Chemical Engineering Heat Conduction MCQ - Set 02 - ObjectiveBooks

Chemical Engineering Heat Conduction MCQ - Set 02

Practice Test: Question Set - 02

1. 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

2. Use of transverse baffles in a shell and tube heat exchanger is done to increase the
    (A) Rate of heat transfer
    (B) Flow velocity
    (C) Turbulence of shell side fluid
    (D) All (a), (b) and (c)

3. All analogy equations connecting friction factor and heat transfer co-efficient apply only to
    (A) Wall or skin friction
    (B) Form friction
    (C) Both (a) and (b)
    (D) Turbulent flow

4. Which of the following situations can be approximated to a steady state heat transfer system?
    (A) A red hot steel slab (having outside surface temperature as 1300°C) exposed to the atmospheric air at 35°C
    (B) 10 kg of dry saturated steam at 8 kgf/cm2 flowing through a short length of stainless steel pipe exposed to atmospheric air at 35°C
    (C) Boiling brine kept in open vessel when the bottom surface temperature of the vessel is maintained constant at 180°C
    (D) A sub-cooled refrigerant liquid at 8°C flowing at the rate of 6 Kg/minute through a copper pipe exposed to atmospheric air at 35°C

5. Reason for operating an evaporator in multiple effects is to secure
    (A) Increased steam economy
    (B) Decreased steam consumption
    (C) Both (a) and (b)
    (D) Increased capacity

6. Heat transfer by __________ may not necessarily require the presence of a medium.
    (A) Conduction
    (B) Natural convection
    (C) Forced convection
    (D) Radiation

7. Fluid motion in the natural convection heat transfer between a solid surface and a fluid in contact with it, results from the
    (A) Existence of thermal boundary layer
    (B) Temperature gradient produced due to density difference
    (C) Buoyancy of the bubbles produced at active nucleation site
    (D) None of these

8. Nusselt number is the ratio of the
    (A) Temperature gradient of the wall to that across the entire pipe
    (B) Temperature difference to the temperature gradient at the wall
    (C) Heat flux at the wall to that across the entire pipe
    (D) None of these

9. Critical value of the __________ number governs the transition from laminar to turbulent flow in free convection heat transfer.
    (A) Grashoff
    (B) Reynolds
    (C) Both 'a' & 'b'
    (D) Prandtl & Grashoff

10. Prandtl number is the reciprocal of
    (A) Thermal diffusivity/Momentum diffusivity
    (B) Thermal diffusivity × Momentum
    (C) Thermal diffusivity × Mass diffusivity
    (D) Mass diffusivity × Momentum diffusivity

11. In case of parallel flow heat exchanger, the lowest temperature theoretically attainable by the hot fluid is __________ the outlet temperature of the cold fluid.
    (A) Equal to
    (B) More than
    (C) Less than
    (D) Either more or less than (depending upon the fluid)

12. For a multipass shell and tube heat exchanger, the LMTD correction factor is always
    (A) 1
    (B) > 1
    (C) < 1
    (D) Between 1 & 2

13. Evaporator tubes are generally
    (A) Horizontal
    (B) Vertical
    (C) Inclined
    (D) Random

14. Thermal conductivity of a gas at low density, __________ with increase in temperature.
    (A) Decreases
    (B) Increases
    (C) Remains unchanged
    (D) May increase or decrease; depends on the gas

15. Which of the following is the most widely used heat insulating material for pipelines carrying steam?
    (A) Tar dolomite bricks followed by asbestos
    (B) Fireclay refractory followed by aluminium sheet
    (C) Cotton followed by aluminium foil
    (D) 85% magnesia cement and glass wool

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