Diseño y construcción de un impactador de cascada para la determinación de la distribución de tamaño de material particulado suspendido en el aire

Abstract

A low-volume cascade impactor was designed and built, with the aim of sampling suspended particulate matter in aerosols and determining its size distribution. The impactor classifies the aerosol particles according to their sizes, by the use of stages that increase the aerosol velocity through orifices and then change the flow direction by 90°. The particles that, owing to their momentum, hit an impaction substrate, will be retained and separated from the aerosol. The impactor is designed to classify the aerosol particles in eight stages, from 20 mðm down to 0.4 mðm, and collect them onto fibre glass substrates. The aerosol flow is induced by a vaccum pump with a maximum flow of 100 L/min, and enters the equipment through a sampling inlet or hosepipe. A set of manometers allows pressure measurement at the pump inlet, and a flowmeter (0 - 70 L/min) and a bypass valve are used to control the aerosol flow through the impactor. The design conditions were 20°C, 560 mmHg and an aerosol flow of 30 L/min. Impaction stages differ in orifice number and diameter, between 2 and 42 orifices, between 0.5 and 15 mm. The impactor was leak tested to verify it was hermetic and kept its flow capacity. Calibration tests and measurements will start in forthcoming projects.