Heat Transfer

341. The advantage of using a 1 - 2 shell and tube heat exchanger over a 1 - 1 shell and tube heat exchanger is

  1. Lower tube side pressure drop
  2. Lower shell side pressure drop
  3. Higher tube side heat transfer co-efficient
  4. Higher shell side heat transfer co-efficient
Correct answer: (C)
Higher tube side heat transfer co-efficient

342. The average heat transfer co-efficient for laminar film condensation on vertical surface is inversely proportional to (where, ΔT = Temperature drop across condensate film)

  1. (ΔT)2
  2. √(ΔT)
  3. (ΔT)1/4
  4. (ΔT)3/2
Correct answer: (C)

(ΔT)1/4

343. The average heat transfer co-efficient over the entire length of the plate (ha) and the local heat transfer co-efficient (hL), in case of heat transfer over a flat plate in laminar zone is related as

  1. ha = 0.8hL
  2. ha = 2hL
  3. ha = hL
  4. ha = 5hL
Correct answer: (B)

ha = 2hL

344. The capacity of double-effect evaporator is less than half of the capacity of two single effects, each of which is operating over same terminal temperature difference, when the

  1. Solution has an elevation of boiling point
  2. Evaporators operate under vacuum
  3. Evaporators operate at atmospheric pressure
  4. None of these
Correct answer: (A)
Solution has an elevation of boiling point

345. The characteristic dimensionless groups for heat transfer to a fluid flowing through a pipe in laminar flow are

  1. Re.Gz
  2. Nu, Pr
  3. Nu, Pr, Re
  4. Nu, Gz
Correct answer: (D)
Nu, Gz

346. The critical radius 'r' of insulation on a pipe is given by

  1. r = 2k/h
  2. r = k/h
  3. r = k/2h
  4. r = h/k
Correct answer: (B)
r = k/h

347. The critical radius of insulation for a spherical shell is (where, K = thermal conductivity of insulating material h0 = heat transfer coefficient at the outer surface)

  1. K/h0
  2. 2K/h0
  3. h0/K
  4. h0/2K
Correct answer: (B)

2K/h0

348. The critical radius of insulation for cylindrical pipe is (where, hi = heat transfer coefficient at inside of the pipe)

  1. K/h0
  2. 2K/h0
  3. hi/K
  4. 2hi/K
Correct answer: (A)

K/h0

349. The dimensionless group in mass transfer that is equivalent to Prandtl number in heat transfer is

  1. Nusselt number
  2. Sherwood number
  3. Schmidt number
  4. Stanton number
Correct answer: (C)
Schmidt number

350. The Dittus-Boelter equation for convective heat transfer [(i.e. h = 0.023 (K/D) (Re)0.8 (Pr)0.8] cannot be used for

  1. Low Reynold's number
  2. Very low Grashoff number
  3. Molten metals
  4. All (A), (B) and (C)
Correct answer: (D)
All (A), (B) and (C)
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