Heat and Mass Transfer
Heat conducted through per unit area and unit thick face per unit time when temperature difference between opposite faces is unity, is called

Thermal resistance
Thermal coefficient
Temperature gradient
Thermal conductivity

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Heat and Mass Transfer
Film coefficient is defined as Inside diameter of tube

Thermal conductivity Equivalent thickness of film Specific heat × Viscosity
Thermal conductivity Molecular diffusivity of momentum Thermal diffusivity
Film coefficient × Inside diameter Thermal conductivity
Equivalent thickness of film

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

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