Enhanced Fluidization of Nanoparticles in an Oscillating Magnetic Field

Some experimental observations on the fluidization characteristics of nanoparticles in the form of agglomerates with magnetic assistance are presented. The nanoagglomerates consist of Degussa Aerosil R974 fumed silica, with a primary particle size of 12 nm. An oscillating AC magnetic field is used to excite large (mm size) permanent magnetic particles mixed in with the nanoparticle agglomerates, and the fluidization behavior of the nanoagglomerates, including the fluidization regime, the minimum fluidization velocity, the bed pressure drop, and the bed expansion are investigated. It is shown that, with the aid of an oscillating magnetic field at low frequencies, the bed of nanoparticle agglomerates can be smoothly fluidized, and the minimum fluidization velocity is significantly reduced. In addition, channeling or slugging of the bed disappears and the bed expands uniformly without bubbles, and with negligible elutriation. The bed expansion and the minimum fluidization velocity depend on the mass ratio of magnetic particles to nanoparticles, and the intensity and frequency of the oscillating magnetic field. © 2005 American Institute of Chemical Engineers AIChE J, 51: 1971–1979, 2005