Heat transfer truths and one false statement: identify the incorrect claim Four statements about heat transfer and temperature differences are given. Select the statement that is wrong.
Mechanical Engineering
Heat Transfer, Refrigeration and Air Conditioning
Difficulty: Medium
Choose an option
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AIn liquids and gases, heat transfer chiefly occurs by convection.
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BThe amount of heat flow through a body depends on the material of the body.
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CFor solid metals, thermal conductivity increases as temperature rises.
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DLogarithmic mean temperature difference (LMTD) is not equal to the arithmetic mean temperature difference.
Answer
Correct Answer: For solid metals, thermal conductivity increases as temperature rises.
Explanation
Concept check(A) True in general: convection dominates bulk heat transfer in fluids (though conduction at the boundary initiates it).(B) True: heat flow depends on thermal conductivity k (a material property) and geometry.(D) True: LMTD ≠ arithmetic mean; LMTD accounts for the varying temperature difference along the exchanger.
Why (C) is wrongFor most solid metals, lattice/electron scattering increases with temperature, so thermal conductivity decreases as temperature rises (over wide ranges of practical interest).
Final Answer“For solid metals, thermal conductivity increases with temperature” is the incorrect statement.