The study of axial dispersion behavior of non-Newtonian fluid at various flow regimes in a liquid-solid magnetofluidized bed
Date Issued
2006
Date
2006
Author(s)
Shiu, Wei-Hua
DOI
zh-TW
Abstract
In this study, the difference of hydrodynamic and dispersion behavior between the liquid-solid magneto-fluidized (0.05 m i.d. × 0.075 m height) bed and the liquid-solid traditional fluidized bed was investigated. The sphere iron particles of 274 μm average diameter were used as the solid phase, water and CMC (carboxymethyl cellulose) (0.03 wt%, 0.1 wt% and 0.2 wt%) solution were used as the liquid phase. A magnetic solenoid coiled by the magnet wire was applied to generate axially magnetic field. The dependency of pressure drop on the velocity was used to establish transition velocities between various regimes. The axial dispersion of various regimes was analyzed by the tracer input-response technique.
By Leva’s method, the minimum fluidization velocity Umf(L) was not affect by magnetic force. However, by Davidson and Harrison’s method, the minimum fluidization velocity Umf(DH) was increased with increasing magnetic field intensity. Further more, the transition velocity Ut(P) determined by the hysteresis phenomenon was increased with increasing magnetic field intensity.
The experimental results show that there were four flow regimes in a magneto-fluidized bed: fixed bed, transition, magnetically stabilized and unstable regime. The boundaries were minimum fluidization velocity Umf(L), minimum fluidization velocity Umf(DH) and transition velocity Ut(P). When the concentration of the CMC solution increased, the range of fixed bed, transition and magnetically stabilized regime was narrowed down, the unstable regime was enlarged.
Both in the magnetic and the traditional fluidized beds, the axial dispersion coefficient was increased with the enhancing fluid velocity. The axial dispersion coefficient of the magnetic fluidized bed was lower than the traditional fluidized bed. The dispersion coefficient of the water (Newtonian) and the CMC solutions (non-Newtonian) both were decreased with the enhancing magnetic field intensity. Besides, the effect of magnetic field on the dispersion coefficient was decreased with the increasing concentration of CMC solution.
Subjects
液固磁流體化床
軸向分散係數
liquid-solid magnetofluidized bed
axial dispersion coefficient
Type
thesis
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