Heat and Mass Transfer
The heat transfer by conduction through a thick cylinder (Q) is given by (where T₁ = Higher temperature, T₂ = Lower temperature, r₁ = Inside radius, r₂ = Outside radius, l = Length of cylinder, and k = Thermal conductivity)

Q = [2π (T₁ - T₂)]/2.3 lk log (r₂/r₁)
Q = = 2πlk/2.3 (T₁ - T₂) log (r₂/r₁)
Q = 2.3 log (r₂/r₁)/[2πlk (T₁ - T₂)]
Q = [2πlk (T₁ - T₂)]/2.3 log (r₂/r₁)

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

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

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