Mechanical Engineering - Heat and Mass Transfer - Heat Exchanger

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Question - 1

Which one of the following heat exchangers gives parallel straight line pattern of temperature distribution for both cold and hot fluid?

  • A Parallel flow with unequal heat capacities
  • B Counter flow with equal heat capacities
  • C Parallel flow with equal heat capacities
  • D Counter flow with unequal heat capacities

Question - 2

Match List I (Heat exchanger process) with List II (Temperature area diagram) and select the correct answer using the codes given below the lists.

List I List II
P. Counter flow sensible heating 1.
Q. Parallel flow sensible heating 2.
R. Evaporating 3.
S. Condensing 4.
  5.
  • A P Q R S 3 4 1 2
  • B P Q R S 3 2 5 1
  • C P Q R S 4 3 2 5
  • D P Q R S 4 2 1 5

Question - 3

In a counter flow heat exchanger, the product of specific heat and mass flow rate is same for the hot and cold fluids. If NTU is equal to 0.5, then the effectiveness of the heat exchanger is

  • A 1.0
  • B 0.5
  • C 0.33
  • D 0.2

Question - 4

Which one of the following diagrams correctly shows the temperature distribution for a gas to gas counter flow heat exchanger?

  • A
  • B
  • C
  • D

Question - 5

A condenser is designed to condense 0.76 kg/min of steam with cooling water entering at 20 oC and leaving at 65 oC. Overall heat transfer coefficient = 3400 W/m2 -K. The surface area required for this heat exchanger is (saturation temperature of steam = 95.6oC, hfgsteam = 2270 kJ/kg)

  • A 0.17 cm2
  • B 0.27m2
  • C 0.17m2
  • D 0.15m2

Question - 6

In a parallel flow double pipe heat exchanger water flows through the inner pipe and is heated from 20°C to 70°C. Oil flowing through the annulus is cooled from 200°C to 100 °C. It is desired to cool the a il to a lower exit temperature by increasing the length of the heat exchanger. The minimum temperature to which the oil may be cooled is

  • A 60°C
  • B 80°C
  • C 70°C
  • D 90°C

Question - 7

In a counter flow heat exchanger, hot fluid enters at 60°C and cold fluid leaves at 30°C. Mass flow rate of the hot fluid is 1kg/s and that the cold fluid is 2 kg/s.Specific heat of the hot fluid is 10 kJ/kg-K and that of the cold fluid is 5 kJ/kg-K. The Log Mean Temperature Difference (LMTD) for the heat exchanger in °C is

  • A 15
  • B 30
  • C 35
  • D 45

Question - 8

AMTD (Arithmetic Mean Temperature Difference) will be 5% higher than LMTD (Log Mean Temperature Difference) when \({\triangle T_1\over \triangle T_2}\) is equal to

  • A 3.2
  • B 2.2
  • C 2.0
  • D 3.0

Question - 9

For a given counter flow heat exchanger, given m1 = m2 = 1 kg/s.

Th1 = 420oC, TC1 = 20oC, C1 = 1 kJ/kg-K, C2 = 4 kJ/kg-K
If effectiveness of heat exchanger is 75%, then heat transfer rate is (in kJ)

  • A 325
  • B 300
  • C 350
  • D 270

Question - 10

For a given counter flow heat exchanger, given m1 = m2 = 1 kg/s.

Th1 = 420oC, TC1 = 20oC, C1 = 1 kJ/kg-K, C2 = 4 kJ/kg-K
Exit temperature To2 of fluid 2 is equal to

  • A 85°C
  • B 95°C
  • C 190°C
  • D 105°C
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