Effect of Sampling Time on the Collection Efficiency of All-Glass Impingers

Abstract

Abstract The changes in the physical collection efficiencies of all-glass impingers were studied experimentally with an aerodynamic particle sizer by dynamically measuring the particle concentrations upstream and downstream of AGI-4 and AGI-30 impingers. Monodisperse PSL particles of aerodynamic sizes ranging from 0.3 to 2.0 μm were used in the tests. The inner diameter of the impingement nozzle was found to be the most critical dimension affecting the collection efficiency. Significant variations were found in the performance of individual impingers due to the variations in the critical dimensions of the impingers tested. About 1% of the initial amount of impinger liquid is evaporated per minute of normal operation. On depletion to a critical minimum volume, the collection efficiency decreases drastically due to insufficient impingement into the liquid and particle bounce from the bottom surface. Particles already collected may be entrained by the air bubbles passing through the liquid and be reaerosolized, thus decreasing the overall collection efficiency. The number of reaerosolized particles increases with sampling time, but is less than 10% within the first hour of sampling with either the AGI-4 or the AGI-30. A graph has been developed for selecting the maximum sampling time for a given initial liquid volume so that the collection efficiency is approximately constant throughout the entire sampling period. The graph also indicates the limits where significant particle bounce, reaerosolization, or liquid splashing occur. The AGI-4 was found to be more efficient in collecting submicrometer particles and to be less particle-size dependent than the AGI-30. Keywords: aerosolcollection efficiencyimpingersamplingsampling time