Radius of equivalent sphere

The average bubble radius (as well as the biggest and smallest size), the maximum distance between the opposite walls of the bubble (relative diameter) [8] and the specific liquid/air interface are involved in the estimation of dispersity. However, the distribution of bubbles by size, for example by radius of equivalent spheres, reveals completely the foam dispersity. Additional information about dispersity which takes into account the difference in polyhedral shapes is gathered from the number and shape of polyhedron faces (see Section 1.2). 

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