No free lunch with vanishing risk

The Blake number in fluid mechanics is a nondimensional number showing the ratio of inertial force to viscous force. It is used in momentum transfer in general and in particular for flow of a fluid through beds of solids. It is a generalisation of the Reynolds number for flow through porous media.

Expressed mathematically the Blake number $B$ is:

$B=\frac{u\rho }{\mu (1-ϵ)D}$

where

$ϵ$	=	void fraction
$\mu$	=	dynamic viscosity
$\rho$	=	fluid density
$D$	=	characteristic particle diameter
$u$	=	flow velocity

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