Comparison of Aerosol Sampling with Shrouded and Unshrouded Probes

Continuous air monitoring is a requirement for many of the stacks and ducts in the nuclear industry. Aerosol sampling systems for these applications should have minimal errors, even though there are variations in operating conditions. In this context a shrouded probe with a nominal sampling rate of 57 L/min (2 fr3/min) was designed and its performance compared with unshrouded sharp-edged probes over a range of particle sizes (5–15 µm aerodynamic diameter [AD]), free stream velocities (9–21 m/sec) and yaw angles (0°–22.5°). Transmission of aerosol through unshrouded probes was typically 60% or less because of internal wall losses, whereas the intrinsic characteristics of the shrouded probe provided a near-unity transmission ratio for the diverse range of operating conditions. When 10-µm AD particles were sampled with a shrouded probe over the previously noted range of free stream velocities and yaw angles, the transmission ratios varied from 0.82 to 1.08. Wall losses in the shrouded probe were generally about one-half of those in the sharp-edged unshrouded probes. The transmission ratio of the shrouded probe was determined for a ±25% variation in sampling flow rate. The results showed values of 0.9 to 1.0 for operation with 10-µm AD aerosol particles at a velocity of 21 m/sec.