Porosity and surface area of a granular bed from measurements of the flow of air through the bed and measurements of the granular shape factors

Flow experiments give an equation relating to S in terms of measurable quantities, where is the inter-granular porosity of the bed, and S is the envelope surface area of the granules in 1 cm 3 of bed. Heywood's shape factors for the granules give a second equation relating to S. Using the two equations and S can be determined uniquely. If the tortuosity factor be taken to be π/2 in the equations given previously (Jones 1956), connecting the friction factor λ and the Reynolds number (Re), then λ = 16/(Re) for granular beds, as for long straight tubes.