Process Equipment and Plant Design
In packed towers provided with pall rings liquid redistributors are positioned at heights of every 6 metres or 5-10 times the column diameter, whichever is less. Maximum size of the pall rings should not exceed __________ of the column diameter.

1/2 to 1/4th
1/5-1/10th
1/10-1/15th
1/20-1/30th

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Process Equipment and Plant Design
Overall distillation column efficiency for most of the refinery columns can be given by (for μ = 0.07 - 1.4 cp and relative volatility < 4) (where η = overall column efficiency, % μ = molal average viscosity of feed at average column temperature and pressure, cp Δp = pressure drop per tray, psi)

Η = 1.66 - 0.25 log μ
Η = 0.25 log μ - 1.67
Η = 24.6 (Δp/μ)
Η = 17 - 61.1 log μ

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

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
Is always less than arithmetic average value
Is always more than arithmetic mean value and the geometric mean value

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