Real-time measurement of fibers using an HY-differential mobility analyzer with an optical particle counter (KOFAM)
This study investigated the applicability of an HY-differential mobility analyzer with an optical particle counter (HY-DMA/OPC), named as KOFAM, for counting fibrous matters in real time. Fibers separated from particles by the HY-DMA were counted with an OPC. To assess the KOFAM performance, the proposed method and the conventional gold standard phase contrast microscopy (PCM) method were compared in terms of variables such as recovery, relative difference, coefficient of determination, and conformity. The optimal sheath-to-aerosol (outlet) flow ratio of the internal flow in the HY-DMA was determined to be 1.6:1. In terms of recovery of the HY-DMA, the highest recovery was obtained at a voltage of 500 V regardless of which type of asbestos was tested. The recovery rate for serpentine was 45.5% and that for amphibole was 34.9%. The coefficients of determination of serpentine (R2 = 0.89) and amphibole (R2 = 0.87) were highly correlated. With respect to the coefficient of variation (CV), the KOFAM demonstrated superior performance over the M7400AD and F-1 methods and showed almost no difference from the PCM method (KOFAM: 22.5%, M7400AD: 32.4%, F-1: 88.8%, and PCM: 21.9%). There was no statistically significant difference between concentration measurements of the KOFAM and PCM analyses. Accordingly, it was concluded that the KOFAM can be used as a superior alternative to conventional fiber measurement methods. The preliminary results support the use of the KOFAM for constant measurement of airborne asbestos concentrations in real time.
Airborne Fiber Separation by Electrophoresis and Dielectrophoresis: Theory and Design Considerations
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-mic...
Numerical modeling of the performance of differential mobility analyzers for nanometer aerosol measurements
Abstract A numerical model was developed to predict the performance of differential mobility analyzers (DMAs) for nanometer aerosol measurements. The model consists of three parts: flow field, electric field, and aerosol transport formulations. In order for the model to be applicable for all the existing DMAs, the swirling flow effect due to tangential aerosol injection is included. The tangential inlet design was used in several recently designed DMAs, e.g. Hauke, SMEC and RDMA. The swirling is incorporated in the model by introducing the assumption of negligible variation of the circumferential flow component. Mixed Galerkin and SUPG finite-element formulations with a nine-node velocity, three-node pressure flow elements and bilinear element are proposed. For the electric field, the space charge effect is neglected and the equation is solved by Galerkin finite element method with the second-order isoparametric element. The aerosol transport is modeled by the convective aerosol transport equation with external electrical force. The equation is further simplified by using the same assumption made for the flow field in the circumferential flow component. A modified adaptive characteristic Petrov-Galerkin finite-element method is proposed to overcome the difficulty involved in numerically solving the simplified equation. The model was used to calculate the transfer functions of TSI-short DMA for particle sizes between 5 and 50 nm. They were then validated by comparing the numerical and experimental results for simulated scans from two DMAs operating in series. The numerical transfer functions are compared with the available experimental data from two sources, namely, Hummes et al. (1996) Part. Part. System Charact. 13, 327–332 and Kousaka et al. (1986) J. Chem. Engng Japan 19, 401–407. A good agreement between them is obtained.