Abstract: For the magnetized fluidized bed (MFB) with the binary mixture of Geldart-B magnetizable and nonmagnetizable particles, the magnetically induced segregation between these two kinds of particles occurs at high magnetic field intensities (H), leading to the deterioration of the fluidization quality. The critical intensity (H_ms) above which such segregation commences varies with the gas velocity (U_g). This work focuses on establishing a segregation model to theoretically derive the H_ms-U_g relationship. In a magnetic field, the magnetizable particles form agglomerates. The magnetically induced segregation in essence refers to the size segregation of the binary mixture of agglomerates and nonmagnetizable particles. Consequently, the segregation model was established in two steps:first, the size of agglomerates (d_A) was calculated by the force balance model; then, the H_ms-U_g relationship was obtained by substituting the expression of d_A into the basic size segregation model for binary mixtures. As per the force balance model, the cohesive and collision forces were 1-2 orders of magnitude greater than the other forces exerted on the agglomerates. Therefore, the balance between these two forces largely determined d_A. The calculated d_A increased with increasing H and decreasing U_g, agreeing qualitatively with the experimental observation. The calculated H_ms-U_g relationship agreed reasonably with the experimental data, indicating that the present segregation model could predict well the segregation behavior in the MFB with the binary mixture.

Key words: Magnetized fluidized bed, Binary mixture, Segregation, Model, Agglomerate, Force balance

摘要： For the magnetized fluidized bed (MFB) with the binary mixture of Geldart-B magnetizable and nonmagnetizable particles, the magnetically induced segregation between these two kinds of particles occurs at high magnetic field intensities (H), leading to the deterioration of the fluidization quality. The critical intensity (H_ms) above which such segregation commences varies with the gas velocity (U_g). This work focuses on establishing a segregation model to theoretically derive the H_ms-U_g relationship. In a magnetic field, the magnetizable particles form agglomerates. The magnetically induced segregation in essence refers to the size segregation of the binary mixture of agglomerates and nonmagnetizable particles. Consequently, the segregation model was established in two steps:first, the size of agglomerates (d_A) was calculated by the force balance model; then, the H_ms-U_g relationship was obtained by substituting the expression of d_A into the basic size segregation model for binary mixtures. As per the force balance model, the cohesive and collision forces were 1-2 orders of magnitude greater than the other forces exerted on the agglomerates. Therefore, the balance between these two forces largely determined d_A. The calculated d_A increased with increasing H and decreasing U_g, agreeing qualitatively with the experimental observation. The calculated H_ms-U_g relationship agreed reasonably with the experimental data, indicating that the present segregation model could predict well the segregation behavior in the MFB with the binary mixture.

关键词: Magnetized fluidized bed, Binary mixture, Segregation, Model, Agglomerate, Force balance