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Heat And Mass Transfer MCQ Questions & Answers | Mechanical Engineering

Learn Heat And Mass Transfer MCQ questions & answers are available for a Mechanical Engineering students to clear GATE exams, various technical interview, competitive examination, and another entrance exam. Heat And Mass Transfer MCQ question is the important chapter for a Mechanical Engineering and GATE students. Page-3 section-2

Each section contains 100 MCQs on Heat and Mass Transfer .
21
A heat exchanger with heat transfer surface area A and overall heat transfer coefficient U handles two fluids of heat capacities Cmax and Cmin. The number of transfer units (NTU) used in the analysis of heat exchanger is specified as
Discuss
Answer & Solution
Answer: Option D
Solution:
The number of transfer units (NTU) is a dimensionless parameter used in heat exchanger analysis.

It is defined as the ratio of the product of the heat transfer surface area (A) and the overall heat transfer coefficient (U) to the minimum heat capacity rate (Cmin) of the two fluids.

In mathematical form, NTU = AU / Cmin.

The NTU method is useful for determining the effectiveness of a heat exchanger when the inlet and outlet temperatures of the fluids are not known.

22
Reynolds number is the ratio of
Discuss
Answer & Solution
Answer: Option C
Solution:
The Reynolds number is the ratio of inertial forces to viscous forces within a fluid which is subjected to relative internal movement due to different fluid velocities.
23
If the temperature of a solid surface changes form 27°C to 627°C, then its emissive power changes in the ratio of
Discuss
Answer & Solution
Answer: Option D
Solution:
$$\frac{{{{\text{E}}_2}}}{{{{\text{E}}_1}}} = {\left( {\frac{{{{\text{T}}_2}}}{{{{\text{T}}_1}}}} \right)^4} = 81.$$
24
Kirchhoff's law states that
Discuss
Answer & Solution
Answer: Option C
Solution:
It states that For an arbitrary body emitting and absorbing thermal radiation in thermodynamic equilibrium, the emissivity is equal to the absorptivity.
The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body
25
Metals are good conductors of heat because
Discuss
Answer & Solution
Answer: Option A
Solution:
Metals are particularly good conductors of heat because their particles are very closely packed so the vibrations are passed on very quickly.
These drift slowly through the structure, giving metals their strength and other properties.
As the metal is heated, the free electrons closest to the heat source are heated.
26
Thermal conductivity of water at 20°C is of the order of
Discuss
Answer & Solution
Answer: Option D
Solution:
Thermal conductivity of water at 20°C is of the order of 0.51
27
Thermal conductivity of air at room temperature in kcal/m hr °C is of the order of
Discuss
Answer & Solution
Answer: Option B
Solution:
Thermal conductivity of air at room temperature in kcal/m hr °C is of the order of 0.02
28
According to Stefan's law, the total radiation from a black body per second per unit area is proportional to
Discuss
Answer & Solution
Answer: Option D
Solution:
The correct answer is Option D: T 4

Explanation: According to Stefan's law, also known as the Stefan-Boltzmann law, the total radiation emitted from a black body per second per unit area is proportional to the fourth power of the absolute temperature (T). Mathematically, this is expressed as E∝T 4, where E is the emissive power and T is the absolute temperature. Therefore, the correct exponent is 4, not any other value.
29
The critical temperature is the temperature
Discuss
Answer & Solution
Answer: Option D
Solution:
The critical temperature of a substance is the temperature at and above which vapor of the substance cannot be liquefied, no matter how much pressure is applied.
30
Thermal conductivity of non-metallic amorphous solids with decrease in temperature
Discuss
Answer & Solution
Answer: Option B
Solution:
Thermal conductivity of non-metallic amorphous solids with decrease in temperature Decreases