Liquid-phase mass transfer of magnetic ion exchangers in magnetically influenced fluidized beds - I. DC fields

Fluidized beds of magnetic ion exchangers exhibit special features because of the additional influence of magnetic forces, which cannot be achieved in conventional fluidized or fixed beds. Specific choice of the magnetic para meters, such as particle magnetization, field strength and frequency of the external magnetic field, allows various operating conditions to be attaine d, the extremes of which may be described by the terms Magnetically Stabili zed Fluidized Bed (MSFB) and Magnetically Stirred Reactor (MSR). The experi ments conducted in this work show that liquid fluidized MSFBs exhibit a mar ked decrease in mass transfer compared to conventional fluidized beds opera ted under the same conditions. We have demonstrated a correlation between t he transition from a fluidized bed to a magnetically stabilized fluidized b ed and an increase in the value of a newly defined dimensionless number, M* . Provided that the physical properties (magnetization, density and diamete r) of the particles are known, it is then possible to obtain a first estima te with regard to the magnetic field required for attaining an MSFB. The ex perimental data clearly show that the magnitude of the decrease in liquid-s ide mass transfer associated with this transition is influenced mainly by t he ratio between the flow velocity, u, and the minimum fluidization velocit y of the particles, u(mf). Based on this observation, an empirical correlat ion is presented, which allows an estimation of the Sherwood number, Sh, of an MSFB to be made as a function of the parameters M* and u/u(mf). (C) 200 1 Elsevier Science B.V. All rights reserved.