Heat Transfer MCQ’s – Types of Convection
1 - Question
Conduction plus fluid flow in motion is known as
a) Radiation
b) Conduction
c) Convection
d) Heat exchanger
View Answer
Explanation: It is convection i.e. conduction plus some velocity. It is the process of energy transport affected by the mixing of a fluid medium.
2 - Question
How many types of convection are there?
a) 4
b) 3
c) 2
d) 1
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Explanation: It is of three types i.e. forced convection, natural convection and mixed convection.
3 - Question
Which of the following heat flow situations pertains to free or natural convection?
a) Air conditioning installations and nuclear reactors
b) Flow of water inside the condenser tubes
c) Cooling of internal combustion engine
d) Cooling of billets in atmosphere
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Explanation: Cooling of billets in atmosphere is both free and natural convection.
4 - Question
Mark the system where heat transfer is given by forced convection
a) Chilling effect of cold wind on warm body
b) Fluid passing through the tubes of a condenser and other heat exchange equipment
c) Heat flow from a hot pavement to surrounding atmosphere
d) Heat exchange on the outside of cold and warm pipes
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Explanation: If the fluid motion involve in the process is induced by some external means then it is called forced convection.
5 - Question
Forced convection in a liquid bath is caused by
a) Intense stirring by an external agency
b) Molecular energy interactions
c) Density difference brought about by temperature gradients
d) Flow of electrons in a random fashion
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Explanation: If the fluid motion involve in the process is induced by some external means then it is called forced convection.
6 - Question
A finned tube hot water radiator with a fan blowing air over it is kept in rooms during winter. The major portion of the heat transfer from the radiation is due to
a) Combined conduction and radiation
b) Radiation to the surroundings
c) Better conduction
d) Convection to the air
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Explanation: Convection is a process in which thermal energy is transferred between solid and fluid flowing through it.
7 - Question
A body cooling from 80 degree Celsius to 70 degree Celsius takes 10 minutes when left exposed to environmental conditions. If the body is to cool further from 70 degree Celsius to 60 degree Celsius under the same external conditions, it will take
a) Same time of 10 minutes
b) More than 10 minutes
c) Less than 10 minutes
d) Time will depend upon the environmental conditions
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Explanation: Q = h A (t b – t a). Apparently, the cooling depends upon the same temperature difference.
8 - Question
On a summer day, a scooter rider feels more comfortable while on the move than while at a stop light because
a) An object in motion captures less radiation
b) Air has a low specific heat and hence it is cooler
c) More heat is loss by convection and radiation while in motion
d) Air is transparent to radiation and hence it is cooler than the body
View Answer
Explanation: The situation corresponds to forced convection when the scooter is in motion and the convective heat transfer coefficient for forced convection is greater than that for free convection.
9 - Question
Answer: d Explanation: The situation corresponds to forced convection when the scooter is in motion and the convective heat transfer coefficient for forced convection is greater than that for free convection.
a) 1460-3000 W/m2 K
b) 460-3000 W/m2 K
c) 60-3000 W/m2 K
d) 160-3000 W/m2 K
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Explanation: In forced convection, the flow of fluid is caused by a pump, fan or by atmospheric winds. Convection mechanism involving phase changes leads to the important fields of boiling and condensation.
10 - Question
A sphere, a cube and a thin circular plate, all made of the same material and having the same mass are initially heated to the temperature of 250 degree Celsius. When left in air at room temperature, what will be their response to cooling?
a) Cube will cool faster than sphere but slower than the circular plate
b) They will cool at the same rate
c) Sphere will cool faster
d) Circular plate will cool at the slower rate
View Answer
Explanation: Q = h A (T – t). Here cooling depends upon the surface area of the body.