Heat Transfer

421. Thermal diffusivity of a material

  1. Has the unit m2 /sec
  2. Is defined as K/ρ . Cp
  3. Is the ratio of thermal conductivity to thermal capacity
  4. All (A), (B) and (C)
Correct answer: (D)
All (A), (B) and (C)

422. Thickness of thermal boundary layer is more compared to that of hydrodynamic boundary layer, when the value of Prandtl number is

  1. 1
  2. < 1
  3. > 1
  4. > 5
Correct answer: (B)
< 1

423. Three materials A, B and C of equal thickness and of thermal conductivity of 20, 40 & 60 kcal/hr. m. °C respectively are joined together. The temperature outside of A and C are 30°C and 100°C respectively. The interface between B and C will be at a temperature of _________ °C.

  1. 40
  2. 95
  3. 70
  4. 50
Correct answer: (C)
70

424. Three solid objects of the same material and of equal mass-a sphere, a cylinder (length = diameter) and a cube are at 500°C initially. These are dropped in a quenching bath containing a large volume of cooling oil each attaining the bath temperature eventually. The time required for 90% change in temperature is the smallest for

  1. Cube
  2. Cylinder
  3. Sphere
  4. Equal for all the three
Correct answer: (A)
Cube

425. To reduce the tube side pressure drop for the same flow rate, the heat exchanger recommended is

  1. 1-2 heat exchanger
  2. 1-1 heat exchanger
  3. 3-2 heat exchanger
  4. 2-4 heat exchanger
Correct answer: (B)

1-1 heat exchanger

426. Trap is used to remove _________ from steam pipe lines.

  1. Steam
  2. Condensate
  3. Non-condensable
  4. None of these
Correct answer: (B)
Condensate

427. Tube expansion allowances exist in _________ heat exchanger.

  1. Multipass fixed tube sheet
  2. U-tube
  3. Single pass fixed tube sheet
  4. None of these
Correct answer: (B)
U-tube

428. Tube pitch is the _________ of tube diameters and the clearances.

  1. Sum
  2. Difference
  3. Ratio
  4. None of these
Correct answer: (A)
Sum

429. Tubes are held between top and bottom tube sheets in Calandria type evaporator by keeping

  1. Both the tube sheets fixed
  2. Both the tube sheets floating
  3. The top tube sheet floating and bottom tube sheet fixed
  4. The top tube sheet fixed and the bottom tube-sheet floating
Correct answer: (A)
Both the tube sheets fixed

430. Unsteady state heat conduction occurs, when

  1. Temperature distribution is independent of time
  2. Temperature distribution is dependent on time
  3. Heat flows in one direction only
  4. Three dimensional heat flow is concerned
Correct answer: (B)
Temperature distribution is dependent on time
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