Heat Transfer

380. The outlet temperature of cooling water in a heat exchanger is generally not allowed to exceed above 50°C in industrial practice mainly to avoid

  1. Its evaporation loss
  2. Excessive corrosion
  3. Uneconomic LMTD
  4. Decrease in heat exchanger efficiency
Correct answer: (B)
Excessive corrosion

381. The overall heat transfer co-efficient for a shell and tube heat exchanger for clean surfaces is U0 = 400 W/m2.K. The fouling factor after one year of operation is found to be hd0 = 2000 W/m2.K. The overall heat transfer co-efficient at this time is

  1. 1200 W/m2.K
  2. 894 W/m2.K
  3. 333 W/m2.K
  4. 287 W/m2.K
Correct answer: (C)

333 W/m2.K

382. The overall resistance for heat transfer through a series of flat resistance, is the _________ of the resistances.

  1. Average
  2. Geometric mean
  3. Product
  4. Sum
Correct answer: (D)
Sum

383. The purpose of floating head in a heat exchanger is to

  1. Avoid buckling of tubes
  2. Provide support for tubes
  3. Decrease the pressure drop
  4. Facilitate its lengthening, if needed
Correct answer: (A)
Avoid buckling of tubes

384. The purpose of providing a 'catchall' in the vapor line of an evaporator is to

  1. Create vacuum
  2. Regulate the vapor flow
  3. Vent the non-condensable gases
  4. Arrest the entrained liquid
Correct answer: (D)
Arrest the entrained liquid

385. The purpose of providing bleed points in the evaporator is to

  1. Admit the feed
  2. Remove the product
  3. Facilitate removal of non-condensable gases
  4. Create vacuum
Correct answer: (C)
Facilitate removal of non-condensable gases

386. The purpose of providing expansion bellows in the shell of tubular exchanger is to

  1. Increase the heating load
  2. Impart structural strength
  3. Account for the uneven expansion of shell and tube bundles
  4. Facilitate increase of shell length, if needed
Correct answer: (C)
Account for the uneven expansion of shell and tube bundles

387. The radiation heat flux from a heating element at a temperature of 800°C, in a furnace maintained at 300°C is 8 kW/m2. The flux, when the element temperature is increased to 1000°C for the same furnace temperature is

  1. 11.2 kW/m2
  2. 12.0 kW/m2
  3. 14.6 kW/m2
  4. 16.5 kW/m2
Correct answer: (D)

16.5 kW/m2

388. The range of electromagnetic spectrum important in heat transfer by radiation is _________ microns.

  1. 0.38-0.78
  2. 0.5-50
  3. 100-1000
  4. 18384
Correct answer: (B)
0.5-50

389. The rate of emission of radiation by a body does not depend upon the

  1. Wavelength of radiation
  2. Surface temperature of the body
  3. Nature of the surface
  4. Shape and porosity of the body
Correct answer: (D)
Shape and porosity of the body

390. The rate of heat transfer from a vertical plate by natural convection depends upon the temperature differences (ΔT) between wall and outside bulk. The proportionality is given as

  1. (ΔT)1/4
  2. (ΔT)1/2
  3. (ΔT)5/4
  4. (ΔT)3/4
Correct answer: (D)
(ΔT)3/4
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