Comparing flow regime transition of magnetized fluidized bed with Geldart-B particles between magnetization-FIRST and -LAST operation modes

Abstract

Different flow regimes existed for the magnetized fluidized bed with purely Geldart-B magnetizable particles (pure MFB) or their admixture with Geldart-B nonmagnetizable particles (admixture MFB). Several unresolved issues about the flow regime transition were addressed first for both the pure and admixture MFBs. Then the flow regime transition was thoroughly compared for the first time between the magnetization-FIRST and -LAST operation modes. The magnetic stabilization flow regime was observed to no longer exist under the magnetization-LAST operation mode. The comparison further indicated that the operating range covered in the literature and this work could be roughly divided into four zones. Particularly in operating zone II, the MFB state was found to depend not only on the magnetic field intensity and superficial gas velocity but also on the operation mode. Such a dependence feature in essence referred to the dependence of the MFB state on the path taken to achieve it. The reason why the bed state was path-dependent in operating zone II lay in that the MFB therein could have two different equilibrium states and different paths led to the two states, respectively. Of the two equilibrium states, the magnetic stabilization was demonstrated to be a metastable equilibrium state. Such unique characteristics of the magnetic stabilization state explained why it could not be obtained under the magnetization-LAST operation mode. Furthermore, the reason why the MFB could have an additional metastable equilibrium state aside from the stable equilibrium state in operating zone II lay in the difficulty in forming a new phase under the magnetization-FIRST operation mode.