Process Equipment and Plant Design
In a rotary drier, the average retention time of solid is(where Z = length of the drier, metres ρ = apparent solid density, kg/m³ L = flow rate of dry solids, kg/see. m² drier cross-section H = hold up of solid.)

L/Z.H.ρ
Z.H.ρ/L
H.ρ/L
Z.H/L.ρ

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Process Equipment and Plant Design
In the case of a shell and tube heat exchanger, the logarithmic mean temperature difference

Is always less than arithmetic average value
Is always more than arithmetic mean value and the geometric mean value
May be either more or less than geometric mean and arithmetic mean value depending upon whether the flow of stream is co-current or counter-current
Is always less than arithmetic mean value, but more than geometric mean value

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Process Equipment and Plant Design
Generally, elliptical dished heads

Are manufactured on 2:1 ratio of major to minor axis and is recommended to be used for pressure vessels operating above a pressure of 1.5 MN/m²
Are approximately as strong as seamless cylindrical shell having the corresponding I.D and O.D
Resist half the pressure rating compared to hemi spherical head provided on the cylindrical shell of the same thickness and diameter
All of these

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