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Abstract Terminal velocity of porous spheres was experimentally measured for a Reynolds number range of 0.2 to 120 for a normalized sphere radius, β = R / R of 15.6 to 33, where R and k are the sphere radius and permeability, respectively. The drag coefficient for 15 < β < 33 was found to be C D = 24Ω/ Re 1 + 0.1315 Re (0.82 ‐ 0.05 w ) for 0.1 < Re ≤ 7 and C D = 24Ω/ Re 1 + 0.0853 Re (1.093 ‐ 0.105 w ) for 7 < Re < 120 with w = log 10 Re where Re is the sphere Reynolds number and Ω=2β 2 1 ‐ ( tanh β/β) / 2β 2 + 31 ‐ tanh β/β) At high Reynolds numbers, it was found that the porous sphere terminal velocity was less affected by the container walls than for the case of an impermeable sphere. However, at very low Reynolds numbers, the wall effects were found to be similar for both the permeable and the impermeable spheres.
Masliyah et al. (Sun,) studied this question.