Equations of gravitational drainage

In a low expansion ratio foam (n 5-10) the liquid distribution along the foam column height is attained very quickly (within seconds), so that the flowing conditions are fulfilled 

Lederer proposed the following kinetic equation about gravitational drainage AVL=VLfl( -e k ) (5.51) 

Erbring and Peter [60] have proposed a hyperbolic dependence for the description of drainage 

However, it looses physical meaning at small times t. 

A power function with three constants (V o a to) has been presented in [62] 

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