When designing or operating a vacuum system based on ejectors, it is
required to estimate the time necessary to bring under vacuum the
process vessel connected to the vacuum system.
2. Time to evacuate
Te = 2.3 V / Ca
= Time to evacuate a system from atmospheric pressure to
design pressure of an ejector (min)
V = System volume, vapor space, (ft3)
= Ejector design rate capacity (lb/h)
The value given by this formula is an approximation.
Rules of Thumbs for Chemical Engineers, Brannan, Gulf, 2005