Browsing by Author "Szymanski, WW"

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Filter efficiency measurement with optical particle counters - Limitations and error sources
(1998)
Szymanski, WW
;
Cheng, YH
;
Tsai, CJ
;
環境工程研究所
;
Institute of Environmental Engineering
Filter efficiency determination by means of the optical particle counting technique can yield information about the filter performance from a single set of upstream and downstream measurements. In principle, optical particle counters provide the possibility of a real time determination of particle size distribution and concentration. However, substantial errors in determination of the filtration efficiency may result from the performance characteristics of optical particle counters. This article presents results of a theoretical and experimental study analyzing the effects of variation of particle refractive index and coincidence on the sizing accuracy and counting ability of optical particle counters and the impact on the efficiency determination. Since both parameters, size and count, are critical for the determination of fractional collection efficiency and the most penetrating particle size, exemplary filter efficiency measurements with optical particle counters under various conditions are presented and critically discussed. Depending on the experimental conditions chosen, the efficiency of the same filter can differ by more than an order of magnitude. The limitations reported here may numerically vary for different instruments; however, they are inherent to this technique, in gaseous as well as in liquid media, and must be taken into account during measurements and data evaluation.
Particle transmission efficiency through the nozzle of the API Aerosizer (TM)
(1999-09-01)
Tsai, CJ
;
Yang, WS
;
Szymanski, WW
;
Chein, HM
;
環境工程研究所
This study has investigated the particle transmission efficiency through the nozzle of the API Aerosizer(TM) numerically. Two-dimensional flow field in the nozzle was first simulated. Particle trajectories for both liquid and solid particles were then calculated to obtain the particle transmission efficiency under various conditions. This study shows that particle aerodynamic diameter, particle materials, particle density and laser beam diameter influence the transmission efficiency. The transmission efficiency is found to increase with increasing particle diameter when the particle aerodynamic diameter is less than several micrometers. The efficiency for liquid particles drops significantly when particle aerodynamic diameter increases from several micrometers because of particle impaction loss in the nozzle. For solid particles, the relationship of the efficiency with particle diameter is found to be more complicated. For particles less than several micrometers in aerodynamic diameter, solid particles behave similarly to the liquid particles. However, as particles are greater than several micrometers, the effect of solid particle bounce is to increase the transmission efficiency with increasing aerodynamic diameter until particles become large enough so that plastic deformation occurs in the particles. Then the transmission efficiency will decrease with increasing particle aerodynamic diameter. (C) 1999 Elsevier Science Ltd. All rights reserved.