Question 1

Condensing film co-efficient for steam on horizontal tubes ranges from 5000 to 15000 Kcal/hr.m².°C. Condensation of vapor is carried out inside the tube in a shell and tube heat exchanger, when the A)Higher condensing film co-efficient is desired B)Condensate is corrosive in nature C)Lower pressure drop through the exchanger is desired D)Temperature of the incoming vapor is very high

Accepted Answer

When the condensate is corrosive in nature, it is safer to carry out condensation inside the tubes to prevent damage to the shell.

Question 2

Viscosity of gases __________ with increase in temperature.
A)Increase very rapidly
B)Increase slowly
C)Decrease slowly
D)Remain unaffected

Accepted Answer

The viscosity of gases increases slowly with an increase in temperature due to the increased kinetic energy of gas molecules, which leads to more frequent and energetic collisions.

Question 3

In case of surface condensers, a straight line is obtained on plotting 1/U vs. __________ on an ordinary graph paper. A)1/V?^-0.8 B)V??^-0.8 C)V^-2 D)1/ V^-2

Accepted Answer

1/U vs. 1/V?^-0.8 is a straight line in case of surface condensers.

Question 4

A cube, sphere & a thin circular plate (all having same mass and made of same material) are all heated to 300°C and allowed to cool in natural air. Which one will cool the slowest?
A)Cube
B)Plate
C)Sphere
D)All will cool at the same rate

Accepted Answer

The sphere will cool the slowest because it has the smallest surface area to volume ratio compared to the cube and the plate, reducing the rate of heat loss.

Question 5

A steel sphere of radius 0.1 m at 400°K is immersed in an oil at 300°K. If the centre of the sphere reaches 350°K in 20 minutes, how long will it take for a 0.05 m radius steel sphere to reach the same temperature (at the centre) under identical conditions? Assume that the conductive heat transfer co-efficient is infinitely large.
A)5 minutes
B)10 minutes
C)20 minutes
D)40 minutes

Accepted Answer

The time taken for the center of a sphere to reach a certain temperature is proportional to the square of its radius when the conductive heat transfer coefficient is infinitely large. Since the radius of the second sphere is half of the first, the time taken will be (0.05/0.1)^2 = 1/4 of the original time, which is 20 minutes. Therefore, it will take 5 minutes.

Question 6

Which of the following material has lest value of thermal diffusivity?
A)Aluminium
B)Rubber
C)Lead
D)Mercury
E)Iron

Accepted Answer

Rubber has the least value of thermal diffusivity among the options given. Thermal diffusivity measures how quickly a material can conduct thermal energy relative to its ability to store thermal energy. Metals like Aluminium, Lead, Mercury, and Iron generally have higher thermal diffusivities due to their good thermal conductivity. Rubber, being a poor conductor of heat, has a much lower thermal diffusivity.

Question 7

For a opaque body
A)reflectivity = 0
B)absorptivity = reflectivity = 1
C)37,500 kg
D)absorptivity + reflectivity = 1
E)absorptivity = 0

Accepted Answer

For an opaque body, the sum of absorptivity and reflectivity equals 1, as it does not transmit any light; all light is either absorbed or reflected.

Question 8

In which case the value of thermal conductivity drops with rising temperature
A)Methane
B)Benzene
C)Carbondioxide
D)Ammonia
E)None of the above

Accepted Answer

The answer of In which case the value of thermal...

Question 9

Which of the following is used as entrainer in acetic acid - water separation?
A)Butyl acetate
B)Methyl alcohol
C)Benzene.
D)Phosphorous
E)Hexane

Accepted Answer

Butyl acetate is used as an entrainer in acetic acid - water separation because it forms an azeotrope with water, which allows for the separation of the two components by distillation.

Question 10

Which of the following provides maximum contact surface for a liquid vapour system?
A)Wetted wall column
B)Packed tower
C)Sieve plant column
D)Benzene.
E)Bubble cap tower

Accepted Answer

The answer of Which of the following provides maximum contact...

Question 11

The lower temperature limit for mercury thermometer is
A)Absolute zero
B)0°F
C)- 39°F
D)0°C
E)100°C

Accepted Answer

The lower temperature limit for a mercury thermometer is -39°F because at this temperature, mercury freezes and cannot expand or contract to measure temperature changes.

Question 12

Cork is a good insulator because
A)It is porous
B)Its density is low
C)It is flexible
D)It can be powdered
E)It can be cast into rolls

Accepted Answer

Cork is a good insulator primarily because it is porous, which traps air and reduces heat transfer.

Question 13

The value of thermal conductivity of water at room temperature is expected to be
A)0.05 kcal/m-hr-°C
B)0.5 kcal/m-hr-°C
C)0.001 kcal/m-hr-°C
D)1.0 kcal/m-hr-°C
E)1.5 kcal/m-hr-°C

Accepted Answer

The thermal conductivity of water at room temperature is approximately 0.6 W/m-K, which is roughly equivalent to 0.5 kcal/m-hr-°C when converted from SI units to the given units. This value indicates how well water can conduct heat, which is neither too high nor too low compared to other materials.

Question 14

The coefficient of linear expansion of a solid is L. The volume V of a cube of this solid on being heated by 1?C will change by
A)VL
B)VL/3
C)3 VL
D)37,500 kg
E)3L

Accepted Answer

The volume expansion coefficient for a solid is approximately three times the linear expansion coefficient. Therefore, the change in volume is given by 3VL.

Question 15

The unit of thermal conductivity in S.I. units is
A)KJ/m-hr-°K
B)KJ/m-hr°C
C)W/m°K
D)W/m-hr°C
E)W/m-hr-°K

Accepted Answer

The unit of thermal conductivity in the International System of Units (S.I.) is Watts per meter Kelvin (W/m°K), which represents the amount of heat that passes through a material with a thickness of one meter, with a temperature difference of one Kelvin, in one second.

Question 16

Two rods one of copper and the other of mild steel, both of diameter 20 mm and length 250 mm are coated with a uniform layer of wax all around. These rods are placed vertically in a boiling water bath with 200 mm, length of each rod projecting outside. If the melting point of wax is 10?C, then
A)equal quantity of wax will meet on the two rods
B)more wax will melt on copper rod as compared to mild steel rod
C)37,500 kg
D)nothing can be predioted as the data is insufficient
E)more wax will melt on mild steel rod as compared to copper rod

Accepted Answer

Copper has a higher thermal conductivity than mild steel, which means it can transfer heat more efficiently from the boiling water to the wax. As a result, more wax will melt on the copper rod compared to the mild steel rod.

Question 17

Oxygen boils at -183°C, this temperature is
A)- 215°F
B)- 361°F
C)- 227°F
D)- 329°F
E)-398°F

Accepted Answer

The answer of Oxygen boils at -183°C, this temperature is
A)-...

Question 18

Heat is transferred from an electric bulb mainly by
A)Conduction, convection and radiation.
B)Radiation
C)Convection and conduction
D)Convection
E)Conduction

Accepted Answer

Heat from an electric bulb is primarily transferred through radiation because the bulb emits heat in the form of infrared radiation, which can travel through air without needing a medium (unlike conduction and convection).

Question 19

The average value of thermal conductivity for air at 20°C is about
A)0.11
B)0.011
C)0.022
D)None of the above
E)Nichrome

Accepted Answer

The average value of thermal conductivity for air at 20°C is approximately 0.0257 W/(m·K), which is closest to the value given in option C, 0.022.

Question 20

A vapour containing liquid particles to the extent of 50% by the volume is known as
A)Saturate vapour
B)Superheated vapour
C)Super saturated liwuid
D)Wet vapour
E)Saturated liquid

Accepted Answer

Wet vapour is a mixture of liquid and vapour phases where the liquid particles are present to a significant extent, in this case, 50% by volume.

Quiz 13: Concepts in Heat Transfer

Condensing film co-efficient for steam on horizontal tubes ranges from 5000 to 15000 Kcal/hr.m2.°C. Condensation of vapor is carried out inside the tube in a shell and tube heat exchanger, when the

Viscosity of gases __________ with increase in temperature.

In case of surface condensers, a straight line is obtained on plotting 1/U vs. __________ on an ordinary graph paper.

A cube, sphere & a thin circular plate (all having same mass and made of same material) are all heated to 300°C and allowed to cool in natural air. Which one will cool the slowest?

Which of the following material has lest value of thermal diffusivity?

For a opaque body

In which case the value of thermal conductivity drops with rising temperature

Which of the following is used as entrainer in acetic acid - water separation?

Which of the following provides maximum contact surface for a liquid vapour system?

The lower temperature limit for mercury thermometer is

Cork is a good insulator because

The value of thermal conductivity of water at room temperature is expected to be

The coefficient of linear expansion of a solid is L. The volume V of a cube of this solid on being heated by 1?C will change by

The unit of thermal conductivity in S.I. units is

Two rods one of copper and the other of mild steel, both of diameter 20 mm and length 250 mm are coated with a uniform layer of wax all around. These rods are placed vertically in a boiling water bath with 200 mm, length of each rod projecting outside. If the melting point of wax is 10?C, then

Oxygen boils at -183°C, this temperature is

Heat is transferred from an electric bulb mainly by

The average value of thermal conductivity for air at 20°C is about

A vapour containing liquid particles to the extent of 50% by the volume is known as

Condensing film co-efficient for steam on horizontal tubes ranges from 5000 to 15000 Kcal/hr.m².°C. Condensation of vapor is carried out inside the tube in a shell and tube heat exchanger, when the