Performance Characteristics of Personal Samplers in Still and Moving Air

Personal samplers or in general blunt body samplers are widely used in occupational hygiene for collecting air contaminants in the work environments. This work is part of an ongoing research into the performance evaluation of personal samplers, particularly in terms of their aerodynamic properties. Velocity profiles have been measured around and within typical cylindrical sampling devices, placed inside of a wind tunnel. A two-component fibre optic laser Doppler anemometer (LDA) is employed to measure the flow field around as well as within the samplers under the test. A variety of conditions, i.e., suction flux, wind speed and orifice size, have been examined. Extensive tests have been carried out in order to verify the reproducibility and reliability of measurements. The results show that reproducibility of the measurements at upstream of samplers are within 1% of the mean velocity. However, analysis of extensive data revealed the presence of noticeable electrostatic effect within and around the sampling device. Attempts were made to eliminate the presence of the electrostatic effect by, for example, spraying the nonconductive sampler with an anti electrostatic liquid, and wire earthing of a sampler made from cooper, but unfortunately these measures were found to be fruitless in eliminating the electrostatic effects. It should nevertheless, be said that the observed velocity is found to be more stable for small inlet orifice size of 4 mm and high suction flux of 3 l/min and this may be because the charged particles have less time to interact with the field produced by the sampler.