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

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Heat and Mass Transfer
Film coefficient is defined as the ratio of

Thickness of film of fluid to the thermal conductivity
Thickness of film of fluid to the temperature drop through the films of fluids
Thermal conductivity to the equivalent thickness of the film of fluid
Temperature drop through the films of fluids to the thickness of film of fluids

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Heat and Mass Transfer
Thermal conductivity of a material may be defined as the

Quantity of heat flowing in one second through a slab of the material of area one cm square, thickness 1 cm when its faces differ in temperature by 1°C
Quantity of heat flowing in one second through one cm cube of material when opposite faces are maintained at a temperature difference of 1°C
All of these
Heat conducted in unit time across unit area through unit thickness when a temperature difference of unity is maintained between opposite faces

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