Sedimentation velocity of bidisperse suspensions

The present study deals with a simple method to predict the sedimentation velocity of suspensions with bidisperse size distribution of particles. The method is developed by modifying the effective-medium theory for monodisperse suspensions. The predictions by the method of the present study are compared with the previous experimental results and the theoretical estimations by Batchelor and Wen [G.K. Batchelor, C.S. Wen, J. Fluid Mech. 124 (1982) 495]. It is shown that the estimations by the effective-medium model of the present study agree well with the experimental results for wider range of concentrations of the suspensions than do those by Batchelor and Wen [G.K. Batchelor, C.S. Wen, J. Fluid Mech. 124 (1982) 495]. However, it is also found that an effective-medium region intrudes the space for the small particle at origin at high total volume fractions near 0.3 when the size ratio of small to large particle is 0.52 and both the volume fractions of the large and small particles are equal. This behavior may be attributed to the segregation of the particles, which has been observed in earlier experiments at the high volume fractions.