ISOKINETIC AND ANISOKINETIC SAMPLING EFFECT IN THE EVALUATION OF PARTICLE SIZE DISTRIBUTION OF AEROSOL
For aerosol measurement, especially those concerned with aerosol particle size distribution, it is important to sample in isokinetic conditions. The isokinetic sampling procedure has been espoused to avoid error in critical parameters (particle concentration, collection efficiency, etc.). Isokinetic sampling can be costly or difficult to achieve. It is known that for Stokes number <<0.01, the aerosol particle follow the gas streamline perfectly and isokinetic sampling condition are ensured. In the present study, isokinetic behavior of sampling for Stokes number <0.01 has been validated using experiment. Graphite sample of known weight was burnt in clean air supplied at a known volumetric flow rate. This air acted as a carrier gas and transported the aerosol generated. Isokinetic and anisokinetic probes was used for sampling. The sample was passed through a dilution system and then through a flow splitter before being sampled by two instruments: the OPS (TSI Model No. 3310) and NANOSCAN (TSI Model No.3910). These instrument measured the size distribution and concentration of the aerosol in a size range of 10 nm − 10 µm.
The results indicates that within the size range considered and with Stokes number less than 0.01, there is negligible difference between the measurements made with isokinetic and anisokinetic sampling probes. Hence, the study indicates that isokinetic sampling would be unnecessary for the present investigation.