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Weber Number

Effect of Weber Number

The Weber number (We) is the most important variable in controlling the drop size of the dispersed phase. The Weber number can be expressed in many ways depending on available data and units. For our purposes the following equation applies: -




Where Q = Flow rate (m3/h)r = Density (kg/m3)s = Interfacial tension (dynes/cm)

D = Pipe Inside Diameter (mm)

Where Q = Flow rate (US gpm)sg = Specific Gravitys = Interfacial tension (dynes/cm)

D = Pipe Inside Diameter (inch)

In general the Weber number expresses the ratio between inertial forces trying to disperse the phases, to the interfacial forces trying to keep them distinct. At a given viscosity ratio, the drop size therefore decreases as the Weber number increases.


Interfacial Tension

Interfacial tensions usually range from 20 to 70 dynes/cm

Increasing values of interfacial tension decreases the Weber number, and therefore increases the drop size. Fluids with lower interfacial tensions will therefore more readily produce smaller drop sizes.