The present paper reports a study conducted to examine several sands with a large spread
of particle size in order to validate the modelling of both Darcy's and Forchheimer's law
parameters, which could be applied to any kind of sand. An experimental set-up has been
specially conceived to generate hydraulic gradients within fine sands higher than 600. We
also present an attempt at using a capillary-type flow model to determine structural
parameters of sand and predict pressure gradients. The specific surface areas calculated …

… In fact, even though flow through pipes does go through a well-known and sudden transition
(from laminar flow to partially developed turbulent flow), the commonly stated figure of Re = 2000
is also known to be an approximate value. The assertion in the abstract that non-Darcy flow
through porous media begins at a Reynolds number of 4.3, made again in the section entitled
"Conclusion", is therefore not justified. … Most naturally occurring instances of non-Darcy flow
through porous media have been in the partially-developed turbulent regime, for which a …