Heat and Mass Transfer
A steam pipe is to be lined with two layers of insulating materials of different thermal conductivities. For the minimum heat transfer,

The better insulation must be put inside
The better insulation must be put outside
One could place either insulation on either side
One should take into account the steam temperature before deciding as to which insulation is put where

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Heat and Mass Transfer
Fourier's law of heat conduction is (where Q = Amount of heat flow through the body in unit time, A = Surface area of heat flow, taken at right angles to the direction of heat flow, dT = Temperature difference on the two faces of the body, dx = Thickness of the body, through which the heat flows, taken along the direction of heat flow, and k = Thermal conductivity of the body)

k. (dx/dT)
k. (dT/dx)
k. A. (dx/dT)
k. A. (dT/dx)

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