flow resistance parameter, Φ in chromatography

https://dx.doi.org/10.1351/goldbook.F02444
A term used to compare packing density and permeability of columns packed with different particles; it is dimensionless.
Φ = d p 2 B 0
where d p is the average particle diameter. In open-tubular columns Φ = 32.
Source:
PAC, 1993, 65, 819 (Nomenclature for chromatography (IUPAC Recommendations 1993)) on page 833