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

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

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

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