CFD elucidation of microscopic particles in a low-volumetric classifier towards effects of Stokes number and density ratio

Abstract

Due to health concerns, a device that separates soot particles based on their size is commonly used to monitor the concentration of soot particles in ambient air. This numerical study aimed to observe particle flow characteristics in low-volumetric separators and assess their performance under recommended operating conditions. The Computational Fluid Dynamics (CFD) technique, specifically the Discrete Particle Model (DPM) approach, was utilized to analyze the behavior of particles and calculate their velocities. The investigation focused on small harmful particles with sizes of 1 µm, 10 µm, and 20 µm. Three volumetric flow rates close to the manufacturer's suggestion, 10 l/min, 15 l/min, and 20 l/min, were examined to evaluate particle separation efficiency in the low-volumetric impact separator. The study revealed that the operating flow rate and the Stokes numbers of the particles significantly impacted the particle behavior, vorticity strength, and the efficiency of particle classification within the separator. The residence time of particles inside the impact chamber was identified as an important factor for assessing separation performance, as it is crucial to monitor and control the key parameters to optimize the separation process. The investigation recommended a flow rate of 15 l/min for efficient impact separation of the particles (PM1, PM10, PM20). The current classifying percentage for particles smaller than PM10 was approximately 70%. Therefore, future work will investigate the effects of the impact chamber's internal configurations to enhance the separator's efficiency, where the modified structure could be explored and recommended.