LENGTH SEPARATION OF FIBERS

A classifier for separating conductive fibers according to length usin g dielectrophoresis has been developed and tested. The classifier cons isted of two concentric steel cylinders with an annular space having a width of 3.18 mm. A high-voltage alternating field applied between th e cylinders caused fibers to drift to the central cylinder. In these e xperiments, chrysotile fibers were generated from a fluidized bed gene rator and collected on the central cylinder in the classifier. Fibers collected on the central cylinder were washed off from ten equal lengt h segments and sized by transmission electron microscopy. The median l engths of classified groups of fibers ranged from 8 to 31 mum. The len gth distributions of these fibers had coefficients of variation rangin g 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 (tot al flow rate through the classifier was 5.35 L/min). Limitations in th e classification process prevent increasing the fiber throughput signi ficantly except by increasing the concentration of the challenge aeros ol. Fiber conductivity is important for accurate classification, but c an be readily achieved for fibers of low bulk conductivity by using hi gh humidity air in the classifier.