It is suggested that the drag coefficient of spheres for Reynolds numbers up to 100,000 and a wide range of porosity E, is given approximately by
where Cds is the drag coefficient of an isolated sphere.
Accurate empirical relationships are available for the drag coefficient of isolated spheres ( i.e. when the porosity E=1) for all Reynolds numbers. A drag expression is suggested in this paper for spheres with porosities or void fractions of from 0.4 to 1, which is applicable for Reynolds numbers of up to 100,000. The expression matches reliable data correlations for the drag of isolated spheres, the drag of spheres in packed beds and the drag of spheres at Reynolds numbers less than 1000. However the lack of data at intermediate porosities and Reynolds numbers about 100,000 means that the estimate cannot be validated in this region. There is a need for more data to assess the accuracy of the estimate in this region.
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Last amended: Jan 02.