Practice Pakistan's most useful MCQs for competitive exams

In a shell and tube heat exchanger, triangular pitch arrangement as compared to square pitch arrangement ?

• (A)  Results in higher shell side pressure drop
• (B)  Can accomodate less number of tubes for a given shell diameter
• (C)  Facilitates easier shell side cleaning; hence is more suitable for handling high dirt factor shell side fluid
• (D)  Creates relatively lower turbulence on the shell side resulting in lower shell side heat transfer co-efficient

Answer

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_____________ heat exchanger is also known as ‘hair pin type’ exchanger?

• (A)  Double pipe
• (B)  Finned
• (C)  Plate type
• (D)  Regenerative

Answer

Submitted By :Ali Uppal

The average velocity in the tubes of a 1-4 heat exchanger is ______________ times that in 1-1 heat exchanger having the same size & number of tubes and operated at same liquid flow rate ?

• (A)  2
• (B)  1/2
• (C)  4
• (D)  1/4

Answer

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A shell may by termed as thin if its thickness to diameter ratio is less than 0.1. The factor which can be neglected in the calculation of membrane stresses is________________?

• (A)  Bending
• (B)  Deformation
• (C)  Shear
• (D)  Elongation

Answer

Submitted By :Ali Uppal

Fouling factor for a heat exchanger is given by (where, U1 = heat transfer co-efficient of dirty surface U2 = heat transfer co-efficient of clean surface) ?

• (A)  U1 – U2
• (B)  1/U1 – 1/U2
• (C)  1/U2 – 1/U1
• (D)  U2 – U1

Answer

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For a laminar flow of fluid in a circular tube, ‘h1’ is the convective heat transfer co-efficient at velocity ‘V1’. If the velocity is reduced by half and assuming the fluid properties are constant, the new convective heat transfer co-efficient is________________?

• (A)  1.26 h1
• (B)  0.794 h1
• (C)  0.574 h1
• (D)  1.741 h1

Answer

Submitted By :Ali Uppal

A graph between _____________ is called Wilson plot?

• (A)  (1/U) Vs. (1/v0.8)
• (B)  (1/v0.8) Vs. U
• (C)  v0.8 Vs . U
• (D)  (1/U) Vs. (1/V)

Answer

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Walls of a cubical oven are of thickness l, and they are made of material of thermal conductivity k. The temperature inside the oven is 100°C and the inside heat transfer coefficient is „3k/l’. If the wall temperature on the outside is held at 25°C, what is the inside wall temperature in degree centigrade ?

• (A)  35.5
• (B)  43.75
• (C)  81.25
• (D)  48.25

Answer

Submitted By :Ali Uppal

For the same heat load and mass flow rate in the tube side of a shell and tube heat exchanger, one may use multipass on the tube side, because it__________________?

• (A)  Decreases the pressure drop
• (B)  Decreases the outlet temperature of cooling medium
• (C)  Increases the overall heat transfer coefficient
• (D)  None of these

Answer

Submitted By :Ali Uppal

Weep holes provided in the plates of a distillation column ____________________?

• (A)  Facilitate draining out liquid from a tray when the unit is not in operation
• (B)  Are normally located near the overflow weir so that any delivery of liquid during operation follows approximately the same path as the overflow fluid
• (C)  Must be large enough (usually 1/4″ to 5/8″ dia) to prevent plugging but should not deliver excessive amount of fluid during operation
• (D)  All

Answer

Submitted By :Ali Uppal