Optimization of the Design of a Semivolatile Aerosol Dichotomous Sampler

Abstract

This article reports the results of an optimization procedure for a semivolatile aerosol dichotomous sampler (SADS) and experimental confirmation of the instrument's performance with an optimized sampler. Using numerical model results, the relationships between four major design and operating parameters significantly affecting the performance of the SADS and four performance parameters were expressed in log polynomial equations. Utilizing an optimization procedure, values for the major parameters giving the best performance were determined and used as the base model for optimizing minor parameters. Five minor parameters were then investigated for their possible contribution to better performance of the SADS. The optimal dimensions found were as follows: the diameter ratio between the nozzle and the collection probe was 1.30 and the length ratio of the distance between the nozzle and the collection probe divided by the nozzle diameter was 0.6. Among the minor parameters, only the entrance angle of the nozzle made noticeable improvement at 45 • . Experimental tests confirmed that the performance of the new sampler was improved although not as much as expected from the numerical simulation.

Experimental Evaluation of Oil Mists Using a Semivolatile Aerosol Dichotomous Sampler

“…(29,30) Approximately 20% and 16% wall loss was found in the single compound and three-way mixture tests, respectively, for BEHS. This difference also can be explained by the probable difference of the size distributions between the two test aerosols as discussed above.…”

“…where η CFC (d ae ) is the aspiration efficiency of 37-mm closedface cassettes; (32) η SADS (d ae ) is the experimental separation efficiency curve of the optimized SADS; (30) Bias FIGURE 9. Estimated bias of particle concentration for nonvolatile particles calculated using the separation efficiency of the optimized SADS (30) and Eq.…”

“…Estimated bias of particle concentration for nonvolatile particles calculated using the separation efficiency of the optimized SADS (30) and Eq. 13 when Q vapor /(Q vapor + Q particle ) = 0.1 GSD) is the lognormal mass distribution density function of an aerosol with a particular MMAD and GSD; and d ae is the aerodynamic particle diameter.…”

“…(30) The dimensions of the optimized SADS are shown in Figure 1. The outer shape has that of a 37-mm cassette and its aspiration efficiency was reported by Kenny et al (31,32) The 50% cutsize of the optimized SADS from experiments was 0.25 µm when the flow rate was 2.0 L/min, and the flow fraction going to the vapor flow direction was 0.1.…”

“…The outer shape has that of a 37-mm cassette and its aspiration efficiency was reported by Kenny et al (31,32) The 50% cutsize of the optimized SADS from experiments was 0.25 µm when the flow rate was 2.0 L/min, and the flow fraction going to the vapor flow direction was 0.1. (30) In this study, we evaluated the sampling performance of the optimized SADS experimentally using polydisperse semivolatile aerosols in a chamber. The individual concentrations of the vapor and particle phases were measured using the SADS, and they were compared with measurements from other sampling methods, such as filtration and electrostatic precipitation.…”