Chemical Heat Transfer Quiz 10

1 / 26

With increase in temperature, the total emissivity of conductors______?

Increases

Decreases linearly

Decreases

Remain same

2 / 26

With increase in porosity, the thermal conductivity of a solid substance___________?

May increase or decrease; depends on the solid

Remains unchanged

Decreases

Increases

3 / 26

Which of the following situations can be approximated to a steady state heat transfer system ?

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

Boiling brine kept in open vessel when the bottom surface temperature of the vessel is maintained constant at 180?C

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

A red hot steel slab (having outside surface temperature as 1300?C) exposed to the atmospheric air at 35?C

4 / 26

Which of the following has the minimum thermal conductivity ?

Carbon black

Steel

Tar

Nitrogen

5 / 26

With increase in temperature, the thermal conductivity of a gas _____?

Decreases

Increases

Remain same

May increase or decrease depending on the type of gas

6 / 26

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

Gases

Liquids

Both B. and C.

Solids

7 / 26

Which of the following is directly concerned with the heat transfer ?

Grashoff number

Sherwood number

Strouhal number

Euler number

8 / 26

Which of the following has the minimum absorptivity ?

Aluminium foil

Refractory bricks

Coal dust

Iron plates

9 / 26

Which one gives the monochromatic emissive power for black body radiation ?

Wien?s law

Planck?s law

Kirchhoff?s law

Stefan-Boltzmann law

10 / 26

Which of the following is the most widely used heat insulating material for pipelines carrying steam ?

Fireclay refractory followed by aluminium sheet

Tar dolomite bricks followed by asbestos

Cotton followed by aluminium foil

85% magnesia cement and glass wool

11 / 26

Which of the following parameters is increased by use of finned tube in a multipass shell and tube heat exchanger ?

All A. B. and C.

Effective tube surface area for convective heat transfer

Convective heat transfer co-efficient

Tube side pressure drop and the heat transfer rate

12 / 26

Which of the following has the highest thermal conductivity ?

Water

Silver

Air

Brick

13 / 26

Which of the following is not used as a medium for high temperature heating ?

Fused salts (e.g., an eutectic mixture of 53% KNO3, 40% NaNO2and 7% NaNO3)

Liquid metal (e.g. molten sodium)

Mercury

Dowtherm

14 / 26

Which of the following is concerned with both heat and mass transfer ?

Lewis relationship

Nusselt number

Kutateladze number

Froude number

15 / 26

Which of the following has the lowest Prandtl number ?

Dilute H2SO4

Molten sodium (a coolant used in fast breeder reactor)

Water

Transformer oil

16 / 26

With increase in temperature, the thermal conductivity of most liquids__________?

Increases

First increases upto a certain temperature and then becomes constant

Decreases

Remain same

17 / 26

Which of the following has the lowest overall heat transfer co-efficient ?

Water

Dowtherm

Molten sodium

Air

18 / 26

Which of the following parameters of the fluid is not very important, while deciding its route in a shell and tube heat exchanger ?

Viscosity

Density

Pressure

Corrosiveness & fouling characteristics

19 / 26

Which of the following is correct ?

Resistance = Driving force ? Rate

Rate = Resistance/Driving force

Rate = Driving force ? Resistance

Driving force = Rate ? Resistance

20 / 26

With the increase of temperature, the Col-burn jH factor_______?

Increases

Remains unchanged

May increase or decrease; depending on temperature

Decreases

21 / 26

With increase in the distance between the heat source and the object receiving the heat, the radiation heat transfer ?

Remain unaffected

Decreases

Increases

Increases exponentially

22 / 26

Which of the following is unimportant in forced convection ?

Grashoff number

None of these

Reynolds number

Prandtl number

23 / 26

Which type of heat exchanger is preferred for heavy heat loads ?

None of these

Double pipe

Plate fine

Series and parallel set of shell and tube

24 / 26

With increase in temperature, the thermal conductivity of non-metallic amorphous solids__________?

Decreases

Remain constant

Increases

First decreases upto certain temperature and then increases

25 / 26

With increase in temperature, the thermal conductivity of fresh lubricating oil _____?

Increases

May increase or decrease; depends on its composition

Remains unchanged

Decreases

26 / 26

While the total emissivity of a perfect black body is unity, the same for a real body is___________?

Between 0 and 1

> 1

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