A Simple Method for Aerosol Transport Efficiency Tests in Sampling Tubes

To obtain representative data, particle loss in sampling tubes must be minimal; otherwise, the magnitude of the losses must be known so it can be corrected. Since particle loss in sample tubes occurs through various mechanisms and depends on particle size, airflow velocity, and Reynolds number, there is no simple method to predict the particle loss of multitudinous configurations of sampling tubes. This study aims to present a simple method for experimentally determining particle loss as a function of particle sizes. Moreover, the applicability of existing models is verified experimentally. An ultrasonic atomizing nozzle was used to generate micrometer-sized polydispersed particles as challenge aerosols. Following charge neutralization, the particle size distribution and number concentration upstream and downstream of the sampling tubes are measured by an Aerodynamic Particle Sizer. The particle loss in the sampling tubes with inner diameters of 4.5, 7.7, and 10 mm are measured at various values of Re (500~5000) and the tube orientations (horizontal and vertical). Both the horizontal and vertical tubes have the lowest loss at a Re of approximately 2100. Gravitational settling and turbulent-induced inertial impaction are the main deposition mechanisms in aerosol transport for particles large than 1 μm. Gravity plays a significant role when the Re is less than 5000, then its dominant position is gradually replaced by turbulence with the Re continuing to increase. Further, the transport efficiency increased with increasing tube diameter. Consequently, each sampling tube needs to be tested according to the methods mentioned in this study to fully grasp the transport efficiency of particles through the sampling tube.