Practice Pakistan's most useful MCQs for competitive exams

The main function of baffles provided in a shell and tube heat exchanger is to______________?

• (A)  Facilitate the cleaning of outer tube surface
• (B)  Enhance turbulence
• (C)  Hold the tubes in position
• (D)  All A , B & C

Answer

Submitted By :Ali Uppal

Steam side heat transfer co-efficient in an evaporator is in the range of ______________ kcal/hr.m2°C?

• (A)  10-50
• (B)  100-500
• (C)  1000-1500
• (D)  5000-15000

Answer

Submitted By :Ali Uppal

The ratio of total radiating power to the absorptivity of the body depends upon the _____________ as per Kirchoff‟s law?

• (A)  Wavelength of radiation
• (B)  Nature of the body
• (C)  Temperature of the body
• (D)  None of these

Answer

Submitted By :Ali Uppal

Steam is to be condensed in a shell and tube heat exchanger, 5 m long with a shell diameter of 1 m. Cooling water is to be used for removing the heat. Heat transfer co-efficient for the cooling water, whether on shell side or tube side is the same. The best arrangement is_____________?

• (A)  Vertical heat exchanger with steam on tube side
• (B)  Vertical heat exchanger with steam on shell side
• (C)  Horizontal heat exchanger with steam on tube side
• (D)  Horizontal heat exchanger with steam on shell side

Answer

Submitted By :Ali Uppal

Which of the following is generally considered as opaque surface towards radiations ?

• (A)  Gases
• (B)  Solids
• (C)  Liquids
• (D)  Both

Answer

Submitted By :Ali Uppal

200 kg of solids (on dry basis) is subjected to a drying process for a period of 5000 seconds. The drying occurs in the constant rate period with the drying rate as, Nc = 0.5 × 10-3 kg/m2.s. The initial moisture content of the solid is 0.2 kg moisture/kg dry solid. The interfacial area available for drying is 4 m2/1000 kg of dry solid. The moisture content at the end of the drying period is (in kg moisture/kg dry solid)?

• (A)  0.5
• (B)  0.05
• (C)  0.1
• (D)  0.15

Answer

Submitted By :Ali Uppal

Harmonic mean temperature difference is given by_________________?

• (A)  √(ΔT1 . ΔT2)
• (B)  2 (ΔT1 . ΔT2)/(ΔT1 + ΔT2)
• (C)  2 (ΔT1 . ΔT2)/(ΔT1 – ΔT2)
• (D)  (ΔT1 – ΔT2)/(ΔT1 . ΔT2)

Answer

Submitted By :Ali Uppal

If average heat transfer co-efficient is ha and the local coefficient at the end of the plate is hl then in case of heat transfer to a fluid flowing over a flat plate, heated over its entire length________________?

• (A)  ha = hl
• (B)  ha = 2hl
• (C)  ha = 0.5 hl
• (D)  ha = 0.75 hl

Answer

Submitted By :Ali Uppal

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______________?

• (A)  (ΔT)1/4
• (B)  (ΔT)1/2
• (C)  (ΔT)5/4
• (D)  (ΔT)3/4

Answer

Submitted By :Ali Uppal

Heat transfer occurs by natural convection because change in temperature causes difference in__________________?

• (A)  Viscosity
• (B)  Density
• (C)  Thermal conductivity
• (D)  Heat capacity

Answer

Submitted By :Ali Uppal