Airborne Fiber Separation by Electrophoresis and Dielectrophoresis: Theory and Design Considerations

Abstract

The separation of airborne fibers by length and diameter is essential for evaluating inhalation dosimetry, understanding mechanisms of toxicity, and estimating risk to humans from inhaled fibers. Aerodynamic separation of fibrous aerosols depends strongly on fiber diameter and weakly on fiber length. Theoretical calculations show that thin, long fibers can be separated from particles by using differences in their electric mobilities. Fiber separation by length under the influence of electrophoretic forces and dielectrophoretic forces was calculated in a design model for fibers 20, 10, and 3 μm in length and 1 μm in diameter. Electrophoresis describes the motion of a charged object in an electric field, whereas dielectrophoresis describes the motion of neutral matter in a nonuniform electric field. Based on simulation results, 1-μm-diameter fibers having aspect ratios of 20, 10, and 3 can be separated from each other by electrophoresis if the charge ratio on these fibers is 10:5:1, respectively. Twenty-micron-long, nonconducting fibers can be separated by dielectrophoresis from 10-μm-long fibers under both plug and parabolic flow conditions, provided the relative humidity of the carrier gas exceeds 30%. The width of the aerosol inlet should be less than 2 mm for a concentric cylindrical separator having radii of 0.5 and 3 cm and total flow rate of 3 L/min. AC fields with high oscillating frequencies, (ω ≥ 50) must be applied to eliminate charge effects in dielectrophoretic separation.