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Test: Introduction To Heat Transfer Level - 2 - Mechanical Engineering MCQ


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10 Questions MCQ Test Heat Transfer - Test: Introduction To Heat Transfer Level - 2

Test: Introduction To Heat Transfer Level - 2 for Mechanical Engineering 2024 is part of Heat Transfer preparation. The Test: Introduction To Heat Transfer Level - 2 questions and answers have been prepared according to the Mechanical Engineering exam syllabus.The Test: Introduction To Heat Transfer Level - 2 MCQs are made for Mechanical Engineering 2024 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests for Test: Introduction To Heat Transfer Level - 2 below.
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Test: Introduction To Heat Transfer Level - 2 - Question 1

For a metal, thermal conductivity decreases with rise in temperature. Which of these is an exception?

Detailed Solution for Test: Introduction To Heat Transfer Level - 2 - Question 1
Because of very big size of uranium atoms, the electrons of neighboring atoms are shared and therefore held in covalent bonds. As a result there are no free electrons and thermal conductivity of uranium depends solely on lattice vibration. Thus even though uranium is a metal but it’s thermal conductivity increases with increasing temperature thereby showing an exceptional behavior.

Test: Introduction To Heat Transfer Level - 2 - Question 2

For a given heat flow rate and for the same thickness, the temperature drop across the material will be maximum for

Detailed Solution for Test: Introduction To Heat Transfer Level - 2 - Question 2
From Fourier’s law,

I.e. T₁ - T₂ will be maximum when k is minimum. k is minimum for glass wool.

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Test: Introduction To Heat Transfer Level - 2 - Question 3

Consider bronze, an alloy of copper and tin. It’s thermal conductivity is __________ the thermal conductivity of copper and tin

Detailed Solution for Test: Introduction To Heat Transfer Level - 2 - Question 3
The thermal conductivity of an alloy is always less than thermal conductivity of both alloying elements. The atoms of secondary metal, sit in void spaces of the lattice of primary metal atoms, not only distorting the lattice structure but also obstructing the flow of free electrons. In metals free electron transfer is the dominant reason for heat conduction. Thus there is a significant drop in thermal conductivity due to alloying of metals, so it is significant that thermal conductivity of alloy is lower than both primary and secondary metal.

*Answer can only contain numeric values
Test: Introduction To Heat Transfer Level - 2 - Question 4

Find out the heat flux (in W/m²) between two fluids separated by a planar wall as shown in the figure.


Detailed Solution for Test: Introduction To Heat Transfer Level - 2 - Question 4
Consider the thermal circuit for the system

Where nodes H, 1, 2 & C represent hot fluid, left surface of wall, right surface of wall and cold fluid respectively. Therefore,

Test: Introduction To Heat Transfer Level - 2 - Question 5

With increase in pressure, the thermal conductivity of an ideal gas __________.

Detailed Solution for Test: Introduction To Heat Transfer Level - 2 - Question 5
For an ideal gas, thermal conductivity is given as

Where ⊽ is the mean travel velocity of molecules Cv, is the specific heat of gas at constant volume, L is the mean free path of molecules and is the density of the gas.

As pressure increases, density of gas increases but based on experiments it is observed that the mean free path diminishes in the same proportions. Thus the product remains constant.

Also ⊽ depends upon temperature only hence if temperature is constant, change in pressure does not bring any change in ⊽ Also for an ideal gas Cv is independent of pressure.

Test: Introduction To Heat Transfer Level - 2 - Question 6

The coefficient of convection, for heat convection between a solid surface and adjacent fluid does not depend upon

Detailed Solution for Test: Introduction To Heat Transfer Level - 2 - Question 6
The mechanism of convection is based on conduction through the layer of fluid in immediate contact with solid surface followed by mixing motion of fluid (advection) because of buoyancy or pressure gradient along with diffusion. Thus any property which affects conduction within the fluid (not in solid) and motion of fluid controls the value of coefficient of convection. Hence, (D) option does not affect the value of h.

Test: Introduction To Heat Transfer Level - 2 - Question 7

Consider a composite slab maintained at steady state as shown in the figure.

If the leftmost and rightmost surface of the slab are maintained at temperature values of 100°C & 40°C respectively, find out the interface temperature.

Detailed Solution for Test: Introduction To Heat Transfer Level - 2 - Question 7
The composite slab is made of two layers arranged in series. Thus the ratio of temperature drops across the two layers is equal to the ratio of their respective thermal resistance.

Therefore

Test: Introduction To Heat Transfer Level - 2 - Question 8

Consider a composite slab as shown in the figure.

If the left most and right most surfaces are maintained at temperatures of 100°C & 40°C respectively, find out the interface temperature in in °C


Detailed Solution for Test: Introduction To Heat Transfer Level - 2 - Question 8
The slab can be represented by the following thermal circuit.

Considering the width of slab to plane of paper to be equal to W,

R₂ and R₃ are arranged in parallel and can be shown by single equivalent resistance Rₑ

By idea of series circuit, that ratio of temperature drops across resistances is equal to ratio of respective thermal resistances.

I.e.,

Test: Introduction To Heat Transfer Level - 2 - Question 9

Consider a light bulb of 100 watts power. When switched on, what is the surface temperature of the tungsten filament in °C. Suppose the surface to be a black surface having value of area equal to 8 x 10-5 m2

Detailed Solution for Test: Introduction To Heat Transfer Level - 2 - Question 9

By Stefan Boltzmann law

T = 2166 K (or) 1893 °C

Test: Introduction To Heat Transfer Level - 2 - Question 10

For the composite slab shown in figure, find out when k represents thermal conductivity and L represents thickness.

Detailed Solution for Test: Introduction To Heat Transfer Level - 2 - Question 10
The thermal circuit of the system can be represent as follows

By idea of circuits ratio of resistances is equal to ratio of temperature drops across them

150 - Ti = 2Ti - 60

210 = 3Ti

Ti = 70°C

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