A newly developed dilution system for optical particle size and concentration measurements in oil-injected screw compressors

Abstract

Oil mist coalescence separators are widely used downstream of screw compressors. Unfortunately, due to high concentration most of the available literature reporting particle sizes in raw or clean gas of screw compressors is on model systems at atmospheric pressure and room temperature. To study oil mist coalescence separators under real-world conditions, the pressurized aerosol needs to be diluted.In this work, two newly developed isobaric and isothermal dilution systems for particle size measurements using an optical particle counter (200 nm–10 µm) in the application scenario are presented. For both systems, one a single-stage and the other a triple-stage system, transfer functions were determined in the laboratory using a pressurized oil atomizer.As a proof of concept, the triple-stage dilution system was used on a compressor test bench to study the influence of operating conditions (varying pressure and volume flow) on the particle size distribution and concentration in raw and clean gas. Both raw and clean gas particle size distributions showed most particles in the size range below 500 nm. The achievable dilution factor of 1000 was sufficient for measuring the raw gas concentration.On a second compressor test bench, the single-stage dilution system was used to study the influence of different coalescence separators on clean gas particle size distribution and concentration. Three separators were used for experiments: one industry-typical reference separator, one with less layers, and one with a weakened entrainment separation fleece. As expected, the particle size distributions showed clear differences, i.e., higher penetration or increased entrainment.Copyright © 2023 American Association for Aerosol Research