Development, Characterization, and Application of a Versatile Single Particle Detection Apparatus for Time-Integrated and Time-Resolved Fluorescence Measurements—Part I: Theoretical Considerations

Abstract

Recent progress in aerosol science has resulted in more challenging demands in the design of new particle beam introduction systems. In this paper, the concept of a variable orifice aerodynamic lens system is presented and supported by the numerical simulation results. This novel particle beam inlet can serve as either a narrow band pass filter (a particle segregator) that only confines particles with a specific size or a broad band pass filter (a particle concentrator) that allows particles with a wide size range to be concentrated on the beam axis. Following a brief description of the inlet system, computational details are described. Simulation of this inlet has been carried out by the commercial computational fluid dynamics protocol FLUENT. Focusing performance and characteristic of single-thin plate orifices have been first revealed and discussed, and then the dynamics and advantages of using multiple lenses with variable orifices are addressed. It is clearly shown that the focusing size range can be primarily adjusted by varying the working pressure, the orifice geometry, and/or the arrangement of orifices. As a result, a selection of the desired particle focusing size range can be achieved without the need of changing the inlet, thus increasing the versatility of the device for a broad range of applications.

Development, Characterization, and Application of a Versatile Single Particle Detection Apparatus for Time-Integrated and Time-Resolved Fluorescence Measurements—Part II: Experimental Evaluation

“…The major advantage of such an inlet system over conventional aerodynamic lenses is that we can focus particle of different size range without changing the inlet. These numerical studies [48] have been encouraging for our future experiments. Particle size and size distribution are basic characteristics for atmospheric aerosols because they largely determine the aerosols behavior in gaseous suspension.…”

“…The system is equipped with a variable-orifice aerodynamic inlet, which is used to form a narrow particle beam and introduce individual particles to the excitation/detection zone defined by the laser beam spot. Theoretically, we have proved that this variable-orifice inlet has the ability to cope with particles over a wide size range [48]. Its focusing size range can be altered dynamically by varying the lens diameter and the working pressure.…”

“…Therefore, it can be expected that a multilens inlet can be used as a size segregator if only one lens is set to the required dimension and the others set to D/2 or larger. Numerical results shown in Figure 6, taken from our previous paper [48], indicate that a five-lens inlet (d i = 6, 6, 2.4, 6, 6 mm) has a focusing capability similar to that of a single lens (d i = 2.4). Only particles with a specific size can be collimated.…”

“…Numerical simulations with the FLUENT protocol have been carried out to evaluate the capability of the newly designed inlet in focusing particles. Figure 5, which is taken from our previous paper [48], compares the detection efficiencies measured 5 cm downstream of the inlet exit for five different aerodynamic inlet systems, terminated with the same two-stage focusing nozzle under the same working conditions. Here, the detection efficiency is defined as the ratio of the number of the particles collected on a 500 μm disc placed 5 cm downstream of the inlet to the total number of particles injected from upstream.…”

“…The theoretical design and calculations of our inlet were given in a previous paper [48]. The aim of this paper is to describe the experimental realization and characterization of a system that integrates an aerodynamic particle beam inlet with a size measurement and fluorescence analysis system.…”