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Heat Transfer Mcqs

Q:

A body at 500 K cools by radiating heat to ambient atmosphere maintained at 300 K. When the body has cooled to 400 K, the cooling rate as a percentage of original rate is about

A) 31.1 B) 41.5
C) 50.3 D) 80.4
 
Answer & Explanation Answer: A) 31.1

Explanation: Q?/Q? = (400)? – (300)4/ (500)? – (300)? = 0.32.

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789
Q:

A concrete column used in bridge construction is cylindrical in shape with a diameter of 1 meter. The column is completely poured in a short interval of time and the hydration of concrete results in the equivalent of a uniform source strength of 0.7 W/kg. Determine the temperature at the center of the cylinder at a time when the outside surface temperature is 75 degree Celsius. The column is sufficiently long so that temperature variation along its length may be neglected. For concrete
Average thermal conductivity = 0.95 W/m K
Average density = 2300 kg/m³

A) 190.92 degree Celsius B) 180.92 degree Celsius
C) 170.92 degree Celsius D) 160.92 degree Celsius
 
Answer & Explanation Answer: B) 180.92 degree Celsius

Explanation: Not available for this question

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719
Q:

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
 
Answer & Explanation Answer: B) More than 10 minutes

Explanation: Not available for this question

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624
Q:

A thin metal plate of 4 cm diameter is suspended in atmospheric air whose temperature is 290 K. This plate attains a temperature of 295 K when one of its face receives radiant energy from a heat source at the rate of 2 W. If heat transfer coefficient on both surfaces of the plate is stated to be 87.5 W/m ² K, workout the energy lost by reflection

A) 0.8 W B) 0.3 W
C) 0.9 W D) 0.10 W
 
Answer & Explanation Answer: C) 0.9 W

Explanation: Heat loss by convection from both sides of the plates = 2 h A d t = 1.1 W. Energy lost by reflection = 2.0 – 1.1 = 0.9 W.

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577
Q:

A composite wall generally consists of

A) One homogenous layer B) Multiple heterogeneous layers
C) One heterogeneous layer D) Multiple homogenous layers
 
Answer & Explanation Answer: B) Multiple heterogeneous layers

Explanation: Walls of houses where bricks are given a layer of plaster on either side.

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427
Q:

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
 
Answer & Explanation Answer: D) Air is transparent to radiation and hence it is cooler than the body

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.

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426
Q:

In transient heat conduction, the two significant dimensionless parameters are

A) Reynolds number and Fourier number B) Reynolds number and Biot number
C) Reynolds number and Prandtl number D) Biot number and Fourier number
 
Answer & Explanation Answer: D) Biot number and Fourier number

Explanation: These two are dimensionless numbers. Biot number is given by the ratio of internal conduction resistance to the surface convection resistance whereas Fourier number signifies the degree of penetration of heating or cooling effect through a solid.

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401
Q:

For an object i.e. spherical the value of critical radius would be

A) 2k/3h B) 3k/h
C) 2k/h D) k/h
 
Answer & Explanation Answer: C) 2k/h

Explanation: It depends on the variation of angle with layers of insulation.

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