Heat Transfer

201. In a laboratory test run, the rate of drying was found to be 0.5 x 10-3 kg/m2.s, when the moisture content reduced from 0.4 to 0.1 on dry basis. The critical moisture content of the material is 0.08 on a dry basis. A tray dryer is used to dry 100 kg (dry basis) of the same material under identical conditions. The surface area of the material is 0.04 m2/kg of dry solid. The time required (in seconds) to reduce the moisture content of the solids from 0.3 to 0.2 (dry basis) is

  1. 2000
  2. 4000
  3. 5000
  4. 6000
Correct answer: (C)
5000

202. In a liquid-liquid heat exchanger, for the same process temperature, the ratio of the LMTD in parallel flow to the LMTD in counter flow is always

  1. < 1
  2. > 1
  3. 1
  4. ∞
Correct answer: (A)
< 1

203. In a multipass shell and tube heat exchanger, tube side return pressure loss is equal to _________ the velocity head.

  1. Twice
  2. Four times
  3. Square root of
  4. Square of
Correct answer: (B)
Four times

204. In a multiple effect evaporator, the effect of boiling point elevation is to

  1. Reduce the capacity
  2. Reduce the economy
  3. Increase the economy
  4. None of these
Correct answer: (A)
Reduce the capacity

205. In a parallel flow heat exchanger, if the outlet temperature of hot and cold fluids are the same, then the log mean temperature difference (LMTD) is

  1. Minimum
  2. Maximum
  3. Zero
  4. Infinity
Correct answer: (C)
Zero

206. In a shell and tube heat exchanger, floating head is used for

  1. Large temperature differentials
  2. High heat transfer co-efficient
  3. Low pressure drop
  4. Less corrosion of tubes
Correct answer: (A)
Large temperature differentials

207. In a shell and tube heat exchanger, putting a longitudinal baffle across the shell, forces the shell side fluid to pass _________ through the heat exchanger.

  1. Once
  2. Twice
  3. Thrice
  4. Four times
Correct answer: (B)
Twice

208. In a shell and tube heat exchanger, square pitch compared to triangular pitch

  1. Gives a higher shell side pressure drop
  2. Gives a lower shell side pressure drop
  3. Can pack more surface area into a shell of given diameter
  4. None of these
Correct answer: (A)
Gives a higher shell side pressure drop

209. In a shell and tube heat exchanger, the height of 25 percent cut baffles is equal to (where, D = inside diameter of shell).

  1. 0.25 D
  2. 0.50 D
  3. 0.75 D
  4. None of these
Correct answer: (C)
0.75 D

210. In a shell and tube heat exchanger, the shell side fluid velocity can‟t be changed by changing the

  1. Tube layout
  2. Tube diameter
  3. Tube pitch
  4. Number of baffles
Correct answer: (B)
Tube diameter
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