1. The original paper by Darcy is not readily available, but a reproduction is in M. K. Hubbert, The Theory of Ground-Water Motion and Related Papers, Hefner Publishing, New York, NY, 1969, pp. 303–311.
2. S. Ergun, Chem. Eng. Prog.
48, 93 (1952).
3. The constant 4.2 is not universally selected; some believe the value to be as high as 5.0, based on a paper by P. C. Carman, Trans. Inst. Chem. Eng.
15, 150 (1937). These are reasonable values for granular materials and spherical particles but are certainly not valid for other solid morphologies or for higher values of ω. For example, these factors are substantially different for packings that comprise fibers or even for uniform size spheres that are not consolidated.
4. V. T. Morgan, Symposium sur la Metallurgie des Poudres, Editions Metaux (sponsored by Société Française de Metallurgie), Paris, June, 1964, page 419.
5. R. M. German, Powder Technol. 30, 81 (1981).