Heat and Mass Transfer
When α is absorptivity, ρ is reflectivity and τ is transmissivity, then for a diathermanous body,

α = 0, ρ = 1 and τ = 0
α + ρ = 1 and τ = 0
α = 1, ρ = 0 and τ = 0
α = 0, ρ = 0 and τ = 1

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Heat and Mass Transfer
Which of the following would lead to a reduction in thermal resistance?

In conduction, reduction in the thickness of the material and an increase in thermal conductivity.
All of these
In radiation, increasing the temperature and reducing the emissivity.
In convection, stirring of the fluid and cleaning the heating surface.

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