings are the safety devices which are fitted on the boiler for its safe and efficient working. It is not the integral part of the boiler.
Hence, blow off cock is the boiler mountings.

S5. Ans. (b)
Sol. The degree of reaction is the ratio of actual enthalpy change in rotor to actual enthalpy change in state.

S6. Ans. (d)
Sol. In case of Brayton cycle, the efficiency (ɳ) is
ɳ=1-1/r^((γ-1)/γ)