All questions of Heat Transfer for Mechanical Engineering Exam

• A:
  Copper
• B:
  Steel
• C:
  Glass-wool
• D:
  Refractory brick

• a)
  Steel
• b)
  Brass
• c)
  Copper
• d)
  Aluminium

For the three-dimensional object shown in thefigure below, five faces are insulated. Thesixth face (PQRS), which is not insulated,interacts thermally with the ambient, with aconvective heat transfer coefficient of 10 W/m².K. The ambient temperature is 30°C. Heatis uniformly generated inside the object at therate of 100 W/m³. Assuming the face PQRS tobe at uniform temperature, its steady statetemperature is:

• a)
  10°C
• b)
  20°C
• c)
  30°C
• d)
  40°C

• a)
  0.25 mm
• b)
  0.5 mm
• c)
  1 mm
• d)
  2 mm

• a)
  18 mm
• b)
  16 mm
• c)
  12 mm
• d)
  8 mm

Match List-I with List-II and select the correct answer using the codes given below the lists:                            

• a)
  (a) 
• b)
  (b)
• c)
  (c)
• d)
  (d)

• a)
  10 cm
• b)
  15 cm
• c)
  19.5 cm
• d)
  20 cm

• a)
  a b c d
• b)
  b c a d
• c)
  d a b c
• d)
  d c b a

• a)
  Both A and R are individually true and R is the correct explanation of A
• b)
  Both A and R are individually true but R is not the correct explanation of A
• c)
  A is true but R is false
• d)
  A is false but R is true

• a)
  Faster in air block
• b)
  Faster in copper block
• c)
  Equal in air as well as copper block
• d)
  Cannot be predicted with the given information

• a)
  23.5°C
• b)
  300°C
• c)
  35°C
• d)
  40°C

Solar energy is absorbed by the wall of a building as shown in the above figure. Assuming that the ambient temperature inside and outside are equal and considering steady-state, the equivalent circuit will be as shown in (Symbols: R_co = R_{convection,outside} RCI = R_{convection,inside}
and R_w = R_Wall)

• a)
  
• b)
  
• c)
  
• d)
  

• a)
  Both A and R are individually true and R is the correct explanation of A
• b)
  Both A and R are individually true but R is not the correct explanation of A
• c)
  A is true but R is false
• d)
  A is false but R is true

• a)
  0.05 m
• b)
  0.1 m
• c)
  0.2 m
• d)
  0.5 m

• a)
  Increase
• b)
  Decrease
• c)
  Remain the same
• d)
  Vary depending upon theelectrical conductivity of the wire

• a)
  238.43 W
• b)
  190.68 W
• c)
  543.67 W
• d)
  675.98 W

• a)
  0.2
• b)
  0.4
• c)
  0.8
• d)
  1.0

• a)
  25mm
• b)
  40 mm
• c)
  160 mm
• d)
  800 mm

• a)
  120W
• b)
  140W
• c)
  160W
• d)
  180W

• a)
  The better insulation must be put inside 
• b)
  The better insulation must be put outside
• c)
  One could place either insulation on either side
• d)
  One should take into account the steam temperature before deciding as towhich insulation is put where.

• a)
  Added insulation increases heat loss
• b)
  Added insulation decreases heat loss
• c)
  Convection heat loss is less than conduction heat loss
• d)
  Heat flux decreases

• a)
  Aluminium
• b)
  Steel
• c)
  Copper
• d)
  Silver

• a)
  3650 K
• b)
  4500 K
• c)
  5800 K
• d)
  6150 K

• A:

  1, 2 and 3 are correct

• B:

  1, 2 and 4 are correct

• C:

  2, 3 and 4 are correct

• D:

  1, 3 and 4 are correct

The answer is d.

• a)
  40°C
• b)
  50°C
• c)
  55°C
• d)
  100°C

• a)
  80°C
• b)
  100°C
• c)
  120°C
• d)
  160°C

• a)
  Both A and R are individually true and R is the correct explanation of A
• b)
  Both A and R are individually true but R is not the correct explanation of A
• c)
  A is true but R is false
• d)
  A is false but R is true

• a)
  0.4
• b)
  1.6
• c)
  2 ln (0.8)
• d)
  2.5

• a)
  Greater for parallel flow heat exchanger than for counter flow heatexchanger.
• b)
  Greater for counter flow heat exchanger than for parallel flow heatexchanger.
• c)
  Same for both parallel and counter flow heat exchangers.
• d)
  Dependent on the properties of the fluids.

The following figure was generated from experimental data relatingspectral black body emissive power to wavelength at threetemperatures T₁, T₂ and T₃ (T₁ > T₂ > T₃). The conclusion is that themeasurements are:

          

• a)
  Correct because the maximain Ebλ show the correct trend
• b)
  Correct because Planck's lawis satisfied
• c)
  Wrong because the StefanBoltzmann law is not satisfied
• d)
  Wrong because Wien's displacement law is not satisfied

For natural convective flow over a vertical flat plate as shown in the given figure, the governing differential
equation for momentum is:

If equation is non-dimensionalized by

then the term gβ (T -  T_∞) , is equal to:

• a)
  Grashof number
• b)
  Prandtl number
• c)
  Rayleigh number
• d)
  

• a)
  Higher than critical radius of insulation​
• b)
  Slightly lower than critical radius of insulation
• c)
  Equal to the critical radius of insulation
• d)
  Considerably higher than critical radius of insulation

• a)
  α = 1, ρ = 0, τ = 0
• b)
  α = 0, ρ = 1, τ = 0
• c)
  α = 0, ρ = 0, τ = 1
• d)
  α + ρ = 1, τ = 0

• a)
  k² ρc
• b)
  1/ρkc
• c)
  k/ρc
• d)
  ρc/k²

• a)
  
• b)
  
• c)
  
• d)
  

• a)
  0.1°C/h
• b)
  0.2°C/h
• c)
  0.3°C/h
• d)
  0.4°C/h

• a)
  25mm
• b)
  40 mm
• c)
  160 mm
• d)
  800 mm

• a)
  ML⁻¹T ⁻¹θ ⁻³
• b)
  MLT ⁻¹θ ⁻¹
• c)
  MLθ ⁻¹T⁻³
• d)
  MLθ ⁻¹T⁻²

• a)
  Convection
• b)
  Conduction
• c)
  Radiation
• d)
  Conduction and convection

• a)
  500 W/m²
• b)
  600 W/m²
• c)
  700 W/m²
• d)
  800 W/m²

• a)
  Both A and R are individually true and R is the correct explanation of A
• b)
  Both A and R individually true but R in not the correct explanation of A
• c)
  A is true but R is false
• d)
  A is false but R is true

Temperature profiles for four cases are shown in the following figures and are labelled A, B, C and D.

Match the above figures with  
1. High conductivity fluid
2. Low conductivity fluid
3. Insulating body
4. Guard heater

Select the correct answer using the codes given below:

• a)
  (a) 
• b)
  (b)
• c)
  (c)
• d)
  (d)

• a)
  1 W/K
• b)
  1.8 W/K
• c)
  1 K/W
• d)
  1.8 K/W

• a)
  Greater than that of sphere B
• b)
  Less than that of sphere B
• c)
  Equal to that of sphere B
• d)
  Equal to double that of sphere B

• a)
  Both A and R are individually true and R is the correct explanation of A
• b)
  Both A and R are individually true but R is not the of A
• c)
  A is true but R is false
• d)
  A is false but R is true

• a)
  Density
• b)
  Coefficient of viscosity
• c)
  Gravitational force
• d)
  Velocity

• a)
  48/11
• b)
  11/48
• c)
  24/11
• d)
  11/24

• a)
  Liquid heating and liquid cooling
• b)
  Gas heating and gas cooling
• c)
  Liquid heating and gas cooling
• d)
  Heating and cooling of any fluid

• a)
  1000 W/m²
• b)
  3400 W/m²
• c)
  5680 W/m²
• d)
  7348 W/m²

• a)
  1, 2 and 3
• b)
  1 and 2
• c)
  1 and 3
• d)
  2 and 3