LENGTH SEPARATION OF FIBERS

A classifier for separating conductive fibers according to length using dielectrophoresis has been developed and tested. The classifier consisted of two concentric steel cylinders with an annular space having a width of 3.18 mm. A high-voltage alternating field applied between the cylinders caused fibers to drift to the central cylinder. In these experiments, chrysotile fibers were generated from a fluidized bed generator and collected on the central cylinder in the classifier. Fibers collected on the central cylinder were washed off from ten equal length segments and sized by transmission electron microscopy. The median lengths of classified groups of fibers ranged from 8 to 31 mum. The length distributions of these fibers had coefficients of variation ranging from 0.17 to 0.33. The quantity of classified fibers was limited by the aerosol flow rate, which in the current system was 2.13 L/min (total flow rate through the classifier was 5.35 L/min). Limitations in the classification process prevent increasing the fiber throughput significantly except by increasing the concentration of the challenge aerosol. Fiber conductivity is important for accurate classification, but can be readily achieved for fibers of low bulk conductivity by using high humidity air in the classifier.