Heat and Mass Transfer
A steam pipe is to be insulated by two insulating materials put over each other. For best results

Whether to put inferior OIL over pipe or the better one would depend on steam temperature
Better insulation should be put over pipe and better one over it
Both may be put in any order
Inferior insulation should be put over pipe and better one over it

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Heat and Mass Transfer
The logarithmic mean temperature difference (tm) is given by (where Δt1 and Δt2 are temperature differences between the hot and cold fluids at entrance and exit)

tm = loge (Δt1/Δt2)/ (Δt1 - Δt2)
tm = (Δt1 - Δt2)/ loge (Δt1/Δt2)
tm = tm = (Δt1 - Δt2) loge (Δt1/Δt2)
tm = loge (Δt1 - Δt2)/ Δt1/Δt2

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Heat and Mass Transfer
According to Prevost theory of heat exchange

Heat transfer by radiation requires no medium
It is impossible to transfer heat from low temperature source to t high temperature source
All bodies above absolute zero emit radiation
Heat transfer in most of the cases takes place by combination of conduction, convection and radiation

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