Process Equipment and Plant Design
Generally, elliptical dished heads

All of these
Resist half the pressure rating compared to hemi spherical head provided on the cylindrical shell of the same thickness and diameter
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

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Process Equipment and Plant Design
Overall tray efficiency of a distillation column is the ratio of the number of

Real trays required to the number of ideal trays required
Overall gas transfer units to the number of ideal trays required
Ideal trays required to the number of real trays required
None of these

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