Two insulating materials of thermal conductivity k and 2k are available for lagging a pipe carrying a hot fluid. If the radial thickness 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 insulating materials are used
none of these
material with lower thermal conductivity should be used for the inner layer and one with higher thermal conductivity for the outer
We know that heat transfer in cylinder is
Where, r = Radial thickness
R = Radius of the pipe
a = Constant of proportionality.
Case 1 :Let k is inner layer and 2k is outer layer
Take k= 1 and R=r
Case 2 : Let 2k is inner layer and k is outer layer
Take k = 1 and R= r
Hence, we get larger temperature difference in case 1, which means material with lower thermal conductivity should be used for the inner layer and one with higher thermal conductivity for the outer layer for better insulation.
Hence, the correct option is (B).
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