NHPC JE'21 ME: Daily Practices Quiz. 22-Nov-2021

Quiz: Mechanical Engineering
Exam: NHPC JE
Topic: Miscellaneous

Each question carries 1 mark
Negative marking: 1/4 mark
Time: 6 Minutes

Q1. What is an azeotrope?
(a) A non-halogenic refrigerant
(b) A refrigerant dissolved in alcohol
(c) A mixture of refrigerants without phase separation
(d) An eco-friendly refrigerant

Q2. Air at 35°C DBT and 25°C dew point temperature passes through the water shower whose temperature is maintained at 20°C. What is the process involved?
(a) cooling and humidification
(b) sensible cooling
(c) cooling and dehumidification
(d) heating and humidification

Q3. For an air-conditioned space, RTH = 100 kW, RSHF = 0.75, volume flow rate = 100 m³/min, and indoor design specific humidity is 0.01 kg/kg of dry air. What is the specific humidity of the supply air?
(a) 0.010
(b) 0.0075
(c) 0.005
(d) 0.0025

Q4. In an air-standard Diesel cycle; r is the compression ratio, ρ is the fuel cut-off ratio and γ is the adiabatic index (C_p/C_V ). Its air standard efficiency is given by
(a) η=1-{1/(γ.r^(γ-1) ).((ρ^γ-1))/((ρ-1))}
(b) η=1-{1/(γ.r^(γ-1) ).((ρ^(γ-1)-1))/((ρ-1))}
(c) η=1-{1/(γ.r^(γ-1) ).((ρ^(γ-1) ))/((ρ-1))}
(d) η=1-{1/(γ.r^γ ).((ρ^(γ-1)-1))/((ρ-1))}

Q5. A Carnot engine receives 100 kJ of heat at 600 K. Heat is rejected at 300 K. The displacement volume is 0.2 m³. The mean effective pressure is
(a) 2 bar
(b) 2.5 bar
(c) 3 bar
(d) 3.5 bar

Q6. Piston compression rings are made of which one of the following?
(a) Cast iron
(b) Bronze
(c) Aluminium
(d) White metal

Solutions

S1. Ans.(c)
Sol. Azeotrope is a mixture of refrigerants without phase separation.

S2. Ans.(c)
Sol. As the temperature of water shower is less than dew point temperature hence, water vapour starts condensing. Thus, process involved is cooling and dehumidification.

S3. Ans.(c)
Sol.
RSHF=RSH/RTH
∴RSH=0.75×100=75 kW
RLH=100-75=25 kW
RLH = 50 cmm (w1 – w2)
W2 = 0.005 kg/kg of dry air

S4. Ans.(a)
Sol.
η_diesel=1-{1/r^(γ-1) (ρ^γ-1)/(γ(ρ-1)}
η of diesel engine increases as the load on the engine decreases and at limiting condition becomes to Otto. With increase in load, cut off ratio increases.

S5. Ans.(b)
Sol.
η=1-T_1/T_2 =1-300/600=0.5
W=ηQ_S=0.5×100=50 kJ
m.e.p. =W/V_s =50/0.2
= 250 kPa = 2.5 bar
Option (b) is correct

S6. Ans.(a)
Sol. Since grey cast iron has properties of self-lubrication and damping of small vibrations they are widely used for machine base, engine frames, drainage pipes, elevator and industrial furnace counter weights, pump housings cylinder and piston rings of IC engines, flywheel etc.