SSC JE Mechanical Engineering 2017 Set 1 Paper

Question : 107 of 200

Marks: +1, -0

Two insulating materials of thermal conductivity K and 2K are available for lagging a pipe carrying a hot fluid. if the radial thinkness of each material is the same______.

Material with higher thermal conductivity should be used for the inner layer and one with layer and one with lower thermal conductivity for the outer.
Material with lower thermal conductivity should be used for the inner layer and one with higher thermal conductivity for the outer.
It is immaterial in which sequence the inulating materials are used .
None of these.

Validate

Solution:

Material with lower thermal conductivity should be used for the inner layer and one with higher thermal conductivity for the outer
if

K_1 = k

; thickness = t (same for both)

K_2 = 2k

⇒ R_1 = (t/\K_1 × A) = (t/kA)

⇒ R2 = (t/\K_2 ×A) = (t/{2k}A)

⇒ R_1 - R_2 > 0

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