For general design, below equation has been used as a velocity guideline for many years:
V=K [(|ρL - ρV)/ ρV] ½
||= liquid density
||= vapour density
||= capacity factor
The recommended value of "K" varies depending on several system factors, including liquid viscosity, surface tension, entrainment loading, content of dissolved and suspended solids, and the operating pressure. Recommended "K" values are also highly dependent on the mesh structure.
K=0.107 m/sec have become the worldwide standard in the chemical process industries. Operating pressure drop is usually negligible <25mm water (1" WC). For high vacuum applications, high performance is routinely achieved with ∆P on the order of 2-3mm water (0.1" WC)