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Mechanical Engineering - Heat Transfer, Refrigeration and Air Conditioning - Discussion

Discussion Forum : Heat Transfer, Refrigeration and Air Conditioning - Section 1 (Q.No. 3)
Heat Transfer, Refrigeration and Air Conditioning
3.
Which of the following statement is wrong?
The heat transfer in liquid and gases takes place according to convection.
The amount of heat flow through a body is dependent upon the material of the body.
The thermal conductivity of solid metals increases with rise in temperature,
Logarithmic mean temperature difference is not equal to the arithmetic mean temperature difference.
Answer: Option
Explanation:
No answer description is available. Let's discuss.
Discussion:
31 comments Page 1 of 4.
Dwaipayan said:   6 years ago
LMTD=MTD is valid only when both the fluids in the heat exchanger are subjected to phase change only.

So option D is not correct.
(1)
Amiq Syed said:   7 years ago
The thermal conductivity of solid metal's decrease with the increase of temperature.
(3)
Sunny said:   7 years ago
Why option A is true?

In liquids in some extent conduction also takes place.
(2)
Sidd said:   7 years ago
Explain the correct statement in clear.
Ilyas said:   7 years ago
K=Ko(1+bT) here b is negative for solid so thermal conductivity decreases while increase in temperature.
Ks37 said:   7 years ago
For metals, the thermal conductivity is mainly a function of the motion of free electrons. As the temperature increases, the molecular vibrations increase (in turn decreasing the mean free path of molecules). So, they obstruct the flow of free electrons, thus reducing the conductivity.
(2)
Sujit said:   8 years ago
For solids, Thermal Conductivity is dependent on lattice vibrations and movement of free electrons, as temp increases movement of free electrons is hampered by lattice vibrations. So that free electrons provide more resistance to heat flow.
according to Fourier's law of conduction

Q= -k*A*(dT/dx).

k=thermal conductivity of material
A=c/s area
dT= temp. difference
dx=thickness

So, k inversely proportional to dT.
(2)
Vilas said:   8 years ago
What is option D? Please explain it.
Updesh yadav said:   8 years ago
If temperature increases thermal conductivity increases according to made easy.
Prabha said:   8 years ago
In solid metals the coducvity decrease as temp rises.
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